When geologist Elizabeth Miller started mapping a fault system in Death Valley, she questioned the origin of some sedimentary rocks previously assumed to be locally derived. Now, analysis has revealed where they really came from: central Nevada, indicating that part of today’s Great Basin was the highest land in North America some 40 million to 20 million years ago.

The journey of these sediments southward in river systems draining into the ancient Pacific Ocean tells a story about the history of the Earth and the much-debated formation of the Sierra Nevada mountain range, the awe-inspiring backbone of eastern California that encompasses three national parks: Sequoia, Kings Canyon and Yosemite.

The ancestral Sierra Nevada began as a volcanic chain more than 100 million years ago, a time when dinosaurs still roamed the Earth. New work published Nov. 15 as chapters in a Geological Society of America Special Paper on the paleogeography and topography of the western U.S. suggests that the mountains later “died” — meaning they were dwarfed by a vast plateau — during a region-wide volcanic flare-up about 40 million to 20 million years ago. Then, they were “reborn” about 10 million years ago, lifting to the scenic heights we know today.

“The highest points 40 to 20 million years ago were in central Nevada. Then, basin and range faulting came along and broke it all up, and now the Sierra Nevada is the westernmost or last of those major fault blocks,” Miller said. “As a mountain range, it’s had three completely different histories.”

The findings from Miller and Jens-Erik Lund Snee, who conducted the research while a PhD student at Stanford, propose that the Continental Divide — which is typically considered to be static — went through a progressive shift eastward. The divide, which separates the watersheds that drain into the Pacific Ocean from those draining eastward, remained in the ancestral Sierra Nevada in eastern California for tens of millions of years before moving into central Nevada when the volcanism that started 40 million years ago lifted the Earth’s surface in a south-migrating wave.

The papers describe how the region-wide flare-up of volcanic activity in southern Idaho, Nevada and Utah caused the inland plateau to rise above the ancestral Sierra. That upheaval in the Earth’s mantle and crust created whole new systems of rivers, some of which carried sediment southward, forming the layers that Miller studied near Death Valley with co-author Mark Raftrey, a former graduate student.

“The material from those volcanoes made it all the way out to the Pacific side of the Sierra Nevada — that’s how we know the region in central Nevada where the eruptions occurred was higher than everything else,” said Miller, noting that previous papers charted the ancient rivers that carried the volcanic material. “Our work adds to this previous work in that we argue that the volcanism itself actually caused a big increase in the topography because there was so much hot material coming up from below the continent.”

For tens of million years after the plateau rose, the ancestral Sierra range was “merely the ramp from the high country in Nevada down to the paleo-ocean in what’s now the Central Valley,” Lund Snee said. That was also when much of the famous California gold was deposited in ancient rivers that flowed west from central Nevada out to the Central Valley. Then, beginning around 10 million years ago, the new Sierra Nevada emerged when the western U.S. was chiseled apart by basin and range faulting, which involved uplift and extension — a process that had very little to do with its earlier history, according to Miller.

“There’s been a lot of recent debate about when the Sierra Nevada came up as a mountain range, and our work is suggesting that both prevailing views are right — it’s old and also young for completely different tectonic reasons,” said Lund Snee, who is now a Mendenhall Research Fellow at the U.S. Geological Survey.

When the ancestral Sierra Nevada first arose over 100 million years ago, the mountains marked the edge of the North American continent, bordered by the Pacific Ocean to the west. East of that area, geologists have long thought the Earth’s crust thickened and became unstable, eventually causing the continent to spread apart and form today’s basin and range topography.

But Miller and Lund Snee found that the region east of the ancestral Sierra was relatively low, supported by thinner, more stable crust until the wave of volcanic eruptions 40 million to 20 million years ago lifted the plateau higher than the ancestral range. The eruptions came from dozens of Yellowstone-like supervolcano calderas in addition to hundreds of smaller volcanoes — an event that blanketed some areas with thousands of feet of lava.

The research paints a picture of the topographic evolution of the western U.S., which has been debated since the area was first explored by geologists in the 1800s and flooded by gold miners seeking fortunes in the Sierra Nevada’s western foothills. It also impacts our understanding of how plants and animals evolved and dispersed across the West; in order to understand migration, biologists need a clear grasp of landscape evolution.

The authors refined geologic maps and used radiometric dating of the minerals zircon and feldspar to gauge the timing of eruptions and changes in topography. They also revised the ages of previous estimates of elevation and climate from stable isotope analyses of calcite in sediments deposited before and after the volcanic rock.

