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Seismologists ask: How close are we to an eruption?

Seismologists ask How close-GeologyPage
In 2012, repairs were made to several seismic monitoring stations around Mount St. Helens, including the September Lobe station shown here. Credit: Marc Biundo/ USGS

Scientists analyzing the data from seismic networks are becoming better at detecting volcanic activity and at depicting the source and structure of the “plumbing” beneath the world’s volcanoes. But a critical question remains: Can these data help predict when a volcano is close to erupting?

In a session at the 2016 Annual Meeting of the Seismological Society of America (SSA) held April 20-22 in Reno, Nevada, researchers will describe how they are using new and repurposed tools to zero in on the sequence of events that precedes a volcanic eruption. The seismologists are looking for patterns of seismic activity to compare with past eruptions to determine when one particular volcano might erupt, as well as larger patterns that could be used to predict when volcanoes of a certain type might erupt.

“In the last ten years, there have been a lot more seismometers placed on volcanoes,” said Weston Thelen, a geophysicist at the U.S. Geological Survey. “We’re now looking for eruption signals from earthquakes that others might cast off as too small to bother with, but we want to use all the different signals that are out there.”

At the SSA meeting, USGS scientist Randall White will present information on a “progression of seismicity” before an eruption that he and others have gleaned from studying more than 35 eruptions at 24 dormant volcanoes over the past 20 years. More than 90% of the eruptions at these dormant volcanoes are preceded by significant (magnitude 3 or larger) volcano-tectonic earthquakes on faults near but not under the volcanoes, they note. Other waves of low-frequency seismicity follow, as magma intrudes into rock and interacts with different parts of the earth’s crust.

At Washington State’s Mount St. Helens volcano and at Little Sitkin Volcano in Alaska’s Western Aleutians, researchers are taking a closer look at the swarms of repeating small earthquakes that appear to precede many eruptions. These swarms can come and go underneath a volcano without being connected to an eruption, however, so seismologists would like to learn more about what each kind of swarm might indicate about the direction and speed of moving magma. At Mount St. Helens, University of Washington researchers are developing an open-source tool called REDPy (Repeating Earthquake Detector in Python) to look at swarms at the volcano in near real-time, to calculate how the number and size of the earthquake clusters might relate to eruption timing. At Little Sitkin Volcano, Alaska Volcano Observatory seismology Matthew Haney and colleagues are analyzing the seismicity surrounding a 2012 swarm there to learn more about how magma is moving between reservoirs under the volcano.

A 2014 swarm beneath Mammoth Mountain in California allowed USGS scientist David Shelly and his colleagues to trace the complex relationship between fluid movement and fault activation at the heavily monitored lava dome. Their analysis yielded a set of more than 6000 precisely located earthquakes that helped to trace a wave of earthquake propagation along multiple faults during the swarm sequence.

Another presentation in the SSA session will discuss how seismic data were used in 2015 to detect a massive magma chamber under the Yellowstone supervolcano, connecting an earlier-known upper crust magma reservoir with the mantle plume that fuels the supervolcano.

Seismic studies such as the Yellowstone report that help to define the structure of magma chambers and movement are key to connecting seismic activity with the timing of a volcanic eruption, said Thelen. “For many volcanoes, we’re still trying to figure out where the magma lies, and where the hydrothermal systems are,” he said. “When we understand that better, we can interpret the seismicity better when it comes up.”

Note: The above post is reprinted from materials provided by Seismological Society of America.

Induced earthquakes come under closer scrutiny at SSA Annual Meeting

seismograph

On March 28, the U.S. Geological Survey issued a one-year seismic forecast for the United States that for the first time includes ground-shaking hazards from both natural and human-induced earthquakes. In the wake of the forecast’s release, researchers are gathering at the Seismological Society of America’s (SSA) 2016 Annual Meeting April 20-22 in Reno, Nevada, to discuss some of the science behind the report.

Presenters at the meeting will speak about factors that may influence the location and strength of induced earthquakes in the central United States and western Canada and what can be done to minimize the occurrence and impacts of this seismic activity.

The USGS report estimates that about 7 million people in the central and eastern United States now live in areas affected by induced earthquakes. In central Oklahoma and southern Kansas, there is a 5 to 12% chance of a damaging (magnitude 4.5 or larger) earthquake occurring within the next year. Other areas at risk for induced earthquake hazards include parts of Texas, Arkansas, Colorado, New Mexico, Ohio and Alabama. At the SSA meeting, Mark Petersen, chief of the USGS National Seismic Hazard Mapping Project, will discuss the data that were used to build the new seismic forecast.

The vast majority of induced seismicity in the United States is related to wastewater from enhanced oil recovery operations being injected back into the ground, says research geophysicist and deputy chief of the USGS Induced Seismicity Project Justin Rubinstein. At the SSA meeting, Rubinstein will discuss how places such as Harper and Sumner counties in southern Kansas have seen a surge in seismic activity since a 2012 increase in oil and gas operations in the area, including a magnitude 4.8 earthquake in 2014. When the Kansas Corporation Commission placed limits on the industry’s wastewater disposal, Rubinstein reports, earthquake activity in the area under the limits decreased by 40 to 50% in the six months following the commission’s order.

A presentation by AECOM seismologist Ivan Wong will address one of the questions on the minds of infrastructure engineers and public policy planners after learning about the new USGS report: what is the potential for damage from these types of earthquakes? There is some disagreement among researchers, Wong notes, about whether the expected ground shaking in induced seismicity might be stronger or weaker in natural earthquakes. It may also be possible that even earthquakes of magnitude 5 or smaller could damage infrastructure in the central U.S. because buildings and roads in those regions have rarely been built with seismic hazards in mind.

Several presentations in the induced seismicity session will examine whether there is a set of seismic features that can be used to distinguish natural from induced earthquakes. This remains a challenging problem, Rubinstein says, “since induced earthquakes involve the same sorts of slip processes as natural earthquakes.” For the moment, induced earthquakes are identified by researchers looking at the full catalog of seismicity for a region, “and determining whether changes to industrial operations have coincided with changes in earthquake rates,” he says.

While the USGS report has raised new interest and concern about induced earthquakes in the central U.S., induced seismicity may have a relatively long history in the region, according to USGS seismologist Susan Hough, who will discuss 20thcentury oil and gas practices in Oklahoma in her SSA talk. She and her colleagues have turned up some interesting documents in the course of tracking down the roots of induced seismicity in the state, including a rare earthquake insurance policy taken out by an prominent Oklahoma City petroleum geologist in 1952, just a couple months before the magnitude 5.7 El Reno earthquake toppled buildings and chimneys and cracked the state capitol building in Oklahoma City.

Note: The above post is reprinted from materials provided by Seismological Society of America.

The first fossilised heart ever found in a prehistoric animal

The first fossilised heart-GeologyPage
This 119 million year old fish, Rhacolepis, is the first fossil to show a 3D preserved heart which gives us a rare window into the early evolution of one of our body’s most important organs. Credit: Dr John Maisey, American Museum of Natural History in New York, Author provided

Palaeontologists and the famous Tin Man in The Wizard of Oz were once in search of the same thing: a heart. But in our case, it was the search for a fossilised heart. And now we’ve found one.

A new discovery, announced today in the journal eLife, shows the perfectly preserved 3D fossilised heart in a 113-119 million-year-old fish from Brazil called Rhacolepis.

This is the first definite fossilised heart found in any prehistoric animal.

For centuries, the fossil remains of back-boned animals – or vertebrates – were studied primarily from their bones or fossilised footprints. The possibility of finding well-preserved soft tissues in really ancient fossils was widely thought to be impossible.

Soft organic material rapidly decays after death, so organs start breaking down from bacterial interactions almost immediately after an animal has died. Once the body has decayed, what remains can eventually become buried and what’s left of the skeleton might one day become a fossil.

Exceptional preservation of fossils

But certain rare fossil deposits, called konservat laggerstätten (meaning “place of storage”), are formed by rapid burial under special chemical conditions. These deposits can preserve a range of soft tissues from the organism.

The famous Burgess Shale fossils from British Columbia in Canada show soft-bodied worms and other invertebrate creatures. These were buried by rapid mudslides around 525 million years ago.

The well-preserved fishes from the 113-119 million-year-old Santana Formation of Brazil were among the first vertebrate fossils to show evidence of preserved soft tissues. These include parts of stomachs and bands of muscles.

The discovery of complete soft tissues preserved as whole internal organs in a fossil was a bit of a Holy Grail for palaeontologists. Such finds could contribute to understanding deeper evolutionary patterns as internal soft organs have their own set of specialised features.

Finding a complete fossilised heart in a fish almost 120 million years old was a major breakthrough for José Xavier-Neto of the Brazilian Biosciences National Laboratory, Lara Maldanis of the University of Campinas, Vincent Fernandez of the European Synchotron Radiation Facility and colleagues from across Brazil and Sweden.

Back in 2000, a group of US scientists claimed to have found a heart preserved in a dinosaur nicknamed Willo, a Thescelosaurus. But recent work has debunked this claim, showing the cavity of the dinosaur body was infilled by sediment and then impregnated with iron-rich minerals to make the cavity inside look a bit heart-like when imaged by CT scanning.

