UW team explores large, restless volcanic field in Chile

If Brad Singer knew for sure what was happening three miles under an odd-shaped lake in the Andes, he might be less eager to spend a good part of his career investigating a volcanic field that has erupted 36 times during the last 25,000 years. As he leads a large scientific team exploring a region in the Andes called Laguna del Maule, Singer hopes the area remains quiet.

But the primary reason to expend so much effort on this area boils down to one fact: The rate of uplift is among the highest ever observed by satellite measurement for a volcano that is not actively erupting.

That uplift is almost definitely due to a large intrusion of magma — molten rock — beneath the volcanic complex. For seven years, an area larger than the city of Madison has been rising by 10 inches per year.

That rapid rise provides a major scientific opportunity: to explore a mega-volcano before it erupts. That effort, and the hazard posed by the restless magma reservoir beneath Laguna del Maule, are described in a major research article in the December issue of the Geological Society of America’s GSA Today.

“We’ve always been looking at these mega-eruptions in the rear-view mirror,” says Singer. “We look at the lava, dust and ash, and try to understand what happened before the eruption. Since these huge eruptions are rare, that’s usually our only option. But we look at the steady uplift at Laguna del Maule, which has a history of regular eruptions, combined with changes in gravity, electrical conductivity and swarms of earthquakes, and we suspect that conditions necessary to trigger another eruption are gathering force.”

Laguna del Maule looks nothing like a classic, cone-shaped volcano, since the high-intensity erosion caused by heavy rain and snow has carried most of the evidence to the nearby Pacific Ocean. But the overpowering reason for the absence of “typical volcano cones” is the nature of the molten rock underground. It’s called rhyolite, and it’s the most explosive type of magma on the planet.

The eruption of a rhyolite volcano is too quick and violent to build up a cone. Instead, this viscous, water-rich magma often explodes into vast quantities of ash that can form deposits hundreds of yards deep, followed by a slower flow of glassy magma that can be tens of yards tall and measure more than a mile in length.

The next eruption could be in the size range of Mount St. Helens — or it could be vastly bigger, Singer says. “We know that over the past million years or so, several eruptions at Laguna del Maule or nearby volcanoes have been more than 100 times larger than Mount St. Helens,” he says. “Those are rare, but they are possible.” Such a mega-eruption could change the weather, disrupt the ecosystem and damage the economy.

Trying to anticipate what Laguna del Maule holds in store, Singer is heading a new $3 million, five-year effort sponsored by the National Science Foundation to document its behavior before an eruption. With colleagues from Chile, Argentina, Canada, Singapore, and Cornell and Georgia Tech universities, he is masterminding an effort to build a scientific model of the underground forces that could lead to eruption. “This model should capture how this system has evolved in the crust at all scales, from the microscopic to basinwide, over the last 100,000 years,” Singer says. “It’s like a movie from the past to the present and into the future.”

Over the next five years, Singer says he and 30 colleagues will “throw everything, including the kitchen sink, at the problem — geology, geochemistry, geochronology and geophysics — to help measure, and then model, what’s going on.”

One key source of information on volcanoes is seismic waves. Ground shaking triggered by the movement of magma can signal an impending eruption. Team member Clifford Thurber, a seismologist and professor of geoscience at UW-Madison, wants to use distant earthquakes to locate the underground magma body.

As many as 50 seismometers will eventually be emplaced above and around the magma at Laguna del Maule, in the effort to create a 3-D image of Earth’s crust in the area.

By tracking multiple earthquakes over several years, Thurber and his colleagues want to pinpoint the size and location of the magma body — roughly estimated as an oval measuring five kilometers (3.1 miles) by 10 kilometers (6.2 miles).

Each seismometer will record the travel time of earthquake waves originating within a few thousand kilometers, Thurber explains. Since soft rock transmits sound less efficiently than hard rock, “we expect that waves that pass through the presumed magma body will be delayed,” Thurber says. “It’s very simple. It’s like a CT scan, except instead of density we are looking at seismic wave velocity.”

As Singer, who has been visiting Laguna del Maule since 1998, notes, “The rate of uplift — among the highest ever observed — has been sustained for seven years, and we have discovered a large, fluid-rich zone in the crust under the lake using electrical resistivity methods. Thus, there are not many possible explanations other than a big, active body of magma at a shallow depth.”

The expanding body of magma could freeze in place — or blow its top, he says. “One thing we know for sure is that the surface cannot continue rising indefinitely.”

UW team explores large, restless volcanic field in Chile

If Brad Singer knew for sure what was happening three miles under an odd-shaped lake in the Andes, he might be less eager to spend a good part of his career investigating a volcanic field that has erupted 36 times during the last 25,000 years. As he leads a large scientific team exploring a region in the Andes called Laguna del Maule, Singer hopes the area remains quiet.

But the primary reason to expend so much effort on this area boils down to one fact: The rate of uplift is among the highest ever observed by satellite measurement for a volcano that is not actively erupting.

That uplift is almost definitely due to a large intrusion of magma — molten rock — beneath the volcanic complex. For seven years, an area larger than the city of Madison has been rising by 10 inches per year.

That rapid rise provides a major scientific opportunity: to explore a mega-volcano before it erupts. That effort, and the hazard posed by the restless magma reservoir beneath Laguna del Maule, are described in a major research article in the December issue of the Geological Society of America’s GSA Today.