“You need to know when things happened and how long it took things to happen to truly understand them in the geologic context,” Miller said. “It’s an evolving story, and as we pick up more pieces, the story begins to get tighter and tighter.”

The research was supported by the National Science Foundation and a Gerald J. Lieberman Fellowship.

Note: The above post is reprinted from materials provided by Stanford University. Original written by Danielle Torrent Tucker.

A team of scientists has identified an additional force that likely contributed to a mass extinction event 250 million years ago. Its analysis of minerals in southern China indicate that volcano eruptions produced a “volcanic winter” that drastically lowered earth’s temperatures — a change that added to the environmental effects resulting from other phenomena at the time.

The research, which appears in the journal Science Advances, examined the end-Permian mass extinction (EPME), which was the most severe extinction event in the past 500 million years, wiping out 80 to 90 percent of species on land and in the sea.

“As we look closer at the geologic record at the time of the great extinction, we are finding that the end-Permian global environmental disaster may have had multiple causes among marine and non-marine species,” says Michael Rampino, a professor in New York University’s Department of Biology and one of the authors of the paper.

For decades, scientists have investigated what could have caused this global ecological catastrophe, with many pointing to the spread of vast floods of lava across what is known as the Siberian Traps — a large region of volcanic rock in the Russian province of Siberia. These eruptions caused environmental stresses, including severe global warming from volcanic releases of carbon dioxide and related reduction in oxygenation of ocean waters — the latter causing the suffocation of marine life.

The team for the Science Advances work, composed of more than two dozen researchers, including scientists from China’s Nanjing University and Guangzhou Institute of Geochemistry as well as Smithsonian Institution’s National Museum of Natural History and Montclair State University, considered other factors that may have contributed to the end of the Permian Period, which stretched from 300 million to 250 million years ago.

Specifically, they found mineral and related deposits on land in the south China region — notably copper and mercury — whose age coincided with the end-Permian mass extinction in non-marine localities. Specifically, these deposits were marked by anomalies in their composition likely due to sulfur-rich emissions from nearby volcanic eruptions — they were covered by layers of volcanic ash.

“Sulfuric acid atmospheric aerosols produced by the eruptions may have been the cause of rapid global cooling of several degrees, prior to the severe warming seen across the end-Permian mass-extinction interval,” explains Rampino.

The team’s findings suggested that the Siberian Traps eruptions were not the sole cause of the end-Permian mass extinction, and that the environmental effects of the eruptions in South China, and elsewhere, may have played a vital role in the disappearance of dozens of species.

Reference:
Hua Zhang, Feifei Zhang, Jiu-bin Chen, Douglas H. Erwin, Drew D. Syverson, Pei Ni, Michael Rampino, Zhe Chi, Yao-feng Cai, Lei Xiang, Wei-qiang Li, Sheng-Ao Liu, Ru-cheng Wang, Xiang-dong Wang, Zhuo Feng, Hou-min Li, Ting Zhang, Hong-ming Cai, Wang Zheng, Ying Cui, Xiang-kun Zhu, Zeng-qian Hou, Fu-yuan Wu, Yi-gang Xu, Noah Planavsky, Shu-zhong Shen. Felsic volcanism as a factor driving the end-Permian mass extinction. Science Advances, 2021; 7 (47) DOI: 10.1126/sciadv.abh1390

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

They’re born. They live once, erupting for a period that might last for days, years or decades. Then, they go dark and die.

This narrative describes the life of a monogenetic volcano, a type of volcanic hazard that can pose important dangers despite an ephemeral existence.

The landscape of the southwestern U.S. is heavily scarred by past eruptions of such volcanoes, and a new study marks a step toward understanding future risks for the region.

The research, which will be published on Nov. 2 in the journal Geosphere, provides a broad overview of what we know — and don’t know — about this type of volcanism in the U.S. Southwest over the past 2.58 million years, a geologic period known as the Quaternary.

During this time, more than 1,800 monogenetic volcanoes erupted in the region, according to a count covering Nevada, Utah, Arizona, Colorado, New Mexico and parts of California’s eastern edge. Add in the Pinacate volcanic field, located mostly in the Mexican state of Sonora, bordering Arizona, and the number goes up to over 2,200, scientists say. (The volcanoes included are ones whose ages are estimated to be in the range of the Quaternary, but many have not been precisely dated.)

“Monogenetic means ‘one life,'” says lead author Greg Valentine, a University at Buffalo volcanologist. “So a monogenetic volcano will erupt once, and that eruption may last for several days to several decades, but after that, the volcano is basically dead.