The only other claims for fossilised vertebrate hearts are stains supposedly made by haemoglobin-rich blood found in the region of the fossil where the heart should be. These, along with stains representing possibly the liver, have recently been documented in 390 million-year-old fishes from Scotland.

Digital heart surgery on a fossil

The new discovery was made by imaging a fossil still entombed within its limestone concretion using synchrotron X-ray tomography down to 6µm sections. The heart is then rendered out slice by slice using software to digitally restore the features of the organ.

This method has now been widely applied in palaeontology for the past decade or so to reveal many intricate soft tissue structures in fossils, including the actual preserved brain of a 300 million-year-old fish from North America and actual muscle bundles attached to 380 million-year-old placoderm fishes from Australia.

The Rhacolepis heart was digitally restored by tomography and from images studied in cross-sections through the rock. It shows clear detail of the conus arteriosus, or bulb at the top of the heart, which has a pattern of five rows of valves inside it.

A detailed comparison with a dissected tarpon heart in the paper shows similar structures in the same relative position as the fossil heart.

The discovery of the fossilised heart is significant in that it shows the valve condition in an early member of the ray-finned fish group. These are the largest group of vertebrates alive today with nearly 30,000 species, and naturally they display a wide range of valve patterns in their hearts.

Some, such as the African reedfish, a very basal member of the ray-finned fishes, has nine rows of valves. But the modern most diverse group of ray-fins, the teleosts, have just a single outflow valve in the heart. In teleosts another structure, the bulbus arteriosus, prevails over the conus arteriosus to dominate outflow of blood from the heart.

Enter our fossil, Rhacolepis, a fish belonging to an entirely extinct family, the Pachyrhizodontidae, named after the extinct fish Pachyrhizodus. This is a group placed close to the base of the teleosts.

The pattern shown by the fossil seems to represent a good intermediate condition between the most primitive pattern and the most advanced type. In biology, simple patterns often hold more complex hidden meanings.

Within some ray-finned fish groups there is also thought to be a secondary simplification of the valve arrangements. For example, in sturgeons and bowfins there is independent pattern of simplification within the conus arteriosus.

There is also evidence for independent increase in the numbers of valves in some basal ray-fins, like the reedfish Polypterus, so interpreting evolutionary patterns from just one data point in time must be open to several explanations.

Nonetheless, for the first time we actually do have a data point to study the anatomy in detail of a fossilised heart in an extinct group of fishes.

The find demonstrates the immense potential for more discoveries of this nature, enabling more discussion of the comparative anatomy of soft organs in extinct organisms and how they have evolved through time.

With increased discoveries like this one, and more detailed knowledge of the soft tissue anatomy of extinct animals, we will one day really get to the heart of understanding the evolution of the first back-boned animals.

Reference:
Heart fossilization is possible and informs the evolution of cardiac outflow tract in vertebrates. DOI: 10.7554/eLife.14698

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

Bigger brains led to bigger bodies in our ancestors

Bigger brains led to bigger-GeologyPage
New research shows that a strong selection to increase brain size alone played a large role in both brain- and body-size increases throughout human evolution. This phenomenon also may have been solely responsible for the major increase in both traits that occurred during the transition from human ancestors like Australopithecus, a model of which is seen here in the American Museum of Natural History’s Hall of Human Origins, to Homo erectus. Credit: © AMNH/R. Mickens

New research suggests that humans became the large-brained, large-bodied animals we are today because of natural selection to increase brain size. The work, published in the journal Current Anthropology, contradicts previous models that treat brain size and body size as independent traits responding to separate evolutionary pressures. Instead, the study shows that brain size and body size are genetically linked and that selection to increase brain size will “pull along” body size. This phenomenon played a large role in both brain- and body-size increases throughout human evolution and may have been solely responsible for the large increase in both traits that occurred near the origins of our genus, Homo.

“Over the last four million years, brain size and body size increased substantially in our human ancestors,” said paper author Mark Grabowski, a James Arthur postdoctoral fellow in the Division of Anthropology at the American Museum of Natural History. “This observation has led to numerous hypotheses attempting to explain why observed changes occurred, but these typically make the assumption that brain- and body-size evolution are the products of separate natural selection forces.”

That assumption is now being questioned, based on a large body of work that has shown that genetic variation–the fuel of evolution–in some traits is due to genes that also cause variation in other traits, with the result that selection on either trait leads to a correlated response in the unselected trait. Consider the leg bone, or femur, of an elephant. As the bone gets longer, it also gets wider. If artificial selection is used to produce a tall elephant, its legs likely won’t just become long, they’ll also get wider. Part of this effect is due to shared genetic variation, or covariation, among traits in the femur. Grabowski set out to explore this kind of genetic relationship between human brain size and body size, and its impact on our evolution.

With brain- and body-size covariation patterns from a range of primates and modern humans, Grabowski created a number of models to examine how underlying genetic relationships and selection pressures likely interacted across the evolution of our lineage. His findings demonstrate, for the first time, that strong selection to increase brain size alone played a large role in both brain- and body-size increases throughout human evolution. This phenomenon also may have been solely responsible for the major increase in both traits that occurred during the transition from human ancestors like Australopithecus (the most famous of which is the Lucy fossil) to Homo erectus.

In other words, while there are many scientific ideas explaining why it would be beneficial for humans to evolve bigger bodies over time, the new work suggests that those hypotheses may be unnecessary; instead, body size just gets pulled along as the brain expands.

“While selection no doubt played a role in refining the physical changes that came with larger body sizes, my findings suggest it was not the driving force behind body-size evolution in our lineage,” Grabowski said. “Therefore, evolutionary models for the origins of Homo based on an adaptive increase in body size need to be reconsidered.”

Reference:
Mark Grabowski. Bigger Brains Led to Bigger Bodies?: The Correlated Evolution of Human Brain and Body Size. Current Anthropology, 2016; 57 (2): 174 DOI: 10.1086/685655

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

Dinosaurs ‘already in decline’ before asteroid apocalypse

Dinosaurs 'already in decline-GeologyPage

Dinosaurs were already in an evolutionary decline tens of millions of years before the meteorite impact that finally finished them off, new research has found.

The findings provide a revolution in the understanding of dinosaur evolution. Palaeontologists previously thought that dinosaurs were flourishing right up until they were wiped out by a massive meteorite impact 66 million years ago. By using a sophisticated statistical analysis in conjunction with information from the fossil record, researchers at the Universities of Reading, UK and Bristol, UK showed that dinosaur species were going extinct at a faster pace than new ones were emerging from 50 million years before the meteorite hit.

The analyses demonstrate that while the decline in species numbers over time was effectively ubiquitous among all dinosaur groups, their patterns of species loss were different. For instance, the long-necked giant sauropod dinosaurs were in the fastest decline, whereas theropods, the group of dinosaurs that include the iconic Tyrannosaurus rex, were in a more gradual decline.

Dr Manabu Sakamoto, University of Reading, the palaeontologist who led the research, said: “We were not expecting this result. While the asteroid impact is still the prime candidate for the dinosaurs’ final disappearance, it is clear that they were already past their prime in an evolutionary sense.”

‘Losing their edge’

“Our work is ground-breaking in that, once again, it will change our understanding of the fate of these mighty creatures. While a sudden apocalypse may have been the final nail in the coffin, something else had already been preventing dinosaurs from evolving new species as fast as old species were dying out.

“This suggests that for tens of millions of years before their ultimate demise, dinosaurs were beginning to lose their edge as the dominant species on Earth.”

Professor Mike Benton of the University of Bristol, one of the co-authors of the research, said: “All the evidence shows that the dinosaurs, which had already been around, dominating terrestrial ecosystems for 150 million years, somehow lost the ability to speciate fast enough. This was likely to have contributed to their inability to recover from the environmental crisis caused by the impact.”

It is thought that a giant asteroid’s impact with Earth 66 million years ago threw up millions of tonnes of dust, blacking out the sun, causing short-term global cooling and widespread loss of vegetation. This ecological disaster meant that large animals reliant on the abundance of plants died out, along with the predators that fed on them.

The new research suggests that other factors, such as the break-up of continental land masses, sustained volcanic activity and other ecological factors, may possibly have influenced the gradual decline of dinosaurs.

‘Room for mammals’

This observed decline in dinosaurs would have had implications for other groups of species. Dr Chris Venditti, an evolutionary biologist from the University of Reading and co-author of paper said: “The decline of the dinosaurs would have left plenty of room for mammals, the group of species which humans are a member of, to flourish before the impact, priming them to replace dinosaurs as the dominant animals on earth.”

Dr Sakamoto points out that the study might provide insight into future biodiversity loss. He said: “Our study strongly indicates that if a group of animals is experiencing a fast pace of extinction more so than they can replace, then they are prone to annihilation once a major catastrophe occurs. This has huge implications for our current and future biodiversity, given the unprecedented speed at which species are going extinct owing to the ongoing human-caused climate change.”