“We’ve always been looking at these mega-eruptions in the rear-view mirror,” says Singer. “We look at the lava, dust and ash, and try to understand what happened before the eruption. Since these huge eruptions are rare, that’s usually our only option. But we look at the steady uplift at Laguna del Maule, which has a history of regular eruptions, combined with changes in gravity, electrical conductivity and swarms of earthquakes, and we suspect that conditions necessary to trigger another eruption are gathering force.”

Laguna del Maule looks nothing like a classic, cone-shaped volcano, since the high-intensity erosion caused by heavy rain and snow has carried most of the evidence to the nearby Pacific Ocean. But the overpowering reason for the absence of “typical volcano cones” is the nature of the molten rock underground. It’s called rhyolite, and it’s the most explosive type of magma on the planet.

The eruption of a rhyolite volcano is too quick and violent to build up a cone. Instead, this viscous, water-rich magma often explodes into vast quantities of ash that can form deposits hundreds of yards deep, followed by a slower flow of glassy magma that can be tens of yards tall and measure more than a mile in length.

The next eruption could be in the size range of Mount St. Helens — or it could be vastly bigger, Singer says. “We know that over the past million years or so, several eruptions at Laguna del Maule or nearby volcanoes have been more than 100 times larger than Mount St. Helens,” he says. “Those are rare, but they are possible.” Such a mega-eruption could change the weather, disrupt the ecosystem and damage the economy.

Trying to anticipate what Laguna del Maule holds in store, Singer is heading a new $3 million, five-year effort sponsored by the National Science Foundation to document its behavior before an eruption. With colleagues from Chile, Argentina, Canada, Singapore, and Cornell and Georgia Tech universities, he is masterminding an effort to build a scientific model of the underground forces that could lead to eruption. “This model should capture how this system has evolved in the crust at all scales, from the microscopic to basinwide, over the last 100,000 years,” Singer says. “It’s like a movie from the past to the present and into the future.”

Over the next five years, Singer says he and 30 colleagues will “throw everything, including the kitchen sink, at the problem — geology, geochemistry, geochronology and geophysics — to help measure, and then model, what’s going on.”

One key source of information on volcanoes is seismic waves. Ground shaking triggered by the movement of magma can signal an impending eruption. Team member Clifford Thurber, a seismologist and professor of geoscience at UW-Madison, wants to use distant earthquakes to locate the underground magma body.

As many as 50 seismometers will eventually be emplaced above and around the magma at Laguna del Maule, in the effort to create a 3-D image of Earth’s crust in the area.

By tracking multiple earthquakes over several years, Thurber and his colleagues want to pinpoint the size and location of the magma body — roughly estimated as an oval measuring five kilometers (3.1 miles) by 10 kilometers (6.2 miles).

Each seismometer will record the travel time of earthquake waves originating within a few thousand kilometers, Thurber explains. Since soft rock transmits sound less efficiently than hard rock, “we expect that waves that pass through the presumed magma body will be delayed,” Thurber says. “It’s very simple. It’s like a CT scan, except instead of density we are looking at seismic wave velocity.”

As Singer, who has been visiting Laguna del Maule since 1998, notes, “The rate of uplift — among the highest ever observed — has been sustained for seven years, and we have discovered a large, fluid-rich zone in the crust under the lake using electrical resistivity methods. Thus, there are not many possible explanations other than a big, active body of magma at a shallow depth.”

The expanding body of magma could freeze in place — or blow its top, he says. “One thing we know for sure is that the surface cannot continue rising indefinitely.”

Climate capers of the past 600,000 years

The researchers remove samples from a core segment taken from Lake Van at the center for Marine environmental sciences MARUM in Bremen, where all of the cores from the PALEOVAN project are stored. -  Photo: Nadine Pickarski/Uni Bonn
The researchers remove samples from a core segment taken from Lake Van at the center for Marine environmental sciences MARUM in Bremen, where all of the cores from the PALEOVAN project are stored. – Photo: Nadine Pickarski/Uni Bonn

If you want to see into the future, you have to understand the past. An international consortium of researchers under the auspices of the University of Bonn has drilled deposits on the bed of Lake Van (Eastern Turkey) which provide unique insights into the last 600,000 years. The samples reveal that the climate has done its fair share of mischief-making in the past. Furthermore, there have been numerous earthquakes and volcanic eruptions. The results of the drilling project also provide a basis for assessing the risk of how dangerous natural hazards are for today’s population. In a special edition of the highly regarded publication Quaternary Science Reviews, the scientists have now published their findings in a number of journal articles.

In the sediments of Lake Van, the lighter-colored, lime-containing summer layers are clearly distinguishable from the darker, clay-rich winter layers — also called varves. In 2010, from a floating platform an international consortium of researchers drilled a 220 m deep sediment profile from the lake floor at a water depth of 360 m and analyzed the varves. The samples they recovered are a unique scientific treasure because the climate conditions, earthquakes and volcanic eruptions of the past 600,000 years can be read in outstanding quality from the cores.

The team of scientists under the auspices of the University of Bonn has analyzed some 5,000 samples in total. “The results show that the climate over the past hundred thousand years has been a roller coaster. Within just a few decades, the climate could tip from an ice age into a warm period,” says Doctor Thomas Litt of the University of Bonn’s Steinmann Institute and spokesman for the PALEOVAN international consortium of researchers. Unbroken continental climate archives from the ice age which encompass several hundred thousand years are extremely rare on a global scale. “There has never before in all of the Middle East and Central Asia been a continental drilling operation going so far back into the past,” says Doctor Litt. In the northern hemisphere, climate data from ice-cores drilled in Greenland encompass the last 120,000 years. The Lake Van project closes a gap in the scientific climate record.

