The brief but violent life of monogenetic volcanoes

Lunar Crater maar in Nevada, a maar-diatreme volcano. A new study is shedding light on the explosive mechanism of these volcanoes, which erupt just once before dying. -  Credit: Greg Valentine
Lunar Crater maar in Nevada, a maar-diatreme volcano. A new study is shedding light on the explosive mechanism of these volcanoes, which erupt just once before dying. – Credit: Greg Valentine

A new study in the journal Geology is shedding light on the brief but violent lives of maar-diatreme volcanoes, which erupt when magma and water meet in an explosive marriage below the surface of the earth.

Maar-diatremes belong to a family of volcanoes known as monogenetic volcanoes. These erupt just once before dying, though some eruptions last for years. Though not particularly famous, monogenetic volcanoes are actually the most common form of land-based volcano on the planet.

Despite their number, monogenetic volcanoes are poorly understood, said Greg A. Valentine, PhD, University at Buffalo geology professor.

He is lead author of the new Geology paper, which provides a novel model for describing what happens underground when maar-diatremes erupt. The research appeared online Sept. 18.

“The hazards that are associated with these volcanoes tend to be localized, but they’re still significant,” Valentine said. “These volcanoes can send ash deposits into populated areas. They could easily produce the same effects that the one in Iceland did when it disrupted air travel, so what we’re trying to do is understand the way they behave.”

Previously, scientists theorized that maar-diatreme eruptions consisted, underground, of a series of explosions that took place as magma reacted violently with water. With each explosion, the subterranean water table would fall, driving the next explosion even deeper.

Taking into account new geological evidence, Valentine and volcanologist James D.L. White of New Zealand’s University of Otago revise this model.

In Geology, they propose that maar-diatreme eruptions consist not of ever-deepening explosions, but of explosions occurring simultaneously over a range of depths.

Under this new paradigm, deep explosions break up buried rock thousands of feet below ground and push it upward. Shallow explosions eject some of this debris from the volcano’s depths, but expel far larger quantities of shallow rock.

This model fits well with recent field studies that have uncovered large deposits of shallow rock ringing maar-diatreme volcanoes, with only small amounts of deeper rock present. This was the case, for example, at two sites that Valentine examined at the San Francisco Volcanic Field in Arizona (see the Journal of Volcanology and Geothermal Research at http://tinyurl.com/9g4hoq5).

White and Valentine’s description of the eruptive process also corresponds well with White’s investigations into the “plumbing” of maar-diatreme volcanoes, the conduits that carry magma toward the surface. These conduits become visible over time as a landscape erodes away, and the main “pipe” — called a diatreme — often shows evidence of explosions, including zones of broken-up rock, at a range of depths.

Such findings contradict the older model that White and Valentine argue against.

According to the old model, Valentine explained, ever-deepening explosions should cause shallow rocks to be ejected from the mouth of the volcano first, followed by deposits of deeper and deeper rock fragments. But this isn’t what scientists are finding when they analyze geological clues at volcanic sites.

The old model doesn’t account for the fact that even when scientists find deep rock fragments at maar-diatreme sites, these bits of rock are mixed mostly with shallow fragments. The old model also doesn’t match with White’s observations indicating that explosions occur at essentially every depth.

The new model uses the strengths of the old model but accounts for new data. The results give scientists a better basis for estimating the hazards associated with maar-diatreme volcanoes, Valentine said.

City of Ottawa sits atop soil, geologic features that amplify seismic waves

Engineers and city planners study surface geology in order to construct buildings that can respond safely to earthquakes. Soft soil amplifies seismic waves, resulting in stronger ground motion than for sites built over bedrock. This study examines the local site response for the city of Ottawa, and the results indicate seismic waves may amplify ground motion greater than expected or referenced in the National Building Code of Canada.

Current knowledge of the earthquake activity in Ottawa area is based on less than 200 years of reported felt events and approximately 100 years of instrumental recordings. While the area has experienced moderate shaking from earthquakes in the range of M 5.2 – 6.2 during this time, historical accounts suggests certain parts of the city have experienced higher levels of ground motion than others during the larger earthquakes. There is also evidence of devastating prehistoric earthquakes, causing widespread landslides, sediment deformation and liquefaction.