Reference:
Sakamoto, M., Benton, M.J., and Venditti, C. Dinosaurs in decline tens of millions of years before their final extinction. Proceedings of the National Academy of Sciences, 2016 DOI: 10.1073/pnas.1521478113

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

Ancient tectonic activity was trigger for ice ages, study says

Ancient tectonic activity-GeologyPage
“Everybody agrees that on geological timescales over hundreds of millions of years, tectonics control the climate, but we didn’t know how to connect this,” says Oliver Jagoutz. Credit: Christine Daniloff/MIT

For hundreds of millions of years, Earth’s climate has remained on a fairly even keel, with some dramatic exceptions: Around 80 million years ago, the planet’s temperature plummeted, along with carbon dioxide levels in the atmosphere. The Earth eventually recovered, only to swing back into the present-day ice age 50 million years ago.

Now geologists at MIT have identified the likely cause of both ice ages, as well as a natural mechanism for carbon sequestration. Just prior to both periods, massive tectonic collisions took place near the Earth’s equator—a tropical zone where rocks undergo heavy weathering due to frequent rain and other environmental conditions. This weathering involves chemical reactions that absorb a large amount of carbon dioxide from the atmosphere. The dramatic drawdown of carbon dioxide cooled the atmosphere, the new study suggests, and set the planet up for two ice ages, 80 million and 50 million years ago.

“Everybody agrees that on geological timescales over hundreds of millions of years, tectonics control the climate, but we didn’t know how to connect this,” says Oliver Jagoutz, associate professor of Earth, Atmospheric and Planetary Sciences (EAPS) at MIT. “I think we’re the first ones to really link large-scale tectonic events to climate change.”

Jagoutz and his colleagues, EAPS Professor Leigh Royden, and Francis McDonald of Harvard University, have published their findings today in the Proceedings of the National Academy of Sciences.

Putting the squeeze on

The two tectonic collisions that the team studied stemmed from the same event: the slow northward migration of Gondwana, a supercontinent that spanned the Southern Hemisphere from 300 million to 180 million years ago and eventually broke up to form Antarctica, South America, Africa, India, and Australia.

Around 180 million years ago, tectonic activity began to push fragments of Gondwana up toward the northern supercontinent of Eurasia, which slowly squeezed and eventually closed the Neo-Tethys Ocean, an ancient body of water lying between the supercontinents.

In previous work, Jagoutz and his colleagues developed a model to simulate the tectonic shifting that occurred in and around that ocean as Gondwana fragments were crushed against Eurasia. Through analysis of ancient rocks in today’s Himalayas, the team determined a sequence of events as the continents merged.

They found that 90 million years ago, the northeastern edge of the African plate collided and slid under an oceanic plate in the Neo-Tethys Ocean, creating a chain of volcanoes. At 80 million years ago, as Africa continued advancing north, the oceanic plate was pushed further up and over the continent, exposing ocean rock to the atmosphere, while simultaneously terminating the volcanoes. Then, 50 million years ago, India merged with Eurasia in a second collision in which a different region of the oceanic plate was pushed up onto that continent.

Both collisions took place in the Intertropical Convergence Zone (ITCZ), an atmospheric region hovering over the Earth’s equator, in which trade winds come together to generate a region of intense temperatures and rainfall.

A weathering trigger

For this new paper, the researchers wondered whether the tectonic collisions in this extremely tropical region may have played a part in pulling huge amounts of carbon dioxide out of the atmosphere and triggering the ice ages.

Certain types of rock, if exposed to high heat and heavy rain, undergo chemical reactions and effectively absorb carbon dioxide, a process known as silicate weathering. These rocks include basalts and “ultramafic” rocks, which are often found within oceanic plates. If these rocks are exposed to the atmosphere in a tropical region, they can act as very efficient carbon sinks.

The team hypothesized that the two collisions, involving Africa and then India, brought basaltic and ultramafic rocks up from the oceans and onto land, creating carbon sinks 80 and 50 million years ago. Both collisions also effectively turned off carbon sources by burying volcanoes that had been emitting carbon dioxide and other gases into the atmosphere.

To know whether such a sequence of events directly reduced carbon dioxide in the atmosphere, the researchers looked to weathering rates of different rock types, including granites, basalts, and ultramafics. These rates, which have been calculated by other researchers, describe the way rocks erode and take up carbon dioxide, given exposure to a certain amount of rainfall.

They then applied these weathering rates to their model’s estimates of the amount of oceanic plate that was pushed up onto Africa and India, at 80 and 50 million years ago, respectively. After determining the amount of carbon dioxide sequestered by these rocks, they calculated the total amount of atmospheric carbon dioxide through time, from 100 million years ago to around 40 million years ago.

The team found that carbon dioxide dipped dramatically at precisely the time the two collisions occurred. The levels of carbon dioxide also mirrored the temperature of the oceans during this interval.

Jagoutz says one reason these two collisions had such an extreme effect on atmospheric carbon dioxide may have been the fact that each continent continued moving north, exposing new basaltic and ultramafic material, “like a bulldozer that brings fresh rock to the surface.”

Interestingly, a similar process is taking place today, albeit at a smaller scale, near the island of Java. The same tectonic activity that shifted Gondwana northward more than 100 million years ago is today pushing the Australian plate north, and as a result, is piling up basaltic material on Java within the ITCZ, which Jagoutz says is “a huge carbon sink.”

“What nature shows us is, if you put a lot of these rocks in the tropics, where it’s hot, muggy, wet, and rains every day, and you also have the effect of removing the soil constantly by tectonics and thus exposing fresh rocks, then you have an excellent trigger for ice ages,” Jagoutz says. “But the question is whether that is a mechanism that works on the timescale that is relevant for us.”

“To confidently estimate the long-term fate of fossil fuel carbon in the atmosphere, we need to fully understand the dynamics of the carbon cycle and how it operates on all time scales,” says Lee Kemp, professor of geosciences at Penn State University. “This study highlights an important restorative force of the carbon cycle. The ‘repair mechanism’ for volcanism-induced warming is the chemical weathering of the volcanic rocks themselves—a repair job that takes millions of years.”

Reference:
Oliver Jagoutz et al. Low-latitude arc–continent collision as a driver for global cooling, Proceedings of the National Academy of Sciences (2016). DOI: 10.1073/pnas.1523667113

Note: The above post is reprinted from materials provided by Massachusetts Institute of Technology.

The seismic risk of Ecuador

The seismic risk of Ecuador-GeologyPage

A doctoral thesis developed at UPM analysed the seismic danger of Ecuador, obtaining maximum values in Esmeraldas province, which was most heavily affected by the earthquake that took place the last 16th April.

The 7.8 magnitude earthquake that took place last Saturday, 16th April in Esmeraldas province (Ecuador), confirms a well-known fact: That the high seismic risk in that region of the Pacific Ocean is associated with the convergence of Nazca and Southamerica plates.

ON 22 February, Lieutenant Colonel Humberto Parra Cárdenas read his doctoral thesis at the Universidad Politécnica de Madrid (UPM), titled “Methodological Developments and Applications to the Calculation of the Seismic Riskness in Continental Ecuador and Study of the Seismic Risk in Quito City”.

The thesis, marked with a cum laude distinction, provided an Ecuador risk map, among other results, observing that Esmeraldas province, which has been the most affected area by the recent earthquake, is the most dangerous territory.

The map developed in this study might have important applications to seismic risk mitigation in Ecuador, suggesting two kinds of measures. On one hand, the seismic-resistant design of buildings to withstand the expected movement (shown in the map) and, on the other hand, risk studies of future earthquakes to create emergency plans, explains the thesis director, Mª Belén Benito.

Nowadays, prevention and contingency measures are the most effective to prevent and/or alleviate the disaster in seismic situations, due to the fact that they can’t be avoided or predicted in a short-term period, adds the UPM professor.

The study from this doctoral thesis has also been accepted for publication in the scientific journal Bulletin of European Earthquake Engineering.

Note: The above post is reprinted from materials provided by Universidad Politécnica de Madrid.

Two volcanoes trigger crises of the late antiquity

Two volcanoes trigger-GeologyPage
Simulated summertime (June-August) average temperature changes in 536 CE due to the stratospheric aerosol cloud resulting from an unknown volcanic eruption reconstructed here based on contemporary written records and ice core sulfate measurements. The simulated temperature changes, ranging from 1-3 ° C over Europe, show good agreement with estimates from two tree-ring temperature reconstructions based on trees in Northern Scandinavia. Credit: Matt Toohey, GEOMAR

Contemporary chronicles, archaeological studies and physical evidence all point to severe climatic changes and ensuing social crises in the middle of the 6th century. New data from ice cores suggest that these events were caused by two major volcanic eruptions. An international team led by scientists at the GEOMAR Helmholtz Centre for Ocean Research Kiel and the Centre for Earth Evolution and Dynamics at the University of Oslo have reconstructed the effects using state-of-the-art climate models. As they present now in the international journal Climatic Change and at the annual meeting of the European Geosciences Union (EGU) in Vienna, the volcanic double event was likely the strongest volcanic driver of Northern Hemisphere climate over the past one and a half millennia.