The sediments reveal six cycles of cold and warm periods


Scientists found evidence for a total of six cycles of warm and cold periods in the sediments of Lake Van. The University of Bonn paleoecologist and his colleagues analyzed the pollen preserved in the sediments. Under a microscope they were able to determine which plants around the eastern Anatolian Lake the pollen came from. “Pollen is amazingly durable and is preserved over very long periods when protected in the sediments,” Doctor Litt explained. Insight into the age of the individual layers was gleaned through radiometric age measurements that use the decay of radioactive elements as a geologic clock. Based on the type of pollen and the age, the scientists were able to determine when oak forests typical of warm periods grew around Lake Van and when ice-age steppe made up of grasses, mugwort and goosefoot surrounded the lake.

Once they determine the composition of the vegetation present and the requirements of the plants, the scientists can reconstruct with a high degree of accuracy the temperature and amount of rainfall during different epochs. These analyses enable the team of researchers to read the varves of Lake Van like thousands of pages of an archive. With these data, the team was able to demonstrate that fluctuations in climate were due in large part to periodic changes in the Earth’s orbit parameters and the commensurate changes in solar insolation levels. However, the influence of North Atlantic currents was also evident. “The analysis of the Lake Van sediments has presented us with an image of how an ecosystem reacts to abrupt changes in climate. This fundamental data will help us to develop potential scenarios of future climate effects,” says Doctor Litt.

Risks of earthquakes and volcanic eruptions in the region of Van

Such risk assessments can also be made for other natural forces. “Deposits of volcanic ash with thicknesses of up to 10 m in the Lake Van sediments show us that approximately 270,000 years ago there was a massive eruption,” the University of Bonn paleoecologist said. The team struck some 300 different volcanic events in its drillings. Statistically, that corresponds to one explosive volcanic eruption in the region every 2000 years. Deformations in the sediment layers show that the area is subject to frequent, strong earthquakes. “The area around Lake Van is very densely populated. The data from the core samples show that volcanic activity and earthquakes present a relatively high risk for the region,” Doctor Litt says. According to media reports, in 2011 a 7.2 magnitude earthquake in the Van province claimed the lives of more than 500 people and injured more than 2,500.

Publication: “Results from the PALEOVAN drilling project: A 600,000 year long continental archive in the Near East”, Quaternary Science Reviews, Volume 104, online publication: (http://dx.doi.org/10.1016/j.quascirev.2014.09.026)

Climate capers of the past 600,000 years

The researchers remove samples from a core segment taken from Lake Van at the center for Marine environmental sciences MARUM in Bremen, where all of the cores from the PALEOVAN project are stored. -  Photo: Nadine Pickarski/Uni Bonn
The researchers remove samples from a core segment taken from Lake Van at the center for Marine environmental sciences MARUM in Bremen, where all of the cores from the PALEOVAN project are stored. – Photo: Nadine Pickarski/Uni Bonn

If you want to see into the future, you have to understand the past. An international consortium of researchers under the auspices of the University of Bonn has drilled deposits on the bed of Lake Van (Eastern Turkey) which provide unique insights into the last 600,000 years. The samples reveal that the climate has done its fair share of mischief-making in the past. Furthermore, there have been numerous earthquakes and volcanic eruptions. The results of the drilling project also provide a basis for assessing the risk of how dangerous natural hazards are for today’s population. In a special edition of the highly regarded publication Quaternary Science Reviews, the scientists have now published their findings in a number of journal articles.

In the sediments of Lake Van, the lighter-colored, lime-containing summer layers are clearly distinguishable from the darker, clay-rich winter layers — also called varves. In 2010, from a floating platform an international consortium of researchers drilled a 220 m deep sediment profile from the lake floor at a water depth of 360 m and analyzed the varves. The samples they recovered are a unique scientific treasure because the climate conditions, earthquakes and volcanic eruptions of the past 600,000 years can be read in outstanding quality from the cores.

The team of scientists under the auspices of the University of Bonn has analyzed some 5,000 samples in total. “The results show that the climate over the past hundred thousand years has been a roller coaster. Within just a few decades, the climate could tip from an ice age into a warm period,” says Doctor Thomas Litt of the University of Bonn’s Steinmann Institute and spokesman for the PALEOVAN international consortium of researchers. Unbroken continental climate archives from the ice age which encompass several hundred thousand years are extremely rare on a global scale. “There has never before in all of the Middle East and Central Asia been a continental drilling operation going so far back into the past,” says Doctor Litt. In the northern hemisphere, climate data from ice-cores drilled in Greenland encompass the last 120,000 years. The Lake Van project closes a gap in the scientific climate record.

The sediments reveal six cycles of cold and warm periods


Scientists found evidence for a total of six cycles of warm and cold periods in the sediments of Lake Van. The University of Bonn paleoecologist and his colleagues analyzed the pollen preserved in the sediments. Under a microscope they were able to determine which plants around the eastern Anatolian Lake the pollen came from. “Pollen is amazingly durable and is preserved over very long periods when protected in the sediments,” Doctor Litt explained. Insight into the age of the individual layers was gleaned through radiometric age measurements that use the decay of radioactive elements as a geologic clock. Based on the type of pollen and the age, the scientists were able to determine when oak forests typical of warm periods grew around Lake Van and when ice-age steppe made up of grasses, mugwort and goosefoot surrounded the lake.

