COULD MT. HOOD GO BOOM

FROM:  NATIONAL SCIENCE FOUNDATION 
Volcanoes, including Mount Hood in the US, can quickly become active
Magma stored for thousands of years can erupt in as little as two months

New research results suggest that magma sitting 4-5 kilometers beneath the surface of Oregon's Mount Hood has been stored in near-solid conditions for thousands of years.

The time it takes to liquefy and potentially erupt, however, is surprisingly short--perhaps as little as a couple of months.

The key to an eruption, geoscientists say, is to elevate the temperature of the rock to more than 750 degrees Celsius, which can happen when hot magma from deep within the Earth's crust rises to the surface.

It was the mixing of hot liquid lava with cooler solid magma that triggered Mount Hood's last two eruptions about 220 and 1,500 years ago, said Adam Kent, an Oregon State University (OSU) geologist and co-author of a paper reporting the new findings.

Results of the research, which was funded by the National Science Foundation (NSF), are in this week's journal Nature.

"These scientists have used a clever new approach to timing the inner workings of Mount Hood, an important step in assessing volcanic hazards in the Cascades," said Sonia Esperanca, a program director in NSF's Division of Earth Sciences.

"If the temperature of the rock is too cold, the magma is like peanut butter in a refrigerator," Kent said. "It isn't very mobile.

"For Mount Hood, the threshold seems to be about 750 degrees (C)--if it warms up just 50 to 75 degrees above that, it greatly decreases the viscosity of the magma and makes it easier to mobilize."

The scientists are interested in the temperature at which magma resides in the crust, since it's likely to have important influence over the timing and types of eruptions that could occur.

The hotter magma from deeper down warms the cooler magma stored at a 4-5 kilometer depth, making it possible for both magmas to mix and be transported to the surface to produce an eruption.

The good news, Kent said, is that Mount Hood's eruptions are not particularly violent. Instead of exploding, the magma tends to ooze out the top of the peak.

A previous study by Kent and OSU researcher Alison Koleszar found that the mixing of the two magma sources, which have different compositions, is both a trigger to an eruption and a constraining factor on how violent it can be.

"What happens when they mix is what happens when you squeeze a tube of toothpaste in the middle," said Kent. "Some comes out the top, but in the case of Mount Hood it doesn't blow the mountain to pieces."

The study involved scientists at OSU and the University of California, Davis. The results are important, they say, because little was known about the physical conditions of magma storage and what it takes to mobilize that magma.

Kent and UC-Davis colleague Kari Cooper, also a co-author of the Nature paper, set out to discover whether they could determine how long Mount Hood's magma chamber has been there, and in what condition.

When Mount Hood's magma first rose up through the crust into its present-day chamber, it cooled and formed crystals.

The researchers were able to document the age of the crystals by the rate of decay of naturally occurring radioactive elements. However, the growth of the crystals is also dictated by temperature: if the rock is too cold, they don't grow as fast.

The combination of the crystals' age and apparent growth rate provides a geologic fingerprint for determining the approximate threshold for making the near-solid rock viscous enough to cause an eruption.

"What we found was that the magma has been stored beneath Mount Hood for at least 20,000 years--and probably more like 100,000 years," Kent said.

"During the time it's been there, it's been in cold storage--like peanut butter in the fridge--a minimum of 88 percent of the time, and likely more than 99 percent of the time."

Although hot magma from below can quickly mobilize the magma chamber at 4-5 kilometers below the surface, most of the time magma is held under conditions that make it difficult for it to erupt.

"What's encouraging is that modern technology should be able to detect when the magma is beginning to liquefy or mobilize," Kent said, "and that may give us warning of a potential eruption.

"Monitoring gases and seismic waves, and studying ground deformation through GPS, are a few of the techniques that could tell us that things are warming."

The researchers hope to apply these techniques to other, larger volcanoes to see if they can determine the potential for shifting from cold storage to potential eruption--a development that might bring scientists a step closer to being able to forecast volcanic activity.