Contemporary chroniclers wrote about a “mystery cloud” which dimmed the light of the sun above the Mediterranean in the years 536 and 537 CE. Tree rings testify poor growing conditions over the whole Northern Hemisphere – the years from 536 CE onward seem to have been overshadowed by an unusual natural phenomenon. Social crises including the first European plague pandemic beginning in 541, are associated with this phenomenon. Only recently have researchers found conclusive proof of a volcanic origin of the 536 solar dimming, based on traces of volcanic sulfur from two major eruptions newly dated to 536 CE and 540 CE in ice cores from Greenland and Antarctica.

An international team of climate scientists led by Dr. Matthew Toohey at the GEOMAR Helmholtz Centre for Ocean Research Kiel and Prof. Dr. Kirstin Krüger of the University of Oslo (UiO), with financial support from the Centre for Earth Evolution and Dynamics (CEED) at the UiO, have investigated the time period using the new ice core data, historical evidence and climate models. As they write in the international journal Climatic Change, the impact of the volcanic double event of 536/540 on Northern Hemisphere climate was stronger than any other documented or reconstructed event of the past 1200 years. “One of the eruptions would have led to a significant cooling of the Earth’s surface. Two of them, so close in time, caused what is probably the coldest decade of the past 2000 years,” says Dr. Matthew Toohey from GEOMAR, lead author of the study today at a press conference at the annual EGU Meeting in Vienna where he presented the results.

To simulate the impact of the 536 and 540 eruptions, the scientists used the available data from ice cores and the descriptions of the solar dimming from contemporary scholars. With this data they estimated the magnitude of the eruptions and their approximate locations on Earth, and then simulated the spread and impacts of the aerosol clouds resulting from the volcanic injection of sulfur into the stratosphere. This revealed that following the eruptions, the solar radiation at the Earth’s surface was strongly reduced over the Northern Hemisphere for several years, and caused decreases in the hemispheric average temperature of up to 2 degrees Celsius.

The relationship between the “mystery cloud” of 536 and the transition from Antiquity to the Middle Ages is an issue of great popular interest. Volcanic eruptions in the more recent past have impacted human societies. For example, in 1815 the Indonesian volcano Tambora hurled so much ash and sulfur into the atmosphere that the year 1816 became known as “the year without summer” in Europe and North America, where unusually low temperatures led to crop failures and famines. For eruptions of the more distance past, connections between eruptions and societal impacts become less clear.

Toohey and his colleagues used their climate model simulations to directly estimate the impact of the eruptions on agriculture in Europe, and identified Northern Europe and in particular Scandinavia as the most likely locations to have suffered under the cold conditions after the eruptions. This result supports the theory of a connection between the eruptions and archaeological evidence of a large-scale societal crisis in Scandinavia in the 6th century. “Each one of the eruptions of 536/540 would have strongly impacted societies, and it happened twice within four years,” says co-author Prof. Dr. Kirstin Krüger from the University of Oslo.

Which volcanoes exactly were responsible for these aerosols clouds is still enigmatic. “Several candidates are being discussed, including volcanoes in Central America, Indonesia and North America. Future studies will be necessary to show the exact source of the aerosol clouds of 536/540,” says Dr. Toohey.

Reference:
Matthew Toohey et al. Climatic and societal impacts of a volcanic double event at the dawn of the Middle Ages, Climatic Change (2016). DOI: 10.1007/s10584-016-1648-7

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

Post-wildfire erosion can be major sculptor of forested western mountains

Post-wildfire erosion can be-GeologyPage
Jon Pelletier, a University of Arizona professor of geosciences, walks through the forest on Cerro del Medio, a mountain in New Mexico’s Valles Grande, after the 2011 Las Conchas fire. Credit: Caitlin Orem

Erosion after severe wildfires can be the dominant force shaping forested mountainous landscapes of the U.S. Intermountain West, suggests a new research paper by two University of Arizona geoscientists.

The study is the first to assess the impact of wildfires on such landscapes by combining several different ways to measure short-term and long-term erosion rates, said study co-author Jon Pelletier, a UA professor of geosciences.

After the 2011 Las Conchas fire in New Mexico, soil and rock eroded from burned watersheds more than 1,000 times faster than from unburned watersheds nearby, the team found. Most of the erosion happened in the first year after the fire.

Caitlin Orem had been studying erosion in seven mountain watersheds near New Mexico’s Valles Grande but wasn’t focused on wildfire. When the Las Conchas fire burned two of her study areas, she seized the opportunity to compare the rates that watersheds were denuded of soil and rocks before and after a severe wildfire.

“We knew that wildfire increased the rate of erosion, but we didn’t know how important it was over long time scales,” said first author Orem. The research was part of her doctoral studies in the UA Department of Geosciences.

“It was a really huge opportunity to learn a lot about wildfires. There are very few times you can see that big of a change and can actually document it.”

Orem and Pelletier calculated total erosion rates for their study area for time scales up to 1 million years ago. The scientists found more than 90 percent of the erosion happened in the geologically brief time intervals right after forest fires. Those post-fire intervals constituted just 3 percent of the total time.

The research is part of the UA Santa Catalina Mountains & Jemez River Basin Critical Zone Observatory, a project funded by the National Science Foundation.

Pelletier, co-director of the CZO, said, “I think we can generalize this to similar landscapes in the Intermountain West – landscapes that are forested, have very little bare ground, and have few areas with slopes steeper than about 25 degrees.”

The paper, “The predominance of post-wildfire erosion in the long-term denudation of the Valles Caldera, New Mexico,” by Orem, now a geologist for BP in Anchorage, Alaska, and Pelletier, has been accepted for publication in the Journal of Geophysical Research: Earth Surface, a publication of the American Geophysical Union.

In 2010, Orem and Pelletier began studying the role of erosion in sculpting the mountain watersheds that drain into the Valles Grande, including those on Redondo Peak and on Cerro del Medio.

Pelletier said, “The goal is to determine topographic change—the volume that has been removed or deposited.”

Working with the National Center for Airborne Laser Mapping, the UA geoscientists used a technology called LIDAR (Light Detection and Ranging) to create a digital map, or digital elevation model, showing the area’s surface relief at that time.

Although Redondo Peak, one of the team’s study areas, now has steep-sided ridges and deep valleys, previous investigators showed that Redondo Peak formed 1.24 million years ago as a rounded volcanic dome.

To calculate long-term erosion rates for Redondo Peak, the team needed to figure out how much rock and soil had been stripped off the mountain and how long it took for that material to be removed.

Using the digital elevation model, known as a DEM, Orem calculated the volume of material that eroded from the original dome over time. Dividing that volume by the mountain’s age gives the average long-term erosion rate.

Such a long-term rate incorporates many different events in the mountain’s history. The researchers already knew events such as flood or wildfire could increase erosion rates.

The team corroborated their DEM-based calculation by measuring how much beryllium-10 had accumulated in the soil. Pelletier said beryllium-10 analyses provide an “erosion clock” over time scales of thousands of years.

To calculate the day-in, day-out background rate of erosion in the absence of disturbance, Orem, Pelletier and colleagues took regular samples of stream water from the Redondo Peak watersheds from 2008 to 2012. By measuring the amount of sediment suspended in the water, Orem calculated the background rate of erosion.

The researchers found the long-term erosion rate for Redondo Peak was 100 times greater than the background rate, indicating erosion rates on the mountain had been greater in the past. Redondo Peak had no wildfires during the time the team took stream samples.

A nearby mountain with similar terrain, Cerro del Medio, had a severe forest fire in 2011, giving the team the opportunity to measure post-wildfire erosion directly. Post-fire, the increase in erosion was obvious—boulders the size of office desks had rolled down the slopes and into the meadow below.

The team had already made a pre-fire digital elevation model, or DEM, of two Cerro del Medio watersheds. The team made new DEMs of the changing landscape right after the fire and again 10, 13 and 22 months later.

By comparing the pre-fire DEM to the series of post-fire DEMs, the scientists found the burned watershed lost 1,000 to 10,000 times more rocks and soil in the first year after the fire than did a similar but unburned watershed on Redondo Peak.

The researchers calculated that over a million years, if such post-wildfire erosion occurred for a year just once every 30 to 300 years, enough material would be removed to sculpt Redondo Peak’s original dome into the steeply incised mountain it is today.

“Over millennia there’s a gradual transfer of soil from high spots to low spots,” Pelletier said. “Most of the post-fire erosion is in the streambed. In the time period between fires, soil is still moving, but it’s moving to fill in the hole created by the flooding just after the fire.”

The team’s estimate of past wildfire frequency matches what other researchers found by studying the natural records of wildfires contained in the region’s tree rings and lake sediments.

Orem said, “Other researchers have found that in the Western U.S., the area being burned and the severity of the burns are increasing. With that increase, we expect to see more wildfire-caused erosion.”

Reference:
Caitlin A. Orem et al. The predominance of post-wildfire erosion in the long-term denudation of the Valles Caldera, New Mexico, Journal of Geophysical Research: Earth Surface (2016). DOI: 10.1002/2015JF003663

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

Magnetic vortices defy temperature fluctuations

Magnetic vortices defy-GeologyPage
Electron microscopy image of a magnetite nanocrystal (left) and the magnetic vortex structure (right), made visible for the first time by researchers from Jülich and the United Kingdom using electron holography. Credit: Imperial College London

Magnetic nanovortices in magnetite minerals are reliable witnesses of the earth’s history, as revealed by the first high-resolution studies of these structures undertaken by scientists from Germany and the United Kingdom. The magnetic structures are built during the cooling of molten rock and reflect the earth’s magnetic field at the time of their formation. The vortices are unexpectedly resilient to temperature fluctuations, as electron holographic experiments in Jülich have verified. These results are an important step in improving our understanding of the history of the earth’s magnetic field, its core and plate tectonics.

