Ol Doinyo Lengai volcano in Tanzania, a source of carbonate-rich magma. Photo by Tobias Fischer, University of New Mexico, 2005 / Courtesy of the National Science Foundation.
Geologists from Florida State University’s Department of Earth, Ocean and Atmospheric Science have discovered how carbon-rich molten rock in the Earth’s upper mantle might affect the movement of seismic waves.
The new research was coauthored by EOAS Associate Professor of Geology Mainak Mookherjee and postdoctoral researcher Suraj Bajgain. Findings from the study were published in the journal Proceedings of the National Academy of Sciences .
“This research is quite important since carbon is a crucial constituent for the habitability of the planet, and we are making strides to understand how solid earth may have played a role in storing and influencing the availability of carbon in the Earth’s surface,” Mookherjee said. “Our research gives us a better understanding of the elasticity, density and compressibility of these rocks and their role in Earth’s carbon cycle.”
Carbon, one of the primary building blocks for life, is widely distributed throughout the Earth’s upper mantle and is mostly stored in forms of carbonate minerals as accessory minerals in mantle rocks. When carbonate-rich magma erupts on the surface, it is notable for its unique, mud-like appearance. These types of eruptions occur at specific locations around the world, such as at the Ol Doinyo Lengai volcano in Tanzania.
Experts believe that the presence of carbonates in rocks significantly lowers the temperature at which they melt. Carbonates that sink to the Earth’s interior, via a process known as subduction, likely cause this low-degree melting of the Earth’s upper mantle rocks, which plays an important role in the planet’s deep carbon cycle.
“Earth’s mantle has less free oxygen available at increasing depths,” Mookherjee said. “As the mantle upwells through a process of mantle convection, the slowly moving rocks that were reduced, or had less oxygen, at a greater depth become progressively more oxidized at shallower depth. The carbon in the mantle is likely to be reduced deeper in the Earth and get oxidized as the mantle upwells.”
This change in depth-dependent oxidation state is likely to cause melting of mantle rocks, a process called redox melting, which could produce carbon-rich molten rock, also known as melts. These melts are likely to affect the physical property of a rock, which can be detected using geophysical probes such as seismic waves, he said.
Prior to this study, geologists had poor knowledge of the elastic properties of these carbonate-induced partial melts, which made them difficult to directly detect.
One set of clues that geologists use to better understand their science are measurements of seismic waves as they move through the layers of the Earth. A type of seismic wave known as a compressional wave is faster than another type known as a shear wave, but at depths of around 180 to 330 kilometers into the Earth, the ratio of their speeds is even higher than is typical.
“This elevated ratio of compressional waves to the shear waves has been a puzzle, and using the findings from our study, we are able to explain this perplexing observation,” Mookherjee said.
Minor quantities of carbon-rich melts, approximately 0.05 percent, might be dispersed pervasively through the Earth’s deep upper mantle, and that may lead to the elevated ratio of compressional to shear sound velocity, researchers explained.
To conduct the study, researchers took high-pressure ultrasonic measurements and density measurements on cores of the carbonate mineral dolomite. These experiments were complemented by theoretical simulations to provide a new understanding of the fundamental physical properties of carbonate melts.
“We have been trying to understand the elastic and transport properties of aqueous fluids, silicate melt and metallic melt properties, to gain better insight into the mass of volatiles stored in the deep solid earth,” Bajgain said.
These findings mean the partially molten rocks in the mantle could hold as much as 80 to 140 parts per million of carbon, which would be 20 to 36 million gigatons of carbon in the deep upper mantle region, making it a substantial carbon reservoir. In comparison, Earth’s atmosphere contains just over 410 ppm of carbon, or around 870 gigatons.
Reference:
Man Xu, Zhicheng Jing, Suraj K. Bajgain, Mainak Mookherjee, James A. Van Orman, Tony Yu, Yanbin Wang. High-pressure elastic properties of dolomite melt supporting carbonate-induced melting in deep upper mantle. Proceedings of the National Academy of Sciences, 2020; 202004347 DOI: 10.1073/pnas.2004347117
Workers excavating Hall’s Cave in Central Texas. Image Courtesy of Michael Waters
Ancient sediment found in a central Texas cave appears to solve the mystery of why the Earth cooled suddenly about 13,000 years ago, according to a research study co-authored by a Texas A&M University professor.
Michael Waters, director of The Center for The Study of the First Americans and Distinguished Professor at Texas A&M University, and colleagues from Baylor University and the University of Houston have had their work published in Science Advances.
Some researchers believed the event — which cooled the Earth by about 3 degrees Centigrade, a huge amount — was caused by an extraterrestrial impact with the Earth, such as a meteor collision.
But Waters and the team found that the evidence left in layers of sediment in Hall’s Cave were almost certainly the result of volcanic eruptions.
Waters said that Hall’s Cave, located in the Texas hill country, has a sediment record extending over 20,000 years and he first began researching the cave in 2017.
“It is an exceptional record that offers a unique opportunity for interdisciplinary cooperation to investigate a number of important research questions,” he said.
“One big question was, did an extraterrestrial impact occur near the end of the last ice age, about 13,000 years ago as the ice sheets covering Canada were melting, and cause an abrupt cooling that thrust the northern hemisphere back into the ice age for an extra 1,200 years?”
Waters and the team found that within the cave are layers of sediment, first identified by Thomas Stafford (Stafford Research Laboratories, Colorado), that dated to the time of the proposed impact that could answer the question and perhaps even identify the trigger that started the ancient cold snap.
The event also likely helped cause the extinction of large mammals such as mammoth, horse and camel that once roamed North America.
“This work shows that the geochemical signature associated with the cooling event is not unique but occurred four times between 9,000 and 15,000 years ago,” said Alan Brandon, professor of geosciences at University of Houston and head of the research team.
“Thus, the trigger for this cooling event didn’t come from space. Prior geochemical evidence for a large meteor exploding in the atmosphere instead reflects a period of major volcanic eruptions.
“I was skeptical,” Brandon said. “We took every avenue we could to come up with an alternative explanation, or even avoid, this conclusion. A volcanic eruption had been considered one possible explanation but was generally dismissed because there was no associated geochemical fingerprint.”
After a volcano erupts, the global spread of aerosols reflects incoming solar radiation away from Earth and may lead to global cooling post eruption for one to five years, depending on the size and timescales of the eruption, the team said.
“The Younger Dryas, which occurred about 13,000 years ago, disrupted distinct warming at the end of the last ice age,” said co-author Steven Forman, professor of geosciences at Baylor.
The Earth’s climate may have been at a tipping point at the end of Younger Dryas, possibly from the ice sheet discharge into the North Atlantic Ocean, enhanced snow cover and powerful volcanic eruptions that may have in combination led to intense Northern Hemisphere cooling, Forman said.
“This period of rapid cooling coincides with the extinction of a number of species, including camels and horses, and the appearance of the Clovis archaeological tradition,” said Waters.
Brandon and fellow University of Houston scientist Nan Sun completed the isotopic analysis of sediments collected from Hall’s Cave. They found that elements such as iridium, ruthenium, platinum, palladium and rhenium were not present in the correct proportions, meaning that a meteor or asteroid could not have caused the event.
“The isotope analysis and the relative proportion of the elements matched those that were found in previous volcanic gases,” said Sun, lead author of the report.
Volcanic eruptions cause their most severe cooling near the source, usually in the year of the eruption, with substantially less cooling in the years after the eruption, the team said.
The Younger Dryas cooling lasted about 1,200 years, “so a sole volcanic eruptive cause is an important initiating factor, but other Earth system changes, such as cooling of the oceans and more snow cover were needed to sustain this colder period, “Forman said.
Waters added that the bottom line is that “the chemical anomalies found in sediments dating to the beginning of the Younger Dryas are the result of volcanism and not an extraterrestrial impact.”
Reference:
N. Sun, A. D. Brandon, S. L. Forman, M. R. Waters and K. S. Befus. Volcanic origin for Younger Dryas geochemical anomalies ca. 12,900 cal B.P.. Science Advances, 2020 DOI: 10.1126/sciadv.aax8587
Note: The above post is reprinted from materials provided by Texas A&M University. Original written by Keith Randall.
A lizard-like creature whose ancestors once roamed the Earth with dinosaurs and today is known to live for longer than 100 years may hold clues to a host of questions about the past and the future.
In a study published Aug. 5 in Nature, an interdisciplinary, international team of researchers, in partnership with Māori tribe Ngātiwai, sequenced, assembled and analyzed the complete genome of the Sphenodon punctatus, or the tuatara, a rare reptile whose ancestors once roamed the earth with dinosaurs. It hasn’t changed much in the 150 million to 250 million years since then.
“We found that the tuatara genome has accumulated far fewer DNA substitutions over time than other reptiles, and the molecular clock for tuataras ticked at a much slower speed than squamates, although faster than turtles and crocodiles, which are the real molecular slowpokes,” said co-author Marc Tollis, an assistant professor in the School of Informatics, Computing, and Cyber Systems at Northern Arizona University. “This means in terms of the rate of molecular evolution, tuataras are kind of the Toyota Corolla — nothing special but very reliable and persistently ticking away over hundreds of millions of years.”
Tuatara have been out on their own for a staggering amount of time, with prior estimates ranging from 150-250 million years, and with no close relatives the position of tuatara on tree of life has long been contentious. Some argue tuatara are more closely related to birds, crocodiles and turtles, while others say they stem from a common ancestor shared with lizards and snakes. This new research places tuatara firmly in the branch shared with lizards and snakes, but they appear to have split off and been on their own for about 250 million years — a massive length of time considering primates originated about 65 million years ago, and hominids, from which humans descend, originated approximately six million years ago.