Once they determine the composition of the vegetation present and the requirements of the plants, the scientists can reconstruct with a high degree of accuracy the temperature and amount of rainfall during different epochs. These analyses enable the team of researchers to read the varves of Lake Van like thousands of pages of an archive. With these data, the team was able to demonstrate that fluctuations in climate were due in large part to periodic changes in the Earth’s orbit parameters and the commensurate changes in solar insolation levels. However, the influence of North Atlantic currents was also evident. “The analysis of the Lake Van sediments has presented us with an image of how an ecosystem reacts to abrupt changes in climate. This fundamental data will help us to develop potential scenarios of future climate effects,” says Doctor Litt.

Risks of earthquakes and volcanic eruptions in the region of Van

Such risk assessments can also be made for other natural forces. “Deposits of volcanic ash with thicknesses of up to 10 m in the Lake Van sediments show us that approximately 270,000 years ago there was a massive eruption,” the University of Bonn paleoecologist said. The team struck some 300 different volcanic events in its drillings. Statistically, that corresponds to one explosive volcanic eruption in the region every 2000 years. Deformations in the sediment layers show that the area is subject to frequent, strong earthquakes. “The area around Lake Van is very densely populated. The data from the core samples show that volcanic activity and earthquakes present a relatively high risk for the region,” Doctor Litt says. According to media reports, in 2011 a 7.2 magnitude earthquake in the Van province claimed the lives of more than 500 people and injured more than 2,500.

Publication: “Results from the PALEOVAN drilling project: A 600,000 year long continental archive in the Near East”, Quaternary Science Reviews, Volume 104, online publication: (http://dx.doi.org/10.1016/j.quascirev.2014.09.026)

Earth’s magnetic field could flip within a human lifetime

Left to right, Biaggio Giaccio, Gianluca Sotilli, Courtney Sprain and Sebastien Nomade sitting next to an outcrop in the Sulmona basin of the Apennines that contains the Matuyama-Brunhes magnetic reversal. A layer of volcanic ash interbedded with the lake sediments can be seen above their heads. -  Paul Renne, UC Berkeley
Left to right, Biaggio Giaccio, Gianluca Sotilli, Courtney Sprain and Sebastien Nomade sitting next to an outcrop in the Sulmona basin of the Apennines that contains the Matuyama-Brunhes magnetic reversal. A layer of volcanic ash interbedded with the lake sediments can be seen above their heads. – Paul Renne, UC Berkeley

Imagine the world waking up one morning to discover that all compasses pointed south instead of north.

It’s not as bizarre as it sounds. Earth’s magnetic field has flipped – though not overnight – many times throughout the planet’s history. Its dipole magnetic field, like that of a bar magnet, remains about the same intensity for thousands to millions of years, but for incompletely known reasons it occasionally weakens and, presumably over a few thousand years, reverses direction.

Now, a new study by a team of scientists from Italy, France, Columbia University and the University of California, Berkeley, demonstrates that the last magnetic reversal 786,000 years ago actually happened very quickly, in less than 100 years – roughly a human lifetime.

“It’s amazing how rapidly we see that reversal,” said UC Berkeley graduate student Courtney Sprain. “The paleomagnetic data are very well done. This is one of the best records we have so far of what happens during a reversal and how quickly these reversals can happen.”

Sprain and Paul Renne, director of the Berkeley Geochronology Center and a UC Berkeley professor-in- residence of earth and planetary science, are coauthors of the study, which will be published in the November issue of Geophysical Journal International and is now available online.

Flip could affect electrical grid, cancer rates

The discovery comes as new evidence indicates that the intensity of Earth’s magnetic field is decreasing 10 times faster than normal, leading some geophysicists to predict a reversal within a few thousand years.

Though a magnetic reversal is a major planet-wide event driven by convection in Earth’s iron core, there are no documented catastrophes associated with past reversals, despite much searching in the geologic and biologic record. Today, however, such a reversal could potentially wreak havoc with our electrical grid, generating currents that might take it down.

And since Earth’s magnetic field protects life from energetic particles from the sun and cosmic rays, both of which can cause genetic mutations, a weakening or temporary loss of the field before a permanent reversal could increase cancer rates. The danger to life would be even greater if flips were preceded by long periods of unstable magnetic behavior.

“We should be thinking more about what the biologic effects would be,” Renne said.

Dating ash deposits from windward volcanoes

The new finding is based on measurements of the magnetic field alignment in layers of ancient lake sediments now exposed in the Sulmona basin of the Apennine Mountains east of Rome, Italy. The lake sediments are interbedded with ash layers erupted from the Roman volcanic province, a large area of volcanoes upwind of the former lake that includes periodically erupting volcanoes near Sabatini, Vesuvius and the Alban Hills. Italian researchers led by Leonardo Sagnotti of Rome’s National Institute of Geophysics and Volcanology measured the magnetic field directions frozen into the sediments as they accumulated at the bottom of the ancient lake.