The earth’s magnetic field performs important functions: it protects us, for example, from charged particles from space and enables migratory birds, bees, and other animals to navigate. However, it is not stable, and constantly changes its intensity and state. Several times in the past it has even reversed its polarity — the north and south poles have changed places. Scientists in the area of paleomagnetism use magnetic minerals to investigate the history of the earth’s magnetic field and its formation from molten metal flowing within the earth’s core, the so-called geodynamo. Furthermore, the movement of continental plates can be monitored with the aid of such rocks.

In the course of millions of years, these minerals could often have been exposed to immense temperature fluctuations, due to extreme climate change or volcanic activity, for instance. How well do the magnetic structures survive such temperature fluctuations and how reliable is the information gained from them? An international research team has now studied this question for the first time at ultra-high resolution on samples of magnetite, the mineral dominating the magnetic properties in the earth’s crust. “It is only in a small part of naturally occurring magnetite that magnetic structures known for being very stable with respect to temperature fluctuations are found,” explains Dr. Trevor Almeida of Imperial College London. “Far more common are tiny magnetic vortices. Their stability could not be demonstrated until now.”

Together with colleagues from Forschungszentrum Jülich, the University of Edinburgh and the University of Nottingham, Almeida has studied the magnetic vortices in magnetite nanocrystals. As the structures are so tiny — each grain is only about the size of a virus — there is only one method with which the nanovortices can directly be observed while they are heated up and cooled down: “A special high-resolution electron microscope at the Ernst Ruska-Centre (ER-C) in Jülich is capable of making magnetic fields on the nanoscale holographically visible,” explains Almeida. “In this way, images of field lines are produced almost like using iron filings around a bar magnet to make its magnetic field visible, but with a resolution in the nanometre range.”

The experiments in Jülich showed that although the magnetic vortices alter in strength and direction when heated up, they go back to their original state as they cool down. “Therefore magnetite rocks, which carry signs of temperature fluctuations, are indeed a reliable source of information about the history of the earth,” enthuses Almeida.

“Electron holography has made it possible for us to gain a completely new insight into the magnetic behaviour of magnetite,” emphasized Prof. Rafal Dunin-Borkowski, Director at the ER-C and at the Peter Grünberg Institute in Jülich. As an expert in electron holography, he works with his Jülich team on further improving the resolution of this technique and in providing German and international scientists the necessary infrastructure to perform this type of study. “Weak magnetic fields in nanocrystals don’t just play a role in paleomagnetism. In information technology, for instance, electron holograms can also be of use to help to push back the physical limits of data storage and processing.”

Reference:
T. P. Almeida, A. R. Muxworthy, A. Kovacs, W. Williams, P. D. Brown, R. E. Dunin-Borkowski. Direct visualization of the thermomagnetic behavior of pseudo-single-domain magnetite particles. Science Advances, 2016; 2 (4): e1501801 DOI: 10.1126/sciadv.1501801

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

Copper gives an answer to the rise of oxygen

Copper gives an answer-GeologyPage
Photo: Catarina Nilsson/Mostphotos

A new study presents evidence that the rise of atmospheric oxygenation did indeed occur 2.4-2.1 billion years ago. It also shows that biological usage of copper became prominent after the so called ‘Great Oxidation Event.’ An international team of researchers has recently published the study in the Proceedings of the National Academy of Sciences.

“Our findings make it possible to reconstruct nutrient content in early marine settings and demonstrate that the iron-rich content of the early oceans must have severely restricted the availability of nutrients important for life”, says Dr Ernest Chi Fru of Stockholm University, who has led the research group.

The study suggests a gradual shift in mainly negative copper isotopic composition of marine carbon-rich sediments, beginning at 2.4 billion years ago (Ga), to permanently positive values after 2.3 Ga. The authors argue that the change reflects the drawn-out nature of the Great Oxidation Event (GOE), when atmospheric oxygen content went from virtually nothing, starting at 2.4 Ga, to peak at near present day levels by 2.3 Ga.

Fundamentally, the high iron content of the early oceans are suggested to have played a critical role in determining trace metal availability, whereby copper levels increased when decreasing marine iron content fell by about 1 000 times after the GOE. The research has been made by examining carbon-rich rocks deposited at the bottom of ancient oceans 2.66-2.1 billion years ago.

“The appearance of oxygen in the atmosphere is one of the most important changes in Earth’s geological history that enabled the evolution of oxygen based life. Understanding the chemistry of the very early oceans and how nutrients were made available, guide our steps towards understanding the processes that govern our own evolution”, says Dr Ernest Chi Fru of Stockholm University.

The study provides a tool for tracking how oxygen levels have fluctuated through Earth’s history and the evolutionary changes that accompanied these fluctuations.

“Our study is highlighting how the isotopic ratios of copper can unlock the evolution of Earth’s early oceans from being oxygen-poor to more like they are today. We now hope to apply this technique to understanding other major geological events in the Earth’s history”, says Professor Dominik Weiss, co-author from Imperial College London.

The article ‘Cu isotopes in marine black shales record the Great Oxidation Event’ was recently published in the Proceedings of the National Academy of Sciences.

Reference:
Cu isotopes in marine black shales record the Great Oxidation Event, PNAS, DOI:10.1073/pnas.1523544113

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

Sierra’s eastern front long overdue for large earthquake

Seismogram2

Scientists say the Sierra’s eastern front is long overdue for a large earthquake along the California-Nevada line, where a magnitude-7 event expected on average every 30 years hasn’t occurred in six decades.

Nevada Seismology Laboratory Director Graham Kent says the region’s earthquake “drought” is likely one of the sources of a public misconception that it is at a low risk of experiencing a serious earthquake.

He planned to discuss details about the latest research Tuesday during an Earthquake Economic Resiliency Forum ahead of the Seismological Society of America’s annual meeting running Wednesday to Friday in Reno.

Kent said a magnitude-6 earthquake or larger typically strikes every 10 years or so along the Sierra Nevada frontal fault system running from south of Yosemite National Park to north of Reno and Lake Tahoe. There were seven magnitude-6.5 or larger in the region from 1915 to 1954, but none since, he said. The last magnitude-6 was 22 years ago in the Carson Valley south of Carson City.

The Federal Emergency Management Agency estimates a 6-magnitude quake could cause up to $1.9 billion in damage in the Reno-Sparks area and $590 million in the populated area of South Lake Tahoe, California, Kent said.

“Let’s take advantage of this extraordinary quiescent period in our earthquake history,” Kent said. “We have a great opportunity to bring experts together with our community—those who need to put plans in place not only for disaster response but, just importantly, a plan for quick economic recovery.”

The experts are gathering in Nevada days after powerful earthquakes killed hundreds of people in Ecuador (magnitude-7.8) and killed dozens and wounded thousands in Japan (magnitude-7.1). Scheduled speakers Tuesday include Dick McCarthy, executive director of the California Seismic Safety Commission, and Cory Lyman, director of the Salt Lake City Emergency Management’s “Fix the Bricks” program.

The largest earthquake ever recorded in the Sierra fault system was a magnitude-7.4 in 1872 in Owens Valley south of Yosemite National Park. It’s still the third largest in California history, behind the magnitude-7.9 at Fort Tejon in 1857 and the 7.8-magnitude in San Francisco in 1906. More recent studies of the fault lines and damage suggest the Owens Valley quake was probably bigger than the one in San Francisco, Kent said.

The Seismology Laboratory at the University of Nevada, Reno chronicled the event in its March newsletter with historical excerpts from naturalist John Muir, who wrote about the violent shaking while at Yosemite.

“I ran out of my cabin near the Sentinel rock, both glad and frightened, shouting, ‘A noble earthquake!’ ” Muir wrote. “The shocks were so violent and varied and succeeded one another so closely, one had to balance in walking as if on the deck of a ship among the waves.”

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

Deceptive feathered dinosaur finally gets a name

Deceptive feathered dinosaur-Geologypage
Apatoraptor pennatus as illustrated by paleontology graduate student and paleoartist Sydney Mohr.

Solving one of the longest cases of mistaken identity, University of Alberta PhD candidate Greg Funston recently described a new genus and species of toothless dinosaur from Alberta. Long thought to be a more common ornithomimid, Apatoraptor pennatus instead turned out to be a member of the notoriously enigmatic caenagnathid family.

“This is my first time naming a new dinosaur,” says Funston of the prestigious honour. “It’s really exciting on a personal level, but what I am most excited about is what it means for this field of paleontology. In future studies, it will help us to better understand these dinosaurs. It’s a really important specimen.”

The mostly complete skeleton was found in 1993, but because it was believed to be a more common ornithomimid, it sat on a shelf at the Royal Tyrrell Museum for 15 years before it was finally prepared for the museum’s 25th anniversary. The mistaken identity laid the foundation for its name, meaning “deceptive thief.”

