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Scientists uncover deep-rooted plumbing system beneath ocean volcanoes

Volcano magma chamber. Credit: Cardiff University
Volcano magma chamber. Credit: Cardiff University

Cardiff University scientists have revealed the true extent of the internal ‘plumbing system’ that drives volcanic activity around the world.

An examination of pockets of magma contained within crystals has revealed that the large chambers of molten rock which feed volcanoes can extend to over 16 km beneath the Earth’s surface.

The new study, published today in Nature, has challenged our understanding of the structure of ocean volcanoes, with previous estimates suggesting that magma chambers were located up to 6 km below the surface.

Interconnected magma chambers and reservoirs are the key driver of the dynamics of volcanic systems around the world, so understanding their nature is an important step towards understanding how volcanoes are supplied with magma, and, ultimately, how they erupt.

Mid-ocean ridges in particular make up the most significant volcanic system on our planet, forming a roughly 80,000 km-long network of undersea mountains along which 75 percent of Earth’s volcanism occurs.

However, because these volcanoes are located under thousands of metres of water, and sometimes permanent sea ice, we are only just starting to understand what the subsurface architecture of these volcanoes look like.

It is known that magma plumbing systems exist below the Earth’s surface, which can be thought of as a series of interconnected magma conduits and reservoirs, much like the pipes and tanks that make up plumbing systems in a house, instead at mid-ocean ridges the tap is a volcano.

In their study, the team analysed common minerals such as olivine and plagioclase which grew deep within the volcanoes and were subsequently erupted from the Gakkel Ridge located beneath the Arctic Ocean between Greenland and Siberia.

These minerals act as tape recorders from which changes in the physical and chemical conditions of the environment within which they grew can be measured. Critically, the team were able to record what processes occurred and at what depths these minerals began to crystallise in magma reservoirs.

Lead author of the study, Ph.D. student Emma Bennett, from the School of Earth and Ocean Sciences, said: “To calculate the depths of magma reservoirs we used melt inclusions, which are small pockets of magma that become trapped within growing crystals at different depths in the magmatic system. These pockets of melt contain dissolved CO2 and H2O.

“Because the melt cannot dissolve as much CO2 at shallow pressure as it can at high pressure, we can determine what pressure the melt inclusion was trapped, and in turn work out the depth at which crystallisation occurred, by measuring the amount of CO2 in the melt inclusions.

“Put simply, crystal growth in a magmatic environment can be likened to the growth rings on a tree; for example, a change in the chemical environment will result in the growth of a new layer with a different crystal composition.

“By analysing multiple melt inclusions we can start to reconstruct the architecture of the magmatic system.”

The study was the first to use the mineral plagioclase as a proxy for the depth of magma reservoirs, with previous studies using the mineral olivine.

The results showed that magma plumbing systems at mid-ocean ridges extend to much greater depths than previously thought. Oceanic crust is normally only around 6 km thick, and conventionally magma chambers were thought of as being located here.

Yet the new data has shown that the plumbing system extends to at least 16 km depth, which means that the magma chambers that fed the Gakkel Ridge volcanoes are located much deeper down in the mantle.

Reference:
Emma N. Bennett et al. Deep roots for mid-ocean-ridge volcanoes revealed by plagioclase-hosted melt inclusions, Nature (2019). DOI: 10.1038/s41586-019-1448-0

Note: The above post is reprinted from materials provided by Cardiff University.

Researchers uncover 2.5 billion years of Earth’s continents breaking up and getting back together

Continents breaking up and getting back together. Image credit: Naeblys / Getty Images
Continents breaking up and getting back together. Image credit: Naeblys / Getty Images

A new study of rocks that formed billions of years ago lends fresh insight into how Earth’s plate tectonics, or the movement of large pieces of Earth’s outer shell, evolved over the planet’s 4.56-billion-year history.

A report of the findings, published August 7 in Nature, reveals that, contrary to previous studies that say plate tectonics has operated throughout Earth’s history or that it emerged only 0.7 billion years ago, plate tectonics actually evolved over the last 2.5 billion years. This new timeline impacts researchers’ models for understanding how Earth has changed.

“One of the key ways to understand how Earth has evolved to become the planet that we know is plate tectonics,” says Robert Holder, a Postdoctoral Fellow in Earth and Planetary Sciences at Johns Hopkins University and the paper’s first author.

Plate tectonics dictates how continents drift apart and come back together, helps explain where volcanoes and earthquakes occur, predicts cycles of erosion and ocean circulation, and how life on Earth has evolved.

In a bid to resolve the mystery of how and when plate tectonics emerged on Earth, Holder and the research team examined a global compilation of metamorphic rocks that formed over the past 3 billion years at 564 sites. Metamorphic rocks are rocks that, through the process of being buried and heated deep in the Earth’s crust, have transformed into a new type of rock. Scientists can measure the depth and temperatures at which metamorphic rocks form, and thereby constrain heat flow at different places in Earth’s crust. Because plate tectonics strongly influences heat flow, ancient metamorphic rocks can be used to study plate tectonics in Earth’s past.

The research team compiled data on the temperatures and depths at which the metamorphic rocks formed and then evaluated how these conditions have changed systematically through geological time. From this, the team found that plate tectonics, as we see it today, developed gradually over the last 2.5 billion years.

“The framework for much of our understanding of the world and its geological processes relies on plate tectonics,” says Holder. “Knowing when plate tectonics began and how it changed impacts that framework.”

Clarity on when plate tectonics began and whether it was different in Earth’s past can help scientists better understand why we find certain rocks and minerals where we do and how they formed, says Holder.

Other authors on this paper include Daniel Viete of the Johns Hopkins University; Michael Brown of the University of Maryland, College Park; and Tim Johnson of Curtin University

Reference:
Robert M. Holder, Daniel R. Viete, Michael Brown & Tim E. Johnson. Metamorphism and the evolution of plate tectonics. Nature, 2019 DOI: 10.1038/s41586-019-1462-2

Note: The above post is reprinted from materials provided by Johns Hopkins University.

Earth’s last magnetic field reversal took far longer than once thought

Study co-author Rob Coe and Trevor Duarte orienting cores from a lava flow site recording the Matuyama-Brunhes magnetic polarity reversal in Haleakala National Park, Hawaii, in 2015
Study co-author Rob Coe and Trevor Duarte orienting cores from a lava flow site recording the Matuyama-Brunhes magnetic polarity reversal in Haleakala National Park, Hawaii, in 2015. Credit: Brad Singer

Earth’s magnetic field seems steady and true — reliable enough to navigate by.

Yet, largely hidden from daily life, the field drifts, waxes and wanes. The magnetic North Pole is currently careening toward Siberia, which recently forced the Global Positioning System that underlies modern navigation to update its software sooner than expected to account for the shift.

And every several hundred thousand years or so, the magnetic field dramatically shifts and reverses its polarity: Magnetic north shifts to the geographic South Pole and, eventually, back again. This reversal has happened countless times over the Earth’s history, but scientists have only a limited understanding of why the field reverses and how it happens.

New work from University of Wisconsin-Madison geologist Brad Singer and his colleagues finds that the most recent field reversal, some 770,000 years ago, took at least 22,000 years to complete. That’s several times longer than previously thought, and the results further call into question controversial findings that some reversals could occur within a human lifetime.

The new analysis — based on advances in measurement capabilities and a global survey of lava flows, ocean sediments and Antarctic ice cores — provides a detailed look at a turbulent time for Earth’s magnetic field. Over millennia, the field weakened, partially shifted, stabilized again and then finally reversed for good to the orientation we know today.

The results provide a clearer and more nuanced picture of reversals at a time when some scientists believe we may be experiencing the early stages of a reversal as the field weakens and moves. Other researchers dispute the notion of a present-day reversal, which would likely affect our heavily electronic world in unusual ways.

Singer published his work Aug. 7 in the journal Science Advances. He collaborated with researchers at Kumamoto University in Japan and the University of California, Santa Cruz.

“Reversals are generated in the deepest parts of the Earth’s interior, but the effects manifest themselves all the way through the Earth and especially at the Earth’s surface and in the atmosphere,” explains Singer. “Unless you have a complete, accurate and high-resolution record of what a field reversal really is like at the surface of the Earth, it’s difficult to even discuss what the mechanics of generating a reversal are.”

Earth’s magnetic field is produced by the planet’s liquid iron outer core as it spins around the solid inner core. This dynamo action creates a field that is most stable going through roughly the geographic North and South poles, but the field shifts and weakens significantly during reversals.

As new rocks form — typically either as volcanic lava flows or sediments being deposited on the sea floor — they record the magnetic field at the time they were created. Geologists like Singer can survey this global record to piece together the history of magnetic fields going back millions of years. The record is clearest for the most recent reversal, named Matuyama-Brunhes after the researchers who first described reversals.

For the current analysis, Singer and his team focused on lava flows from Chile, Tahiti, Hawaii, the Caribbean and the Canary Islands. The team collected samples from these lava flows over several field seasons.

“Lava flows are ideal recorders of the magnetic field. They have a lot of iron-bearing minerals, and when they cool, they lock in the direction of the field,” says Singer. “But it’s a spotty record. No volcanoes are erupting continuously. So we’re relying on careful field work to identify the right records.”

The researchers combined magnetic readings and radioisotope dating of samples from seven lava flow sequences to recreate the magnetic field over a span of about 70,000 years centered on the Matuyama-Brunhes reversal. They relied on upgraded methods developed in Singer’s WiscAr geochronology lab to more accurately date the lava flows by measuring the argon produced from radioactive decay of potassium in the rocks.

They found that the final reversal was quick by geological standards, less than 4,000 years. But it was preceded by an extended period of instability that included two excursions — temporary, partial reversals — stretching back another 18,000 years. That span is more than twice as long as suggested by recent proposals that all reversals wrap up within 9,000 years.

The lava flow data was corroborated by magnetic readings from the seafloor, which provides a more continuous but less precise source of data than lava rocks. The researchers also used Antarctic ice cores to track the deposition of beryllium, which is produced by cosmic radiation colliding with the atmosphere. When the magnetic field is reversing, it weakens and allows more radiation to strike the atmosphere, producing more beryllium.