The area’s geological structure complicates site response analyses. Roughly 20 percent of the Ottawa area is built on bedrock, while the remaining area contains unconsolidated surface deposits.

In this study, the authors reconfirmed the unusually large seismic amplification values for weak motion, prompting an extensive site response analysis as part of seismic microzonation studies for the entire city.

Researchers study clam shells for clues to the Atlantic’s climate history

Iowa State University's Alan Wanamaker studies Atlantic clam shells for clues to the ocean's past. -  Photo by Bob Elbert/Iowa State University
Iowa State University’s Alan Wanamaker studies Atlantic clam shells for clues to the ocean’s past. – Photo by Bob Elbert/Iowa State University

Two Iowa State University graduate students are just back from the Gulf of Maine with another big catch of clam shells.

Shelly Griffin and Madelyn Mette recently boarded a lobster boat, dropped a scallop dredge into 30 meters of ocean water and pulled up load after load of Arctica islandica.

“These are the clams that end up in clam chowder,” said Alan Wanamaker, an assistant professor of geological and atmospheric sciences in the College of Liberal Arts and Sciences. Wanamaker studies paleoclimatology, the variations and trends of past climates and environments, with the goal of better understanding future climate changes.

The Iowa State researchers only need a few live, meaty clams for their studies. They’re really after the old, dead shells. Off the coast of Maine, clams can live up to 240 years, year after year adding another band to their shells, just like a tree adds another growth ring. In the colder waters of the North Atlantic near Iceland, the clams can live up to 500 years, recording even more information in what scientists call annual shell increments.

Wanamaker and his research team bring those shells back to Iowa State’s Stable Isotope Laboratory where they’re cleaned, sorted, measured, cut, polished, drilled and otherwise prepared for careful microscopic imaging, geochemical testing and radiocarbon analysis.

It turns out those shell increments are a lot like sensors at the bottom of the ocean – they record long records of information about the ocean, including growing conditions, temperatures and circulation patterns.

A paper published by Nature Communications in June 2012 reported how Wanamaker (the lead author) and an international team of researchers used radiocarbon data from shells to determine when clams collected north of Iceland were living in “young” or “old” water. Young water had been at the surface more recently and probably came from the Atlantic. Old water had been removed from the surface much longer and probably came from the Arctic Ocean.

The paper reports warmer, younger water from the Gulf Stream during the warmer Medieval Climate Anomaly from about A.D. 950 to 1250. The paper also reports that shell data showed older, colder water during Europe’s Little Ice Age from about A.D. 1550 to 1850.

The researchers’ interpretation of the data says the Gulf Stream carrying warm water from the subtropical Atlantic was strong in the medieval era, weakened during the Little Ice Age and strengthened again after A.D. 1940. Those fluctuations amplified the relative warmth and coolness of the times.

Wanamaker said a better understanding of the ocean’s past can help researchers understand today’s climate trends and changes.

“Is the natural variability only that, or is it influenced by burning fossil fuels?” he said. “Maybe we can understand what will happen in the next 100 years if we understand oceans over the past 1,000 years.”

And so Wanamaker – a former high school science teacher in Maine whose fascination with climate change sent him back to graduate school – works with students to carefully collect, process and study clam shells.

The research is painstaking – the shell increments are measured in millionths of a meter and microscopes are required at the most important steps. And the tools are sophisticated – two mass spectrometers measure shell fragments for different isotopes of carbon and oxygen. (Isotopes are elements with varying numbers of neutrons. Heavier isotopes of oxygen in the shell material generally correspond to colder ocean temperatures.)

“Isotopes are just wonderful tracers in nature,” Wanamaker said, noting he also takes isotope measurements for research projects across campus and beyond.

When it comes to Wanamaker’s own work with clam shells, “In the broadest sense, we’re trying to add to our understanding of oceans over the last several thousand years,” he said. “We have a terrestrial record – we can get an excellent chronology from tree rings and there is a climate signal there. But that’s missing 70 percent of the planet.”