Sprain and Renne used argon-argon dating, a method widely used to determine the ages of rocks, whether they’re thousands or billions of years old, to determine the age of ash layers above and below the sediment layer recording the last reversal. These dates were confirmed by their colleague and former UC Berkeley postdoctoral fellow Sebastien Nomade of the Laboratory of Environmental and Climate Sciences in Gif-Sur-Yvette, France.

Because the lake sediments were deposited at a high and steady rate over a 10,000-year period, the team was able to interpolate the date of the layer showing the magnetic reversal, called the Matuyama-Brunhes transition, at approximately 786,000 years ago. This date is far more precise than that from previous studies, which placed the reversal between 770,000 and 795,000 years ago.

“What’s incredible is that you go from reverse polarity to a field that is normal with essentially nothing in between, which means it had to have happened very quickly, probably in less than 100 years,” said Renne. “We don’t know whether the next reversal will occur as suddenly as this one did, but we also don’t know that it won’t.”

Unstable magnetic field preceded 180-degree flip

Whether or not the new finding spells trouble for modern civilization, it likely will help researchers understand how and why Earth’s magnetic field episodically reverses polarity, Renne said.

The magnetic record the Italian-led team obtained shows that the sudden 180-degree flip of the field was preceded by a period of instability that spanned more than 6,000 years. The instability included two intervals of low magnetic field strength that lasted about 2,000 years each. Rapid changes in field orientations may have occurred within the first interval of low strength. The full magnetic polarity reversal – that is, the final and very rapid flip to what the field is today – happened toward the end of the most recent interval of low field strength.

Renne is continuing his collaboration with the Italian-French team to correlate the lake record with past climate change.

Renne and Sprain’s work at the Berkeley Geochronology Center was supported by the Ann and Gordon Getty Foundation.

Earth’s magnetic field could flip within a human lifetime

Left to right, Biaggio Giaccio, Gianluca Sotilli, Courtney Sprain and Sebastien Nomade sitting next to an outcrop in the Sulmona basin of the Apennines that contains the Matuyama-Brunhes magnetic reversal. A layer of volcanic ash interbedded with the lake sediments can be seen above their heads. -  Paul Renne, UC Berkeley
Left to right, Biaggio Giaccio, Gianluca Sotilli, Courtney Sprain and Sebastien Nomade sitting next to an outcrop in the Sulmona basin of the Apennines that contains the Matuyama-Brunhes magnetic reversal. A layer of volcanic ash interbedded with the lake sediments can be seen above their heads. – Paul Renne, UC Berkeley

Imagine the world waking up one morning to discover that all compasses pointed south instead of north.

It’s not as bizarre as it sounds. Earth’s magnetic field has flipped – though not overnight – many times throughout the planet’s history. Its dipole magnetic field, like that of a bar magnet, remains about the same intensity for thousands to millions of years, but for incompletely known reasons it occasionally weakens and, presumably over a few thousand years, reverses direction.

Now, a new study by a team of scientists from Italy, France, Columbia University and the University of California, Berkeley, demonstrates that the last magnetic reversal 786,000 years ago actually happened very quickly, in less than 100 years – roughly a human lifetime.

“It’s amazing how rapidly we see that reversal,” said UC Berkeley graduate student Courtney Sprain. “The paleomagnetic data are very well done. This is one of the best records we have so far of what happens during a reversal and how quickly these reversals can happen.”

Sprain and Paul Renne, director of the Berkeley Geochronology Center and a UC Berkeley professor-in- residence of earth and planetary science, are coauthors of the study, which will be published in the November issue of Geophysical Journal International and is now available online.

Flip could affect electrical grid, cancer rates

The discovery comes as new evidence indicates that the intensity of Earth’s magnetic field is decreasing 10 times faster than normal, leading some geophysicists to predict a reversal within a few thousand years.

Though a magnetic reversal is a major planet-wide event driven by convection in Earth’s iron core, there are no documented catastrophes associated with past reversals, despite much searching in the geologic and biologic record. Today, however, such a reversal could potentially wreak havoc with our electrical grid, generating currents that might take it down.

And since Earth’s magnetic field protects life from energetic particles from the sun and cosmic rays, both of which can cause genetic mutations, a weakening or temporary loss of the field before a permanent reversal could increase cancer rates. The danger to life would be even greater if flips were preceded by long periods of unstable magnetic behavior.

“We should be thinking more about what the biologic effects would be,” Renne said.

Dating ash deposits from windward volcanoes

The new finding is based on measurements of the magnetic field alignment in layers of ancient lake sediments now exposed in the Sulmona basin of the Apennine Mountains east of Rome, Italy. The lake sediments are interbedded with ash layers erupted from the Roman volcanic province, a large area of volcanoes upwind of the former lake that includes periodically erupting volcanoes near Sabatini, Vesuvius and the Alban Hills. Italian researchers led by Leonardo Sagnotti of Rome’s National Institute of Geophysics and Volcanology measured the magnetic field directions frozen into the sediments as they accumulated at the bottom of the ancient lake.

Sprain and Renne used argon-argon dating, a method widely used to determine the ages of rocks, whether they’re thousands or billions of years old, to determine the age of ash layers above and below the sediment layer recording the last reversal. These dates were confirmed by their colleague and former UC Berkeley postdoctoral fellow Sebastien Nomade of the Laboratory of Environmental and Climate Sciences in Gif-Sur-Yvette, France.

