Alpine Fault study shows new evidence for regular magnitude 8 earthquakes

University of Nevada - Reno seismologist Glenn Biasi spent eight days in the dense forests on the western side of the Southern Alps on the South Island of New Zealand to study the Alpine Fault, among the world's longest, straightest and fastest moving plate boundary faults. Photo courtesy University of Nevada, Reno. -  Photo courtesy University of Nevada, Reno.
University of Nevada – Reno seismologist Glenn Biasi spent eight days in the dense forests on the western side of the Southern Alps on the South Island of New Zealand to study the Alpine Fault, among the world’s longest, straightest and fastest moving plate boundary faults. Photo courtesy University of Nevada, Reno. – Photo courtesy University of Nevada, Reno.

A new study published in the prestigious journal Science, co-authored by University of Nevada, Reno’s Glenn Biasi and colleagues at GNS Science in New Zealand, finds that very large earthquakes have been occurring relatively regularly on the Alpine Fault along the southwest coastline of New Zealand for at least 8,000 years.

The Alpine Fault is the most hazardous fault on the South Island of New Zealand, and about 80 miles northwest of the South Island’s main city of Christchurch.

The team developed evidence for 22 earthquakes at the Hokuri Creek site, which, with two additional from nearby, led to the longest continuous earthquake record in the world for a major plate boundary fault. The team established that the Alpine Fault causes, on average, earthquakes of around a magnitude 8 every 330 years. Previous data put the intervals at about 485 years.

Relative motion of Australian and Pacific plates across the Alpine Fault averages almost an inch per year. This motion builds up, and then is released suddenly in large earthquakes. The 530-mile-long fault is among the longest, straightest and fastest moving plate boundary faults in the world. More than 23 feet of potential slip has accumulated in the 295 years since the most recent event in A.D. 1717.

Biasi, working with the GNS Science team led by Kelvin Berryman, used paleoseismology to extend the known seismic record from 1000 years ago to 8,000 years ago. They estimated earthquake dates by combining radiocarbon dating leaves, small twigs and marsh plants with geologic and other field techniques.

“Our study sheds new light on the frequency and size of earthquakes on the Alpine Fault. Earthquakes have been relatively periodic, suggesting that this may be a more general property of simple plate boundary faults worldwide,” Biasi, of the Nevada Seismological Laboratory said. “By comparison, large earthquakes on California’s San Andreas Fault have been less regular in size and timing.”

“Knowing the average rate of earthquakes is useful, but is only part of the seismic hazard equation,” he said. “If they are random in time, then the hazard does not depend on how long it has been since the most recent event. Alpine Fault earthquakes are more regular in their timing, allowing us to use the time since the last earthquake to adjust the hazard estimate. We estimate the 50-year probability of a large Alpine fault earthquake to be about 27 percent.”

A magnitude 7.1 earthquake centered near Christchurch, the largest city in the South Island of New Zealand, caused extensive damage to buildings on Sept. 2, 2010, and no deaths. On Feb. 22, 2011, a triggered aftershock measuring magnitude 6.3, with one of the strongest ground motions ever recorded worldwide in an urban area, struck the city killing 185 people.

Alpine Fault study shows new evidence for regular magnitude 8 earthquakes

University of Nevada - Reno seismologist Glenn Biasi spent eight days in the dense forests on the western side of the Southern Alps on the South Island of New Zealand to study the Alpine Fault, among the world's longest, straightest and fastest moving plate boundary faults. Photo courtesy University of Nevada, Reno. -  Photo courtesy University of Nevada, Reno.
University of Nevada – Reno seismologist Glenn Biasi spent eight days in the dense forests on the western side of the Southern Alps on the South Island of New Zealand to study the Alpine Fault, among the world’s longest, straightest and fastest moving plate boundary faults. Photo courtesy University of Nevada, Reno. – Photo courtesy University of Nevada, Reno.

A new study published in the prestigious journal Science, co-authored by University of Nevada, Reno’s Glenn Biasi and colleagues at GNS Science in New Zealand, finds that very large earthquakes have been occurring relatively regularly on the Alpine Fault along the southwest coastline of New Zealand for at least 8,000 years.