Extreme climate change linked to early animal evolution

This photo shows researchers studying exposures of the Doushanto Formation. Located in China, the formation is most notable for its scientific contributions in the hunt for Precambrian life. -  M. Kennedy.
This photo shows researchers studying exposures of the Doushanto Formation. Located in China, the formation is most notable for its scientific contributions in the hunt for Precambrian life. – M. Kennedy.

An international team of scientists, including geochemists from the University of California, Riverside, has uncovered new evidence linking extreme climate change, oxygen rise, and early animal evolution.

A dramatic rise in atmospheric oxygen levels has long been speculated as the trigger for early animal evolution. While the direct cause-and-effect relationships between animal and environmental evolution remain topics of intense debate, all this research has been hampered by the lack of direct evidence for an oxygen increase coincident with the appearance of the earliest animals – until now.

In the Sept. 27 issue of the journal Nature, the research team, led by scientists at the University of Nevada, Las Vegas, offers the first evidence of a direct link between trends in early animal diversity and shifts in Earth system processes.

The fossil record shows a marked increase in animal and algae fossils roughly 635 million years ago. An analysis of organic-rich rocks from South China points to a sudden spike in oceanic oxygen levels at this time – in the wake of severe glaciation. The new evidence pre-dates previous estimates of a life-sustaining oxygenation event by more than 50 million years.

“This work provides the first real evidence for a long speculated change in oxygen levels in the aftermath of the most severe climatic event in Earth’s history – one of the so-called ‘Snowball Earth’ glaciations,” said Timothy Lyons, a professor of biogeochemistry at UC Riverside.

The research team analyzed concentrations of trace metals and sulfur isotopes, which are tracers of early oxygen levels, in mudstone collected from the Doushantuo Formation in South China. The team found spikes in concentrations of the trace metals, denoting higher oxygen levels in seawater on a global scale.

“We found levels of molybdenum and vanadium in the Doushantuo Formation mudstones that necessitate that the global ocean was well ventilated. This well-oxygenated ocean was the environmental backdrop for early animal diversification,” said Noah Planavsky, a former UCR graduate student in Lyons’s lab now at CalTech.

The high element concentrations found in the South China rocks are comparable to modern ocean sediments and point to a substantial oxygen increase in the ocean-atmosphere system around 635 million years ago. According to the researchers, the oxygen rise is likely due to increased organic carbon burial, a result of more nutrient availability following the extreme cold climate of the ‘Snowball Earth’ glaciation when ice shrouded much of Earth’s surface.

Lyons and Planavsky argued in research published earlier in the journal Nature that a nutrient surplus associated with the extensive glaciations may have initiated intense carbon burial and oxygenation. Burial of organic carbon – from photosynthetic organisms – in ocean sediments would result in the release of vast amounts of oxygen into the ocean-atmosphere system.

“We are delighted that the new metal data from the South China shale seem to be confirming these hypothesized events,” Lyons said.

The joint research was supported by grants from the National Science Foundation, the NASA Exobiology Program, and the National Natural Science Foundation of China. Besides Lyons and Planavsky, the research team includes Swapan K. Sahoo (first author of the research paper) and Ganqing Jiang (principal investigator of the study) of the University of Nevada, Las Vegas; Brian Kendall and Ariel D. Anbar of Arizona State University; Xinqiang Wang and Xiaoying Shi of the China University of Geosciences (Beijing); and UCR alumnus Clint Scott of United States Geological Survey.

Big quake was part of crustal plate breakup

This map of the Indian Ocean region shows boundaries of Earth's tectonic plates in the area, and the epicenters (red stars) of two great earthquakes that happened April 11, 2012. A new study from the University of Utah and University of California, Santa Cruz, says the main shock measured 8.7 in magnitude, about 40 times larger than the previous estimate of 8.6. An 8.2-magnitude quake followed two hours later.The scientists explain how at least four faults ruptured during the 8.7 main shock, and how both great quakes are likely part of the breakup of the Indo-Australian Plate into separate subplates. The northeastward-moving plate is breaking up over scores of millions of years because the western part of the plate is bumping into Asia and slowing down, while the eastern part is sliding more easily beneath Sumatra and the Sunda plate. -  Keith Koper, University of Utah Seismograph Stations.
This map of the Indian Ocean region shows boundaries of Earth’s tectonic plates in the area, and the epicenters (red stars) of two great earthquakes that happened April 11, 2012. A new study from the University of Utah and University of California, Santa Cruz, says the main shock measured 8.7 in magnitude, about 40 times larger than the previous estimate of 8.6. An 8.2-magnitude quake followed two hours later.The scientists explain how at least four faults ruptured during the 8.7 main shock, and how both great quakes are likely part of the breakup of the Indo-Australian Plate into separate subplates. The northeastward-moving plate is breaking up over scores of millions of years because the western part of the plate is bumping into Asia and slowing down, while the eastern part is sliding more easily beneath Sumatra and the Sunda plate. – Keith Koper, University of Utah Seismograph Stations.