The Apatoraptor pennatus fossil is the first articulated caenagnathid skeleton from anywhere in the world—meaning the bones are still in the same position as when the animal died—and is by far the most complete caenagnathid skeleton from Alberta. The discovery helps fill in some of the missing puzzle pieces on this elusive group of animals.

“Because it is a relatively complete skeleton, it helps resolve the relationships of caenagnathids, which have always been problematic,” notes Funston. “Most caenagnathids are represented by isolated material or single bones, which means that we can’t tell if they came from the same animal. Apatoraptor gives us a better idea of what these animals looked like, which tells us if the features we’ve been using to separate species are significant or not.”

Feathers used for sexual display

With such a beautifully preserved fossil, the scientists were able to use CT scanning technology to fully examine the bones. They were surprised to find pits on an arm bone corresponding with feather scars. “These feather scars suggest that Apatoraptor had a wing of feathers on its arms, although it couldn’t have used these wings to fly,” says Funston. Instead, he explains, the wings were likely used for sexual display to attract mates.

“Oviraptorosaurs, the bigger group to which Apatoraptor and other caenagnathids belong, were probably some of the flashiest dinosaurs. We know of three separate ways—head crests, tail feathers and now arm feathers—that they would display to their mates.”

Funston worked on the findings with his supervisor, world-renowned paleontologist Philip Currie, professor at the University of Alberta and Canada Research Chair in Dinosaur Paleobiology. He worked with his fellow grad student, paleoartist Sydney Mohr, on the life reconstruction. Mohr used modern birds as inspiration for the colouring.

“A new caenagnathid (Dinosauria: Oviraptorosauria) from the Horseshoe Canyon Formation of Alberta, Canada, and a reevaluation of the relationships of Caenagnathidae” appears in the April 14 edition of the Journal of Vertebrate Paleontology.

Video

Reference:
Gregory F. Funston et al. A new caenagnathid (Dinosauria: Oviraptorosauria) from the Horseshoe Canyon Formation of Alberta, Canada, and a reevaluation of the relationships of Caenagnathidae, Journal of Vertebrate Paleontology (2016). DOI: 10.1080/02724634.2016.1160910

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

Into the belly of a glacier

Into the belly of a glacier-GeologyPage
Kiya Riverman peers at ice crystals growing from the ceiling of an ice cave in the Larsbreen glacier in Svalbard, Norway. Credit: Ethan Welty

Dropping into an ice cave is like entering another world: There’s no wind, no ambient sound, and no discernible smell—unless you’re eating a peanut butter sandwich; then the scent tends to overwhelm the cold, dark space. Headlamps light up sparkling rooms of ice crystals, towering waterfalls, and narrow passages, while heavy ski boots leave footsteps behind where no other human has ventured.

“It’s kind of just you and the ice down there, and I love that,” said Kiya Riverman, a Penn State graduate student in geosciences. Riverman’s glaciology research involves climbing, crawling, and squeezing through an ice cave in Svalbard, Norway, in the Larsbreen glacier, every few years. Her research explores how waterfalls form and move within the glacier, which impacts its overall hydrology.

In the summer, meltwater from the glacier cuts through the ice, Riverman said, forming and altering cave passageways as it flows down to the earth below. There, under the ice, the meltwater can speed or slow the glacier’s movement. By studying the changing pathways of water flow, Riverman hopes to better ascertain how glaciers will respond to climate warming and increased ice melt.

“We’re describing the hydrology of this glacier by crawling around inside of it,” she continued. “In general, I’d say these systems are incredibly underutilized” in the research community. Not enough scientists actually study glaciers from the inside out, she explained.

The ice cave research started as a fun weekend hobby in 2010 when Riverman was an undergraduate studying abroad in Svalbard. A glaciologist in her program needed help mapping the ice cave, and being an avid caver back in Pennsylvania, Riverman jumped at the chance.

“It’s like a fish to water at that point,” Riverman said. “Sure, you’re in a system that’s completely ice-filled instead of rock, but it’s a lot of the same kind of exploration mentality that we have in the normal caving world.”

In 2014, Riverman traveled back to Svalbard as part of her graduate program and decided to map the cave again. Because the cave is near the town of Longyearbyen and frequently used for tourism (although the guides don’t take the tourists very deep), the entrance to the cave is easy to spot; someone always leaves behind a flag denoting the entrance’s location under the snow. Riverman and her caving companions just dig it out and rappel down. Earlier this year, Riverman again traveled to the cave to map its icy twists and turns, and she was surprised at how much the cave had changed from her initial adventures 6 years prior. Since her first visit in 2010, the cave now sits noticeably deeper in the ice.

Riverman always takes fellow cavers with her, mostly for safety reasons but also because it’s fun.

“There have been some beautiful moments connecting with my fellow scientists underground,” Riverman said. Her caving companions have to rely on each other for hours at a time underneath the ice. “The time I get to spend with the people I’m mapping [caves] with is always magical.”

There have been some scary moments as well. Once while dangling over a 9-meter drop, safely secured to a rope, Riverman had a brief moment of existential panic about the ice screws that were the only things protecting her from a swift death. Still, Riverman feels drawn again and again to exploring the otherworldly cave.

“To be standing within the system and have some kind of appreciation for how it changes and evolves, that’s what keeps drawing me back,” Riverman said.

Reference:
JoAnna Wendel. Into the Belly of a Glacier, Eos (2016). DOI: 10.1029/2016EO050257

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

A magnitude 7.8 earthquake in Ecuador “April 16, 2016”

A magnitude 7.8-GeologyPage

Tectonic Summary

The April 16, 2016 M 7.8 earthquake, offshore of the west coast of northern Ecuador, occurred as the result of shallow thrust faulting on or near the plate boundary between the Nazca and Pacific plates. At the location of the earthquake, the Nazca plate subducts eastward beneath the South America plate at a velocity of 61 mm/yr. The location and mechanism of the earthquake are consistent with slip on the primary plate boundary interface, or megathrust, between these two major plates. Subduction along the Ecuador Trench to the west of Ecuador, and the Peru-Chile Trench further south, has led to uplift of the Andes mountain range and has produced some of the largest earthquakes in the world, including the largest earthquake on record, the 1960 M 9.5 earthquake in southern Chile.

While commonly plotted as points on maps, earthquakes of this size are more appropriately described as slip over a larger fault area. Events of the size of the April 16, 2016 earthquake are typically about 160×60 km in size (length x width).

Ecuador has a history of large subduction zone related earthquakes. Seven magnitude 7 or greater earthquakes have occurred within 250 km of this event since 1900. On May 14th, 1942, a M 7.8 earthquake occurred 43 km south of this April 16th, 2016 event. On January 31st, 1906 a M 8.3 earthquake (reportedly as large as M 8.8 in some sources) nucleated on the subduction zone interface 90 km to the northeast of the April 2016 event, and ruptured over a length of approximately 400-500 km, resulting in a damaging tsunami that caused in the region of 500-1,500 fatalities. The April 2016 earthquake is at the southern end of the approximate rupture area of the 1906 event. A shallow, upper crustal M 7.2 earthquake 240 km east of the April 2016 event on March 6th, 1987 resulted in approximately 1,000 fatalities.

Seismotectonics of South America (Nazca Plate Region)

The South American arc extends over 7,000 km, from the Chilean margin triple junction offshore of southern Chile to its intersection with the Panama fracture zone, offshore of the southern coast of Panama in Central America. It marks the plate boundary between the subducting Nazca plate and the South America plate, where the oceanic crust and lithosphere of the Nazca plate begin their descent into the mantle beneath South America. The convergence associated with this subduction process is responsible for the uplift of the Andes Mountains, and for the active volcanic chain present along much of this deformation front. Relative to a fixed South America plate, the Nazca plate moves slightly north of eastwards at a rate varying from approximately 80 mm/yr in the south to approximately 65 mm/yr in the north. Although the rate of subduction varies little along the entire arc, there are complex changes in the geologic processes along the subduction zone that dramatically influence volcanic activity, crustal deformation, earthquake generation and occurrence all along the western edge of South America.

Most of the large earthquakes in South America are constrained to shallow depths of 0 to 70 km resulting from both crustal and interplate deformation. Crustal earthquakes result from deformation and mountain building in the overriding South America plate and generate earthquakes as deep as approximately 50 km. Interplate earthquakes occur due to slip along the dipping interface between the Nazca and the South American plates. Interplate earthquakes in this region are frequent and often large, and occur between the depths of approximately 10 and 60 km. Since 1900, numerous magnitude 8 or larger earthquakes have occurred on this subduction zone interface that were followed by devastating tsunamis, including the 1960 M9.5 earthquake in southern Chile, the largest instrumentally recorded earthquake in the world. Other notable shallow tsunami-generating earthquakes include the 1906 M8.5 earthquake near Esmeraldas, Ecuador, the 1922 M8.5 earthquake near Coquimbo, Chile, the 2001 M8.4 Arequipa, Peru earthquake, the 2007 M8.0 earthquake near Pisco, Peru, and the 2010 M8.8 Maule, Chile earthquake located just north of the 1960 event.