“In the United States, most volcanic hazards-related attention has rightly gone to places like Hawaii, and to the Pacific Northwest and Alaska, where we have big stratovolcanoes like Mount Rainier and Mount St. Helens, which will have many eruptive episodes over a long life, with widespread hazardous effects. In the past, these smaller monogenetic volcanoes really haven’t been looked at from a focus on hazards; they have been instead studied mainly for what they tell us about the deep earth. Recently, however, there has been more buzz in the research community about how we need to take a look at the kinds of hazards these volcanoes might pose.

“My experience with the general public is that most people are surprised to know that there are so many young volcanoes in the Southwest.”

The paper’s authors are Valentine, PhD, professor of geology in the UB College of Arts and Sciences; Michael H. Ort, PhD, professor emeritus of geology at Northern Arizona University; and Joaquín A. Cortés, PhD, senior lecturer of geology at Edge Hill University in England.

These volcanoes won’t erupt again. So why study them?

The 2,000-plus volcanoes noted in the paper are done erupting, so they no longer pose a threat. But studying them is important because of the potential for new ones to bloom.

“Monogenetic volcanoes tend to occur in areas that we call volcanic fields, and the American Southwest is just dotted with these,” says Valentine, who grew up in New Mexico. “These are areas of high volcanic activity where future eruptions could happen, but we don’t know when, and we don’t know exactly where.”

The city of Flagstaff, Arizona, is located in a volcanic field where multiple monogenetic volcanoes have erupted in the past, so a better understanding of possible hazards is important for people who live there.

“Two of the most recent eruptions in the Southwest occurred near Flagstaff about 1,000 years ago, one just outside of town and the other on the north rim of the Grand Canyon,” Ort says. Northern Arizona University is in Flagstaff. “People living there at the time adapted to the effects of the eruptions, changing agricultural and cultural practices as well as where they lived. We will need to do the same when the next one erupts. Albuquerque also has young volcanoes along its western margin.”

Mercifully, most volcanoes in the southwestern U.S. are in remote locations, away from large population centers. In isolated areas, threats from eruptions could include ash plumes that disrupt travel (including air) or power distribution infrastructure, researchers say.

“One of the younger eruptions in the Southwest occurred south of Grants, New Mexico a few thousand years ago, and flowed for many miles parallel to what is now Interstate 40 and part of the Burlington Northern Santa Fe railroad,” Ort says. “A similar eruption today would take out one of the most important east-west transportation routes in the country. Several volcanic fields lie along these routes, from the Mojave Desert of California to eastern New Mexico, including the one around Flagstaff.”

“The fundamental pieces of information that you need to have in order to start understanding the hazards and the chances of a future eruption are the number of volcanoes, their ages and the types of eruptions they have,” Valentine says. “What we set out to do in the study is find every bit of information that we could about these monogenetic volcanoes in the southwestern U.S. and compile it all in one place. How many of these are there? What are their characteristics? We got information from state geological surveys, published papers and other sources.”

What are the chances of a new eruption within a century?

Based solely on the total count of volcanoes that have erupted in the study region during the Quaternary Period, the chances of a new volcano emerging in the area within 100 years would be about 8%, Valentine says.

But he notes that this figure embodies lots of uncertainty. It doesn’t account for buried volcanoes, or the fact that a single eruption can create multiple vents. More research will be needed to refine this estimate and to forecast likely locations for a new eruption.

“There’s so much uncertainty here, and this is part of the problem,” he says. “It’s kind of a wide-open research field. When you look at the region from the perspective of volcanic hazards, we really have very little information. Most of the volcanoes have not been dated, so we don’t know how old they are, except that they likely formed sometime within the Quaternary Period. Very few have been studied in detail.”

That said, the study’s findings indicate that the frequency of eruptions across the study region may approach that of individual volcanoes in the Pacific Northwest, Valentine and Ort say. The new paper highlights gaps in knowledge, and the scientists hope that it can act as a launchpad for future, more detailed research. As Ort and Valentine point out, a new Southwest volcano could appear anywhere in any active volcanic field.

“We don’t have infinite resources, so we have to prioritize the efforts we put into forecasting and planning for hazards,” Valentine says. “But how do you set priorities? If you’re monitoring volcanic fields in the Southwest, where do you put the instruments? Being able to better answer questions like these is what we’re moving toward.”

Reference:
Greg A. Valentine, Michael H. Ort, Joaquín A. Cortés. Quaternary basaltic volcanic fields of the American Southwest. Geosphere, 2021; DOI: 10.1130/GES02405.1

Note: The above post is reprinted from materials provided by University at Buffalo. Original written by Charlotte Hsu.