“Proving the phylogenetic position of tuatara in a robust way is exciting, but we see the biggest discovery in this research as uncovering the genetic code and beginning to explore aspects of the biology that makes this species so unique, while also developing new information that will help us better conserve this taonga or special treasure,” said lead author Neil Gemmell, a professor at the University of Otago.
One area of particular interest is to understand how tuataras, which can live to be more than 100 years old, achieve such longevity. Examining some of the genes implicated in protecting the body from the ravages of age found that tuatara have more of these genes than any other vertebrate species thus far examined, including humans. This could offer clues into how to increase humans’ resistance to the ailments that kill humans.
But the genome, and the tuatara itself, has so many other unique features all on its own. For one, scientists have found tuatara fossils dating back 150 million years, and they look exactly the same as the animals today. The fossil story dates the tuatara lineage to the Triassic Period, when dinosaurs were just starting to roam the Earth.
“The tuatara genome is really a time machine that allows us to understand what the genetic conditions were for animals that were vying for world supremacy hundreds of millions of years ago,” he said. “A genome sequence from an animal this ancient and divergent could give us a better idea about what the ancestral amniote genome might have looked like.”
While modern birds are the descendants of dinosaurs, they are less suitable for this type of research because avian genomes have lost a significant amount of DNA since diverging from their dinosaur ancestors.
But the tuataras, which used to be spread throughout the world, have other unusual features. Particularly relevant to this research is the size of its genome; the genome of this little lizard has 5 billion bases of DNA, making it 67 percent larger than a human genome. Additionally, tuataras have temperature-based sex determination, which means the ratio of males to females in a clutch of eggs depends on the temperatures at which they are incubated. They also have a pronounced “third eye” — a light sensory organ that sticks through the top of their skulls. Mammals’ skulls have completely covered the third eye, though they still contain the pineal gland underneath, which helps maintain circadian rhythms.
The tuatara also is unique in that it is sacred to the M?ori people. This research, for all the scientific knowledge that came from it, was groundbreaking for its collaboration with the Indigenous New Zealanders. The purpose was to ensure the research aligned with and respected the importance of the tuatara in their culture, which has never been done before in genomic research.
“Tuatara are a taonga, and it’s pleasing to see the results of this study have now been published,” Ng?tiwai Trust Board resource management unit manager Alyx Pivac said. “Our hope is that this is yet another piece of information that will help us understand tuatara and aid in the conservation of this special species. We want to extend a big mihi to all of those who have been involved in this important piece of work.”
With the genome now sequenced, the international science community has a blueprint through which to examine the many unique features of tuatara biology, which will aid human understanding of the evolution of the amniotes, a group that includes birds, reptiles and mammals.
Reference:
Neil J. Gemmell, Kim Rutherford, Stefan Prost, Marc Tollis, David Winter, J. Robert Macey, David L. Adelson, Alexander Suh, Terry Bertozzi, José H. Grau, Chris Organ, Paul P. Gardner, Matthieu Muffato, Mateus Patricio, Konstantinos Billis, Fergal J. Martin, Paul Flicek, Bent Petersen, Lin Kang, Pawel Michalak, Thomas R. Buckley, Melissa Wilson, Yuanyuan Cheng, Hilary Miller, Ryan K. Schott, Melissa D. Jordan, Richard D. Newcomb, José Ignacio Arroyo, Nicole Valenzuela, Tim A. Hore, Jaime Renart, Valentina Peona, Claire R. Peart, Vera M. Warmuth, Lu Zeng, R. Daniel Kortschak, Joy M. Raison, Valeria Velásquez Zapata, Zhiqiang Wu, Didac Santesmasses, Marco Mariotti, Roderic Guigó, Shawn M. Rupp, Victoria G. Twort, Nicolas Dussex, Helen Taylor, Hideaki Abe, Donna M. Bond, James M. Paterson, Daniel G. Mulcahy, Vanessa L. Gonzalez, Charles G. Barbieri, Dustin P. DeMeo, Stephan Pabinger, Tracey Van Stijn, Shannon Clarke, Oliver Ryder, Scott V. Edwards, Steven L. Salzberg, Lindsay Anderson, Nicola Nelson, Clive Stone. The tuatara genome reveals ancient features of amniote evolution. Nature, 2020; DOI: 10.1038/s41586-020-2561-9
Malignant cancer diagnosed in a dinosaur for the first time
A collaboration led by the Royal Ontario Museum (ROM) and McMaster University has led to the discovery and diagnosis of an aggressive malignant bone cancer — an osteosarcoma — for the first time ever in a dinosaur. No malignant cancers (tumours that can spread throughout the body and have severe health implications) have ever been documented in dinosaurs previously. The paper was published August 3rd in the medical journal The Lancet Oncology.
The cancerous bone in question is the fibula (lower leg bone) from Centrosaurus apertus, a horned dinosaur that lived 76 to 77 million years ago. Originally discovered in Dinosaur Provincial Park in Alberta in 1989, the badly malformed end of the fossil was originally thought to represent a healing fracture. Noting the unusual properties of the bone on a trip to the Royal Tyrrell Museum in 2017, Dr. David Evans, James and Louise Temerty Endowed Chair of Vertebrate Palaeontology from the ROM, and Drs. Mark Crowther, Professor of Pathology and Molecular Medicine, and Snezana Popovic, an osteopathologist, both at McMaster University, decided to investigate it further using modern medical techniques. They assembled a team of multidisciplinary specialists and medical professionals from fields including pathology, radiology, orthopaedic surgery, and palaeopathology. The team re-evaluated the bone and approached the diagnosis similarly to how it would be approached for the diagnosis of an unknown tumour in a human patient.
“Diagnosis of aggressive cancer like this in dinosaurs has been elusive and requires medical expertise and multiple levels of analysis to properly identify,” says Crowther, who is also a Royal Patrons Circle donor and volunteer at the ROM. “Here, we show the unmistakable signature of advanced bone cancer in 76-million-year-old horned dinosaur — the first of its kind. It’s very exciting.”
After carefully examining, documenting, and casting the bone, the team performed high-resolution computed tomography (CT) scans. They then thin-sectioned the fossil bone and examined it under a microscope to assess it at the bone-cellular level. Powerful three-dimensional CT reconstruction tools were used to visualize the progression of the cancer through the bone. Using this rigorous process, the investigators reached a diagnosis of osteosarcoma.
To confirm this diagnosis, they then compared the fossil to a normal fibula from a dinosaur of the same species, as well as to a human fibula with a confirmed case of osteosarcoma. The fossil specimen is from an adult dinosaur with an advanced stage of cancer that may have invaded other body systems. Yet it was found in a massive bonebed, suggesting it died as part of a large herd of Centrosaurus struck down by a flood.
“The shin bone shows aggressive cancer at an advanced stage. The cancer would have had crippling effects on the individual and made it very vulnerable to the formidable tyrannosaur predators of the time,” says Evans, an expert on these horned dinosaurs. “The fact that this plant-eating dinosaur lived in a large, protective herd may have allowed it to survive longer than it normally would have with such a devastating disease.”
Osteosarcoma is a bone cancer that usually occurs in the second or third decade of life. It is an overgrowth of disorganized bone that spreads rapidly both through the bone in which it originates and to other organs, including most commonly, the lung. It is the same type of cancer that afflicted Canadian athlete Terry Fox and led to the partial amputation of his right leg prior to Fox’s heroic Marathon of Hope in 1980.
“It is both fascinating and inspiring to see a similar multidisciplinary effort that we use in diagnosing and treating osteosarcoma in our patients leading to the first diagnosis of osteosarcoma in a dinosaur,” says Seper Ekhtiari, an Orthopaedic Surgery Resident at McMaster University. “This discovery reminds us of the common biological links throughout the animal kingdom and reinforces the theory that osteosarcoma tends to affect bones when and where they are growing most rapidly.”
This study aims to establish a new standard for the diagnosis of unclear diseases in dinosaur fossils and opens the door to more precise and more certain diagnoses. Establishing links between human disease and the diseases of the past will help scientists to gain a better understanding of the evolution and genetics of various diseases. Evidence of many other diseases that we share with dinosaurs and other extinct animals may yet be sitting in museum collections in need of re-examination using modern analytical techniques.
Funding for David Evans was provided by an NSERC Discovery Grant, and research computers for 3D visualization were generously supported by The Dorothy Strelsin Foundation.
Reference:
Seper Ekhtiari, Kentaro Chiba, Snezana Popovic, Rhianne Crowther, Gregory Wohl, Andy Kin On Wong, Darren H Tanke, Danielle M Dufault, Olivia D Geen, Naveen Parasu, Mark A Crowther, David C Evans. First case of osteosarcoma in a dinosaur: a multimodal diagnosis. The Lancet Oncology, 2020; 21 (8): 1021 DOI: 10.1016/S1470-2045(20)30171-6
A new analysis of sandstones from Antarctica indicates there may be important links between the generation of mountain belts and major transitions in Earth’s atmosphere and oceans.
A team of researchers analyzed the chemistry of tiny zircon grains commonly found in the Earth’s continental rock record to determine their ages and chemical compositions. The team included scientists from the University of Wisconsin Oshkosh, Michigan Technological University and ETH Zurich in Switzerland.
The study was published recently in the international peer-reviewed journal Terra Nova, which features short innovative papers about the solid Earth and planetary sciences.
“Mountain building occurs in association with the plate tectonic motions of the continents,” said Paulsen, the lead author on the paper. “Geologists have long recognized that the generation of significant mountainous relief has the potential to profoundly influence the chemistry of the Earth’s oceans and atmosphere.”
Yet there are significant questions about the patterns of mountain building in Earth’s past, especially associated with the ancient rock record leading up to the explosion of life about 541 million years ago.