Because the lake sediments were deposited at a high and steady rate over a 10,000-year period, the team was able to interpolate the date of the layer showing the magnetic reversal, called the Matuyama-Brunhes transition, at approximately 786,000 years ago. This date is far more precise than that from previous studies, which placed the reversal between 770,000 and 795,000 years ago.

“What’s incredible is that you go from reverse polarity to a field that is normal with essentially nothing in between, which means it had to have happened very quickly, probably in less than 100 years,” said Renne. “We don’t know whether the next reversal will occur as suddenly as this one did, but we also don’t know that it won’t.”

Unstable magnetic field preceded 180-degree flip

Whether or not the new finding spells trouble for modern civilization, it likely will help researchers understand how and why Earth’s magnetic field episodically reverses polarity, Renne said.

The magnetic record the Italian-led team obtained shows that the sudden 180-degree flip of the field was preceded by a period of instability that spanned more than 6,000 years. The instability included two intervals of low magnetic field strength that lasted about 2,000 years each. Rapid changes in field orientations may have occurred within the first interval of low strength. The full magnetic polarity reversal – that is, the final and very rapid flip to what the field is today – happened toward the end of the most recent interval of low field strength.

Renne is continuing his collaboration with the Italian-French team to correlate the lake record with past climate change.

Renne and Sprain’s work at the Berkeley Geochronology Center was supported by the Ann and Gordon Getty Foundation.

Living in the shadow of Mauna Loa: A silent summit belies a volcano’s forgotten fury

Earth’s largest active volcano, Mauna Loa on Hawaii’s Big Island, is taking a nap. And after 30 years, no one is sure when the sleeping giant will awaken. Scientists say it’s likely to erupt again within the next couple of decades and, when it does, it will be spectacular – and potentially dangerous.

Although Mauna Loa often takes a back seat to the more famous Kilauea, which has been erupting nearly continuously since 1983, history warns us that Mauna Loa’s current silence is anomalous. Meanwhile, more people and more buildings pack into potentially hazardous areas: locations where Mauna Loa’s lava has reached in the past and likely will reach again. Read more about the steps geologists are already taking – such as upgrading their monitoring tools and talking with the public – to prepare for another eruption of Mauna Loa in the September issue of EARTH Magazine: http://bit.ly/1p1SXiU.

For more stories about the science of our planet, check out EARTH magazine online or subscribe at http://www.earthmagazine.org. The September issue, now available on the digital newsstand, features stories about a new Neanderthal ancestor found in a Spanish cave, the effect of volcanic ash on Southern Ocean plankton, and a tribute to Nereus, the United States’ only full-ocean-depth submersible, which was lost at sea in May, plus much, much more.

Living in the shadow of Mauna Loa: A silent summit belies a volcano’s forgotten fury

Earth’s largest active volcano, Mauna Loa on Hawaii’s Big Island, is taking a nap. And after 30 years, no one is sure when the sleeping giant will awaken. Scientists say it’s likely to erupt again within the next couple of decades and, when it does, it will be spectacular – and potentially dangerous.

Although Mauna Loa often takes a back seat to the more famous Kilauea, which has been erupting nearly continuously since 1983, history warns us that Mauna Loa’s current silence is anomalous. Meanwhile, more people and more buildings pack into potentially hazardous areas: locations where Mauna Loa’s lava has reached in the past and likely will reach again. Read more about the steps geologists are already taking – such as upgrading their monitoring tools and talking with the public – to prepare for another eruption of Mauna Loa in the September issue of EARTH Magazine: http://bit.ly/1p1SXiU.

For more stories about the science of our planet, check out EARTH magazine online or subscribe at http://www.earthmagazine.org. The September issue, now available on the digital newsstand, features stories about a new Neanderthal ancestor found in a Spanish cave, the effect of volcanic ash on Southern Ocean plankton, and a tribute to Nereus, the United States’ only full-ocean-depth submersible, which was lost at sea in May, plus much, much more.

Yellowstone supereruption would send ash across North America

An example of the possible distribution of ash from a month-long Yellowstone supereruption. The distribution map was generated by a new model developed by the US Geological Survey using wind information from January 2001. The improved computer model, detailed in a new study published in Geochemistry, Geophysics, Geosystems, finds that the hypothetical, large eruption would create a distinctive kind of ash cloud known as an umbrella, which expands evenly in all directions, sending ash across North America. Ash distribution will vary depending on cloud height, eruption duration, diameter of volcanic particles in the cloud, and wind conditions, according to the new study. -  Credit: USGS
An example of the possible distribution of ash from a month-long Yellowstone supereruption. The distribution map was generated by a new model developed by the US Geological Survey using wind information from January 2001. The improved computer model, detailed in a new study published in Geochemistry, Geophysics, Geosystems, finds that the hypothetical, large eruption would create a distinctive kind of ash cloud known as an umbrella, which expands evenly in all directions, sending ash across North America. Ash distribution will vary depending on cloud height, eruption duration, diameter of volcanic particles in the cloud, and wind conditions, according to the new study. – Credit: USGS

In the unlikely event of a volcanic supereruption at Yellowstone National Park, the northern Rocky Mountains would be blanketed in meters of ash, and millimeters would be deposited as far away as New York City, Los Angeles and Miami, according to a new study.

An improved computer model developed by the study’s authors finds that the hypothetical, large eruption would create a distinctive kind of ash cloud known as an umbrella, which expands evenly in all directions, sending ash across North America.