Seismologists have known for years that the Indo-Australian plate of Earth’s crust is slowly breaking apart, but they saw it in action last April when at least four faults broke in a magnitude-8.7 earthquake that may be the largest of its type ever recorded.

The great Indian Ocean quake of April 11, 2012 previously was reported as 8.6 magnitude, and the new estimate means the quake was 40 percent larger than had been believed, scientists from the University of Utah and University of California, Santa Cruz, report in the Sept. 27 issue of the journal Nature.

The quake was caused by at least four undersea fault ruptures southwest of Sumatra, Indonesia, within a 2-minute, 40-second period. It killed at least two people, and eight others died from heart attacks. The quake was felt from India to Australia, including throughout South Asia and Southeast Asia.

If the four ruptures were considered separate quakes, their magnitudes would have been 8.5, 7.9, 8.3 and 7.8 on the “moment magnitude” scale used to measure the largest quakes, the scientists report.

The 8.7 main shock broke three faults that were parallel but offset from each other – known as en echelon faults – and a fourth fault that was perpendicular to and crossed the first fault.

The new study concludes that the magnitude-8.7 quake and an 8.2 quake two hours later were part of the breakup of the Indian and Australian subplates along a yet-unclear boundary beneath the Indian Ocean west of Sumatra and southeast of India – a process that started roughly 50 million years ago and that will continue for millions more.

“We’ve never seen an earthquake like this,” says study co-author Keith Koper, an associate professor geophysics and director of the University of Utah Seismograph Stations. “This is part of the messy business of breaking up a plate. ? This is a geologic process. It will take millions of years to form a new plate boundary and, most likely, it will take thousands of similar large quakes for that to happen.”

All four faults that broke in the 8.7 quake and the fifth fault that ruptured in the 8.2 quake were strike-slip faults, meaning ground on one side of the fault moves horizontally past ground on the other side.

The great quake of last April 11 “is possibly the largest strike-slip earthquake ever seismically recorded,” although a similar size quake in Tibet in 1950 was of an unknown type, according to the new study, which was led by two University of California, Santa Cruz, seismologists: graduate student Han Yue and Thorne Lay, a professor of Earth and planetary sciences. The National Science Foundation funded the study.

The 8.7 jolt also “is probably the largest intraplate [within a single tectonic plate of Earth’s crust] ever seismically recorded,” Lay, Yue and Koper add. Most of Earth’s earthquakes occur at existing plate boundaries.

The researchers cannot be certain the April great quake was the largest intraplate quake or the largest strike-slip quake because “we are comparing it against historic earthquakes long before we had modern seismometers,” says Koper.

Why the Great Quake Didn’t Unleash Major Tsunamis

Koper says the 2012 quakes likely were triggered, at least in part, by changes in crustal stresses caused by the magnitude-9.1 Sumatra-Andaman earthquake of Dec. 26, 2004 – a jolt that generated massive tsunamis that killed most of the 228,000 victims in the Indian Ocean region.

The fact the 8.7 and 8.2 quakes were generated by horizontal movements along seafloor strike-slip faults – not by vertical motion along thrust faults – explains why they didn’t generate major tsunamis. The 8.7 quake caused small tsunamis, the largest of which measured about 12 inches in height at Meulaboh, Indonesia, according to the U.S. Geological Survey.

Without major tsunamis, the great earthquake caused “very little damage and death, especially for this size of an earthquake, because it happened in the ocean and away from coastlines,” and on strike-slip faults, says Koper.