The Alpine Fault is the most hazardous fault on the South Island of New Zealand, and about 80 miles northwest of the South Island’s main city of Christchurch.

The team developed evidence for 22 earthquakes at the Hokuri Creek site, which, with two additional from nearby, led to the longest continuous earthquake record in the world for a major plate boundary fault. The team established that the Alpine Fault causes, on average, earthquakes of around a magnitude 8 every 330 years. Previous data put the intervals at about 485 years.

Relative motion of Australian and Pacific plates across the Alpine Fault averages almost an inch per year. This motion builds up, and then is released suddenly in large earthquakes. The 530-mile-long fault is among the longest, straightest and fastest moving plate boundary faults in the world. More than 23 feet of potential slip has accumulated in the 295 years since the most recent event in A.D. 1717.

Biasi, working with the GNS Science team led by Kelvin Berryman, used paleoseismology to extend the known seismic record from 1000 years ago to 8,000 years ago. They estimated earthquake dates by combining radiocarbon dating leaves, small twigs and marsh plants with geologic and other field techniques.

“Our study sheds new light on the frequency and size of earthquakes on the Alpine Fault. Earthquakes have been relatively periodic, suggesting that this may be a more general property of simple plate boundary faults worldwide,” Biasi, of the Nevada Seismological Laboratory said. “By comparison, large earthquakes on California’s San Andreas Fault have been less regular in size and timing.”

“Knowing the average rate of earthquakes is useful, but is only part of the seismic hazard equation,” he said. “If they are random in time, then the hazard does not depend on how long it has been since the most recent event. Alpine Fault earthquakes are more regular in their timing, allowing us to use the time since the last earthquake to adjust the hazard estimate. We estimate the 50-year probability of a large Alpine fault earthquake to be about 27 percent.”

A magnitude 7.1 earthquake centered near Christchurch, the largest city in the South Island of New Zealand, caused extensive damage to buildings on Sept. 2, 2010, and no deaths. On Feb. 22, 2011, a triggered aftershock measuring magnitude 6.3, with one of the strongest ground motions ever recorded worldwide in an urban area, struck the city killing 185 people.

Hidden rift valley discovered beneath West Antarctica reveals new insight into ice loss

Scientists have discovered a one mile deep rift valley hidden beneath the ice in West Antarctica, which they believe is contributing to ice loss from this part of the continent.

Experts from the University of Aberdeen and British Antarctic Survey (BAS) made the discovery below Ferrigno Ice Stream, a region visited only once previously, over fifty years ago, in 1961, and one that is remote even by Antarctic standards.

Their findings, reported in Nature this week reveal that the ice-filled ancient rift basin is connected to the warming ocean which impacts upon contemporary ice flow and loss.

The West Antarctic Ice Sheet is of great scientific interest and societal importance as it is losing ice faster than any other part of Antarctica with some glaciers shrinking by more than one metre per year.

Understanding the processes that influence ice loss from West Antarctica is important to improve predictions of its future behaviour in a warming world.

Dr Robert Bingham, a glaciologist working in the University of Aberdeen’s School of Geosciences and lead author of the study, discovered the rift valley whilst undertaking three months of fieldwork with British Antarctic Survey in 2010.

Dr Bingham, whose fieldwork was funded by the UK’s Natural Environment Research Council (NERC) said: “Over the last 20 years we have used satellites to monitor ice losses from Antarctica, and we have witnessed consistent and substantial ice losses from around much of its coastline.

“For some of the glaciers, including Ferrigno Ice Stream, the losses are especially pronounced, and, to understand why, we needed to acquire data about conditions beneath the ice surface.”

The team gathered the data using an ice-penetrating radar system towed behind a skidoo driven across the relatively flat ice surface, over a distance of 1500 miles – greater than that between London and Athens.

Dr Bingham continued: “What we found is that lying beneath the ice there is a large valley, parts of which are approximately a mile deeper than the surrounding landscape.

“If you stripped away all of the ice here today, you’d see a feature every bit as dramatic as the huge rift valleys you see in Africa and in size as significant as the Grand Canyon.