-NSF-

NSF REPORTS TRIASSIC VOLCANIC ERUPTIONS CAUSED MASS EXTINCTION

Photo:  Volcanic Killer.  Credit:  NSF

FROM: NATIONAL SCIENCE FOUNDATION
Before Dinosaurs' Era, Volcanic Eruptions Triggered Mass Extinction

More than 200 million years ago, a massive extinction decimated 76 percent of marine and terrestrial species, marking the end of the Triassic period and the onset of the Jurassic.

The event cleared the way for dinosaurs to dominate Earth for the next 135 million years, taking over ecological niches formerly occupied by other marine and terrestrial species.

It's not clear what caused the end-Triassic extinction, although most scientists agree on a likely scenario.

Over a relatively short time period, massive volcanic eruptions from a large region known as the Central Atlantic Magmatic Province (CAMP) spewed forth huge amounts of lava and gas, including carbon dioxide, sulfur and methane.

This sudden release of gases into the atmosphere may have created intense global warming, and acidification of the oceans, which ultimately killed off thousands of plant and animal species.

Now, researchers at MIT, Columbia University and other institutions have determined that these eruptions occurred precisely when the extinction began, providing strong evidence that volcanic activity did indeed trigger the end-Triassic extinction.

Results of the research, funded by the National Science Foundation (NSF), are published this week in the journal Science.

"These scientists have come close to confirming something we had only guessed at: that the mass extinction of this ancient time was indeed related to a series of volcanic eruptions," says Lisa Boush, program director in NSF's Division of Earth Sciences.

"The effort is also the result of the EARTHTIME initiative, an NSF-sponsored project that's developing an improved geologic time scale for scientists to interpret Earth's history."

The scientists determined the age of basaltic lavas and other features found along the East Coast of the United States, as well as in Morocco--now-disparate regions that, 200 million years ago, were part of the supercontinent Pangaea.

The rift that ultimately separated these landmasses was also the site of CAMP's volcanic activity.

Today, the geology of both regions includes igneous rocks from the CAMP eruptions as well as sedimentary rocks that accumulated in an enormous lake. The researchers used a combination of techniques to date the rocks and to pinpoint CAMP's beginning and duration.

From its measurements, they reconstructed the region's volcanic activity 201 million years ago, discovering that the eruption of magma--along with carbon dioxide, sulfur and methane--occurred in repeated bursts over a period of 40,000 years, a short span in geologic time.

"This extinction happened at a geological instant in time," says Sam Bowring, a geologist at MIT. "There's no question the extinction occurred at the same time as the first eruption."

In addition to Bowring, the paper's co-authors are Terrence Blackburn and Noah McLean of MIT; Paul Olsen and Dennis Kent of Columbia; John Puffer of Rutgers University; Greg McHone, an independent researcher from New Brunswick, N.J.; E. Troy Rasbury of Stony Brook University; and Mohammed Et-Touhami of the Université Mohammed Premier (Mohammed Premier University) Oujda, Morocco.

Blackburn is the paper's lead author.

More than a coincidence

The end-Triassic extinction is one of five major mass extinctions in the last 540 million years of Earth's history.

For several of these events, scientists have noted that large igneous provinces, which provide evidence of widespread volcanic activity, arose at about the same time.

But, as Bowring points out, "just because they happen to approximately coincide doesn't mean there's cause and effect."

For example, while massive lava flows overlapped with the extinction that wiped out the dinosaurs, scientists have linked that extinction to an asteroid collision.

"If you want to make the case that an eruption caused an extinction, you have to be able to show at the highest possible precision that the eruption and the extinction occurred at exactly the same time," Bowring says.

For the time of the end-Triassic, Bowring says that researchers have dated volcanic activity to right around the time fossils disappear from the geologic record, providing evidence that CAMP may have triggered the extinction.

But these estimates have a margin of error of one to two million years. "A million years is forever when you're trying to make that link," Bowring says.

For example, it's thought that CAMP emitted a total of more than two million cubic kilometers of lava.