“Mountains tend to be worn down by water and wind that ultimately transports their sedimentary remains to the oceans, leaving an incomplete puzzle for geologists to fit together,” said Deering, a coauthor on the paper. “However, there is increasing evidence that missing pieces of the puzzle are found in the sands of ancient beaches and rivers, which are essentially the remnants of mountains produced by weathering and erosion.”
The researchers’ findings, based on an analysis of a large sample of zircon grains from sandstone recovered in Antarctica, may signify key links in the evolution of the Earth’s rock cycle and its atmosphere and oceans.
“We found two primary periods of increased average crustal thickness associated with volcanic chains along convergent plate boundaries, implying an increased proportion of higher mountains at these times,” Paulsen said.
“Both episodes occurred during major reorganization of the continents when they separated and drifted on the Earth’s surface over time. They also overlap with snowball Earth glaciations — when the whole Earth was frozen over — and associated steps in oxygenation of the atmosphere, which may have been critical for the evolution of life. These correlations suggest an important causal link between plate tectonics and major transitions in Earth’s atmosphere and oceans.”
Reference:
Timothy Paulsen, Chad Deering, Jakub Sliwinski, Snehamoy Chatterjee, Olivier Bachmann, Marcel Guillong. Crustal thickness, rift‐drift and potential links to key global events. Terra Nova, 2020; DOI: 10.1111/ter.12485
A large number of the valley networks scarring Mars’s surface were carved by water melting beneath glacial ice, not by free-flowing rivers as previously thought, according to new UBC research published today in Nature Geoscience. The findings effectively throw cold water on the dominant “warm and wet ancient Mars” hypothesis, which postulates that rivers, rainfall and oceans once existed on the red planet.
To reach this conclusion, lead author Anna Grau Galofre, former PhD student in the department of earth, ocean and atmospheric sciences, developed and used new techniques to examine thousands of Martian valleys. She and her co-authors also compared the Martian valleys to the subglacial channels in the Canadian Arctic Archipelago and uncovered striking similarities.
“For the last 40 years, since Mars’s valleys were first discovered, the assumption was that rivers once flowed on Mars, eroding and originating all of these valleys,” says Grau Galofre. “But there are hundreds of valleys on Mars, and they look very different from each other. If you look at Earth from a satellite you see a lot of valleys: some of them made by rivers, some made by glaciers, some made by other processes, and each type has a distinctive shape. Mars is similar, in that valleys look very different from each other, suggesting that many processes were at play to carve them.”
The similarity between many Martian valleys and the subglacial channels on Devon Island in the Canadian Arctic motivated the authors to conduct their comparative study. “Devon Island is one of the best analogues we have for Mars here on Earth — it is a cold, dry, polar desert, and the glaciation is largely cold-based,” says co-author Gordon Osinski, professor in Western University’s department of earth sciences and Institute for Earth and Space Exploration.
In total, the researchers analyzed more than 10,000 Martian valleys, using a novel algorithm to infer their underlying erosion processes. “These results are the first evidence for extensive subglacial erosion driven by channelized meltwater drainage beneath an ancient ice sheet on Mars,” says co-author Mark Jellinek, professor in UBC’s department of earth, ocean and atmospheric sciences. “The findings demonstrate that only a fraction of valley networks match patterns typical of surface water erosion, which is in marked contrast to the conventional view. Using the geomorphology of Mars’ surface to rigorously reconstruct the character and evolution of the planet in a statistically meaningful way is, frankly, revolutionary.”
Grau Galofre’s theory also helps explain how the valleys would have formed 3.8 billion years ago on a planet that is further away from the sun than Earth, during a time when the sun was less intense. “Climate modelling predicts that Mars’ ancient climate was much cooler during the time of valley network formation,” says Grau Galofre, currently a SESE Exploration Post-doctoral Fellow at Arizona State University. “We tried to put everything together and bring up a hypothesis that hadn’t really been considered: that channels and valleys networks can form under ice sheets, as part of the drainage system that forms naturally under an ice sheet when there’s water accumulated at the base.”
These environments would also support better survival conditions for possible ancient life on Mars. A sheet of ice would lend more protection and stability of underlying water, as well as providing shelter from solar radiation in the absence of a magnetic field — something Mars once had, but which disappeared billions of years ago.
While Grau Galofre’s research was focused on Mars, the analytical tools she developed for this work can be applied to uncover more about the early history of our own planet. Jellinek says he intends to use these new algorithms to analyze and explore erosion features left over from very early Earth history.
“Currently we can reconstruct rigorously the history of global glaciation on Earth going back about a million to five million years,” says Jellinek. “Anna’s work will enable us to explore the advance and retreat of ice sheets back to at least 35 million years ago — to the beginnings of Antarctica, or earlier — back in time well before the age of our oldest ice cores. These are very elegant analytical tools.”
Reference:
Grau Galofre, A., Jellinek, A.M. & Osinski, G.R. Valley formation on early Mars by subglacial and fluvial erosion. Nat. Geosci., 2020 DOI: 10.1038/s41561-020-0618-x
One of the big questions in biology is why certain plants and animals are found in some places and not others. Figuring out how species evolve and spread, and why some places are richer in species than others, is key to understanding and protecting the world around us. Mountains make a good laboratory for scientists tackling these questions: mountains are home to tons of biodiversity, in part due to all the different habitats at different elevations. In a new study in Science, researchers examined the plant life in the China’s Hengduan Mountains, the Himalaya Mountains, and the Qinghai-Tibet Plateau. Using DNA to build family trees of species, they learned that the diversity of plants in that region today can be traced back to newly-formed mountain ranges 30 million years ago, and monsoons that came later. It’s a concrete example of how climatic and environmental changes influence life on Earth.
“This paper addresses the fundamental question of why there are so many species in some parts of the world and not others,” says Rick Ree, a curator at Chicago’s Field Museum and corresponding author of the Science study. “The formation of this very species-rich community was fueled by ancient mountain-building and then subsequent effects of the monsoon. The biodiversity that we see today has been profoundly shaped by geology and climate.”
The paper focuses on plants growing above the treeline (called the alpine zone) in the Hengduan Mountains of southwestern China. “It’s an incredibly interesting part of the world, it’s a relatively small area that harbors one-third of all the plant species in China,” says Ree. “In the Hengduan Mountains, you can see coniferous forests, rushing glacial streams, craggy valleys, and meadows just teeming with wildflowers.” Some of the flowers, Ree notes, might be familiar to Western gardeners, including rhododendrons and delphiniums.
Ree and his colleagues wanted to find out how plants are distributed in the alpine regions of the Hengduan Mountains, Himalaya, and Qinghai-Tibet Plateau, and how they got there in the first place. To figure it out, they turned to phylogenetic reconstructions: essentially, using DNA and key pieces of fossil evidence to piece together the plants’ family trees, going back tens of millions of years.
The researchers compared the DNA of different plant species that live in the region, determining how closely related they were to each other and how they evolved. If you have DNA sequences for a bunch of different plants, by looking at the differences in their DNA and using fossil plants as benchmarks for how long it takes new species to arise, you can make an educated guess as to how long ago their common ancestor lived and figure out the family tree that makes the most sense.
In this study, Ree and his colleagues were able to trace the origins of alpine plants in the Hengduan, Himalaya, and Qinghai-Tibet Plateau. Many of the plants first evolved in the Hengduan Mountains. Then, as the Indian tectonic plate collided with Asia, slowly creating new mountains, a bunch of new habitats formed up the mountains’ sides and in the valleys below. And as the new mountains formed, the region began to experience more intense monsoons, possibly because the mountains altered the prevailing winds, creating new weather conditions.
“The combined effect of mountain-building and monsoons was like pouring jet fuel onto this flame of species origination,” says Ree. “The monsoon wasn’t simply giving more water for plants to grow, it had this huge role in creating a more rugged topography. It caused erosion, resulting in deeper valleys and more incised mountain ranges.”
“The theory is, if you increase the ruggedness of a landscape, you’re more likely to have populations restricted in their movement because it’s harder to cross a deeper valley than a shallow valley. So any time you start increasing the patchiness and barriers between populations, you expect evolution to accelerate,” says Ree.
And that’s exactly what the team found in reconstructing the plants’ genetic family tree: as the landscape grew more rugged over time, the now-isolated populations of plants veered off into their own separate species, resulting in the biodiversity we see today.
In addition to showing how geological and climate changes over the last 30 million years affect today’s spread of plants, Ree notes that the study has implications for better understanding the climate change the Earth is currently experiencing.
“This study sheds light on the conditions under which we get rich versus poor biodiversity,” says Ree. “Mountain ecosystems tend to be very sensitive to things like global warming, because the organisms that live there are dependent on a tight range of elevation and temperature. Understanding how historical environmental change affected alpine plants twenty million years ago can help us predict how today’s climate change will affect their descendants.”
Reference:
Wen-Na Ding, Richard H. Ree, Robert A. Spicer, Yao-Wu Xing. Ancient orogenic and monsoon-driven assembly of the world’s richest temperate alpine flora. Science, 2020; 369 (6503): 578 DOI: 10.1126/science.abb4484
An African Elephant walks through the drying streambed of Chitake Springs as the drought season descends on Mana Pools National Park in Zimbabwe Photo credit: Trisha Atwood.
One million years ago, the extinction of large-bodied plant-eaters changed the trajectory of life on Earth. The disappearance of these large herbivores reshaped plant life, altered fire regimes across Earth’s landscapes, and modified biogeochemical cycling in such a way that Earth’s climate became slightly colder. A new study out today by Utah State University Assistant Professor of Watershed Sciences, Trisha Atwood, suggests that modern-day megaherbivores (plant-eaters weighing more than 1000 kg) could soon suffer the same fate as their ancient ancestors, with unknown consequences for Earth and all of its inhabitants.