“This is at odds with the flat ice surface that we were driving across – without these measurements we would never have known that it was there.

“What’s particularly important is that this spectacular valley aligns perfectly with the recordings of ice-surface lowering and ice loss that we have witnessed with satellite observations over this area for the last twenty years.”

Co-author and geophysicist Dr Fausto Ferraccioli from British Antarctic Survey added: “The newly discovered Ferrigno Rift is part of a huge and yet poorly understood rift system that lies beneath the West Antarctic Ice Sheet.

“What this study shows is that this ancient rift basin, and the others discovered under the ice that connect to the warming ocean can influence contemporary ice flow and may exacerbate ice losses by steering coastal changes further inland.”

Professor David Vaughan, from British Antarctic Survey leads Ice2sea, a major EU-funded FP7 research programme to improve projections of global and regional sea-level. He said, “Thinning ice in West Antarctica is currently contributing nearly 10 per cent of global sea level rise. It’s important to understand this hot spot of change so we can make more accurate predictions for future sea level rise.”

The research in Nature is part of the British Antarctic Survey Icesheets Programme, which examines the role of ice sheets in the Earth System, and the processes that control ice-sheet change. It monitors current change and sets this in context with the past allowing more accurate projections for increases in global sea level to be made.

Hidden rift valley discovered beneath West Antarctica reveals new insight into ice loss

Scientists have discovered a one mile deep rift valley hidden beneath the ice in West Antarctica, which they believe is contributing to ice loss from this part of the continent.

Experts from the University of Aberdeen and British Antarctic Survey (BAS) made the discovery below Ferrigno Ice Stream, a region visited only once previously, over fifty years ago, in 1961, and one that is remote even by Antarctic standards.

Their findings, reported in Nature this week reveal that the ice-filled ancient rift basin is connected to the warming ocean which impacts upon contemporary ice flow and loss.

The West Antarctic Ice Sheet is of great scientific interest and societal importance as it is losing ice faster than any other part of Antarctica with some glaciers shrinking by more than one metre per year.

Understanding the processes that influence ice loss from West Antarctica is important to improve predictions of its future behaviour in a warming world.

Dr Robert Bingham, a glaciologist working in the University of Aberdeen’s School of Geosciences and lead author of the study, discovered the rift valley whilst undertaking three months of fieldwork with British Antarctic Survey in 2010.

Dr Bingham, whose fieldwork was funded by the UK’s Natural Environment Research Council (NERC) said: “Over the last 20 years we have used satellites to monitor ice losses from Antarctica, and we have witnessed consistent and substantial ice losses from around much of its coastline.

“For some of the glaciers, including Ferrigno Ice Stream, the losses are especially pronounced, and, to understand why, we needed to acquire data about conditions beneath the ice surface.”

The team gathered the data using an ice-penetrating radar system towed behind a skidoo driven across the relatively flat ice surface, over a distance of 1500 miles – greater than that between London and Athens.

Dr Bingham continued: “What we found is that lying beneath the ice there is a large valley, parts of which are approximately a mile deeper than the surrounding landscape.

“If you stripped away all of the ice here today, you’d see a feature every bit as dramatic as the huge rift valleys you see in Africa and in size as significant as the Grand Canyon.

“This is at odds with the flat ice surface that we were driving across – without these measurements we would never have known that it was there.

“What’s particularly important is that this spectacular valley aligns perfectly with the recordings of ice-surface lowering and ice loss that we have witnessed with satellite observations over this area for the last twenty years.”

Co-author and geophysicist Dr Fausto Ferraccioli from British Antarctic Survey added: “The newly discovered Ferrigno Rift is part of a huge and yet poorly understood rift system that lies beneath the West Antarctic Ice Sheet.

“What this study shows is that this ancient rift basin, and the others discovered under the ice that connect to the warming ocean can influence contemporary ice flow and may exacerbate ice losses by steering coastal changes further inland.”

Professor David Vaughan, from British Antarctic Survey leads Ice2sea, a major EU-funded FP7 research programme to improve projections of global and regional sea-level. He said, “Thinning ice in West Antarctica is currently contributing nearly 10 per cent of global sea level rise. It’s important to understand this hot spot of change so we can make more accurate predictions for future sea level rise.”