If that amount of lava were spewed over a period of one to two million years, it wouldn't have the same effect as if it were emitted over tens of thousands of years.

"The timescale over which the eruption occurred has a big effect," Bowring says.

Tilting toward extinction

To determine how long the volcanic eruptions lasted, the group combined two dating techniques: astrochronology and geochronology.

The former is a technique that links sedimentary layers in rocks to changes in the tilt of the Earth.

For decades, scientists have observed that the Earth's orientation changes in regular cycles as a result of gravitational forces exerted by neighboring planets.

The Earth's axis tilts at regular cycles, returning to its original tilt every 26,000 years. Such orbital variations change the amount of solar radiation reaching the Earth's surface, which in turn has an effect on the planet's climate, known as Milankovich cycles.

This cyclical change in climate can be seen in the types of sediments deposited in the Earth's crust.

Scientists can determine a rock's age by first identifying cyclical variations in deposition of sediments in quiet bodies of water, such as deep oceans or large lakes.

A cycle of sediment corresponds with a cycle of the Earth's tilt, established as a known period of years.

By seeing where a rock lies in those sedimentary layers, scientists can get a good idea of how old it is. To obtain precise estimates, researchers have developed mathematical models to determine the Earth's tilt over millions of years.

Bowring says the technique is good for directly dating rocks up to 35 million years old, but beyond that, it's unclear how reliable the technique is.

He and colleagues used astrochronology to estimate the age of the sedimentary rocks, then tested those estimates against high-precision dates from 200-million-year-old rocks in North America and Morocco.

The geologists broke apart rock samples to isolate tiny crystals known as zircons, which they analyzed to determine the ratio of uranium to lead.

The technique enabled the team to date the rocks to within approximately 30,000 years--a precise measurement in geologic terms.

Taken together, the geochronology and astrochronology techniques gave the geologists precise estimates for the onset of volcanism 200 million years ago.

The techniques revealed three bursts of magmatic activity over 40,000 years--a short period of time during which massive amounts of carbon dioxide and other gas emissions may have drastically altered Earth's climate.

While the evidence is the strongest thus far for linking volcanic activity with the end-Triassic extinction, Bowring says that more work can be done.

"The CAMP province extends from Nova Scotia all the way to Brazil and West Africa," he says. "I'm dying to know whether those are exactly the same age."

-NSF-

DINOSAURS, WHAT HAPPENED?

Dinosaur Photo Composite.  Credit:  Wikimedia Commons

FROM: NATIONAL SCIENCE FOUNDATION
Looking for a 'Smoking Gun' in Dinosaur Die-off
Scientists determine most precise dates yet for dinosaur extinction 66 million years ago

February 7, 2013
The demise of the dinosaurs has been called the world's ultimate whodunit.
Was the cause a comet or an asteroid impact? Volcanic eruptions? Climate change?

In an attempt to resolve the issue, scientists at the Berkeley Geochronology Center (BGC) at the University of California, Berkeley, and at universities in the Netherlands and the United Kingdom, have determined that an impact event occurred at about the same time as the mass extinction of the dinosaurs.

Using a recalibrated technique for dating Earth minerals, the researchers hypothesize that impact happened 66,038,000 years ago, and that it produced the final atmospheric conditions needed to wipe out the dinosaurs.

The newly determined date of the impact is the same, within error limits, as the date for the mass extinction event, which also occurred about 66 million years ago, according to Paul Renne, BGC director.

He and colleagues report their findings in this week's issue of the journal Science.

The dates are so close, the researchers say, that it was likely that a comet or asteroid that, if not wholly responsible for the global extinction, at least dealt the death blow.

"An impact was clearly the final straw, the tipping point," said Renne. "We've shown that [the impact and extinction] are synchronous to within a gnat's eyebrow, and therefore an impact clearly played a major role in the extinction. But it probably wasn't just the impact."

The revised date clears up lingering confusion over whether the impact actually occurred before or after the extinction, which was characterized by the almost overnight disappearance from the fossil record of land-based dinosaurs and many ocean creatures, Renne said.