Since humanity began recording the strength of the magnetic field, it has decreased in strength about five percent each century. As records like Singer’s show, a weakening field seems to be a precursor to an eventual reversal, although it’s far from clear that a reversal is imminent.

A reversing field might significantly affect navigation and satellite and terrestrial communication. But the current study suggests that society would have generations to adapt to a lengthy period of magnetic instability.

“I’ve been working on this problem for 25 years,” says Singer, who stumbled into paleomagnetism when he realized the volcanoes he was studying served as a good record of Earth’s magnetic fields. “And now we have a richer record and better-dated record of this last reversal than ever before.”

This study was supported by National Science Foundation grant EAR-1250446.

Reference:
Brad S. Singer, Brian R. Jicha, Nobutatsu Mochizuki, Robert S. Coe. Synchronizing volcanic, sedimentary, and ice core records of Earth’s last magnetic polarity reversal. Science Advances, 2019; 5 (8): eaaw4621 DOI: 10.1126/sciadv.aaw4621

Note: The above post is reprinted from materials provided by University of Wisconsin-Madison. Original written by Eric Hamilton.

A voracious Cambrian predator, Cambroraster, is a new species from the Burgess Shale

Reconstruction by Lars Fields. Credit: Lars Fields Royal Ontario Museum
Reconstruction by Lars Fields. Credit: Lars Fields Royal Ontario Museum

Palaeontologists at the Royal Ontario Museum and University of Toronto have uncovered fossils of a large new predatory species in half-a-billion-year-old rocks from Kootenay National Park in the Canadian Rockies. This new species has rake-like claws and a pineapple-slice-shaped mouth at the front of an enormous head, and it sheds light on the diversity of the earliest relatives of insects, crabs, spiders, and their kin. The findings were announced July 31, 2019, in a study published in Proceedings of the Royal Society B.

Reaching up to a foot in length, the new species, named Cambroraster falcatus, comes from the famous 506-million-year-old Burgess Shale. “Its size would have been even more impressive at the time it was alive, as most animals living during the Cambrian Period were smaller than your little finger,” said Joe Moysiuk, a graduate student based at the Royal Ontario Museum who led the study as part of his Ph.D. research in Ecology & Evolutionary Biology at the University of Toronto. Cambroraster was a distant cousin of the iconic Anomalocaris, the top predator living in the seas at that time, but it seems to have been feeding in a radically different way,” continued Moysiuk.

The name Cambroraster refers to the remarkable claws of this animal, which bear a parallel series of outgrowths, looking like forward-directed rakes. “We think Cambroraster may have used these claws to sift through sediment, trapping buried prey in the net-like array of hooked spines,” added Jean-Bernard Caron, Moysiuk’s supervisor and the Richard M. Ivey Curator of Invertebrate Palaeontology at the Royal Ontario Museum.

With the interspace between the spines on the claws at typically less than a millimeter, this would have enabled Cambroraster to feed on very small organisms, although larger prey could also likely be captured, and ingested into the circular tooth-lined mouth. This specialized mouth apparatus is the namesake of the extinct group Radiodonta, which includes both Cambroraster and Anomalocaris. Radiodonta is considered to be one of the earliest offshoots of the arthropod lineage (today including all animals with an exoskeleton, a segmented body and jointed limbs).

The second part of the species name falcatus was given in tribute to another of Cambroraster’s distinctive features: the large shield-like carapace covering its head, which is shaped like the Millennium Falcon spaceship from the Star Wars films. “With its broad head carapace with deep notches accommodating the upward facing eyes, Cambroraster resembles modern living bottom-dwelling animals like horseshoe crabs. This represents a remarkable case of evolutionary convergence in these radiodonts,” Moysiuk explained. Such convergence is likely reflective of a similar environment and mode of life—like modern horseshoe crabs, Cambroraster may have used its carapace to plough through sediment as it fed.

Perhaps even more astonishing is the large number of specimens recovered. “The sheer abundance of this animal is extraordinary,” added Dr. Caron, who is also an Assistant Professor in Ecology & Evolutionary Biology and Earth Sciences at the University of Toronto, and the leader of the field expeditions that unearthed the new fossils. “Over the past few summers we found hundreds of specimens, sometimes with dozens of individuals covering single rock slabs.”

Based on over a hundred exceptionally well-preserved fossils now housed at the Museum, researchers were able to reconstruct Cambroraster in unprecedented detail, revealing characteristics that had not been seen before in related species.

“The radiodont fossil record is very sparse; typically, we only find scattered bits and pieces. The large number of parts and unusually complete fossils preserved at the same place are a real coup, as they help us to better understand what these animals looked like and how they lived,” said Dr. Caron. “We are really excited about this discovery. Cambroraster clearly illustrates that predation was a big deal at that time with many kinds of surprising morphological adaptations.”

Fossils from the Cambrian period, particularly from sites like the Burgess Shale, record a dramatic “explosion” of biodiversity at this time, culminating in the evolution of most of the major groups of animals that survive today. But, the story has far more intricacy than a straight line leading from simple ancestors to the vast diversity of modern species. “Far from being primitive, radiodonts show us that at the very outset of complex ecosystems on Earth, early representatives of the arthropod lineage rapidly radiated to play a wide array of ecological roles,” remarked Moysiuk.

The fossils were found at several sites in the Marble Canyon area in Kootenay National Park, British Columbia, which have been discovered by ROM-led field teams since 2012, with some of the key specimens unearthed just last summer. These sites are about 40 kilometers away from the original Burgess Shale fossil site in Yoho National Park that was first discovered in 1909. What is also exciting for researchers is the realization that there is a large new area in northern Kootenay National Park worth scientific exploration, holding the potential for the discovery of many more new species.

The Burgess Shale fossil sites are located within Yoho and Kootenay National Parks and are managed by Parks Canada. Parks Canada is proud to work with leading scientific researchers to expand our knowledge and understanding of this key period of earth history and to share these sites with the world through award-winning guided hikes. The Burgess Shale was designated a UNESCO World Heritage Site in 1980 due to its outstanding universal value, and is now part of the larger Canadian Rocky Mountain Parks World Heritage Site.

Reference:
A new hurdiid radiodont from the Burgess Shale evinces the exploitation of Cambrian infaunal food sources, Proceedings of the Royal Society B, rspb.royalsocietypublishing.or … .1098/rspb.2019.1079

Note: The above post is reprinted from materials provided by Royal Ontario Museum .

Colossal dinosaur bone find in France thrills scientists

Scientists say the femur might have belonged to a gigantic sauropod. Credit: AFP / GEORGES GOBET
Scientists say the femur might have belonged to a gigantic sauropod. Credit: AFP / GEORGES GOBET

Scientists have unearthed a huge two-metre (6.5-foot) dinosaur bone in a winegrowing village in southwestern France dubbed a “national treasure” for its prehistoric gems.

The 140-million-year-old thigh bone, which weighs 400 kilogrammes (880 pounds), is the latest discovery at the vast Angeac-Charente palaeontological site near Bordeaux, where experts and volunteers have dug up thousands of bones over the past decade.

But thanks to its remarkably good condition, the femur—which scientists say probably belonged to a gigantic sauropod—could help piece together an incomplete set of bones which the latest find resembles.

“We were wondering how big it was. We kept saying, ‘Oh, there’s more!'” said Maxime Lasseron, the doctoral student who made the gigantic discovery.

The largest land animals ever to roam the Earth, sauropods were massive plant-eating dinosaurs with a long neck and tail, towering up to 18 metres (59 feet) tall.

“It cost me a bit of money, because I had promised to bring champagne if it was complete,” said Jean-Francois Tournepiche, the operations coordinator at what he calls “one of Europe’s biggest dinosaur sites”.

Tests will now compare the femur to another thigh bone discovered in 2010 to find out if they belonged to the same type of sauropod or even the same creature.

The bone’s “preservation and perfect fossilisation makes it really unique”, said Ronan Allain, a paleontologist at the French Museum of Natural History in Paris.

Prehistoric ecosystem

Now known for its cognac vineyards, Angeac-Charente was home to a vast ecosystem of dinosaurs, invertebrates and vegetation thanks to its humid, subtropical climate millions of years ago.

“There was a river and large coniferous trees,” Allain said.

“Amphibians, crocodiles and fish lived in the swamp, and on dry land, small and large dinosaurs. It was full of life”.

The discovery coincides with the 10th annual dig at the site, which stretches over 750 square metres (nearly 8,100 square feet).

But with more discoveries expected on the horizon, the site’s owners have given diggers the go-ahead to excavate in another 4,000 square metres of land.

“Another surprise for our 10-year anniversary,” Tournepiche said. “At this rate, we’ll be busy for the next 30 years!”

Note: The above post is reprinted from materials provided by AFP.

Predicting earthquake hazards from wastewater injection

Wells drilled into Oklahoma's Arbuckle formation inject wastewater (1) which then disperses through the rock. As it spreads, the wastewater can trigger earthquakes in fault zones (2), but their size depends on the amount injected and the rock's properties. The new model can predict quake probabilities by the quantity of wastewater injected.
Wells drilled into Oklahoma’s Arbuckle formation inject wastewater (1) which then disperses through the rock. As it spreads, the wastewater can trigger earthquakes in fault zones (2), but their size depends on the amount injected and the rock’s properties. The new model can predict quake probabilities by the quantity of wastewater injected. Credit: Guang Zhai, Manoochehr Shirzaei/ASU

A byproduct of oil and gas production is a large quantity of toxic wastewater called brine. Well-drillers dispose of brine by injecting it into deep rock formations, where its injection can cause earthquakes. Most quakes are relatively small, but some of them have been large and damaging.

Yet predicting the amount of seismic activity from wastewater injection is difficult because it involves numerous variables. These include the quantity of brine injected, how easily brine can move through the rock, the presence of existing geological faults, and the regional stresses on those faults.