Armed with a dataset of the diets of over 24,500 mammals, birds, and reptiles, Atwood and her team set out to answer the question “Are plant-eaters, meat-eaters, or animals who eat both plants and meat, at the greatest risk of extinction?” Their findings, published in the journal Science Advances, would challenge a two-decade-long perception that meat-eating predators were the most likely group to meet the ire of Earth’s six mass extinction.
The results indicate that with over a quarter of the world’s modern-day herbivores threatened with extinction, plant eaters have the highest representation of at-risk species in the present day. The study also highlights that this attack on herbivores is not a new phenomenon. Human activities have led to the disproportionate extinction of herbivores compared to predators since at least the late Pleistocene (11,000-50,000 years ago).
“The results were somewhat shocking,” said Atwood. “Our highly publicized and fraught relationship with predatory animals such as lions and wolves has led to the unfounded perception that we are losing predators more than any other trophic group.”
Using evidence-based science to challenge misconceptions like the one Atwood’s team uncovered is essential for getting society on the right track towards addressing future extinctions. Because a species’ role in its ecosystem is intricately linked to what it eats, understanding whether predators, herbivores, or omnivores are at the highest risk of extinction helps scientists and society understand what the potential consequences of losing those species are.
Already the consequences of declines in modern herbivores from land-use change and hunting have begun to echo those that occurred on Earth 1 million years ago; alterations to plant life, changes to fire regimes, and disruptions to nutrient cycling. This study highlights that we must redouble our efforts to strategically invest in conservation and management of herbivores to avoid future dramatic changes in the functions arising from animals at the base of global foodwebs.
Although the results of the study indicate that herbivores are the most at-risk group, it is not clear sailing for predators. The study also identified scavengers, which eat the remains of recently deceased animals (e.g., vultures) and animals that primarily eat fish, such as seabirds, as having a heightened risk of extinction.
“Our results enable us to identify specialized diets within the carnivores that are associated with higher extinction risk, and also identify the habitats these species live in,” says Edd Hammill an Assistant Professor of Watershed Sciences at Utah State University and co-author of the study. “It would appear that seabirds across the globe suffer disproportionately high levels of extinction”
To better inform conservation actions, the researchers are now wrestling to understand what it is about herbivores, scavengers, and piscivores (animals that consume fish) that make them more susceptible to extinction compared to other animals.
“Documenting a pattern in extinctions is only the first step towards curbing the loss of species,” says Atwood. “Our next step is to understand the intricacies of why this pattern is occurring; only then will we really have a chance at stopping these future extinctions.”
Reference:
Trisha B. Atwood, Shaley A. Valentine, Edd Hammill, Douglas J. McCauley, Elizabeth M. P. Madin, Karen H. Beard, William D. Pearse. Herbivores at the highest risk of extinction among mammals, birds, and reptiles. Science Advances, 2020; 6 (32): eabb8458 DOI: 10.1126/sciadv.abb8458
The first dinosaurs laid soft-shelled eggs that resembled those of a turtle, a new study led by the Museum and Yale University has found, contradicting the long-held thought that all dinosaur eggs were hard-shelled. It also suggests that calcified eggs evolved independently at least three times in the dinosaur family tree.
“Over the last 20 years, we’ve found dinosaur eggs around the world. But for the most part, they only represent three groups—theropod dinosaurs, which includes modern birds, advanced hadrosaurs like the duck-bill dinosaurs, and advanced sauropods, the long-necked dinosaurs,” said Mark Norell, chair and Macaulay Curator in the Museum’s Division of Paleontology and lead author of the study, which is published today in the journal Nature. “At the same time, we’ve found thousands of skeletal remains of ceratopsian dinosaurs, but almost none of their eggs. So why weren’t their eggs preserved? My guess—and what we ended up proving through this study—is that they were soft-shelled.”
Amniotes—the group that includes birds, mammals, and reptiles—produce eggs with an inner membrane or “amnion” that helps to prevent the embryo from drying out. Some amniotes, such as many turtles, lizards, and snakes, lay soft-shelled eggs. Others, such as birds, lay eggs with hard, heavily calcified shells. Because modern crocodilians and birds, which are living dinosaurs, lay hard-shelled eggs, it was long assumed that all non-avian dinosaurs laid hard eggs.
The researchers studied embryo-containing fossil eggs belonging to two species of dinosaur: Protoceratops, a sheep-sized plant-eating dinosaur that lived in what is now Mongolia between about 75 and 71 million years ago, and Mussaurus, a long-necked, plant-eating dinosaur that grew to 20 feet in length and lived between 227 and 208.5 million years ago in what is now Argentina.
In the well-preserved Protoceratops specimen, researchers noticed a black-and-white egg-shaped halo associated with skeletal embryos in the fossilized clutch. When the scientists took a closer look with a suite of sophisticated geochemical methods, they found evidence of the proteinaceous membrane that makes up the innermost eggshell layer of all modern archosaur eggs, those of birds and crocodilians. The same was true for the Mussaurus specimen.
When researchers compared the biomineralization signature of the dinosaur eggs with eggshell data from other animals, they determined that the Protoceratops and Mussaurus eggs were not biomineralized but rather leathery and soft.
“It’s an exceptional claim, so we need exceptional data,” said study author and Yale graduate student Jasmina Wiemann. “We had to come up with a brand-new proxy to be sure that what we were seeing was how the eggs were in life, and not just a result of some strange fossilization effect.”
With data on the chemical composition and mechanical properties of eggshells from 112 other extinct and living relatives, the researchers constructed a “super tree” to track the evolution of the eggshell structure and properties through time. They found that hard-shelled, calcified eggs evolved independently at least three times in dinosaurs.
Soft eggshells are sensitive to water loss and would not hold up well under the weight of a brooding parent. Because of this, the researchers propose that the eggs were likely buried in moist soil or sand and incubated with heat from decomposing plant matter, much like what some reptiles do with their eggs today.
The depth of a hydraulic fracturing well in Oklahoma, among other factors, increases the probability that fracking will lead to earthquake activity, according to a new report in the Bulletin of the Seismological Society of America.
The researchers hope their findings, published as part of an upcoming BSSA special issue on observations, mechanisms and hazards of induced seismicity, will help oil and gas operators and regulators in the state refine drilling strategies to avoid damaging earthquakes.
During hydraulic fracturing, well operators inject a pressurized liquid into a rock layer after drilling vertically and often horizontally through the rock. The liquid breaks apart — fractures — the rock layer and allows natural gas or petroleum to flow more freely. A growing number of studies suggest that this process can induce seismic activity large enough for people to feel, possibly by increasing fluid pressures within the rock that relieve stress on faults and allow them to slip.
In one rock layer examined in the BSSA study, the likelihood that hydraulic fracturing triggered seismic activity increased from 5 to 50 percent as well operations moved from 1.5 to 5.5 kilometers (0.9 to 3.4 miles) deep, the researchers found.
Although the exact mechanisms linking well depth and seismic probability are still being examined, Michael Brudzinski and colleagues suggest that the overpressure of fluids trapped inside the rock may be important.
“The deeper the rock layers are, the more rock that is sitting on top of a well, and that is going to potentially increase the fluid pressures at depth,” said Brudzinski, the study’s corresponding author from Miami University in Ohio.
Oklahoma has been at the center of a dramatic increase in earthquake activity over the past decade, mostly caused by oil and gas companies injecting wastewater produced by drilling back into deeper rock layers. However, a 2018 study identified places in the state where significant amounts of seismic activity were linked to nearly 300 hydraulic fracture wells.
Hydraulic fracturing is associated with a magnitude 4.6 earthquake in Canada and a magnitude 5.7 earthquake in China, although fracking-induced earthquakes tend to be smaller in magnitude than those caused by wastewater disposal. As a result, oil and gas operators and regulators would like to know more about why some wells trigger seismic activity, and how to adjust their operations to prevent damaging earthquakes.
Brudzinski and colleagues found the link between depth and seismic probability in their examination of data from 929 horizontal and 463 vertical hydraulic fracturing wells in Oklahoma. The scientists used publicly available data on injected volume at well sites, the number of wells on a drilling pad, what kind of fluid was injected, and the vertical depth of the well, among other features.
The total volume of injected liquid at the Oklahoma wells did not affect the probability of seismic activity near the wells — a surprising finding that differs from other studies of induced seismicity. Some previous hydraulic fracturing (and wastewater disposal) studies show an increase in seismic activity with increasing volume.
Most of the wells in the current study are single wells, however, and not multiple wells clustered on a drilling pad, Brudzinski noted. In some places in western Canada and Texas, where there is a link between the injected volume and seismicity, multiple wells on a pad are more common.
“So that’s where we started to think that perhaps that’s the difference between what we’re seeing in our study versus other studies,” Brudzinski said. “We’re proposing that multiple wells injecting next to each other may be why volume does matter in those cases, although we need to study it more.”
“It could be that volume does still matter, but more so in a cumulative way than for any given well,” he added. “An isolated well with a large volume may not have nearly as much of a [seismic] risk as a large volume well that is in close proximity to other large volume wells.”
The researchers also compared the probability of seismic activity in wells where the injected liquid was a gel versus “slickwater” — water with chemicals added to increase flow. They found a lower level of seismicity in gel operations compared to slickwater, although the difference wasn’t as statistically significant as the other trends.
Simulation studies suggest that the more viscous gel may not flow as far as the slickwater, limiting its effects on faults, Brudzinski said.