A supereruption is the largest class of volcanic eruption, during which more than 1,000 cubic kilometers (240 cubic miles) of material is ejected. If such a supereruption were to occur, which is extremely unlikely, it could shut down electronic communications and air travel throughout the continent, and alter the climate, the study notes.

A giant underground reservoir of hot and partly molten rock feeds the volcano at Yellowstone National Park. It has produced three huge eruptions about 2.1 million, 1.3 million and 640,000 years ago. Geological activity at Yellowstone shows no signs that volcanic eruptions, large or small, will occur in the near future. The most recent volcanic activity at Yellowstone-a relatively non-explosive lava flow at the Pitchstone Plateau in the southern section of the park-occurred 70,000 years ago.

Researchers at the U.S. Geological Survey used a hypothetical Yellowstone supereruption as a case study to run their new model that calculates ash distribution for eruptions of all sizes. The model, Ash3D, incorporates data on historical wind patterns to calculate the thickness of ash fall for a supereruption like the one that occurred at Yellowstone 640,000 years ago.

The new study provides the first quantitative estimates of the thickness and distribution of ash in cities around the U.S. if the Yellowstone volcanic system were to experience this type of huge, yet unlikely, eruption.

Cities close to the modeled Yellowstone supereruption could be covered by more than a meter (a few feet) of ash. There would be centimeters (a few inches) of ash in the Midwest, while cities on both coasts would see millimeters (a fraction of an inch) of accumulation, according to the new study that was published online today in Geochemistry, Geophysics, Geosystems, a journal of the American Geophysical Union. The paper has been made available at no charge at http://onlinelibrary.wiley.com/doi/10.1002/2014GC005469/abstract.

The model results help scientists understand the extremely widespread distribution of ash deposits from previous large eruptions at Yellowstone. Other USGS scientists are using the Ash3D model to forecast possible ash hazards at currently restless volcanoes in Alaska.

Unlike smaller eruptions, whose ash deposition looks roughly like a fan when viewed from above, the spreading umbrella cloud from a supereruption deposits ash in a pattern more like a bull’s eye – heavy in the center and diminishing in all directions – and is less affected by prevailing winds, according to the new model.

“In essence, the eruption makes its own winds that can overcome the prevailing westerlies, which normally dominate weather patterns in the United States,” said Larry Mastin, a geologist at the USGS Cascades Volcano Observatory in Vancouver, Washington, and the lead author of the new paper. Westerly winds blow from the west.

“This helps explain the distribution from large Yellowstone eruptions of the past, where considerable amounts of ash reached the west coast,” he added.

The three large past eruptions at Yellowstone sent ash over many tens of thousands of square kilometers (thousands of square miles). Ash deposits from these eruptions have been found throughout the central and western United States and Canada.

Erosion has made it difficult for scientists to accurately estimate ash distribution from these deposits. Previous computer models also lacked the ability to accurately determine how the ash would be transported.

Using their new model, the study’s authors found that during very large volcanic eruptions, the expansion rate of the ash cloud’s leading edge can exceed the average ambient wind speed for hours or days depending on the length of the eruption. This outward expansion is capable of driving ash more than 1,500 kilometers (932 miles) upwind – westward — and crosswind – north to south — producing a bull’s eye-like pattern centered on the eruption site.

In the simulated modern-day eruption scenario, cities within 500 kilometers (311 miles) of Yellowstone like Billings, Montana, and Casper, Wyoming, would be covered by centimeters (inches) to more than a meter (more than three feet) of ash. Upper Midwestern cities, like Minneapolis, Minnesota, and Des Moines, Iowa, would receive centimeters (inches), and those on the East and Gulf coasts, like New York and Washington, D.C. would receive millimeters or less (fractions of an inch). California cities would receive millimeters to centimeters (less than an inch to less than two inches) of ash while Pacific Northwest cities like Portland, Oregon, and Seattle, Washington, would receive up to a few centimeters (more than an inch).

Even small accumulations only millimeters or centimeters (less than an inch to an inch) thick could cause major effects around the country, including reduced traction on roads, shorted-out electrical transformers and respiratory problems, according to previous research cited in the new study. Prior research has also found that multiple inches of ash can damage buildings, block sewer and water lines, and disrupt livestock and crop production, the study notes.

The study also found that other eruptions – powerful but much smaller than a Yellowstone supereruption — might also generate an umbrella cloud.

“These model developments have greatly enhanced our ability to anticipate possible effects from both large and small eruptions, wherever they occur,” said Jacob Lowenstern, USGS Scientist-in-Charge of the Yellowstone Volcano Observatory in Menlo Park, California, and a co-author on the new paper.

Yellowstone supereruption would send ash across North America

An example of the possible distribution of ash from a month-long Yellowstone supereruption. The distribution map was generated by a new model developed by the US Geological Survey using wind information from January 2001. The improved computer model, detailed in a new study published in Geochemistry, Geophysics, Geosystems, finds that the hypothetical, large eruption would create a distinctive kind of ash cloud known as an umbrella, which expands evenly in all directions, sending ash across North America. Ash distribution will vary depending on cloud height, eruption duration, diameter of volcanic particles in the cloud, and wind conditions, according to the new study. -  Credit: USGS
An example of the possible distribution of ash from a month-long Yellowstone supereruption. The distribution map was generated by a new model developed by the US Geological Survey using wind information from January 2001. The improved computer model, detailed in a new study published in Geochemistry, Geophysics, Geosystems, finds that the hypothetical, large eruption would create a distinctive kind of ash cloud known as an umbrella, which expands evenly in all directions, sending ash across North America. Ash distribution will vary depending on cloud height, eruption duration, diameter of volcanic particles in the cloud, and wind conditions, according to the new study. – Credit: USGS

In the unlikely event of a volcanic supereruption at Yellowstone National Park, the northern Rocky Mountains would be blanketed in meters of ash, and millimeters would be deposited as far away as New York City, Los Angeles and Miami, according to a new study.