Now a team of Arizona State University-led geoscientists, working under a Department of Energy grant, has developed a method to predict seismic activity from wastewater disposal. The team’s study area is in Oklahoma, a state where much fracking activity has been carried out with a lot of wastewater injection, and where there have been several induced earthquakes producing damage.

The team’s paper reporting their findings appeared in the Proceedings of the National Academy of Sciences on July 29, 2019.

“Overall, earthquake hazards increase with background seismic activity, and that results from changes in the crustal stress,” says Guang Zhai, a postdoctoral research scientist in ASU’s School of Earth and Space Exploration and a visiting assistant researcher at the University of California, Berkeley. “Our focus has been to model the physics of such changes that result from wastewater injection.”

Zhai is lead author for the paper, and the other scientists are Manoochehr Shirzaei, associate professor in the School, plus Michael Manga, of UC Berkeley, and Xiaowei Chen, of the University of Oklahoma.

“Seismic activity soared in one area for several years after wastewater injection was greatly reduced,” says Shirzaei. “That told us that existing prediction methods were inadequate.”

Back to basics

To address the problem, his team went back to basics, looking at how varying amounts of injected brine perturbed the crustal stresses and how these lead to earthquakes on a given fault.

“Fluids such as brine (and natural groundwater) can both be stored and move through rocks that are porous,” says Zhai.

The key was building a physics-based model that combined the rock’s ability to transport injected brine, and the rock’s elastic response to fluid pressure. Explains Shirzaei, “Our model includes the records collected for the past 23 years of brine injected at more than 700 Oklahoma wells into the Arbuckle formation.”

He adds that to make the scenario realistic, the model also includes the mechanical properties of the rocks in Oklahoma. The result was that the model successfully predicted changes in the crustal stress that come from brine injection.

For the final step, Shirzaei says, “We used a well-established physical model of how earthquakes begin so we could relate stress perturbations to the number and size of earthquakes.”

The team found that the physics-based framework does a good job of reproducing the distribution of actual earthquakes by frequency, magnitude, and time.

“An interesting finding,” says Zhai, “was that a tiny change in the rocks’ elastic response to changes in fluid pressure can amplify the number of earthquakes by several times. It’s a very sensitive factor.”

Making production safer

While wastewater injection can cause earthquakes, all major oil and gas production creates a large amount of wastewater that needs to be disposed of, and injection is the method the industry uses.

“So to make this safer in the future,” says Shirzaei, “our approach offers a way to forecast injection-caused earthquakes. This provides the industry with a tool for managing the injection of brine after fracking operations.”

Knowing the volume of brine to be injected and the location of the disposal well, authorities can estimate the probability that an earthquake of given size will result. Such probabilities can be used for short-term earthquake hazard assessment.

Alternatively, the team says, given the probability that an earthquake of certain size will happen, oil and gas operators can manage the injected brine volume to keep the probability of large earthquakes below a chosen value.

The end result, says Zhai, “is that this process will allow a safer practice, benefiting both the general public and the energy industry.”

Reference:
Guang Zhai, Manoochehr Shirzaei, Michael Manga, Xiaowei Chen. Pore-pressure diffusion, enhanced by poroelastic stresses, controls induced seismicity in Oklahoma. Proceedings of the National Academy of Sciences, 2019; 201819225 DOI: 10.1073/pnas.1819225116

Note: The above post is reprinted from materials provided by Arizona State University.

How to recognise where a volcano will erupt

Multiple volcanic craters cover the 'Campi Flegrei' near Naples, Italy. A new method aims at forecasting where new vents will occur.
Multiple volcanic craters cover the ‘Campi Flegrei’ near Naples, Italy. A new method aims at forecasting where new vents will occur. Credit: Mauro Antonio di Vito / INGV

On television, the eruption of volcano shoots magma right out of the top. However, it is not so uncommon that magma erupts from the volcano’s flank rather than its summit. After leaving the underground magma chamber, the magma forces its way sideways by fracturing rock, sometimes for tens of kilometres. Then, when it breaches the Earth’s surface, it forms one or more vents from which it spills out, sometimes explosively. This, for example, occurred at Bardarbunga in Iceland in August 2014, and Kilauea in Hawaii in August 2018.

It is a big challenge for volcanologists to guess where magma is heading and where it will breach the surface. A lot of effort is spent on this task, as it could minimize the risk for villages and cities endangered by eruptions. Now, Eleonora Rivalta and her team from the GFZ German Research Centre for Geosciences in Potsdam and institutional collaborators have devised a new method to generate vent location forecasts. The study is published in the journal Science Advances.

“Previous methods were based on the statistics of the locations of past eruptions,” says Eleonora Rivalta. “Our method combines physics and statistics: We calculate the paths of least resistance for ascending magma and tune the model based on statistics.” The researchers successfully tested the new approach with data from the Campi Flegrei caldera in Italy, one of the Earth’s highest-risk volcanoes.

“Calderas often look like a lawn covered in molehills”

Vents opened at the flank of a volcano are often used by just one eruption. All volcanoes may produce such one-time vents, but some do more than others. Their flanks are punctured by tens of vents whose alignment marks the locations where subsurface magma pathways have intersected the Earth’s surface.

At calderas, that is large cauldron-like hollows that form shortly after the emptying of a magma chamber in a volcanic eruption, vents may also open inside and on its rim. That is because they lack a summit to focus eruptions. “Calderas often look like a lawn covered in molehills,” says GFZ’s Eleonora Rivalta.

Most vents at calderas have only been used once. The resulting scattered, sometimes seemingly random spatial vent distribution threatens wide areas, presenting a challenge to volcanologists who draw forecast maps for the location of future eruptions. Such maps are also necessary for accurate forecasts of lava and pyroclastic flows or the expansion of ash plumes.

Vent forecast maps have so far been mainly based on the spatial distribution of past vents: “Volcanologists often assume that the volcano will behave like it did in the past,” says Eleonora Rivalta. “The problem is that often only a few tens of vents are visible on the volcano surface as major eruptive episodes tend to cover or obliterate past eruptive patterns. Hence, as mathematically sophisticated as the procedure can be, sparse data lead to coarse maps with large uncertainties. Moreover, the dynamics of a volcano may change with time, so that vent locations will shift.”

Succesful tests at the Campi Flegrei

Rivalta, a trained physicist, and a team of geologists and statisticians used volcano physics to improve the forecasts. “We employ the most up-to-date physical understanding of how magma fractures rock to move underground and combine it with a statistical procedure and knowledge of the volcano structure and history. We tune the parameters of the physical model until they match previous eruptive patterns. Then, we have a working model and can use it to forecast future eruption locations,” says Eleonora Rivalta.

The new approach was applied in southern Italy to the Campi Flegrei, a caldera close to Naples, which has a population of nearly one million. In the more than ten kilometres wide caldera, about eighty vents have fed explosive eruptions in the last 15,000 years. The approach performs well in retrospective tests, that is correctly forecasting the location of vents that were not used to tune the model, the researchers report.

“The most difficult part was to formulate the method in a way that works for all volcanoes and not just one—to generalize it,” Rivalta explains. “We will now perform more tests. If our method works well on other volcanoes too, it may help planning land usage in volcanic areas and forecasting the location of future eruptions with a higher certainty than previously possible.”

Reference:
E. Rivalta el al., “Stress inversions to forecast magma pathways and eruptive vent location,” Science Advances (2019). DOI: 10.1126/sciadv.aau9784

Note: The above post is reprinted from materials provided by Helmholtz Association of German Research Centres.

Faint foreshocks foretell California quakes

Earthquakes run in packs, but you can hear them coming, as noted in research from Los Alamos National Laboratory and California Institute of Technology.
Earthquakes run in packs, but you can hear them coming, as noted in research from Los Alamos National Laboratory and California Institute of Technology.

New research mining data from a catalog of more than 1.8 million southern California earthquakes found that nearly three-fourths of the time, foreshocks signalled a quake’s readiness to strike from days to weeks before the the mainshock hit, a revelation that could advance earthquake forecasting.

“We are progressing toward statistical forecasts, though not actual yes or no predictions, of earthquakes,” said Daniel Trugman, a seismologist at Los Alamos National Laboratory and coauthor of a paper out today in the journal Geophysical Research Letters. “It’s a little like the history of weather forecasting, where it has taken hundreds of years of steady progress to get where we are today.”

The paper, titled “Pervasive foreshock activity across southern Californa,” notes foreshocks preceded nearly 72 percent of the “mainshocks” studied (the largest quakes in a particular sequence), a percentage that is significantly higher than was previously understood.

Many of these foreshocks are so small, with magnitudes less than 1, that they are difficult to spot through visual analysis of seismic waveforms. To detect such small events requires advanced signal processing techniques and is a huge, data-intensive problem. Significant computing capabilities were key to extracting these new insights from the southern California Quake Template Matching Catalog, recently produced by Trugman and coauthor Zachary Ross, an assistant professor in seismology at Caltech. The template matching took approximately 300,000 GPU-hours on an array of 200 NVIDIA-P100 GPUs, involving 3-4 weeks of computing time for the final run. GPUs are special types of computers, optimal for massively parallel problems, as each GPU has thousands of cores, and each core is capable of handling its own computational thread. For perspective, a standard laptop has either 2 or 4 cores.The earthquake catalog is archived by the Southern California Earthquake Data Center.

The small foreshocks may be too difficult to discern in real time to be of use in earthquake forecasting. Another important issue is that quakes run in packs: they cluster in both space and time, so sorting the foreshocks of a particular quake out from the family of preliminary, main and aftershock rumbles of its fellow earth adjustments is no simple task.

An earthquake prediction tool is still far off, Trugman explains, and for humans who like a yes or no answer, a statistical analysis that suggests a quake’s probability is frustrating. But the potential insights and early warnings are improving, quake by quake.

Reference:
Daniel T. Trugman et al, Pervasive foreshock activity across southern California, Geophysical Research Letters (2019). DOI: 10.1029/2019GL083725

Note: The above post is reprinted from materials provided by Los Alamos National Laboratory.