The research in Nature is part of the British Antarctic Survey Icesheets Programme, which examines the role of ice sheets in the Earth System, and the processes that control ice-sheet change. It monitors current change and sets this in context with the past allowing more accurate projections for increases in global sea level to be made.

An earthquake in a maze

The colored circles on the large map indicate the complex spatial rupture pattern as a function of time during the Sumatra earthquake in April 2012. The white star indicates the epicenter of the magnitude-8.6 mainshock. The area shaded in darker red in the inset indicates the location of the area of study. -  Caltech/Meng et al.
The colored circles on the large map indicate the complex spatial rupture pattern as a function of time during the Sumatra earthquake in April 2012. The white star indicates the epicenter of the magnitude-8.6 mainshock. The area shaded in darker red in the inset indicates the location of the area of study. – Caltech/Meng et al.

The powerful magnitude-8.6 earthquake that shook Sumatra on April 11, 2012, was a seismic standout for many reasons, not the least of which is that it was larger than scientists thought an earthquake of its type could ever be. Now, researchers from the California Institute of Technology (Caltech) report on their findings from the first high-resolution observations of the underwater temblor, they point out that the earthquake was also unusually complex-rupturing along multiple faults that lie at nearly right angles to one another, as though racing through a maze.

The new details provide fresh insights into the possibility of ruptures involving multiple faults occurring elsewhere-something that could be important for earthquake-hazard assessment along California’s San Andreas fault, which itself is made up of many different segments and is intersected by a number of other faults at right angles.

“Our results indicate that the earthquake rupture followed an exceptionally tortuous path, breaking multiple segments of a previously unrecognized network of perpendicular faults,” says Jean-Paul Ampuero, an assistant professor of seismology at Caltech and one of the authors of the report, which appears online today in Science Express. “This earthquake provided a rare opportunity to investigate the physics of such extreme events and to probe the mechanical properties of Earth’s materials deep beneath the oceans.”

Most mega-earthquakes occur at the boundaries between tectonic plates, as one plate sinks beneath another. The 2012 Sumatra earthquake is the largest earthquake ever documented that occurred away from such a boundary-a so-called intraplate quake. It is also the largest that has taken place on a strike-slip fault-the type of fault where the land on either side is pushing horizontally past the other.

The earthquake happened far offshore, beneath the Indian Ocean, where there are no geophysical monitoring sensors in place. Therefore, the researchers used ground-motion recordings gathered by networks of sensors in Europe and Japan, and an advanced source-imaging technique developed in Caltech’s Seismological Laboratory as well as the Tectonics Observatory to piece together a picture of the earthquake’s rupture process.

Lingsen Meng, the paper’s lead author and a graduate student in Ampuero’s group, explains that technique by comparing it with how, when standing in a room with your eyes closed, you can often still sense when someone speaking is walking across the room. “That’s because your ears measure the delays between arriving sounds,” Meng says. “Our technique uses a similar idea. We measure the delays between different seismic sensors that are recording the seismic movements at set locations.” Researchers can then use that information to determine the location of a rupture at different times during an earthquake. Recent developments of the method are akin to tracking multiple moving speakers in a cocktail party.

Using this technique, the researchers determined that the three-minute-long Sumatra earthquake involved at least three different fault planes, with a rupture propagating in both directions, jumping to a perpendicular fault plane, and then branching to another.

“Based on our previous understanding, you wouldn’t predict that the rupture would take these bends, which were almost right angles,” says Victor Tsai, an assistant professor of geophysics at Caltech and a coauthor on the new paper.

The team also determined that the rupture reached unusual depths for this type of earthquake-diving as deep as 60 kilometers in places and delving beneath the Earth’s crust into the upper mantle. This is surprising given that, at such depths, pressure and temperature increase, making the rock more ductile and less apt to fail. It has therefore been thought that if a stress were applied to such rocks, they would not react as abruptly as more brittle materials in the crust would. However, given the maze-like rupture pattern of the earthquake, the researchers believe another mechanism might be in play.