The researchers studied the quake using a variety of methods to analyze the seismic waves it generated. Because the same data can be interpreted in various ways, Koper says it is conceivable that more than four fault segments broke during the 8.7 quake – conceivably five or even six – although four fault ruptures is most likely.

Breaking Up is Hard to Do


The Indo-Australian plate is breaking into two or perhaps three pieces (some believe a Capricorn subplate is separating from the west side of the Indian subplate). The magnitude-8.7 and 8.2 great quakes on April 11 occurred over a broad area where the India and Australian subplates are being sheared apart.

“What we’re seeing here is the Indo-Australian plate fragmenting into two separate plates,” says Lay.

The breakup of the northeast-moving Indo-Australian plate is happening because it is colliding with Asia in the northwest, which slows down the western part of the plate, while the eastern part of the plate continues moving more easily by diving or “subducting” under the island of Sumatra to the northeast. The subduction zone off Sumatra caused the catastrophic 2004 magnitude-9.1 quake and tsunami.

Seismic analysis shows the April 11 quakes “involve rupture of a very complex network of faults, for which we have no documented precedent in recorded seismic history,” the researchers write.

The analysis revealed this sequence for the faults ruptures that generated the 8.7 quake, and the estimated fault rupture lengths and slippage amounts:

– The quake began with the 50-second rupture of a fault extending west-northwest to east-southeast, with an epicenter a few hundred miles southwest of Sumatra. The fault ruptured along a roughly 90-mile length, breaking “bilaterally” both west-northwestward and east-southeastward, and also at least 30 miles deep, “almost ripping through the whole plate,” Koper says. The seafloor on one side of the fault slipped about 100 feet past the seafloor on the fault’s other side.

— The second fault, which slipped about 25 feet, began to rupture 40 seconds after the quake began. This rupture extended an estimated 60 miles to 120 miles north-northeast to south-southwest – perpendicular to the first fault and crossing it.

– The third fault was parallel to the first fault and about 90 to the miles southwest of it. It started breaking 70 seconds after the quake began and ruptured along a length of about 90 miles. This fault slipped about 70 feet.

– The fourth fault paralleled the first and third faults, but was to the northwest of both of them. It began to rupture 145 seconds after the quake began and continued to do so for 15 seconds until the quake ended after a total time of 2 minutes and 40 seconds. The fault rupture was roughly 30 miles to 60 miles long. The ground on one side of this fault slipped about 20 feet past ground on the other side.

Researcher’s calculations will help unlock new energy sources

A Wayne State University researcher is part of a national project to find accessible sources of natural gas.

Jaewon Jang, Ph.D., assistant professor of civil and environmental engineering in the College of Engineering, recently received a two-year, $178,000 grant from the U.S. Department of Energy (DOE) to aid in the search for methane hydrates in oceans and permafrost, such as the Gulf of Mexico and Alaska’s North Slope.

Methane hydrates are three-dimensional ice-lattice structures with natural gas locked inside, and are found both onshore and offshore – including under the Arctic permafrost and in ocean sediments along nearly every continental shelf in the world.

The DOE effort, which includes 14 projects in 11 states, builds on the completion of what officials called a “successful, unprecedented test” earlier this year that was able to safely extract a steady flow of natural gas from methane hydrates on the North Slope. Department officials believe methane hydrates are an untapped resource holding great potential for economic and energy security.

Jang’s project, “Verification of Capillary Pressure Functions and Relative Permeability Equations for Modeling Gas Production from Gas Hydrates,” will try to obtain reliable parameters for equations that can be used by computer simulation programs to provide reliable information on how fast or how much methane is recovered.

Finding those parameters will direct extractors to the best locations, maximizing gas yields and minimizing costs.

Jang said many in the industry might not be inclined to pursue methane hydrates as an energy source right now because of the large quantities of shale gas currently available and its resultant low prices. But because those quantities are the result of research money invested by the DOE in the 1970s and 1980s to develop production methods, he believes that bodes well for the future of the current effort.

“Thanks to those investments, we now have a large amount of shale gas,” Jang said. “The total is about $5.6 million for these 14 projects, which is not big money, but could prove to be worth much more in the next couple of decades – or even hundreds of years.”