Predicting seismic activity at fracking sites to prevent earthquakes

Aerial view of the hydraulic fracturing rig at Cuadrilla’s Preston New Road site. Credit: Matthew Hampson, Cuadrilla Resources Ltd
Aerial view of the hydraulic fracturing rig at Cuadrilla’s Preston New Road site. Credit: Matthew Hampson, Cuadrilla Resources Ltd

Scientists from the University of Bristol have found a more effective way to predict seismic activity at hydraulic fracturing sites, ensuring that potential earthquake activity remains within safe levels.

Hydraulic fracturing, or fracking, is a technique designed to recover gas and oil from shale rock by drilling down into the earth and injecting a mixture of water and sand at high-pressure, creating fractures that allow the gas or oil to flow out.

Like many other industries, such as coal mining, hydro-electricity and geothermal energy, fracking has in some cases been known to cause earthquakes.

In 2011 test operations near Blackpool had to be suspended after tremors of 1.5 and 2.2 magnitude were detected.

Investigations carried out after this concluded that it was highly probable that the drilling had caused the tremors and new ‘traffic light’ regulations were introduced at fracking sites across the country.

If earthquake magnitudes are below a certain level, then the injection can proceed as normal. If the earthquakes exceed a certain amber light magnitude, then the operator must proceed with caution by, for example, reducing the injection rate, pressure or volume. If the magnitude exceeds the red light magnitude, then the injection must pause.

Currently, there is little scientific basis for how the amber and red-light thresholds should be decided.

Lead author, Dr. James Verdon from the University’s School of Earth Sciences, said: “Many industries can create induced earthquakes, including both longstanding ones like coal mining and hydroelectricity, and newer ones like geothermal and hydraulic fracturing for shale gas.

“Our goal is to manage induced seismicity, ensuring that these industries conduct their activities in a safe manner, without posing a risk to nearby buildings and infrastructure.”

The Bristol-led research, published today in the journal Seismological Research Letters,shows that using microseismic data to make forecasts about expected seismicity can provide a far more effective approach than the simple traffic light scheme (TLS) system which is currently used.

Dr. Verdon added: “The TLS is a retroactive method. This means that the red-light threshold must be set far below the actual level we need to avoid, otherwise the operator would only stop after larger earthquakes have occurred.

“This is a problem because on the one hand operators may be required to stop their work even though everything is actually at a safe level. However, on the other hand if they set the red-light level too high then they may allow damaging events to occur.

“Our work is about developing and testing a model that can take the observations we have at an early stage in the operation and make predictions that are robust and accurate about what will happen as the injection proceeds, thus allowing an operator to make decisions while ensuring that any earthquakes remain within a safe level.”

All subsurface industries (for example, oil production, mining and geothermal) produce very small magnitude “microseismic events”—these are far too small to be detected even by sensitive instruments at the surface.

Instead, recording instruments called geophones are installed in monitoring boreholes that are within a few 100 meters of the injection point.

This allows them to pick up the pops and cracks of the rock as the fluid is injected. To give an idea of scale, a typical microseismic event might consist of a fracture the size of a dinner plate moving by less than a millimeter.

Dr. Verdon said: “These microseismic events can give us clues about whether the injection might be about to reactivate a larger fault and give us larger events, and it can give us clues as to what magnitude that event might be.

“So, our aim is to use the microseismic data, which is far too small to be felt by people at the surface and make models and predictions of whether the injection might be about to give us a larger event, and therefore should be stopped.”

The team developed a statistical model that takes the small-magnitude microseismic data and makes predictions about what magnitude the tremors might reach as injection continues.

Previously they tested their approach using past data from older sites. However, in this case they were analyzing live data from the Preston New Road site in Lancashire, and providing the operator, Cuadrilla, with their results, which they used to inform real-time decisions about how to proceed.

Dr. Verdon said: “Importantly, our modeling approach was successful—the magnitudes that actually occurred were in line with the magnitudes that we predicted from our model. This gives us confidence that our approach is robust and can be used for decision making at future injection sites.

“This approach has implications not only for today’s shale gas industry, but for future industries like geothermal energy and carbon capture and storage that are being planned in the UK.

Reference:
Huw Clarke, et al. Real-Time Imaging, Forecasting, and Management of Human-Induced Seismicity at Preston New Road, Lancashire, England. Seismological Research Letters, 19.06.2019.

Note: The above post is reprinted from materials provided by University of Bristol.

World’s smallest fossil monkey found in Amazon jungle

These fossil-rich sediments along the Alto Madre de Dios River in southern Peru have yielded hundreds of fossil teeth and bones, clues to what life in the Amazon was like 18 million years ago.
These fossil-rich sediments along the Alto Madre de Dios River in southern Peru have yielded hundreds of fossil teeth and bones, clues to what life in the Amazon was like 18 million years ago. Credit: Wout Salenbien, Duke University

A team of Peruvian and American scientists have uncovered the 18-million-year-old remains of the smallest fossil monkey ever found.

A fossilized tooth found in Peru’s Amazon jungle has been identified as belonging to a new species of tiny monkey no heavier than a hamster.

The specimen is important because it helps bridge a 15-million-year gap in the fossil record for New World monkeys, says a team led by Duke University and the National University of Piura in Peru.

The new fossil was unearthed from an exposed river bank along the RĂ­o Alto Madre de Dios in southeastern Peru. There, researchers dug up chunks of sandstone and gravel, put them in bags, and hauled them away to be soaked in water and then strained through sieves to filter out the fossilized teeth, jaws, and bone fragments buried within.

The team searched through some 2,000 pounds of sediment containing hundreds of fossils of rodents, bats and other animals before they spotted the lone monkey tooth.

“Primate fossils are as rare as hen’s teeth,” said first author Richard Kay, a professor of evolutionary anthropology at Duke who has been doing paleontological research in South America for nearly four decades.

A single upper molar, the specimen was just “double the size of the head of a pin” and “could fall through a window screen,” Kay said.

Paleontologists can tell a lot from monkey teeth, particularly molars. Based on the tooth’s relative size and shape, the researchers think the animal likely dined on energy-rich fruits and insects, and weighed in at less than half a pound—only slightly heavier than a baseball. Some of South America’s larger monkeys, such as howlers and muriquis, can grow to 50 times that heft.

“It’s by far the smallest fossil monkey that’s ever been found worldwide,” Kay said. Only one monkey species alive today, the teacup-sized pygmy marmoset, is smaller, “but barely,” Kay said.

In a paper published online July 23 in the Journal of Human Evolution, the team dubbed the animal Parvimico materdei, or “tiny monkey from the Mother of God River.”

Now stored in the permanent collections of the Institute of Paleontology at Peru’s National University of Piura, the find is important because it’s one of the few clues scientists have from a key missing chapter in monkey evolution.

Monkeys are thought to have arrived in South America from Africa some 40 million years ago, quickly diversifying into the 150-plus New World species we know today, most of which inhabit the Amazon rainforest. Yet exactly how that process unfolded is a bit of a mystery, in large part because of a gap in the monkey fossil record between 13 and 31 million years ago with only a few fragments.

In that gap lies Parvimico. The new fossil dates back 17 to 19 million years, which puts it “smack dab in the time and place when we would have expected diversification to have occurred in the New World monkeys,” Kay said.

The team is currently on another fossil collecting expedition in the Peruvian Amazon that will wrap up in August, concentrating their efforts in remote river sites with 30-million-year-old sediments.

“If we find a primate there, that would really be pay dirt,” Kay said.

Reference:
Richard F. Kay et al, Parvimico materdei gen. et sp. nov.: A new platyrrhine from the Early Miocene of the Amazon Basin, Peru, Journal of Human Evolution (2019). DOI: 10.1016/j.jhevol.2019.05.016

Note: The above post is reprinted from materials provided by Duke University.

Careful analysis of volcano’s plumbing system may give tips on pending eruptions

Pressure changes in the summit reservoirs of Kīlauea may help explain the number of earthquakes — or seismicity — in the volcano’s upper East Rift Zone.
Pressure changes in the summit reservoirs of Kīlauea may help explain the number of earthquakes — or seismicity — in the volcano’s upper East Rift Zone. Credit: USGS

A volcano will not send out an official invitation when it’s ready to erupt, but a team of researchers suggest that scientists who listen and watch carefully may be able to pick up signs that an eruption is about to happen.

In a study of Hawaii’s KÄ«lauea volcano, the researchers reported that pressure changes in the volcano’s summit reservoirs helped explain the number of earthquakes—or seismicity—in the upper East Rift Zone. This zone is a highly active region where several eruptions have occurred over the last few decades, including a spectacular one in 2018.

“We are interested in looking at the mechanisms that trigger seismicity at a very active and dynamic volcano, like KÄ«lauea Volcano in Hawaii,” said Christelle Wauthier, assistant professor of geosciences and Institute for CyberScience co-hire, Penn State. “There are several physical processes that can drive seismicity and, in this study, we were trying to find out which one was the most likely.”

According to Wauthier, the pressure changes that occur in the summit reservoir—an underground chamber hosting hot magma—causes stresses in the rocks and ground that surround the magma, even not at its immediate proximity. These stress changes can trigger small magnitude volcano-tectonic earthquakes, most of the time imperceptible to humans but that are picked up by the sensitive seismic equipment that monitor the volcano. This seismic activity, then, may better predict magma movements and resulting eruptions.

The researcher’s work challenges a previous theory that suggested the seismic activity in the rift zone was being triggered by the volcano’s gradual slip toward the sea. The southern flank of KÄ«lauea is gradually moving toward the ocean at about six centimeters a year.

While most people picture volcanoes violently erupting at their summits, KÄ«lauea is different because its sprawling system of underground tunnels and chambers where magma flows results in eruptions that can happen at various points miles from its summit. When magma travels out of these chambers and onto the Earth’s surface, it is called lava.

“Underneath, there is a conduit system that is extremely long—we’re talking 20 miles or so,” said Wauthier. “And it’s just like the plumbing in a house. A volcano’s plumbing system can be plugged up or blocked and that just might lead to an eruption.”