“One possible explanation for the complicated rupture is there might have been reduced friction as a result of interactions between water and the deep oceanic rocks,” says Tsai. “And,” he says, “if there wasn’t much friction on these faults, then it’s possible that they would slip this way under certain stress conditions.”

Adding to the list of the quake’s surprising qualities, the researchers pinpointed the rupture to a region of the seafloor where seismologists had previously considered such large earthquakes unlikely based on the geometry of identified faults. When they compared the location they had determined using source-imaging with high-resolution sonar data of the topography of the seafloor, the team found that the earthquake did not involve what they call “the usual suspect faults.”

“This part of the oceanic plate has fracture zones and other structures inherited from when the seafloor formed here, over 50 million years ago,” says Joann Stock, professor of geology at Caltech and another coauthor on the paper. “However, surprisingly, this earthquake just ruptured across these features, as if the older structure didn’t matter at all.”

Meng emphasizes that it is important to learn such details from previous earthquakes in order to improve earthquake-hazard assessment. After all, he says, “If other earthquake ruptures are able to go this deep or to connect as many fault segments as this earthquake did, they might also be very large and cause significant damage.”

An earthquake in a maze

The colored circles on the large map indicate the complex spatial rupture pattern as a function of time during the Sumatra earthquake in April 2012. The white star indicates the epicenter of the magnitude-8.6 mainshock. The area shaded in darker red in the inset indicates the location of the area of study. -  Caltech/Meng et al.
The colored circles on the large map indicate the complex spatial rupture pattern as a function of time during the Sumatra earthquake in April 2012. The white star indicates the epicenter of the magnitude-8.6 mainshock. The area shaded in darker red in the inset indicates the location of the area of study. – Caltech/Meng et al.

The powerful magnitude-8.6 earthquake that shook Sumatra on April 11, 2012, was a seismic standout for many reasons, not the least of which is that it was larger than scientists thought an earthquake of its type could ever be. Now, researchers from the California Institute of Technology (Caltech) report on their findings from the first high-resolution observations of the underwater temblor, they point out that the earthquake was also unusually complex-rupturing along multiple faults that lie at nearly right angles to one another, as though racing through a maze.

The new details provide fresh insights into the possibility of ruptures involving multiple faults occurring elsewhere-something that could be important for earthquake-hazard assessment along California’s San Andreas fault, which itself is made up of many different segments and is intersected by a number of other faults at right angles.

“Our results indicate that the earthquake rupture followed an exceptionally tortuous path, breaking multiple segments of a previously unrecognized network of perpendicular faults,” says Jean-Paul Ampuero, an assistant professor of seismology at Caltech and one of the authors of the report, which appears online today in Science Express. “This earthquake provided a rare opportunity to investigate the physics of such extreme events and to probe the mechanical properties of Earth’s materials deep beneath the oceans.”

Most mega-earthquakes occur at the boundaries between tectonic plates, as one plate sinks beneath another. The 2012 Sumatra earthquake is the largest earthquake ever documented that occurred away from such a boundary-a so-called intraplate quake. It is also the largest that has taken place on a strike-slip fault-the type of fault where the land on either side is pushing horizontally past the other.

The earthquake happened far offshore, beneath the Indian Ocean, where there are no geophysical monitoring sensors in place. Therefore, the researchers used ground-motion recordings gathered by networks of sensors in Europe and Japan, and an advanced source-imaging technique developed in Caltech’s Seismological Laboratory as well as the Tectonics Observatory to piece together a picture of the earthquake’s rupture process.

Lingsen Meng, the paper’s lead author and a graduate student in Ampuero’s group, explains that technique by comparing it with how, when standing in a room with your eyes closed, you can often still sense when someone speaking is walking across the room. “That’s because your ears measure the delays between arriving sounds,” Meng says. “Our technique uses a similar idea. We measure the delays between different seismic sensors that are recording the seismic movements at set locations.” Researchers can then use that information to determine the location of a rupture at different times during an earthquake. Recent developments of the method are akin to tracking multiple moving speakers in a cocktail party.