Reference:
Rosamiel Ries, Michael R. Brudzinski, Robert J. Skoumal, Brian S. Currie. Factors Influencing the Probability of Hydraulic Fracturing-Induced Seismicity in Oklahoma. Bulletin of the Seismological Society of America, 2020; DOI: 10.1785/0120200105
Amud 9 fossils. Credit: Osborjn M. Pearson and Adrián Pablos
Adrián Pablos, a scientist at the Centro Nacional de Investigación sobre la Evolución Humana (CENIEH), led a study published in PaleoAnthropology, the official journal of the PaleoAnthropology Society, looking at the morphology and anatomy of a partial foot recovered over 25 years ago at Amud Cave, which confirms that the individual Amud 9 was a Neandertal woman from the Late Pleistocene, with a stature of some 160-166 cm and weight of 60 kg.
Over the course of several excavations conducted in the 20th century at Amud Cave, remains of at least 15 Neandertals were found. A systematic and detailed study of one of these individuals, Amud 9, has found that the fossil possesses the traits usually associated with Neanderthals in the characteristics of the foot, tarsals, metatarsals and phalanges, which differ from those of modern humans, both fossil and recent.
“Most of these traits are related to the typical, exceptional robustness of the postcranial skeleton, that is, from the neck down, observed in the majority of Neandertals,” explains Pablos.
Sex, weight and height
Sex, weight, and height estimates in fossil populations are normally based on the dimensions of the large leg bones. However, in the case of Amud 9, only a fragment of tibia, the talus or ankle bone, one metatarsal or instep bone, and several phalanges are conserved.
As no long leg bones have been found, the researchers applied different mathematical estimates based upon the foot bones, thus obtaining an approximation to important paleobiological parameters.
“Knowing parameters such as the body size and sex of this individual helps us learn a bit more about what the Neandertals were like,” he says.
Reference:
Pearson, O.M., Pablos, et al. A partial Neandertal foot from the Late Middle Paleolithic of Amud cave. PaleoAnthropology 2020, 98-125. DOI: 10.4207/PA.2020.ART144
Note: The above post is reprinted from materials provided by CENIEH .
Broad surfaces called terraces preserve ancient river floodplains and landscape history up to hundreds of meters above the Fortymile River, a tributary of the Yukon River, in eastern Alaska. Researchers from the USGS, the University of Vermont, Purdue University and Utah State University publish definitive support that increases in sediment deposited to oceans from river erosion coincide with dramatic changes in glacial cycles. Credit: USGS
Scientists have long debated the idea that global climate changes have forced river erosion rates to increase over the past five million years. New field data gleaned from a multi-institution, collaborative study of North America’s rugged Yukon River basin, near storied Klondike goldfields, reveal profound increases in river erosion during abrupt global intensification of climate fluctuations about 2.6 and one million years ago.
“These results provide the first definitive support that increases in sediment deposited to oceans from river erosion coincide with dramatic changes in glacial cycles,” says Utah State University geoscientist Tammy Rittenour. “Our ability to date former river deposits was the game-changing factor in allowing us to pursue this hypothesis.”
Rittenour and colleagues from the U.S. Geological Survey, the University of Vermont and Purdue University published findings in the July 20, 2020, issue of Nature Geoscience.
“Oxygen isotope values in marine sediment show worldwide fluctuations between cold and warm climates that abruptly intensified during the early Pleistocene period,” says Rittenour, professor in USU’s Department of Geosciences. “Rates of river sediment accumulation also jumped during this time.”
Since rivers do the work of erosion and sediment transport over most of the Earth’s surface, scientists have long suggested patterns of global precipitation mimic climate fluctuations.
“If that’s the case, enhanced river discharge resulting from intensified global precipitation would increase rates of river erosion,” she says.
To test this idea, the team took advantage of the landscape history preserved in the study site’s prominent river terraces — ancient river floodplains — perched up to hundreds of meters above the modern Fortymile River, a Yukon River tributary that flows from northwestern Canada to Alaska.
“This ‘Rosetta-stone’ location, with exposed terraces, provided a long-sought window from which to obtain data,” says Rittenour, a Geological Society of America Fellow. “We geochronologists often repeat the adage, ‘No Dates, No Rates,’ meaning we can’t calculate rates of erosion without age control. Using relatively new dating techniques, we were able, for the first time, to establish ages for river deposits that span these key time periods of global climate change.”
Co-authors Lee Corbett and Paul Bierman of UVM and Marc Caffee of Purdue provided age control on the site’s older terraces, using cosmogenic nuclide burial dating methods that use differing decay rates of unique radiogenic isotopes of beryllium and aluminum produced by sediment exposure to cosmic radiation.
Rittenour, director of USU’s Luminescence Laboratory, used optically stimulated luminescence dating of younger river sediments.
“OSL dating provides an age estimate of the last time the sediment was exposed to light,” she says.
Corroborating the team’s new results, Bering Sea sediment records show concurrent increases in accumulation of sediment eroded from the Fortymile River.
“It’s exciting to apply new tools to test foundational ideas that have been only previously speculated,” Rittenour says. “These results represent an important step toward understanding the influence of climate in shaping landscapes inhabited by people, and provide clues regarding future landscape response to human activity.”
Reference:
Adrian M. Bender, Richard O. Lease, Lee B. Corbett, Paul R. Bierman, Marc W. Caffee, Tammy M. Rittenour. Late Cenozoic climate change paces landscape adjustments to Yukon River capture. Nature Geoscience, 2020; DOI: 10.1038/s41561-020-0611-4
Note: The above post is reprinted from materials provided by Utah State University. Original written by Mary-Ann Muffoletto.
If you’ve ever held a trilobite fossil, seen one in a classroom, or walked by one in a store, chances are it was Elrathia kingii, one of the most common and well-recognized trilobites, and collected by the hundreds of thousands in western Utah. But despite the popularity of this species, scientists had not determined how it grew—from hatchling to juvenile to adult—until now. New work from the American Museum of Natural History published today in the journal Papers in Palaeontology describes the development and growth rate of Elrathia kingii—only the second such dataset to be compiled for a trilobite—allowing for the first comparison among trilobite species.
“There’s quite a big size range among trilobites. Some never got bigger than about a centimeter, while the largest on record is 72 centimeters (28 inches),” said Melanie Hopkins, an associate curator in the Museum’s Division of Paleontology and the study’s author. “Growth-rate studies like this one can help us tackle some of the big-picture questions: How did some trilobites get so big? What was the environmental context for that? And how did body size evolve over the evolutionary history of the clade?”
Trilobites are a group of extinct marine arthropods—distantly related to the horseshoe crab—that lived for almost 300 million years. They were incredibly diverse, with more than 20,000 described species. Their fossilized exoskeletons are preserved in sites all over the world, from the United States to China. Like insects, they molted throughout their lifetimes, leaving clues to how they changed during development. But to calculate the species’ growth rate, scientists need fossils representing all stages of the animal’s life—and lots of them.
“There are tons of specimens of Elrathia kingii out there but most of them are adults, and data from exactly where they were collected is inconsistent,” Hopkins said. “I needed material that I could collect from as small a section as possible that included a lot of juveniles.”
So in May 2018, Hopkins spent five days in Utah with a crew consisting of Museum staff and volunteers at a new fossil site said to preserve bucketloads of Elrathia kingii. By the end of the trip, they had collected about 500 specimens—many of them juveniles, which can be as small as half a millimeter long—from a section of outcrop just 1.5 meters (about 5 feet) long.
Hopkins estimated the growth rate and compared it to previously published data on a different trilobite, Aulacopleura konincki—the first time two trilobite species have been compared in this way. The two species look very similar and Hopkins found that they also grow in similar ways: for example, the growth of the trunk—the area immediately below the trilobite’s head made up of segments that increase with age—was controlled by a growth gradient, with those that were younger and closer to the back of the body undergoing faster growth. But while Elrathia kingii was smaller in early development and went through fewer molts before adulthood, it had faster growth rates, ultimately reaching sizes on par with Aulacopleura konincki, the largest of which are about 4 centimeters long.
In future studies, Hopkins is planning to add growth-rate data on different, more diverse-looking trilobite species to her models.
Reference:
Melanie J. Hopkins et al, Ontogeny of the trilobite Elrathia kingii (Meek) and comparison of growth rates between Elrathia kingii and Aulacopleura koninckii (Barrande), Papers in Palaeontology (2020). DOI: 10.1002/spp2.1331
Graduate student Mike Duvall is pictured here in southeastern Nepal during fieldwork in 2017. Image credit: John Waldron
A newly identified fault system in southeastern Nepal has the potential to cause earthquakes in a densely populated area, according to two University of Alberta scientists who were part of an international team that made the discovery.
“We discovered a series of faults at the foot of the Himalayan mountain range that have never been seen before,” explained U of A geologist John Waldron, who was a co-author of the study with graduate student Mike Duvall.
Waldron explained that the newly found faults show that the front of tectonic movement in the mountain belt is 40 kilometres farther south than scientists previously thought.
“Our research highlights the need to look below the surface, and farther afield, to fully understand earthquakes and structures within the Himalaya,” said Duvall, whose work on the study was supervised by Waldron.
“This network of faults shows that Himalayan deformation reaches farther than we previously thought and provides a glimpse into the geometry and formation of nascent mountain ranges.”
The research team used seismic profiles—images that look like slices through the top few kilometres of the Earth’s crust. These profiles were originally collected during petroleum exploration, by recording sound waves bounced off sedimentary layers buried beneath the Ganga flood plain of the Ganges River, which carries much of the sediment eroded from the Himalaya.
The data show that while southeastern Nepal is currently nearly flat, the thrusting produced by movement of the tectonic plates has already reached this area.
Waldron said that while there has not been an earthquake recorded in the area since accurate scientific records began about a century ago, his research results suggest there is potential for earthquakes to happen.