By better understanding the forces that are triggering seismicity, scientists monitoring seismic activity at other volcanoes could predict future eruptions more accurately, according to the researchers, who reported their findings in a recent issue of Geology. Because KÄ«lauea is one of the world’s most closely and densely monitored volcanic systems, it serves as a living laboratory to study volcanic activity that can be applied to study other volcanoes, added Wauthier, who worked with Diana C. Roman, staff scientist, Carnegie Institution for Science, and Michael P. Poland, scientist-in-charge, Yellowstone Volcano Laboratory, U.S. Geological Survey.

“While there are only a few volcanoes that are as highly instrumented as KÄ«lauea, which has a super-dense seismic network and GPS, so it’s very well-monitored, but other volcanoes are not monitored like that,” said Wauthier. “However, for volcanoes that have good seismic networks—and there are many of them—you can apply the exact same approach as this one to look if your volcano-tectonic seismicity—these small earthquakes—are due to magma being injected into a magma reservoir, or due to something else.”

The team used both seismic and satellite imagery data from mid- to late-2007 for the study. Seismic analysis was conducted with data collected on the upper East Rift Zone from the U.S. Geological Survey Hawaiian Volcano Observatory (HVO). Using information from global positioning satellites, also collected by HVO, the researchers were also able to analyze physical changes to the mountain’s shape and paying particular attention to ground surface deformations at the summit. They then looked at how these factors correlated with models of the stress changes caused by inflations and deflations of the summit reservoir.

By carefully analyzing movements to a volcano’s summit reservoir, researchers may be able to better predict when and where eruptions are likely to occur, then, according to the researchers. However, more work needs to be done, said Wauthier. Future research plans include looking at seismic activity and ground deformation data from other time periods of the volcano.

“We’ve been looking at the period in 2007, but that’s just a subset,” said Wauthier. “We could imagine just looking at a longer time period where we have other inflation-deflation events happening and see if we still conclude that same thing that it’s magma reservoir inflating that triggers the seismicity. It is likely that over the course of a long-term eruption like the 1983-2008 one, things are changing.”

Reference:
Christelle Wauthier et al. Modulation of seismic activity in KÄ«lauea’s upper East Rift Zone (HawaiĘ»i) by summit pressurization, Geology (2019). DOI: 10.1130/G46000.1

Note: The above post is reprinted from materials provided by Pennsylvania State University.

Research could protect cities in active earthquake zones

U of T's Jeremy Rimando sets up Differential Global Positioning System (DGPS) survey equipment to measure the amount of displacement on the Las Chacras Fault in San Juan, Argentina.
U of T’s Jeremy Rimando sets up Differential Global Positioning System (DGPS) survey equipment to measure the amount of displacement on the Las Chacras Fault in San Juan, Argentina. Credit: Cesar Distante

A study from the University of Toronto Mississauga reveals new clues about an earthquake that rocked Argentina’s San Juan province in the 1950s. The results add important data about one of the Earth’s most active thrust zones and could help to protect cities in the region from earthquake damage in the future.

Jeremy Rimando, the lead author of the study and a Ph.D. candidate in the lab of study co-author Lindsay Schoenbohm, an associate professor in the department of chemical and physical sciences. Their study, published in the journal Tectonics, focuses on the La Rinconada Fault in the western central area of Argentina.

“This region is seismically active and is bound by many thrust faults where one block of land moves over top of another,” says Rimando, who has conducted field research at several sites in the area. “It’s an area that experiences frequent earthquakes.”

The 30-kilometre-long La Rinconada Fault line marks a tectonic transition zone where the thin-skinned crust of the Eastern Precordillera meets the thick-skinned crust of Sierras Pampeanas in the Andes mountain range. The area is arid and rocky, with steep gravel-strewn hills and terraces that reveal the displacement of the Earth’s surface as the land shifts and slips along the fault line.

San Juan, with a population of 500,000, lies 15 kilometres to the north in an area bounded by several faults, including La Rinconada. A 1944 earthquake devastated the city and killed 10,000 people. Eight years later, San Juan experienced another severe earthquake with a recorded magnitude of 6.8. Rimando’s data points to the La Rinconada Fault as a potential generator of the second quake.

To determine if La Rinconada might be connected to the 1952 quake, Rimando calculated the slip rate—how fast two sides of the fault are moving relative to one another—which can provide clues about how often an earthquake might occur.

“We looked at features that were displaced by the fault line,” he says. “A low slip rate is usually associated with a long recurrence interval.”

Long recurrence intervals can mean that earthquakes may not happen often, but when they do, they can be big because of the strain that has built up over time. “If the slip rate is moving slowly, it can eventually build up a large amount of strain, resulting in big earthquakes that take place on a less frequent basis,” he says.

“Our data shows that La Rinconada is moving slowly at 0.4 mm per year,” Rimando says. He notes that the La Rinconada slip rate is associated with earthquakes ranging in magnitude from 6.6 to 7.2. “This is within the range of the 1952 earthquake.”

“Further investigation is required to determine the timing and recurrence interval on this fault, but knowing the very specific likely magnitude is helpful for planners,” says Schoenbohm. “Buildings shake at different frequencies depending on the earthquake, so the most likely magnitude is more important to know than the maximum magnitude. Narrowing that range as much as possible is really useful.

He adds that researchers “can’t definitively say that this was the fault, but we have added to possible proof that it could be because of the similarity in magnitude of the 1952 earthquake and the possible earthquake magnitudes that this fault caused. This information could impact building locations, zoning requirements and engineering infrastructure.”

Reference:
Jeremy M. Rimando et al. Late Quaternary Activity of the La Rinconada Fault Zone, San Juan, Argentina, Tectonics (2019). DOI: 10.1029/2018TC005321

Note: The above post is reprinted from materials provided by University of Toronto.

Underwater glacial melting is occurring at higher rates than modeling predicts

Researchers on the MV Steller are in front of the terminus of Alaska's LeConte Glacier in August 2016. An over-the-side pole holds the sonar instrument that collects data on the subsurface ice face as the vessel moves slowly through the icy water. Credit: David Sutherland
Researchers on the MV Steller are in front of the terminus of Alaska’s LeConte Glacier in August 2016. An over-the-side pole holds the sonar instrument that collects data on the subsurface ice face as the vessel moves slowly through the icy water. Credit: David Sutherland

Researchers have developed a new method to allow for the first direct measurement of the submarine melt rate of a tidewater glacier, and, in doing so, they concluded that current theoretical models may be underestimating glacial melt by up to two orders of magnitude.

In a National Science Foundation-funded project, a team of scientists, led by University of Oregon oceanographer Dave Sutherland, studied the subsurface melting of the LeConte Glacier, which flows into LeConte Bay south of Juneau, Alaska.

The team’s findings, which could lead to improved forecasting of climate-driven sea level rise, were published in the July 26 issue of the journal Science.

Direct melting measurements previously have been made on ice shelves in Antarctica by boring through to the ice-ocean interface beneath. In the case of vertical-face glaciers terminating at the ocean, however, those techniques are not available.

“We don’t have that platform to be able to access the ice in this way,” said Sutherland, a professor in the UO’s Department of Earth Sciences. “Tidewater glaciers are always calving and moving very rapidly, and you don’t want to take a boat up there too closely.”

Most previous research on the underwater melting of glaciers relied on theoretical modeling, measuring conditions near the glaciers and then applying theory to predict melt rates. But this theory had never been directly tested.

“This theory is used widely in our field,” said study co-author Rebecca H. Jackson, an oceanographer at Rutgers University who was a postdoctoral researcher at Oregon State University during the project. “It’s used in glacier models to study questions like: how will the glacier respond if the ocean warms by one or two degrees?”

To test these models in the field, the research team of oceanographers and glaciologists deployed a multibeam sonar to scan the glacier’s ocean-ice interface from a fishing vessel six times in August 2016 and five times in May 2017.

The sonar allowed the team to image and profile large swaths of the underwater ice, where the glacier drains from the Stikine Icefield. Also gathered were data on the temperature, salinity and velocity of the water downstream from the glacier, which allowed the researchers to estimate the meltwater flow.

They then looked for changes in melt patterns that occurred between the August and May measurements.

“We measured both the ocean properties in front of the glacier and the melt rates, and we found that they are not related in the way we expected,” Jackson said. “These two sets of measurements show that melt rates are significantly, sometimes up to a factor of 100, higher than existing theory would predict.”

There are two main categories of glacial melt: discharge-driven and ambient melt. Subglacial discharge occurs when large volumes, or plumes, of buoyant meltwater are released below the glacier. The plume combines with surrounding water to pick up speed and volume as it rises up swiftly against the glacial face. The current steadily eats away from the glacier face, undercutting the glacier before eventually diffusing into the surrounding waters.

Most previous studies of ice-ocean interactions have focused on these discharge plumes. The plumes, however, typically affect only a narrow area of the glacier face, while ambient melt instead covers the rest of the glacier face.

Predictions have estimated ambient melt to be 10-100 times less than the discharge melt, and, as such, it is often disregarded as insignificant, said Sutherland, who heads the UO’s Oceans and Ice Lab.

The research team found that submarine melt rates were high across the glacier’s face over both of the seasons surveyed, and that the melt rate increases from spring to summer.

While the study focused on one marine-terminating glacier, Jackson said, the new approach should be useful to any researchers who are studying melt rates at other glaciers. That would help to improve projections of global sea level rise, she added.

“Future sea level rise is primarily determined by how much ice is stored in these ice sheets,” Sutherland said. “We are focusing on the ocean-ice interfaces, because that’s where the extra melt and ice is coming from that controls how fast ice is lost. To improve the modeling, we have to know more about where melting occurs and the feedbacks involved.”

Reference:
D. A. Sutherland, R. H. Jackson, C. Kienholz, J. M. Amundson, W. P. Dryer, D. Duncan, E. F. Eidam, R. J. Motyka, J. D. Nash. Direct observations of submarine melt and subsurface geometry at a tidewater glacier. Science, 2019 DOI: 10.1126/science.aax3528

Note: The above post is reprinted from materials provided by University of Oregon. Original written by Carolyn Levinn and Jim Barlow, University Communications.