Using this technique, the researchers determined that the three-minute-long Sumatra earthquake involved at least three different fault planes, with a rupture propagating in both directions, jumping to a perpendicular fault plane, and then branching to another.

“Based on our previous understanding, you wouldn’t predict that the rupture would take these bends, which were almost right angles,” says Victor Tsai, an assistant professor of geophysics at Caltech and a coauthor on the new paper.

The team also determined that the rupture reached unusual depths for this type of earthquake-diving as deep as 60 kilometers in places and delving beneath the Earth’s crust into the upper mantle. This is surprising given that, at such depths, pressure and temperature increase, making the rock more ductile and less apt to fail. It has therefore been thought that if a stress were applied to such rocks, they would not react as abruptly as more brittle materials in the crust would. However, given the maze-like rupture pattern of the earthquake, the researchers believe another mechanism might be in play.

“One possible explanation for the complicated rupture is there might have been reduced friction as a result of interactions between water and the deep oceanic rocks,” says Tsai. “And,” he says, “if there wasn’t much friction on these faults, then it’s possible that they would slip this way under certain stress conditions.”

Adding to the list of the quake’s surprising qualities, the researchers pinpointed the rupture to a region of the seafloor where seismologists had previously considered such large earthquakes unlikely based on the geometry of identified faults. When they compared the location they had determined using source-imaging with high-resolution sonar data of the topography of the seafloor, the team found that the earthquake did not involve what they call “the usual suspect faults.”

“This part of the oceanic plate has fracture zones and other structures inherited from when the seafloor formed here, over 50 million years ago,” says Joann Stock, professor of geology at Caltech and another coauthor on the paper. “However, surprisingly, this earthquake just ruptured across these features, as if the older structure didn’t matter at all.”

Meng emphasizes that it is important to learn such details from previous earthquakes in order to improve earthquake-hazard assessment. After all, he says, “If other earthquake ruptures are able to go this deep or to connect as many fault segments as this earthquake did, they might also be very large and cause significant damage.”

Croscat Volcano may have been the last volcanic eruption in Spain 13,000 years ago

The volcanic region of La Garrotxa, with some forty volcanic cones and some twenty lava flows, is considered to be the best conserved region in the Iberian Peninsula. It is also the youngest volcanic area. Although the approximate age of some of these volcanic constructions is known, one of the main problems when studying volcanoes is to pinpoint the chronology of each of their eruptions. Several geochronological studies have been conducted, but existing data is scarce and imprecise. With regard to the chronology of the Croscat Volcano, considered one of the most recent volcanic constructions, the latest dating was obtained with the technique of thermoluminescence conducted in the 1980s.

A group of scientists from the Universitat Autònoma de Barcelona, the University of Girona and the Catalan Institute of Human Palaeoecology and Social Evolution (IPHES), together with researchers from the Garrotxa Volcanoes Natural Park and the environmental sector firms Axial Geologia i Medi Ambient and Tosca, developed a programme to locate chronologically the final moment of volcanic eruptions in the region.

Researchers recently published the first results in an article in the journal Geologica Acta. The first volcano they worked on was the Croscat Volcano. Soil dating was carried out using the C-14 dating method – very precise and easy to conduct in many laboratories – with the organic material found on the surface of the earth right before the moment of eruption.

“The general idea is based on the hypothesis that if scientists could date the palaeosoil found right below the lava clay ejected by the volcano, they would have the dating of the moment before the eruption” explains Maria Saña, researcher at the UAB Department of Prehistory.

Scientists perforated the clay found in the region of Pla del Torn, a few metres to the northeast of the volcanic cone. Two tests were carried out, at 12 and 15 metres deep, which reached the base of the clay layer and the surface of the palaeosoil.

Pollinic analysis was conducted with the samples obtained from the surface of this pre-volcano level. This aided scientists in learning about the vegetation of the area in the moment before the Croscat Volcano erupted. Several 14C analyses were later made to determine the organic material contained in the samples.