“Most of these faults only slip every thousand years or so,” he explained. “We discovered that a substantial part of this area has an almost horizontal fault underneath it, which has the potential to slip and cause a damaging earthquake.”
For more than 100 million years, the Indian subcontinent has been drifting northwards. In the last 40 or 50 million years, the subcontinent started to collide with Asia, giving rise to the Himalaya, the largest mountain range in the world. India is still sliding northwards into Asia at a rate of nearly two centimetres per year—about as fast as your fingernails grow, Waldron noted.
“Along the front of the mountains in Nepal are thrust faults, formed where the Indian subcontinent is being pushed underneath Asia,” he said. “The movement is jerky, which produces earthquakes. Because this is a densely populated part of the world, these earthquakes can be catastrophic.”
In 2015, a serious earthquake in Kathmandu, Nepal, with a magnitude of 7.8 on the Richter scale, destroyed hundreds of thousands of homes, killing nearly 9,000 people and injuring more than 20,000. Though the newly identified faults are not in the city of Kathmandu, the southeastern portion of Nepal is densely populated.
Collaborators on the research include Laurent Godin from Queen’s University and Yani Najman from Lancaster University.
The study, “Active Strike-Slip Faults and an Outer Frontal Thrust in the Himalayan Foreland Basin,” was published in Proceedings of the National Academy of Sciences.
Reference:
Michael J. Duvall et al. Active strike-slip faults and an outer frontal thrust in the Himalayan foreland basin, Proceedings of the National Academy of Sciences (2020). DOI: 10.1073/pnas.2001979117
Note: The above post is reprinted from materials provided by University of Alberta. The original article was written by Katie Willis.
A dinosaur-like reptile leaves muddy footprints along the shoreline of a lake during a rainstorm some 234 million years ago in northwestern Argentina. Credit: Jorge Gonzalez/NHMU
The Triassic Period, about 252 to 201 million years ago, was a time of volatile change, particularly during an interval known as the Carnian (about 237 to 227 million years ago). Three dramatic events occurred on Earth: the first dinosaurs appeared, gigantic volcanic eruptions called the Wrangellia large igneous province spewed out greenhouse gasses and the climate suddenly shifted to warmer, more humid conditions that scientists call the Carnian Pluvial Episode (CPE).
Recent work suggests that the Wrangellia eruptions caused the CPE, and that the resulting climate change may have spurred the early diversification of dinosaurs. But the lack of precise absolute dates for many Carnian sediments makes comparisons difficult. Additionally, few detailed paleoclimatic data exist for many regions outside of Europe, making it unclear whether the CPE was truly a global climate event or conclusively linking it to dinosaur diversification.
In a new study in the journal Gondwana Research, an international group led by Adriana Mancuso, a National Scientific and Technical Research Council (CONICET) researcher at the Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales in Mendoza, Argentina, demonstrated that the CPE affected the southern hemisphere, specifically South America, which strengthens the case that it was a global climate event. The study was published online on June 15, 2020.
“There are ample Triassic, and specifically Carnian, rocks and fossils in South America, and Argentina in particular, but until now there were no paleoclimatic studies that could conclusively show that the Carnian Pluvial Episode occurred in the southern hemisphere,” Mancuso said.
The Triassic Period, about 252 to 201 million years ago, was a time of volatile change, particularly during an interval known as the Carnian (about 237 to 227 million years ago). Three dramatic events occurred on Earth: the first dinosaurs appeared, gigantic volcanic eruptions called the Wrangellia large igneous province spewed out greenhouse gasses and the climate suddenly shifted to warmer, more humid conditions that scientists call the Carnian Pluvial Episode (CPE).
Recent work suggests that the Wrangellia eruptions caused the CPE, and that the resulting climate change may have spurred the early diversification of dinosaurs. But the lack of precise absolute dates for many Carnian sediments makes comparisons difficult. Additionally, few detailed paleoclimatic data exist for many regions outside of Europe, making it unclear whether the CPE was truly a global climate event or conclusively linking it to dinosaur diversification.
In a new study in the journal Gondwana Research, an international group led by Adriana Mancuso, a National Scientific and Technical Research Council (CONICET) researcher at the Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales in Mendoza, Argentina, demonstrated that the CPE affected the southern hemisphere, specifically South America, which strengthens the case that it was a global climate event. The study was published online on June 15, 2020.
“There are ample Triassic, and specifically Carnian, rocks and fossils in South America, and Argentina in particular, but until now there were no paleoclimatic studies that could conclusively show that the Carnian Pluvial Episode occurred in the southern hemisphere,” Mancuso said.
The team, which included researchers at the University of Utah and the Berkeley Geochronology Center, studied Carnian rocks of the Los Rastros Formation, which are preserved in the Ischigualasto-Villa Unión Basin in northwest Argentina. For the first time, the team precisely dated volcanic ash preserved in lake sediments and pieced together the paleoclimate at this time.
“Our study focused on these rocks because they had the perfect combination of a good fossil record, dateable ash layers, and rich climate data preserved in lake sediments,” said Randall Irmis of the Natural History Museum of Utah and Department of Geology & Geophysics at the University of Utah.
In order to date the ash layer, the scientists isolated small needle-like crystals of zircon, minerals that act like time-capsules. When zircon crystallizes during an eruption, it traps the element uranium in its crystal structure, but never incorporates lead. Any lead preserved in the crystals today is a result of the radioactive decay of uranium. Because scientists know this decay rate, they can measure the ratio of uranium and lead in each zircon crystal and calculate how far back in time the crystals formed. In the present study, this measurement was done on a precise mass spectrometer at the Berkeley Geochronology Center.
Reference:
Adriana C. Mancuso et al, Evidence for the Carnian Pluvial Episode in Gondwana: New multiproxy climate records and their bearing on early dinosaur diversification, Gondwana Research (2020). DOI: 10.1016/j.gr.2020.05.009
268 seismometers (red) in 117 countries detected a drop on seismic noise. “Global quieting of high-frequency seismic noise due to COVID-19 pandemic lockdown measures” by Thomas Lecocq et al., published Thursday 23 July 2020 in Science Credits:Photo of seismometer: Stephen Hicks/Imperial College London
The lack of human activity during lockdown caused human-linked vibrations in the Earth to drop by an average of 50% between March and May 2020.
This quiet period, likely caused by the total global effect of social distancing measures, closure of services and industry, and drops in tourism and travel, is the longest and most pronounced quiet period of seismic noise in recorded history.
The new research, led by the Royal Observatory of Belgium and five other institutions around the world including Imperial College London, showed that the dampening of ‘seismic noise’ caused by humans was more pronounced in more densely populated areas.
The relative quietness allowed researchers to listen in to previously concealed earthquake signals, and could help us differentiate between human and natural seismic noise more clearly than ever before.
Co-author Dr Stephen Hicks, from Imperial’s Department of Earth Science and Engineering, said: “This quiet period is likely the longest and largest dampening of human-caused seismic noise since we started monitoring the Earth in detail using vast monitoring networks of seismometers.
“Our study uniquely highlights just how much human activities impact the solid Earth, and could let us see more clearly than ever what differentiates human and natural noise.”
The paper is published today in Science.
Anthropause
Measured by instruments called seismometers, seismic noise is caused by vibrations within the Earth, which travel like waves. The waves can be triggered by earthquakes, volcanoes, and bombs — but also by daily human activity like travel and industry.
Although 2020 has not seen a reduction in earthquakes, the drop in human-caused seismic noise is unprecedented. The strongest drops were found in urban areas, but the study also found signatures of the lockdown on sensors buried hundreds of metres underground and in more remote areas.
Human-generated noise usually dampens during quiet periods like over the Christmas/New Year period and Chinese New Year, and during weekends and overnight. However, the drop in vibrations caused by COVID-19 lockdown measures eclipse even those seen during these periods.
Some researchers are dubbing this drop in anthropogenic (human-caused) noise and pollution the ‘anthropause’.
Dr Hicks said: “This is the first global study of the impact of the coronavirus anthropause on the solid Earth beneath our feet.”
To gather the data, researchers looked at seismic data from a global network of 268 seismic stations in 117 countries and found significant noise reductions compared to before any lockdown at 185 of those stations. Beginning in China in late January 2020, and followed by Europe and the rest of the world in March to April 2020, researchers tracked the ‘wave’ of quietening between March and May as worldwide lockdown measures took hold.
The largest drops in vibrations were seen in the most densely populated areas, like Singapore and New York City, but drops were also seen in remote areas like Germany’s Black Forest and Rundu in Namibia. Citizen-owned seismometers, which tend to measure more localised noise, noted large drops around universities and schools around Cornwall, UK and Boston, USA — a drop in noise 20 per cent larger than seen during school holidays. Countries like Barbados, where lockdown coincided with the tourist season, saw a 50 per cent decrease in noise. This coincided with flight data that suggested tourists returned home in the weeks before official lockdown.
Listening in
Over the past few decades, seismic noise has gradually increased as economies and populations have grown.
The drastic changes to daily life caused by the pandemic have provided a unique opportunity to study their environmental impacts, such as reductions in emissions and pollution in the atmosphere. The changes have also given us the opportunity to listen in to the Earth’s natural vibrations without the distortions of human input.
The study reports the first evidence that previously concealed earthquake signals, especially during daytime, appeared much clearer on seismometers in urban areas during lockdown.
The researchers say the lockdown quietening could also help them differentiate between human-caused noise and natural signals that might warn of upcoming natural disasters.
Lead author Dr Thomas Lecocq from the Royal Observatory of Belgium said: “With increasing urbanisation and growing global populations, more people will be living in geologically hazardous areas. It will therefore become more important than ever to differentiate between natural and human-caused noise so that we can ‘listen in’ and better monitor the ground movements beneath our feet. This study could help to kick-start this new field of study.”