‘Crystal clocks’ used to time magma storage before volcanic eruptions

Magma erupting at the Holuhraun lava field in August 2014. Credit: Bob White
Magma erupting at the Holuhraun lava field in August 2014. Credit: Bob White

The molten rock that feeds volcanoes can be stored in the Earth’s crust for as long as a thousand years, a result which may help with volcanic hazard management and better forecasting of when eruptions might occur.

Researchers from the University of Cambridge used volcanic minerals known as ‘crystal clocks’ to calculate how long magma can be stored in the deepest parts of volcanic systems. This is the first estimate of magma storage times near the boundary of the Earth’s crust and the mantle, called the Moho. The results are reported in the journal Science.

“This is like geological detective work,” said Dr Euan Mutch from Cambridge’s Department of Earth Sciences, and the paper’s first author. “By studying what we see in the rocks to reconstruct what the eruption was like, we can also know what kind of conditions the magma is stored in, but it’s difficult to understand what’s happening in the deeper parts of volcanic systems.”

“Determining how long magma can be stored in the Earth’s crust can help improve models of the processes that trigger volcanic eruptions,” said co-author Dr John Maclennan, also from the Department of Earth Sciences. “The speed of magma rise and storage is tightly linked to the transfer of heat and chemicals in the crust of volcanic regions, which is important for geothermal power and the release of volcanic gases to the atmosphere.”

The researchers studied the Borgarhraun eruption of the Theistareykir volcano in northern Iceland, which occurred roughly 10,000 years ago, and was fed directly from the Moho. This boundary area plays an important role in the processing of melts as they travel from their source regions in the mantle towards the Earth’s surface. To calculate how long the magma was stored at this boundary area, the researchers used a volcanic mineral known as spinel like a tiny stopwatch or crystal clock.

Using the crystal clock method, the researchers were able to model how the composition of the spinel crystals changed over time while the magma was being stored. Specifically, they looked at the rates of diffusion of aluminium and chromium within the crystals and how these elements are ‘zoned’.

“Diffusion of elements works to get the crystal into chemical equilibrium with its surroundings,” said Maclennan. “If we know how fast they diffuse we can figure out how long the minerals were stored in the magma.”

The researchers looked at how aluminium and chromium were zoned in the crystals, and realised that this pattern was telling them something exciting and new about magma storage time. The diffusion rates were estimated using the results of previous lab experiments. The researchers then used a new method, combining finite element modelling and Bayesian nested sampling to estimate the storage timescales.

“We now have really good estimates in terms of where the magma comes from in terms of depth,” said Mutch. “No one’s ever gotten this kind of timescale information from the deeper crust.”

Calculating the magma storage time also helped the researchers determine how magma can be transferred to the surface. Instead of the classical model of a volcano with a large magma chamber beneath, the researchers say that instead, it’s more like a volcanic ‘plumbing system’ extending through the crust with lots of small ‘spouts’ where magma can be quickly transferred to the surface.

A second paper by the same team, recently published in Nature Geoscience, found that that there is a link between the rate of ascent of the magma and the release of CO2, which has implications for volcano monitoring.

The researchers observed that enough CO2 was transferred from the magma into gas over the days before eruption to indicate that CO2 monitoring could be a useful way of spotting the precursors to eruptions in Iceland. Based on the same set of crystals from Borgarhraun, the researchers found that magma can rise from a chamber 20 kilometres deep to the surface in as little as four days.

The research was supported by the Natural Environment Research Council (NERC).

Reference:
Euan J. F. Mutch*, John Maclennan, Tim J. B. Holland, Iris Buisman. Millennial storage of near-Moho magma. Science, 2019, Vol. 365, Issue 6450, pp. 260-264 DOI: http://dx.doi.org/10.1126/science.aax4092

Note: The above post is reprinted from materials provided by University of Cambridge. The original story is licensed under a Creative Commons License.

Jurassic fossil shows how early mammals could swallow like their modern descendants

The fossil of Microdocodon gracilis is preserved in two rock slabs, found in a site near the Wuhua village in the Daohugou area of Inner Mongolia, China. Credit: Zhe-Xi Luo
The fossil of Microdocodon gracilis is preserved in two rock slabs, found in a site near the Wuhua village in the Daohugou area of Inner Mongolia, China. Credit: Zhe-Xi Luo

The 165-million-year-old fossil of Microdocodon gracilis, a tiny, shrew-like animal, shows the earliest example of modern hyoid bones in mammal evolution.

The hyoid bones link the back of the mouth, or pharynx, to the openings of the esophagus and the larynx. The hyoids of modern mammals, including humans, are arranged in a “U” shape, similar to the saddle seat of children’s swing, suspended by jointed segments from the skull. It helps us transport and swallow chewed food and liquid — a crucial function on which our livelihood depends.

Mammals as a whole are far more sophisticated than other living vertebrates in chewing up food and swallowing it one small lump at a time, instead of gulping down huge bites or whole prey like an alligator.

“Mammals have become so diverse today through the evolution of diverse ways to chew their food, weather it is insects, worms, meat, or plants. But no matter how differently mammals can chew, they all have to swallow in the same way,” said Zhe-Xi Luo, PhD, a professor of organismal biology and anatomy at the University of Chicago and the senior author of a new study of the fossil, published this week in Science.

“Essentially, the specialized way for mammals to chew and then swallow is all made possible by the agile hyoid bones at the back of the throat,” Luo said.

‘A pristine, beautiful fossil’

This modern hyoid apparatus is mobile and allows the throat muscles to control the intricate functions to transport and swallow chewed food or drink fluids. Other vertebrates also have hyoid bones, but their hyoids are simple and rod-like, without mobile joints between segments. They can only swallow food whole or in large chunks.

When and how this unique hyoid structure first appeared in mammals, however, has long been in question among paleontologists. In 2014, Chang-Fu Zhou, PhD, from the Paleontological Museum of Liaoning in China, the lead author of the new study, found a new fossil of Microdocodon preserved with delicate hyoid bones in the famous Jurassic Daohugou site of northeastern China. Soon afterwards, Luo and Thomas Martin from the University of Bonn, Germany, met up with Zhou in China to study the fossil.

“It is a pristine, beautiful fossil. I was amazed by the exquisite preservation of this tiny fossil at the first sight. We got a sense that it was unusual, but we were puzzled about what was unusual about it,” Luo said. “After taking detailed photographs and examining the fossil under a microscope, it dawned on us that this Jurassic animal has tiny hyoid bones much like those of modern mammals.”

This new insight gave Luo and his colleagues added context on how to study the new fossil. Microdocodon is a docodont, from an extinct lineage of near relatives of mammals from the Mesozoic Era called mammaliaforms. Previously, paleontologists anticipated that hyoids like this had to be there in all of these early mammals, but it was difficult to identify the delicate bones. After finding them in Microdocodon, Luo and his collaborators have since found similar fossilized hyoid structures in other Mesozoic mammals.

“Now we are able for the first time to address how the crucial function for swallowing evolved among early mammals from the fossil record,” Luo said. “The tiny hyoids of Microdocodon are a big milestone for interpreting the evolution of mammalian feeding function.”

New insights on mammal evolution as a whole

Luo also worked with postdoctoral scholar Bhart-Anjan Bhullar, PhD, now on the faculty at Yale University, and April Neander, a scientific artist and expert on CT visualization of fossils at UChicago, to study casts of Microdocodon and reconstruct how it lived.

The jaw and middle ear of modern mammals are developed from (or around) the first pharyngeal arch, structures in a vertebrate embryo that develop into other recognizable bones and tissues. Meanwhile, the hyoids are developed separately from the second and the third pharyngeal arches. Microdocodon has a primitive middle ear still attached to the jaw like that of other early mammals like cynodonts, which is unlike the ear of modern mammals. Yet its hyoids are already like those of modern mammals.

“Hyoids and ear bones are all derivatives of the primordial vertebrate mouth and gill skeleton, with which our earliest fishlike ancestors fed and respired,” Bhullar said. “The jointed, mobile hyoid of Microdocodon coexists with an archaic middle ear — still attached to the lower jaw. Therefore, the building of the modern mammal entailed serial repurposing of a truly ancient system.”

The tiny, shrew-like creature likely weighed only 5 to 9 grams, with a slender body, and an exceptionally long tail. The dimensions of its limb bones match up with those of modern tree-dwellers.

“Its limb bones are as thin as matchsticks, and yet this tiny Mesozoic mammal still lived an active life in trees,” Neander said.

The fossil beds that yielded Microdocodon are dated 164 to 166 million years old. Microdocodon co-existed with other docodonts like the semiaquatic Castorocauda, the subterranean Docofossor, the tree-dwelling Agilodocodon, as well as some mammaliaform gliders.

Reference:
Chang-Fu Zhou, Bhart-Anjan S. Bhullar, April I. Neander, Thomas Martin, Zhe-Xi Luo. New Jurassic mammaliaform sheds light on early evolution of mammal-like hyoid bones. Science, 19 Jul 2019: Vol. 365, Issue 6450, pp. 276-279 DOI: 10.1126/science.aau9345

Note: The above post is reprinted from materials provided by University of Chicago Medical Center. Original written by Matt Wood.

Cosmic pearls: Fossil clams in Florida contain evidence of ancient meteorite

Researchers searching for fossils kept finding tiny glassy spheres inside ancient clams. After more than a decade, testing suggests they are evidence of one or more undocumented meteorite impacts in Florida’s distant past. Credit: Florida Museum photo by Kristen Grace

Researchers picking through the contents of fossil clams from a Sarasota County quarry found dozens of tiny glass beads, likely the calling cards of an ancient meteorite.

Analysis of the beads suggests they are microtektites, particles that form when the explosive impact of an extraterrestrial object sends molten debris hurtling into the atmosphere where it cools and recrystallizes before falling back to Earth.

They are the first documented microtektites in Florida and possibly the first to be recovered from fossil shells.

Mike Meyer was a University of South Florida undergraduate when he discovered the microtektites during a 2006 summer fieldwork project led by Roger Portell, invertebrate paleontology collections director at the Florida Museum of Natural History.