Large intermediate-depth earthquakes (those occurring between depths of approximately 70 and 300 km) are relatively limited in size and spatial extent in South America, and occur within the Nazca plate as a result of internal deformation within the subducting plate. These earthquakes generally cluster beneath northern Chile and southwestern Bolivia, and to a lesser extent beneath northern Peru and southern Ecuador, with depths between 110 and 130 km. Most of these earthquakes occur adjacent to the bend in the coastline between Peru and Chile. The most recent large intermediate-depth earthquake in this region was the 2005 M7.8 Tarapaca, Chile earthquake.

Earthquakes can also be generated to depths greater than 600 km as a result of continued internal deformation of the subducting Nazca plate. Deep-focus earthquakes in South America are not observed from a depth range of approximately 300 to 500 km. Instead, deep earthquakes in this region occur at depths of 500 to 650 km and are concentrated into two zones: one that runs beneath the Peru-Brazil border and another that extends from central Bolivia to central Argentina. These earthquakes generally do not exhibit large magnitudes. An exception to this was the 1994 Bolivian earthquake in northwestern Bolivia. This M8.2 earthquake occurred at a depth of 631 km, which was until recently the largest deep-focus earthquake instrumentally recorded (superseded in May 2013 by a M8.3 earthquake 610 km beneath the Sea of Okhotsk, Russia), and was felt widely throughout South and North America.

Subduction of the Nazca plate is geometrically complex and impacts the geology and seismicity of the western edge of South America. The intermediate-depth regions of the subducting Nazca plate can be segmented into five sections based on their angle of subduction beneath the South America plate. Three segments are characterized by steeply dipping subduction; the other two by near-horizontal subduction. The Nazca plate beneath northern Ecuador, southern Peru to northern Chile, and southern Chile descend into the mantle at angles of 25° to 30°. In contrast, the slab beneath southern Ecuador to central Peru, and under central Chile, is subducting at a shallow angle of approximately 10° or less. In these regions of “flat-slab” subduction, the Nazca plate moves horizontally for several hundred kilometers before continuing its descent into the mantle, and is shadowed by an extended zone of crustal seismicity in the overlying South America plate. Although the South America plate exhibits a chain of active volcanism resulting from the subduction and
partial melting of the Nazca oceanic lithosphere along most of the arc, these regions of inferred
shallow subduction correlate with an absence of volcanic activity.

Video

Map

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

The Cozier the Better for Bubbles Inside Powerful Volcanoes

The Cozier the Better for-GeologyPage

How did the eruptions of Katmai, Taupo and Santorini grow into a massive blast that spewed fine ash, sulfur and crystal-poor magma into the atmosphere? New research from Georgia Institute of Technology and Eidgenössische Technische Hochschule Zurich (ETH) suggests they occurred due in part to how light vapor bubbles migrate and accumulate in some parts of shallow volcanic chambers. The findings are published online by Nature.

Volcanic chambers are a maze of crystal-rich and crystal-poor regions, especially in the last place where magma stalls and builds before eruption. The Georgia Tech-ETH team used lab experiments and computer models to focus on how bubbles move to and through these shallow reservoirs, which are typically about three to five miles below the surface.

“We know that bubbles control the style and power of eruptions, but we don’t fully understand how they behave,” said Georgia Tech Assistant Professor Christian Huber, a faculty member in the School of Earth and Atmospheric Sciences. “It’s probably like opening a soda and watching the bubbles race to the top of the bottle.”

According to their study, Huber and his colleagues believe these bubbles maneuver their way through crystal filled magma until they settle in these open-spaced reservoirs — areas without many crystals — and build up the necessary energy for an impending eruption.

“When we started this project, we thought that the bubbles, as they moved through compact, crystal-rich areas, would be significantly slowed down on their way to the reservoirs,” said Huber. “Instead, these seem to be the best conditions for their ascent through the chamber.”

The team’s experiments indicate that bubbles squeeze through the narrow openings to create finger-like paths. These long paths allow the bubbles to merge and form connected pathways that transport low density vapor efficiently through the crystal-rich parts of magma chambers.

“Once they reach the end of this crystal-rich area and get more space, the water vapor fingers transform back into their usual, spherical bubble shape,” said Andrea Parmigiani, who led the study during his postdoctoral work in Huber’s group at Georgia Tech and in Olivier Bachmann’s group at ETH. “Once vapor forms these bubbles, the ascent of the light vapor bubbles is slow and bubbles accumulate.”

The team says the bubbles, once free to move around in their natural, spherical shape, settle into crystal-poor areas of the reservoir. That’s where their accumulation provides additional potential energy that can drive large volcanic eruptions that release large amounts of sulfur to the atmosphere and result in voluminous crystal-poor deposits.

The Georgia Tech team also included Salah Faroughi and Yanqing Su, who are both co-authors on the paper and Ph.D. candidates in Huber’s group. Faroughi’s lab experiments demonstrated the accumulation of bubbles in the crystal-poor areas. Su’s calculations measured sulfur releases.

Video

A simulation showing bubbles forming in a crystal-free environment as a result of the break-up of MVP fingers migrating through the underlying porous medium.

Reference:
A. Parmigiani, S. Faroughi, C. Huber, O. Bachmann & Y. Su. Bubble accumulation and its role in the evolution of magma reservoirs in the upper crust. DOI:10.1038/nature17401

Note: The above post is reprinted from materials provided by Georgia Institute of Technology.

Ancient volcanoes could be key to predicting the impact of climate change

Ancient volcanoes could be-GeologyPage
The destructive power of volcanoes was captured by William Morgan in 1840 in a hand-colored lithograph. Ancient volcanic activity could serve as a model for modern-day climate change studies. Credit: USC Libraries Special Collections

Just over 200 million years ago, long before the demise of the dinosaurs, a cataclysm killed off a significant chunk of the planet’s animal life. The leading theory implicates massive volcanic eruptions, triggered when the supercontinent of Pangea was ripped apart into separate continents.

A new study co-authored by USC Dornsife researchers strengthens evidence for that theory and has wider implications for how rapid climate change can affect life on Earth. Along with lava flows, the volcanic eruptions released massive amounts of the greenhouse gas carbon dioxide, creating havoc in the ecosystem.

The study, published April 6 in Nature Communications, charts the sharp escalation of the element mercury in samples of rock preserved from the Triassic-Jurassic extinction event. It isn’t the ordinary mercury you’d find on the surface of the planet: Isotopic data suggests it can be traced to the eruptions.

Frank Corsetti, professor of earth sciences, was a co-author on the study along with: David Bottjer, professor of earth sciences, biological sciences and environmental studies; Josh West, Wilford and Daris Zinsmeyer Early Career Chair in Marine Studies and associate professor of earth sciences and environmental studies; and William Berelson, professor of earth sciences and environmental studies and chair of earth sciences. Graduate student Joyce Yager and a host of current and past graduate students, including Kathleen Ritterbush, now an assistant professor at the University of Utah, and Yadira Ibarra, now a postdoctoral research fellow at Stanford University, were also authors.

Mercury rising

Corsetti said the rise in mercury seems to match changes in the planet’s biosphere during the era. As the mercury was found to rise in the rock samples, it matched a wave of animal extinctions on the planet’s surface and in its seas. The mass extinction peaks just as the level of mercury does; biodiversity begins to return once the mercury level recedes, about 700,000 years after the event began.

The mercury, Corsetti said, serves as a kind of fingerprint for a massive volcanic eruption in what’s known as the Central Atlantic Magmatic Province (CAMP). Essentially, CAMP was the spot in Pangea where the Atlantic Ocean would later appear after the land mass split.

CAMP’s appearance was a cataclysm on its own.

“If that much material erupted today, it would cover the contiguous United States with about 400 meters of lava—it was an enormous series of eruptions,” Corsetti said.

But the reason CAMP is suspected of being the culprit in the mass extinction has to do with carbon dioxide—the gas that climate change experts now worry is being released into the atmosphere in rapid and massive quantities.

“By some estimates, it rose nearly as rapidly as we’re putting CO2 into the atmosphere today,” Corsetti said. “We wanted to see how the Earth system responded from a rapid rise of CO2. The spoiler alert is that there was a mass extinction. What we’ve been able to do is use this mercury as a fingerprint to tie the event to the volcanos, and therefore the emissions.”

The Triassic-Jurassic extinction is particularly pertinent because it was selective, Corsetti said. It preferentially affected coral reefs and animals most similar to the ones common in today’s oceans. An earlier and more severe event, the Permian extinction—sometimes called “the mother of all extinctions”—was even bigger, but the dominant organisms affected were different from the ones common today.

That makes the Triassic-Jurassic event perhaps the most relevant mass extinction to study when trying to predict what might happen with rising CO2 levels, Corsetti said.

Reference:
Alyson M. Thibodeau et al. Mercury anomalies and the timing of biotic recovery following the end-Triassic mass extinction, Nature Communications (2016). DOI: 10.1038/ncomms11147

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

Dino dinner, dead or alive

Dino dinner, dead or alive-GeologyPage

When asked to think of meat-eating dinosaurs we usually conjure images of voracious predators chasing down helpless prey. These visions are no doubt inspired by the depiction of species such as Tyrannosaurs rex and Velociraptor in the movie Jurassic Park; however, new research conducted at Trinity College Dublin suggests that many of these species might be better remembered as oversized, scaly or feathered hyenas.