The study’s authors hope that their work will spawn further research on the seismic lockdown, as well as finding previously hidden signals from earthquakes and volcanoes.
Dr Hicks said: “The lockdowns caused by the coronavirus pandemic may have given us a glimmer of insight into how human and natural noise interact within the Earth. We hope this insight will spawn new studies that help us listen better to the Earth and understand natural signals we would otherwise have missed.”
Reference:
Thomas Lecocq, Stephen P. Hicks, Koen Van Noten, Kasper van Wijk, Paula Koelemeijer, Raphael S. M. De Plaen, Frédérick Massin, Gregor Hillers, Robert E. Anthony, Maria-Theresia Apoloner, Mario Arroyo-Solórzano, Jelle D. Assink, Pinar Büyükakpınar, Andrea Cannata, Flavio Cannavo, Sebastian Carrasco, Corentin Caudron, Esteban J. Chaves, David G. Cornwell, David Craig, Olivier F. C. den Ouden, Jordi Diaz, Stefanie Donner, Christos P. Evangelidis, Läslo Evers, Benoit Fauville, Gonzalo A. Fernandez, Dimitrios Giannopoulos, Steven J. Gibbons, Társilo Girona, Bogdan Grecu, Marc Grunberg, György Hetényi, Anna Horleston, Adolfo Inza, Jessica C. E. Irving, Mohammadreza Jamalreyhani, Alan Kafka, Mathijs R. Koymans, Celeste R. Labedz, Eric Larose, Nathaniel J. Lindsey, Mika McKinnon, Tobias Megies, Meghan S. Miller, William Minarik, Louis Moresi, Víctor H. Márquez-Ramírez, Martin Möllhoff, Ian M. Nesbitt, Shankho Niyogi, Javier Ojeda, Adrien Oth, Simon Proud, Jay Pulli, Lise Retailleau, Annukka E. Rintamäki, Claudio Satriano, Martha K. Savage, Shahar Shani-Kadmiel, Reinoud Sleeman, Efthimios Sokos, Klaus Stammler, Alexander E. Stott, Shiba Subedi, Mathilde B. Sørensen, Taka’aki Taira, Mar Tapia, Fatih Turhan, Ben van der Pluijm, Mark Vanstone, Jerome Vergne, Tommi A. T. Vuorinen, Tristram Warren, Joachim Wassermann, Han Xiao. Global quieting of high-frequency seismic noise due to COVID-19 pandemic lockdown measures. Science, July 23, 2020; DOI: 10.1126/science.abd2438
Decomposition of dinosaurian remains inferred by invertebrate traces on vertebrate bone reveal new insights into Late Jurassic ecology, decay, and climate in western Colorado Credit: Brian Engh
Top predator dinosaurs like the Allosaurus and Ceratosaurus devouring dinosaur remains isn’t all that surprising, but the smaller creatures feasting on dinosaur remains may just give us a more complete picture of what life was like at Mygatt-Moore Quarry outside Fruita, Colorado 152 million years ago. A new study out in PeerJ on Wednesday, July 15th, 2020 authored by Museums of Western Colorado’s Paleontologist Dr. Julia McHugh, looks at the insect species who feasted on decaying dinosaurs back in the Jurassic period.
Researchers Dr. Julia McHugh (Museums of Western Colorado, Colorado Mesa University), Dr. Stephanie K. Drumheller (University of Tennessee), Anja Riedel (Colorado Mesa University), and Miriam Kane (Colorado Mesa University) examined more than 2,300 fossil bones over a two-year study and found over 400 traces left by insects and snails, a surprisingly high number. The marks researchers found on the fossils also came from at least six different invertebrates. These findings are a huge step to understanding the long-lost paleo diversity, and paleo climate of the Jurassic period.
It also gave researchers a better understanding of just how stinky the Jurassic period was too. The abundance of traces meant that the dinosaur carcasses must have been unburied for a long time—5 months to 6 years or more according to this new study. “Large carcasses take a long time to decompose. The smell from a dead mouse in your basement is bad enough, but then imagine that mouse was a 65-foot long animal! The stench of rotting meat would have been a magnet for carrion insects and other scavengers,” Dr. McHugh explains.
Reference:
Julia B. McHugh et al, Decomposition of dinosaurian remains inferred by invertebrate traces on vertebrate bone reveal new insights into Late Jurassic ecology, decay, and climate in western Colorado, PeerJ (2020). DOI: 10.7717/peerj.9510
Note: The above post is reprinted from materials provided by PeerJ.
A new study suggests that last year’s Ridgecrest earthquakes increased the chance of a large earthquake on California’s San Andreas fault.
The study, published in the Bulletin of the Seismological Society of America on Monday, says there is now a 2.3% chance of an earthquake of magnitude 7.5 or greater in the next 12 months on a section of the 160-mile-long Garlock fault, which runs along the northern edge of the Mojave Desert.
That increased likelihood, in turn, would cause there to be a 1.15% chance of a large earthquake on the San Andreas fault in the next year.
Those odds may seem small. But they’re a substantial jump from what the chances were before last year’s Ridgecrest, California, earthquakes, whose epicenters were about 125 miles northeast of downtown L.A.
The new odds mean a large quake on the Garlock fault is now calculated to be 100 times more likely—rising from 0.023% in the next year to 2.3%.
And the chance of a large quake on the San Andreas has roughly tripled, from 0.35% in the next year to 1.15%, said Ross Stein, a co-author of the study and the CEO of Temblor, a catastrophe modeling company in the Bay Area that has built a free earthquake hazards app for smartphones.
The Ridgecrest quakes could trigger a large quake on the Garlock fault, and that could trigger a quake on the San Andreas.
Seismologist Lucy Jones, who did not play a role in the report released Monday, called the study “elegant science” but added that its conclusions are not confirmed.
“It’s really interesting science, and I like the way they’ve been able to increase the complexity of how they do their modeling. That’s a real advance. But it’s not yet proven,” Jones said.
That said, Jones said that government officials in California should be prepared for a scenario in which an earthquake occurs that immediately raises the risk of a large quake on the San Andreas fault.
“If the Garlock happens, yes, we will be saying the San Andreas is at increased risk,” Jones said. “What do you do when there’s an earthquake that could be a foreshock to the San Andreas? What do you say? What do you do?”
The study is the latest suggestion of a plausible scenario in which last summer’s earthquakes in a remote part of California might have started a chain of events that could result in a devastating earthquake on the San Andreas fault that has not been seen in Southern California in 163 years.
At its closest, the San Andreas fault comes within 35 miles of downtown Los Angeles.
“Now, you can think of the Ridgecrest earthquake as being so far from Greater Los Angeles … that it is nearly harmless,” said Stein, an earthquake scientist emeritus of the U.S. Geological Survey and adjunct professor of geophysics at Stanford University.
“But the problem is that … the Ridgecrest earthquake brought the Garlock fault closer to rupture. If that fault ruptures—and it gets within about 25 miles of the San Andreas—then there’s a high likelihood, maybe a 50/50 shot, that it would immediately rupture on the San Andreas,” Stein said. Stein’s co-author on the study is Shinji Toda, of Tohoku University in Japan.
If the Garlock fault did rupture close to the San Andreas fault—but the San Andreas did not immediately rupture—Los Angeles would face the prospect of having a metaphorical sword of Damocles hanging over its neck, Stein said, with the prospect of L.A. facing a larger risk of a San Andreas quake within a matter of months, or perhaps decades.
“In a way, if the fault ruptures all at once, life is simpler. It’s done,” Stein said. “But if it doesn’t—if it hangs, and plenty of faults do hang—that would put the city in a really difficult … position.”
A hypothetical magnitude 7.8 quake on the San Andreas could cause more than 1,800 deaths, injure 5,000, displace some 500,000 to 1 million people from their homes and hobble the region economically for a generation. A quake of that magnitude produces 45 times more energy than the 1994 magnitude 6.7 Northridge quake.
Out of the many faults in California, the San Andreas is singularly poised to be the one that unleashes a megaquake in our lifetime because it is the main tectonic plate boundary between the Pacific and North American plates, and because of how fast the fault accumulates seismic strain.
Another troubling scenario Jones has mentioned before was a hypothetical magnitude 6 earthquake at the Cajon Pass north of San Bernardino. It’s a particularly vexing scenario because such a quake could trigger large quakes on three major faults: the San Andreas, the San Jacinto and the Cucamonga.
The last time scientists in California warned about an increased risk of a big earthquake on the San Andreas fault, however, the initial statewide response was flatfooted.
In 2016, state officials didn’t issue a statement of the increased threat of a big quake on the San Andreas fault until about 39 hours after the first concerning quake hit in the Salton Sea.
Even when state officials finally put out a statement, they inserted an error that inaccurately downplayed the increased seismic risk. It was corrected after an inquiry from the Los Angeles Times.
A hypothetical magnitude 7 earthquake along the San Francisco Bay Area’s Hayward fault would cause severe, violent or extreme shaking along large swaths of the East Bay, North Bay and Silicon Valley, according to the U.S. Geological Survey. By contrast, the magnitude 6.9 Loma Prieta earthquake of 1989 caused only such shaking in the Santa Cruz Mountains, Watsonville and Gilroy.
The study published Monday is not the first time scientists have suggested the Ridgecrest earthquakes could be the first domino to fall that eventually leads Southern California’s section of the San Andreas fault to rupture in a significant way for the first time since 1857, when a magnitude 7.8 earthquake ruptured 225 miles of fault between Monterey County and the Cajon Pass in San Bernardino County.
A year ago, the U.S. Geological Survey—the nation’s primary earthquake science agency—calculated that there was an extremely remote chance the San Andreas could be triggered by the Ridgecrest quakes.