As part of the project, students systematically collected fossils from the shell-packed walls of a quarry that offered a cross-section of the last few million years of Florida’s geological history. They pried open fossil clams, washing the sediment trapped inside through very fine sieves. Meyer was looking for other tiny objects — the shells of single-celled organisms known as benthic foraminifera — when he noticed the translucent glassy balls, smaller than grains of salt.

“They really stood out,” said Meyer, now an assistant professor of Earth systems science at Harrisburg University in Pennsylvania. “Sand grains are kind of lumpy, potato-shaped things. But I kept finding these tiny, perfect spheres.”

After the fieldwork ended, his curiosity about the spheres persisted. But his emails to various researchers came up short: No one knew what they were. Meyer kept the spheres — 83 in total — in a small box for more than a decade.

“It wasn’t until a couple years ago that I had some free time,” he said. “I was like, ‘Let me just start from scratch.'”

Meyer analyzed the elemental makeup and physical features of the spheres and compared them to microtektites, volcanic rock and byproducts of industrial processes, such as coal ash. His findings pointed to an extraterrestrial origin.

“It did blow my mind,” he said.

He thinks the microtektites are the products of one or more small, previously unknown meteorite impacts, potentially on or near the Florida Platform, the plateau that undergirds the Florida Peninsula.

Initial results from an unpublished test suggest the spheres have traces of exotic metals, further evidence they are microtektites, Meyer said.

Most of them had been sealed inside fossil Mercenaria campechiensis or southern quahogs. Portell said that as clams die, fine sediment and particles wash inside. As more sediment settles on top of the clams over time, they close, becoming excellent long-term storage containers.

“Inside clams like these we can find whole crabs, sometimes fish skeletons,” Portell said. “It’s a nice way of preserving specimens.”

During the 2006 fieldwork, the students recovered microtektites from four different depths in the quarry, which is “a little weird,” Meyer said, since each layer represents a distinct period of time.

“It could be that they’re from a single tektite bed that got washed out over millennia or it could be evidence for numerous impacts out on the Florida Platform that we just don’t know about,” he said.

The researchers plan to date the microtektites, but Portell’s working guess is that they are “somewhere around 2 to 3 million years old.”

One oddity is that they contain high amounts of sodium, a feature that sets them apart from other impact debris. Salt is highly volatile and generally boils off if thrust into the atmosphere at high speed, Meyer said.

“This high sodium content is intriguing because it suggests a very close location for the impact,” Meyer said. “Or at the very least, whatever impact created it likely hit a very large reserve of rock salt or the ocean. A lot of those indicators point to something close to Florida.”

Meyer and Portell suspect there are far more microtektites awaiting discovery in Florida and have asked amateur fossil collectors to keep an eye out for the tiny spheres.

But no one will be recovering microtektites from the original quarry any time soon. It’s now part of a housing development.

“Such is the nature of Florida,” Meyer said.

Peter Harries of North Carolina State University also co-authored the study.

Reference:
Mike Meyer, Peter J. Harries, Roger W. Portell. A first report of microtektites from the shell beds of southwestern Florida. Meteoritics & Planetary Science, 2019; DOI: 10.1111/maps.13299

Note: The above post is reprinted from materials provided by Florida Museum of Natural History.

Drilling Deeper : A new study shows Americans are drilling deeper than ever for fresh water

Groundwater well drilling equipment in California's Central Valley. Photo Credit: Chad Ress
Groundwater well drilling equipment in California’s Central Valley. Photo Credit: Chad Ress

Groundwater may be out of sight, but for over 100 million Americans who rely on it for their lives and livelihoods it’s anything but out of mind. Unfortunately, wells are going dry and scientists are just beginning to understand the complex landscape of groundwater use.

Now, researchers at UC Santa Barbara have published the first comprehensive account of groundwater wells across the contiguous United States. They analyzed data from nearly 12 million wells throughout the country in records stretching back decades. Their findings appear in the journal Nature Sustainability.

In tackling the work, Debra Perrone and Scott Jasechko had a number of different questions about groundwater usage they wanted to address. First they set out to determine both where in the country wells are located and what purposes they serve — domestic, industrial or agricultural. They also wanted to track the depths of wells in different areas and test to see if wells are being drilled deeper over time.

Focusing on regions known to depend on groundwater, such as California’s Central Valley, the pair collected a wealth of information about different types of wells across the country. Groundwater is generally a matter of state management, so they had to cull their data from a variety of sources. “[That was] one of the biggest hurdles,” said Perrone, an assistant professor in UC Santa Barbara’s environmental studies department.

“It took us about four years to collect and quality-assure all these data sources,” added Jasechko, an assistant professor based in the Bren School of Environmental Science & Management.

Scientists know that groundwater depletion is causing some wells to run dry. Where conditions are right, drilling new and deeper wells can stave off this issue, for those who can afford it. Indeed, Perrone and Jasechko found that new wells are getting deeper between 1.4 and 9.2 times as often as they are being drilled shallower.

What’s more, the researchers found that 79% of areas they looked at showed well-deepening trends across a window spanning 1950 to 2015. Hotspots of this activity include California’s Central Valley, the High Plains of southwestern Kansas, and the Atlantic Coastal Plain, among other regions.

“We were surprised how widespread deeper well drilling is,” Jasechko said. News media had documented the trend in places like the Central Valley, but it is pervasive in many other parts of the country as well. This includes places like Iowa, where groundwater hasn’t been studied as intensively, he noted.

The reasons for drilling deeper are varied, according to Perrone. For instance, people drill deeper to avoid contamination seeping into aquifers from the surface, or to access aquifers that have less stringent withdrawal regulations, she explained. Some people may drill deeper to source more water.

“What we’re finding is that in places where water levels are declining, some people are drilling deeper, maybe to avoid having their primary water supply go dry,” Perrone said. “Regardless of the reasons why Americans are drilling deeper, we suggest that deeper well drilling is an unsustainable stopgap to groundwater depletion.”

Four major factors explain why deeper drilling won’t solve water woes indefinitely. For starters, it costs more, and it requires more energy to pump water from deep underground compared to water closer to the surface.

Geology presents another challenge: Deeper strata are generally less conducive to groundwater extraction. And finally, groundwater tends to get saltier at depth, so at a certain point it becomes unusable if not treated. As a result, in many regions there’s a floor to how deep we can productively drill for water.

This issue hits rural communities particularly hard. “Groundwater is a crucial resource for rural communities,” Perrone said. “Our previous work found that rural groundwater wells are especially vulnerable to going dry.” What’s more, these communities often have less capacity to update their groundwater infrastructure. Groundwater is also important to the agricultural sector, which often relies on it for irrigation, especially during droughts, she added.

Deliberate groundwater governance and management have emerged as active areas in addressing this challenge. The idea is to become more conscientious about how groundwater is used and regulate and monitor the practices more effectively. Additional research is underway on managed aquifer recharge, namely encouraging water to percolate back underground. This could be normal surface water, flood water or treated water. And particularly dry areas are considering whether to increase their use of recycled water.

Researchers, practitioners and policymakers from around the world will discuss the challenges facing groundwater use as well as potential solutions at an upcoming conference on groundwater sustainability. Perrone is one of the lead organizers for the event, which will convene in Valencia, Spain this October.

This new paper provides additional context to one of Perrone and Jasechko’s past studies — completed with professors Grant Ferguson of the University of Saskatchewan, and Jennifer McIntosh at the University of Arizona — where they found that the United States may have less usable groundwater than previously thought. It also ties into Perrone’s work regarding groundwater policy across the U.S. In the future, she plans to look at the legal frameworks surrounding groundwater use. “My goal is to understand what types of laws are being passed in the western 17 states to manage groundwater withdrawals in more sustainable ways,” she said.

Note: The above post is reprinted from materials provided by University of California – Santa Barbara.

Solving the salt problem for seismic imaging

The output of the proposed methodology, which is a two-part optimization process that refines a common technique used to image salt bodies. The black area represents the salt region. Credit: Mahesh Kalita
The output of the proposed methodology, which is a two-part optimization process that refines a common technique used to image salt bodies. The black area represents the salt region. Credit: Mahesh Kalita

The efficient extraction of oil and gas from within the Earth’s crust requires accurate images of subsurface rock structures. Some materials are hard to capture, so KAUST researchers have developed a computational method for modeling large accumulations of subsurface salt, a challenging material to derive accurately from seismic imaging data.

Seismic imaging involves sending soundwaves into the ground, where they will be reflected at boundaries between rock structures. Scientists analyze the reflected soundwaves to determine subsurface rock types and formations, and to pinpoint fossil fuel reservoirs.

However, in some regions, such as the Gulf of Mexico, the subsurface is peppered with salt bodies, which are huge accumulations of salt formed millions of years ago deep inside the Earth. Salt is a low-density, buoyant substance, meaning that salt bodies gradually rise through the Earth’s crust over time. This causes stress-related complexities between the salt and the surrounding rock layers. Furthermore, the salt’s crystal structure means that soundwaves are reflected at random, and there are no useable low frequencies retained in the seismic data.

“Data from salt zones are presently analyzed by highly trained experts rather than modeled by a computer,” explains Mahesh Kalita, a KAUST Ph.D. student in Tariq Alkhalifah’s group. “This is a time-consuming and expensive process that carries the risk of human error. We’ve developed a robust computational method for interpreting seismic data from salt bodies quickly and more accurately.”

Existing models use a technique called full waveform inversion (FWI) to minimize the disparity between observed and modeled data. However, the lack of low frequencies in soundwave data from salt bodies means that a traditional FWI fails. Kalita and the team developed a two-part optimization process to refine FWI for salt body imaging.

“For the topmost layer of salt, we get a good enough signal to determine where the salt body begins, but then the soundwave energy rapidly disperses,” says Kalita. “Our technique takes the initial data from this top layer and ‘smears’ it across the most likely area that the salt body encompasses. We call this technique ‘flooding’.”

The resulting model is then tested alongside observed data to check that the surrounding rock structures match up and to ensure the model has not been “over-flooded.” Initial trials using a 1990s dataset from the Gulf of Mexico showed promise, with the new technique generating an accurate representation of local salt bodies.