An improved computer model developed by the study’s authors finds that the hypothetical, large eruption would create a distinctive kind of ash cloud known as an umbrella, which expands evenly in all directions, sending ash across North America.

A supereruption is the largest class of volcanic eruption, during which more than 1,000 cubic kilometers (240 cubic miles) of material is ejected. If such a supereruption were to occur, which is extremely unlikely, it could shut down electronic communications and air travel throughout the continent, and alter the climate, the study notes.

A giant underground reservoir of hot and partly molten rock feeds the volcano at Yellowstone National Park. It has produced three huge eruptions about 2.1 million, 1.3 million and 640,000 years ago. Geological activity at Yellowstone shows no signs that volcanic eruptions, large or small, will occur in the near future. The most recent volcanic activity at Yellowstone-a relatively non-explosive lava flow at the Pitchstone Plateau in the southern section of the park-occurred 70,000 years ago.

Researchers at the U.S. Geological Survey used a hypothetical Yellowstone supereruption as a case study to run their new model that calculates ash distribution for eruptions of all sizes. The model, Ash3D, incorporates data on historical wind patterns to calculate the thickness of ash fall for a supereruption like the one that occurred at Yellowstone 640,000 years ago.

The new study provides the first quantitative estimates of the thickness and distribution of ash in cities around the U.S. if the Yellowstone volcanic system were to experience this type of huge, yet unlikely, eruption.

Cities close to the modeled Yellowstone supereruption could be covered by more than a meter (a few feet) of ash. There would be centimeters (a few inches) of ash in the Midwest, while cities on both coasts would see millimeters (a fraction of an inch) of accumulation, according to the new study that was published online today in Geochemistry, Geophysics, Geosystems, a journal of the American Geophysical Union. The paper has been made available at no charge at http://onlinelibrary.wiley.com/doi/10.1002/2014GC005469/abstract.

The model results help scientists understand the extremely widespread distribution of ash deposits from previous large eruptions at Yellowstone. Other USGS scientists are using the Ash3D model to forecast possible ash hazards at currently restless volcanoes in Alaska.

Unlike smaller eruptions, whose ash deposition looks roughly like a fan when viewed from above, the spreading umbrella cloud from a supereruption deposits ash in a pattern more like a bull’s eye – heavy in the center and diminishing in all directions – and is less affected by prevailing winds, according to the new model.

“In essence, the eruption makes its own winds that can overcome the prevailing westerlies, which normally dominate weather patterns in the United States,” said Larry Mastin, a geologist at the USGS Cascades Volcano Observatory in Vancouver, Washington, and the lead author of the new paper. Westerly winds blow from the west.

“This helps explain the distribution from large Yellowstone eruptions of the past, where considerable amounts of ash reached the west coast,” he added.

The three large past eruptions at Yellowstone sent ash over many tens of thousands of square kilometers (thousands of square miles). Ash deposits from these eruptions have been found throughout the central and western United States and Canada.

Erosion has made it difficult for scientists to accurately estimate ash distribution from these deposits. Previous computer models also lacked the ability to accurately determine how the ash would be transported.

Using their new model, the study’s authors found that during very large volcanic eruptions, the expansion rate of the ash cloud’s leading edge can exceed the average ambient wind speed for hours or days depending on the length of the eruption. This outward expansion is capable of driving ash more than 1,500 kilometers (932 miles) upwind – westward — and crosswind – north to south — producing a bull’s eye-like pattern centered on the eruption site.

In the simulated modern-day eruption scenario, cities within 500 kilometers (311 miles) of Yellowstone like Billings, Montana, and Casper, Wyoming, would be covered by centimeters (inches) to more than a meter (more than three feet) of ash. Upper Midwestern cities, like Minneapolis, Minnesota, and Des Moines, Iowa, would receive centimeters (inches), and those on the East and Gulf coasts, like New York and Washington, D.C. would receive millimeters or less (fractions of an inch). California cities would receive millimeters to centimeters (less than an inch to less than two inches) of ash while Pacific Northwest cities like Portland, Oregon, and Seattle, Washington, would receive up to a few centimeters (more than an inch).

Even small accumulations only millimeters or centimeters (less than an inch to an inch) thick could cause major effects around the country, including reduced traction on roads, shorted-out electrical transformers and respiratory problems, according to previous research cited in the new study. Prior research has also found that multiple inches of ash can damage buildings, block sewer and water lines, and disrupt livestock and crop production, the study notes.

The study also found that other eruptions – powerful but much smaller than a Yellowstone supereruption — might also generate an umbrella cloud.

“These model developments have greatly enhanced our ability to anticipate possible effects from both large and small eruptions, wherever they occur,” said Jacob Lowenstern, USGS Scientist-in-Charge of the Yellowstone Volcano Observatory in Menlo Park, California, and a co-author on the new paper.