And a USC professor of earth sciences, James Dolan, articulated the same Ridgecrest-to-Garlock-to-San Andreas scenario in an interview with The Times last year.
The Garlock fault ruptures on average every 1,300 years, said Tim Dawson, senior engineering geologist with the California Geological Survey, but earthquakes can occur as often as every few hundred years or have a drought between large quakes of as long as 3,000 years. The last big earthquake on the Garlock fault happened about 500 years ago, Dawson said.
Big quakes on the southern San Andreas fault along the Grapevine section of Interstate 5 can happen on average every 100 years, although there’s wide variation in how often they can happen; there has been a time when it was just 20 years between major quakes, and another when there was a gap of 200 years between huge quakes.
Though it’s far from a sure bet the Garlock fault will rupture in our lifetime, the southern San Andreas is a likely candidate for such a big quake in our lifetime. “It’s really the fastest moving fault in California,” Dawson said of the San Andreas, meaning it accumulates strain far faster than other faults. “It’s always going to play the most significant role in earthquake hazard in California.”
Ken Hudnut, a U.S. Geological Survey geophysicist, drops, covers and holds on in Ridgecrest as a magnitude 7.1 earthquake ruptures through a nearby fault.
There’s a popular conception that earthquakes relieve seismic strain—they do—but they also increase seismic strain in other areas.
“An earthquake will relieve stress on the fault that it occurs on. But by relieving that, you’re transferring the stress onto something else,” Dawson said. “For every action, there’s a reaction.”
Scientists—and the public—have long been fascinated about the prospect of triggered earthquakes. It was a main plot point in the movie “San Andreas,” starring Dwayne Johnson in 2015.
It’s for a good reason.
Last year’s Fourth of July Ridgecrest quake, a magnitude 6.4 temblor, imparted greater stress on a fault that eventually ruptured a day later, causing the more powerful magnitude 7.1 quake on July 5.
The most powerful earthquake in California of the last 68 years, the magnitude 7.3 Landers earthquake that hit the sparsely populated Mojave Desert on June 28, 1992—and a magnitude 6.3 aftershock hours later near Big Bear—was believed to be related to the Joshua Tree earthquake, a magnitude 6.1 event, that occurred two months earlier.
The trio of quakes raised concerns that the San Andreas was next.
The theory at the time was that the Joshua Tree-Landers-Big Bear sequence of quakes essentially unclamped a section of the San Andreas fault. That made it plausible the San Andreas fault might be next to rupture, said Ken Hudnut, geophysicist with the USGS.
But the southern San Andreas fault has remained as quiet as it has since the 1850s.
Instead, the next big quakes in Southern California occurred where few scientists were expecting them to hit—the magnitude 6.7 earthquake that struck Northridge in 1994, and the magnitude 7.1 Hector Mine earthquake in 1999 that was located even deeper in the remote Mojave Desert.
“What has been actually happening in the real world is quite different than what we thought was a plausible scenario back at the time in ’92,” Hudnut said.
Note: The above post is reprinted from materials provided by Los Angeles Times Distributed by Tribune Content Agency, LLC.
Map of the Earth showing the present-day deviation from expected magnetic field direction. The star is Saint Helena
Research by the University of Liverpool has revealed that strange behaviour of the magnetic field in the South Atlantic region existed as far back as eight to 11 million years ago, suggesting that today’s South Atlantic Anomaly is a recurring feature and unlikely to represent an impending reversal of the Earth’s magnetic field.
The South Atlantic Anomaly is an area characterized by a significant reduction in the strength of Earth’s magnetic field compared with areas at similar geographic latitudes. Here, protection from harmful radiation from space is reduced. The most significant signs of this are technical malfunctions aboard satellites and spacecraft.
In a study published in the Proceedings of the National Academy of Sciences, Liverpool paleomagnetic researchers analysed the record of Earth’s magnetic field which is preserved in igneous rocks from the island Saint Helena which lies in the midst of the South Atlantic Anomaly.
The geomagnetic records from the rocks covering 34 different volcanic eruptions that took place between eight and 11 million years ago revealed that at these occurrences the direction of the magnetic field for St Helena often pointed far from the North pole, just like it does today.
The Earth’s magnetic field, or the geomagnetic field, not only gives us the ability of navigating with a compass, but also protects our atmosphere from charged particles coming from the sun, called solar wind. However, it is not completely stable in strength and direction, both over time and space, and it has the ability to completely flip or reverse itself with substantial implications.
The South Atlantic Anomaly is a topic of debate between scientists in this field. Besides the fact that it causes damages to space technology, it also raises the question of where it comes from and whether it represents the start of the total weakening of the field and a possible upcoming pole reversal.
Lead author of the paper, University of Liverpool PhD student Yael Engbers, said: “Our study provides the first long term analysis of the magnetic field in this region dating back millions of years. It reveals that the anomaly in the magnetic field in the South Atlantic is not a one-off, similar anomalies existed eight to 11 million years ago.
“This is the first time that the irregular behaviour of the geomagnetic field in the South Atlantic region has been shown on such a long timescale. It suggests that the South Atlantic Anomaly is a recurring feature and probably not a sign of an impending reversal.
“It also supports earlier studies that hint towards a link between the South Atlantic Anomaly and anomalous seismic features in the lowermost mantle and the outer core. This brings us closer to linking behaviour of the geomagnetic field directly to features of the Earth’s interior”
Reference:
Yael A. Engbers, Andrew J. Biggin, Richard K. Bono. Elevated paleomagnetic dispersion at Saint Helena suggests long-lived anomalous behavior in the South Atlantic. Proceedings of the National Academy of Sciences, 2020; 202001217 DOI: 10.1073/pnas.2001217117
A team of Penn State researchers studied Telica Volcano, a persistently active volcano in western Nicaragua, to both observe and quantify small-scale intra-crater change associated with background and eruptive activity. IMAGE: Google Earth
The shape of volcanoes and their craters provide critical information on their formation and eruptive history. Techniques applied to photographs — photogrammetry — show promise and utility in correlating shape change to volcanic background and eruption activity.
Changes in volcano shape — morphology — that occur with major eruptions are quantifiable, but background volcanic activity, manifesting as small volume explosions and crater wall collapse, can also cause changes in morphology and are not well quantified.
A team of Penn State researchers studied Telica Volcano, a persistently active volcano in western Nicaragua, to both observe and quantify small-scale intra-crater change associated with background and eruptive activity. Geologists consider Telica ‘persistently’ active because of its high levels of seismicity and volcanic degassing, and it erupts on less than 10-year time periods.
The team used direct observations of the crater, photographic observations from 1994 to 2017 and photogrammetric techniques on photos collected between 2011 and 2017 to analyze changes at Telica in the context of summit crater formation and eruptive processes. They used structure-from-motion (SfM), a photogrammetric technique, to construct 3D models from 2D images. They also used point cloud differencing, a method used to measure change between photo sampling periods, to compare the 3D models, providing a quantitative measure of change in crater morphology. They reported their results in Geochemistry, Geophysics, Geosystems.
“Photos of the crater were taken as part of a multi-disciplinary study to investigate Telica’s persistent activity,” said Cassie Hanagan, lead author on the study. “Images were collected from our collaborators to make observations of the crater’s features such as the location and number of fumaroles or regions of volcanic degassing in the crater. For time periods that had enough photos, SfM was used to create 3D models of the crater. We could then compare the 3D models between time periods to quantify change.”
Using the SfM-derived 3D models and point cloud differencing allowed the team to quantify how the crater changed through time.
“We could see the changes by visually looking at the photos, but by employing SfM, we could quantify how much change had occurred at Telica,” said Peter La Femina, associate professor of geosciences in Penn State’s Department of Geosciences. “This is one of the first studies to look at changes in crater morphology associated with background and eruptive activity over a relatively long time span, almost a 10-year time period.”
Telica’s morphological changes were then compared to the timing of eruptive activity to investigate the processes leading to crater formation and eruption.
Volcanoes erupt when pressure builds beyond a breaking point. At Telica, two mechanisms for triggering eruptions have been hypothesized. These are widespread mineralization within the underground hydrothermal system that seals the system and surficial blocking of the vent by landslides and rock fall from the crater walls. Both mechanisms could lead to increases in pressure and then eruption, according to the researchers.
“One question was whether or not covering the vents on the crater floor could cause pressure build up, and if that would cause an explosive release of this pressure if the vent were sufficiently sealed,” said Hanagan.
Comparing the point cloud differencing results and the photographic observations indicated that vent infill by mass wasting from the crater walls was not likely a primary mechanism for sealing of the volcanic system prior to eruption.
“We found that material from the crater walls does fall on the crater floor, filling the eruptive vent,” said La Femina. “But at the same time, we still see active fumaroles, which are vents in the crater walls where high temperature gases and steam are emitted. The fumaroles remained active even though the talus from the crater walls covered the vents. This suggests that at least the deeper magma-hydrothermal system is not directly sealed by landslides.”
The researchers further note that crater wall material collapse is spatially correlated to where degassing is concentrated, and that small eruptions blow out this fallen material from the crater floor. They suggest these changes sustain a crater shape similar to other summit craters that formed by collapse into an evacuated magma chamber.
“What we found is that during the explosions, Telica is throwing out a lot of the material that came from the crater walls,” said La Femina. “In the absence of magmatic eruptions, the crater is forming through this background process of crater wall collapse, and the regions of fumarole activity collapse preferentially.”
Reference:
Catherine Hanagan, Peter C. La Femina, Mel Rodgers. Changes in Crater Morphology Associated With Volcanic Activity at Telica Volcano, Nicaragua. Geochemistry, Geophysics, Geosystems, 2020; 21 (7) DOI: 10.1029/2019GC008889