“We will next trial our automated technique on recent, high-quality datasets that incorporate more three-dimensional details,” says Kalita.

Reference:
Mahesh Kalita et al, Regularized full-waveform inversion with automated salt flooding, Geophysics (2019). DOI: 10.1190/geo2018-0146.1

Note: The above post is reprinted from materials provided by King Abdullah University of Science and Technology.

Scientists discover how and when a subterranean ocean emerged

Schematic diagram of water and chlorine transfer by the oceanic crust into the transitional zone of the mantle and the subsequent capture of the resulting material by an Archaean mantle plume. Credit: Evgeny Asafov
Schematic diagram of water and chlorine transfer by the oceanic crust into the transitional zone of the mantle and the subsequent capture of the resulting material by an Archaean mantle plume. Credit: Evgeny Asafov

“The mechanism which caused the crust that had been altered by seawater to sink into the mantle functioned over 3.3 billion years ago. This means that a global cycle of matter, which underpins modern plate tectonics, was established within the first billion years of the Earth’s existence, and the excess water in the transition zone of the mantle came from the ancient ocean on the planet’s surface,” said project leader and co-author of the article Alexander Sobolev, a member of the Russian Academy of Sciences (RAS) and Doctor of Geological and Mineralogical Sciences who is a Professor at Vernadsky Institute for Geochemistry and Analytical Chemistry under the Russian Academy of Sciences.

The Earth’s crust consists of large continuously moving blocks known as tectonic plates. Mountains are produced when these plates collide and rise up, and the shock of the collisions leads to earthquakes and tsunamis. These plates move very actively under the World Ocean: old oceanic crust, including the minerals that have absorbed seawater, sinks deep into the Earth’s mantle. Some of this water is released again due to the effect of high temperatures and plays a role in volcanic eruptions, such as those that occur in Kamchatka, the Kuril islands and Japan. The water that remains in minerals of the oceanic crust at higher temperatures continues to descend into the deep mantle and accumulates at a depth of 410-660 km in the structure of the minerals wadsleyite and ringwoodite and high-pressure modifications of olivine (magnesium iron silicate), the main mineral of the mantle. Experiments have shown that these minerals can contain significant quantities of water and chlorine. This is how the greatest part of the World Ocean could be “pumped” into the planet’s interior over the billions of years of its existence.

This process is only a part of the global cycle of the Earth’s matter, which is called convection and underpins plate tectonics, a feature that distinguishes our planet from all other bodies in the Solar System. Many scientists study this mechanism, trying to understand at which stage of the Earth’s history it appeared.

In order to study the mantle of our planet and investigate its composition, geochemists (scientists who specialise in the chemical composition of the Earth and the processes of rock formation) use samples of volcanic rocks that consist of solidified magma of the mantle. This is a silicate melt enriched in volatile components, such as water, carbon dioxide, chlorine and sulphur. There are different types of magma: scientists commonly use basaltic lava (with a temperature of approximately 1200°C), but komatiitic magma, which was erupted during the early history of the Earth, is hotter (at 1500-1600°C). It can help to describe the evolution of the Earth’s inner layers, as it matches the composition of the mantle more completely.

Komatiites are a type of volcanic rock that formed from komatiitic magma billions of years ago and whose composition has changed dramatically in the intervening epochs. It no longer provides information about the content of volatile components, such as water and chlorine. But these rocks still contain remnants of the magmatic mineral olivine, which trapped inclusions of solidified magma during the crystallisation process and protected them from subsequent changes. Such inclusions, just tens of microns across, retain detailed information about the composition of komatiitic melts, including the content of water and chlorine and the isotopic composition of hydrogen. In order to extract this information, inclusions of solidified magma must be heated to the natural melting point of over 1500°C and then immediately tempered to produce clear tempered glass that can later be used for chemical analyses.

In 2016, an international group headed by scientists from the Vernadsky Institute for Geochemistry and Analytical Chemistry studied komatiitic magma of the Abitibi greenstone belt in Canada, which is 2.7 billion years old. Greenstone belts are territories consisting of magmatic rocks that contain greenish minerals. This was the first article that the team published in Nature as part of the project supported by the Russian Science Foundation grant. At that time, the scientists collected initial data on the content of water and a variety of labile elements, such as chlorine, lead and barium, in the transition zone between the upper and lower mantle layers at a depth of 410-660 km, which led them to hypothesise that an ancient subterranean water reservoir once existed that was comparable in mass to the present-day World Ocean. The scientists believe that such a quantity of water was accumulated at the early stages of the Earth’s development.

“In the new article, we presented geochemical data indicating that the cycle of global immersion of oceanic crust into the mantle began much earlier than most experts believed, and it could have functioned as early as the first billion years of the Earth’s history,” noted Alexander Sobolev.

In the course of the work, the scientists once again investigated the composition of komatiite magma, but of a different origin: it was collected from the Barberton greenstone belt in South Africa, which is 3.3 billion years old. The magma was heated using a specialised high-temperature apparatus that can withstand temperatures of up to 1700°C. The geochemists found out that the previously discovered deep water-containing reservoir was already present in the Earth’s mantle in the Palaeoarchaean era, 600 million years earlier than established in the previous study.

Reference:
Alexander V. Sobolev et al, Deep hydrous mantle reservoir provides evidence for crustal recycling before 3.3 billion years ago, Nature (2019). DOI: 10.1038/s41586-019-1399-5

Note: The above post is reprinted from materials provided by AKSON Russian Science Communication Association .

How a drilling ship pulls cores from 2.5 miles below the sea

The floormen (in yellow jackets) and drillers (in white booths in background) of Expedition 383 retrieve core barrels and sediment cores around the clock. Credit: Jenny Middleton/Lamont-Doherty Earth Observatory
The floormen (in yellow jackets) and drillers (in white booths in background) of Expedition 383 retrieve core barrels and sediment cores around the clock. Credit: Jenny Middleton/Lamont-Doherty Earth Observatory

An ocean drilling ship is not an ocean drilling ship without the skilled and experienced personnel that control, execute and overview the drilling operations. The JOIDES Resolution is no exception.

Of the 123 souls currently onboard, about 30 people facilitate the success and safety of all ocean drilling operations—about the same number as scientists onboard. Among them are five drillers, two tool pushers, six floormen and two derrickmen. While drillers control the advance of the drill pipe and the motion of the core barrel within the drill pipe from a control booth, tool pushers oversee the operations and maintain equipment and tools. Floormen and derrickmen perform all actions on the rig floor, from putting the drill pipe together and sending the core barrel down the drill pipe to the sea floor, to eventually pulling a sediment-laden core out of the core barrel. Most of the drill crew have decades of experience.

Drilling ocean sediments for scientific purposes is not simply achieved by forcing a steel rod into the sea floor and hoping for the best recovery. It actually involves building a multi-piece drill bit (called the bottom-hole assembly) that cuts into the seabed, as well as carefully maneuvering and documenting the location of the drill bit near and below the seafloor, and adjusting the drilling tools according to the stiffness and composition of the material. Most importantly, seafloor drilling requires facilitating safe drilling operations, in particular for those right in the center of action on the JOIDES Resolution rig floor, our floormen.

As a sedimentologist onboard, I primarily work in the core laboratory. On the live feed monitors of the core laboratory, we can watch the drill team work on the rig floor. It is winter in the Southern Ocean at the moment, so it is mostly windy or rainy outside, or in fact both. Sometimes this makes me feel a little bit like I am in a golden tower in the core lab, far away from all the danger, grease, and noise of the drill floor. However, this does not diminish my respect and gratitude towards the drill crew and their work, as the quality of the drilled sediments they recover often governs the quality and impact of our scientific results. This particularly struck me when I had the chance to climb up the derrick of the JOIDES Resolution, six weeks into our expedition.

The top of the derrick ascends 65 meters (over 200 feet!) above the sea level, and is used to raise the drill pipe to a vertical position from the hull of the ship, in order to lower it to the sea floor. If you want to be at the highest point of the derrick (called the “crown”), you have to trust your arms, legs and your fall protection device to bring you all the way to the top of the drill rig. I thank Wouter, our Dutch driller, who talked me through the process of how to wear the required six-pound harness, how to use the safety carabiners, and how to change my fall protection system at each of the six wet and greasy ladders.

In order to drill ocean sediments, the drill pipe must first be extended to the seafloor, which requires lowering the pipes through the water column. This is done by adding 30-meter segments of drill pipe (a “stand”) on top of each other using the winch system of the derrick—a process that is called “tripping pipe.” Depending on the water depth of our study site, this usually takes several hours. I, as an impatient person, always have to remind myself that, for the length of a stand of 30m relative to the mean ocean depth of 4,000m (~2.5 miles), a few hours of tripping pipe is actually very fast. For an equivalent scale using the 10cm derrick of our paper model JOIDES Resolution, below, the whole sedimentology team onboard must stand next to each other to mimic the average depth of the ocean and the distance over which we have to trip the pipe.

Tripping pipe only brings us to the bottom of the ocean, but not into the sea floor. Drill tools need to be lowered through the drill pipe in order to recover seabed samples, 4,000 meters below the ship. For marine sediments, this is done through Advanced Piston Coring (APC) or Half-APC, where a piston assembly with an empty core liner is lowered by wireline through the drill pipe. At the chosen depth, the “firing depth,” the driller increases the hydraulic pressure on the core barrel, which allows the piston to suddenly, but in a controlled manner, penetrate 10 meters (APC) or 5 meters (Half-APC) into the sediments below. This firing process fills up the plastic core liner with precious ocean mud samples. This cycle repeats after the core barrel is raised to the rig floor through the wireline, and the outer drill pipe advances 10 meters further into the sea floor.

Ocean drilling is easier said than done. It is fascinating at the same time how technology and the expertise of our drilling and operations team come together to retrieve a mostly undisturbed and continuous climate archive from a far away place and time. I cannot thank them enough for their work as they are a crucial part in the long process of unveiling the inner workings and mechanisms that govern our Earth system.

Note: The above post is reprinted from materials provided by Earth Institute, Columbia University .

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