"Accurately dating this major extinction, including that of the dinosaurs, has long been controversial," said H. Richard Lane, program director in the National Science Foundation's (NSF) Division of Earth Sciences, which funded the research. "These new results give us a sharper view of what happened in Earth's distant past."

Renne decided to recalculate the date of the boundary between the Cretaceous and Tertiary periods--the KT boundary--after recalibrating the argon-argon method used to date rocks, which relies on the decay rate of a radioactive isotope of potassium.

The impact in question left a 110-mile-wide crater in the Caribbean off the Yucatan coast of Mexico.

Called Chicxulub (cheek'-she-loob), the crater was excavated by an object some six miles across. It threw debris into the atmosphere that can be found around the globe in the form of glassy spheres or tektites, shocked quartz and a layer of iridium-enriched dust.

"Everybody had always looked at the age for the KT boundary and compared it with the ages that we had gotten for the tektites and the melt rock from the Chicxulub crater and said, 'oh yeah, this is pretty much the same age,'" Renne said.

"But they're not. They differ by 180,000 years. From this calibration issue, I started to realize, ‘Wow, there is a real problem here.'"

Renne and colleagues dated tektites from Haiti, analyzing them using the recalibrated argon-argon technique to determine how long ago the impact occurred.

The tektite results agreed with previously recalibrated data but were more precise.

The geologists then did the same for altered volcanic ash collected from the Hell Creek Formation in Montana, the source of many dinosaur fossils--and one of the best sites to study the change in fossils from before and after the extinction.

The new extinction date is precise to within 11,000 years, and is 200,000 years earlier than the recalibrated date determined in 1993.

Despite the synchronous impact and extinction, Renne cautions that this doesn't mean that the impact was the sole cause.

Dramatic climate variation over the previous million years, including long cold snaps amid a general Cretaceous hothouse environment, probably brought many creatures to the brink of extinction.

"The impact was the coup de grace," said Renne.

"These precursory phenomena made the global ecosystem much more sensitive to even relatively small triggers, so that what otherwise might have been a fairly minor effect shifted the ecosystem into a new state."

One cause of the climate variability could have been a sustained series of volcanic eruptions in India that produced the extensive Deccan Traps, ancient rock formations that represent one of the largest volcanic features on Earth. The Deccan Traps are believed to have formed between 60 and 68 million years ago.

Renne plans to re-date those volcanic rocks.

He and colleagues also dated rocks above the KT boundary. They concluded that Earth's atmospheric carbon cycle returned to normal within about 5,000 years of the impact.

This is in stark contrast to the world's oceans, which studies show took between one and two million years to return to normal.

Renne attributes this to a sluggish recovery of pre-impact ocean circulation patterns.

The study's results also clarify some inconsistencies between different estimates for the age of the KT boundary based on Earth's orbital rhythms recorded in sedimentary rocks.

Dutch colleagues Frederik Hilgen of Utrecht University and Klaudia Kuiper of Vrije University had previously determined an age of 65,957,000 years for the boundary using this approach, which agrees with the new independent results within the margins of error.

"This study shows the power of high precision geochronology," said paper co-author Darren Mark of the Scottish Universities Environmental Research Center in Kilbride, UK, who conducted independent argon-argon analyses on samples provided by Renne.

"Many people think precision is just about adding another decimal place to a number. But it's far more exciting than that," he said.

"It's more like putting a sharper lens on a camera. It allows us to dissect the geological record at greater resolution and piece together the sequence of Earth history."

The paper's co-authors, in addition to Mark, Hilgen and Kuipler, are William Mitchell III at UC Berkeley, Alan Deino and Roland Mundil at BGC, Leah Morgan of the Scottish Universities Environmental Research Center and Jan Smit of Vrije University in Amsterdam.

In addition to funding from NSF, the work was also supported by the Ann and Gordon Getty Foundation and UC Berkeley's Esper S. Larsen Jr. Fund.

-NSF-