This is because Irish and Scottish researchers have now shown that scavenging would have been a particularly rewarding strategy for some carnivorous dinosaurs.

Most predators rely on scavenging (feeding on already dead material) to meet their energetic needs; for example, even lions scavenge up to nearly 50% of their food in some populations. Unlike lions though, meat-eating dinosaurs ranged from the chicken-sized to the whale-sized and lived in environments that featured prey that were often larger still.

By using computer simulations to create models of the Mesozoic environments in which these meat-eating dinosaurs lived (think of a prehistoric Pacman searching his maze for food, or a Dino-themed version of The Sims), the researchers found that species weighing around half a tonne would have been the most efficient scavengers.

Dinos that slotted into this niche included juvenile T. rexes and mid-sized species such as Dilophosaurus and Utahraptor.

Research Fellow in Trinity’s School of Natural Sciences, and co-lead author, Dr Kevin Healy, said: “In effect, these species occupied a Goldilocks zone. They were big enough to search large areas in order to find carcasses and defend them, but not so large that simply moving became too energetically costly.”

The researchers also confirmed previous studies that meat-eating dinosaurs could not have survived on scavenging alone, and must therefore have hunted as well.

“Our results also confirm that scavenging alone was unlikely to be a successful strategy in meat-eating dinosaurs and that practically all species would have likely shown predatory behaviour,” added Dr Healy.

As a result, there is no need to soften Tyrannosaurs rex’s iconic image too much, as he and other large meat-eating dinosaurs should remain safe in our imagination as predators supreme. Perhaps, though, the next time we imagine their smaller cousins, something with the acquired taste for carrion that Hyenas have might be closer to the mark.

Video

Reference:
Andrew L. Jackson et al. Body Size as a Driver of Scavenging in Theropod Dinosaurs. American Naturalist, April 2016 DOI: 10.1086/686094

Note: The above post is reprinted from materials provided by Trinity College Dublin.

Chemical weathering controls erosion rates in rivers

Chemical weathering-GeologyPage
A bedrock-floored streambed after a recent flow event in Kohala Peninsula. Credit: Brendan Murphy

Chemical weathering can control how susceptible bedrock in river beds is to erosion, according to new research. In addition to explaining how climate can influence landscape erosion rates, the results also may improve scientists’ ability to interpret and predict feedbacks between erosion, plate tectonics and Earth’s climate.

The research, led by The University of Texas at Austin, was published in Nature on April 14, 2016.

“Our research presents a specific, process-based mechanism to explain how and why river erosion depends on climate, and also perhaps why previous studies have found conflicting sensitivities to climate in different landscapes,” said Brendan Murphy, a Ph.D. student at The University of Texas Jackson School of Geosciences who led the research.

Murphy conducted the research with Joel Johnson, a professor in the Jackson School’s Department of Geological Sciences, Nicole Gasparini of Tulane University and Leonard Sklar of San Francisco State University.

Chemical weathering occurs when minerals in rock react with water. These chemical reactions physically weaken rock by altering its structure. Rocks in streambeds then become more susceptible to erosion by physical processes, such as impacts by sediment carried in flowing water.

It has been established that chemical weathering influences rock strength, Murphy said. But scientists have lacked data on the extent to which chemical weathering influences river erosion. To explore the issue, the team travelled to the Big Island of Hawaii, where the bedrock is made entirely of volcanic basalt, to collect data on chemical weathering, rock strength, and erosion rates in streams across wet and dry regions of the island.

“Hawaii is a simple, natural laboratory for studying how climate controls river erosion because it has uniform lithology and a very extreme precipitation gradient,” Murphy said. “We went to investigate if the local precipitation rate was changing the rock strength in the rivers and then looked for a mechanism to explain it.”

They measured the strength of the rock using a Schmidt hammer, a device that measures surface hardness in the field, and also analyzed the chemistry and density of rock samples back in the lab to determine the influence of chemical weathering.

Consistent with their hypothesis, they found that bedrock was more chemically weathered and physically weaker where local precipitation rates were greater. More significant, Murphy said, was their finding that locations of high precipitation could maintain high erosion rates despite continuously exposing “fresh rock” — rock that was previously below the eroded surface and is not chemically altered.

Fresh bedrock weathers rapidly when exposed at the surface, which weakens rock and allows it to be efficiently eroded by the river, the researchers found.

“This presents a positive feedback allowing river streambeds to maintain high weathering rates, weaker rock, and high erosion rates,” Murphy said.

Based on their findings, the researchers modified a numerical model that describes how rivers cut into a landscape, Johnson said, finding that chemical weathering data drastically improved their ability to predict patterns of river incision.

“Once we included the climate effect demonstrating that the chemical weathering is weakening the bedrock and making it more erodible, we can do a much better job of matching the pattern and rates of incision that occur across this landscape.” Johnson said.

Even though researchers examined only a single rock type, Murphy said that the mechanism linking chemical weathering to rock strength and erosion should apply to all types of rock. Understanding the relationship between erosion and chemical weathering can help tease out the role climate has on sculpting landscapes and influencing global cycles, Murphy said.

“The ability to better understand how landscapes erode is important, because bedrock erosion affects chemical weathering, which is a major component of the global carbon cycle and can influence global climate by the removal of carbon dioxide from the atmosphere,” Murphy said. “The ability to model landscape evolution and how climate plays into it is important for tying these larger global cycles together.”

The research was funded by the National Science Foundation and a Tulane Research Enhancement grant.

Reference:
Brendan P. Murphy, Joel P. L. Johnson, Nicole M. Gasparini, Leonard S. Sklar. Chemical weathering as a mechanism for the climatic control of bedrock river incision. Nature, 2016; 532 (7598): 223 DOI: 10.1038/nature17449

Note: The above post is reprinted from materials provided by University of Texas at Austin.

Surviving an asteroid strike that wiped out the dinosaurs

Surviving an asteroid-GeologyPage

A team led by experts at Cardiff University has provided new evidence to explain why deep sea creatures were able to survive the catastrophic asteroid strike that wiped out the dinosaurs 65m years ago.

Like the dinosaurs themselves, giant marine reptiles, invertebrates and microscopic organisms became extinct after the catastrophic asteroid impact in an immense upheaval of the world’s oceans, yet deep sea creatures managed to survive.

This has puzzled researchers as it is widely believed that the asteroid impact cut off the food supply in the oceans by destroying free-floating algae and bacteria.

However, in a study published in the April issue of the journal Geology, a team led by researchers from Cardiff University’s School of Earth and Ocean Sciences provides strong evidence suggesting that some forms of algae and bacteria were actually living in the aftermath of the asteroid disaster, and that they acted as a constant, sinking, slow trickle of food for creatures living near the seafloor.

The team were able to draw these conclusions by analysing new data from the chemical composition of the fossilised shells of sea surface and seafloor organisms from that period, taken from drilling cores from the ocean floor in the South Atlantic.

This gave the researchers an idea of the flux, or movement, of organic matter from the sea surface to the seafloor in the aftermath of the asteroid strike, and led them to conclude that a slow trickle of food was constantly being delivered to the deep ocean.

Furthermore, the team were able to calculate that the food supply in the ocean was fully restored around 1.7m years after the asteroid strike, which is almost half the original estimates, showing that marine food chains bounced back quicker than originally thought.

Heather Birch, a Cardiff University PhD from the School of Earth and Ocean Sciences who led the study, said: “The global catastrophe that caused the extinction of the dinosaurs also devastated ocean ecosystems. Giant marine reptiles met their end as did various types of invertebrates such as the iconic ammonites.

“Our results show that despite a wave of massive and virtually instantaneous extinctions among the plankton, some types of photosynthesising organisms, such as algae and bacteria, were living in the aftermath of the asteroid strike.

“This provided a slow trickle of food for organisms living near the ocean floor which enabled them to survive the mass extinction, answering one of the outstanding questions that still remained regarding this period of history.

“Even so, it took almost two million years before the deep sea food supply was fully restored as new species evolved to occupy ecological niches vacated by extinct forms.”

Many scientists currently believe that the mass extinction of life on Earth around 65m years ago was caused by a 110km-wide asteroid that hit Mexico’s Yucatán Peninsula. It is believed the debris from impact starved Earth of the Sun’s energy and, once settled, led to greenhouse gases locking in the Sun’s heat and causing temperatures to rise drastically.

This period of darkness followed by soaring heat, known as the Cretaceous-Paleogene boundary, was thought to obliterate almost half of the world’s species.

Scientists also claim that the impact of the asteroid would have filled Earth’s atmosphere with sulphur trioxide, subsequently creating a gas cloud that would have caused a mass amount of sulphuric acid rain to fall in just a few days, making the surface of the ocean too acidic for upper ocean creatures to live.

Reference:
Heather S. Birch, Helen K. Coxall, Paul N. Pearson, Dick Kroon, Daniela N. Schmidt. Partial collapse of the marine carbon pump after the Cretaceous-Paleogene boundary. Geology, 2016; 44 (4): 287 DOI: 10.1130/G37581.1

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

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