The palynological analysis of the soil at the time of eruption, conducted by IPHES, revealed that the landscape of La Garrotxa was quite open, with Mediterranean meadows and steppes cotaining gramineae, asteraceae and artemisia. Oaks and holm oaks were also discovered, which indicates that temperatures were mild, a symptom of the beginning of the thawing period following the last Ice Age. The presence of riverside trees (elms, alders and willows), as well as aquatic herbs and plants (cyperaceae, bulrush, alisma, etc.) are proof that during that period there was also an increase in rainfalls.

Dating has shown that the age of the upper part of the soil dates back approximately between 13,270 and 13,040 years and that immediately after that moment the eruption of the Croscat Volcano took place.

Croscat Volcano may have been the last volcanic eruption in Spain 13,000 years ago

The volcanic region of La Garrotxa, with some forty volcanic cones and some twenty lava flows, is considered to be the best conserved region in the Iberian Peninsula. It is also the youngest volcanic area. Although the approximate age of some of these volcanic constructions is known, one of the main problems when studying volcanoes is to pinpoint the chronology of each of their eruptions. Several geochronological studies have been conducted, but existing data is scarce and imprecise. With regard to the chronology of the Croscat Volcano, considered one of the most recent volcanic constructions, the latest dating was obtained with the technique of thermoluminescence conducted in the 1980s.

A group of scientists from the Universitat Autònoma de Barcelona, the University of Girona and the Catalan Institute of Human Palaeoecology and Social Evolution (IPHES), together with researchers from the Garrotxa Volcanoes Natural Park and the environmental sector firms Axial Geologia i Medi Ambient and Tosca, developed a programme to locate chronologically the final moment of volcanic eruptions in the region.

Researchers recently published the first results in an article in the journal Geologica Acta. The first volcano they worked on was the Croscat Volcano. Soil dating was carried out using the C-14 dating method – very precise and easy to conduct in many laboratories – with the organic material found on the surface of the earth right before the moment of eruption.

“The general idea is based on the hypothesis that if scientists could date the palaeosoil found right below the lava clay ejected by the volcano, they would have the dating of the moment before the eruption” explains Maria Saña, researcher at the UAB Department of Prehistory.

Scientists perforated the clay found in the region of Pla del Torn, a few metres to the northeast of the volcanic cone. Two tests were carried out, at 12 and 15 metres deep, which reached the base of the clay layer and the surface of the palaeosoil.

Pollinic analysis was conducted with the samples obtained from the surface of this pre-volcano level. This aided scientists in learning about the vegetation of the area in the moment before the Croscat Volcano erupted. Several 14C analyses were later made to determine the organic material contained in the samples.

The palynological analysis of the soil at the time of eruption, conducted by IPHES, revealed that the landscape of La Garrotxa was quite open, with Mediterranean meadows and steppes cotaining gramineae, asteraceae and artemisia. Oaks and holm oaks were also discovered, which indicates that temperatures were mild, a symptom of the beginning of the thawing period following the last Ice Age. The presence of riverside trees (elms, alders and willows), as well as aquatic herbs and plants (cyperaceae, bulrush, alisma, etc.) are proof that during that period there was also an increase in rainfalls.

Dating has shown that the age of the upper part of the soil dates back approximately between 13,270 and 13,040 years and that immediately after that moment the eruption of the Croscat Volcano took place.

Fools’ gold found to regulate oxygen

As sulfur cycles through Earth’s atmosphere, oceans and land, it undergoes chemical changes that are often coupled to changes in other such elements as carbon and oxygen. Although this affects the concentration of free oxygen, sulfur has traditionally been portrayed as a secondary factor in regulating atmospheric oxygen, with most of the heavy lifting done by carbon. However, new findings that appeared this week in Science suggest that sulfur’s role may have been underestimated.

Drs. Itay Halevy of the Weizmann Institute’s Environmental Science and Energy Research Department (Faculty of Chemistry), Shanan Peters of the University of Wisconsin and Woodward Fischer of the California Institute of Technology, were interested in better understanding the global sulfur cycle over the last 550 million years – roughly the period in which oxygen has been at its present atmospheric level of around 20%. They used a database developed and maintained by Peters at the University of Wisconsin, called Macrostrat, which contains detailed information on thousands of rock units in North America and beyond.

The researchers used the database to trace one of the ways in which sulfur exits ocean water into the underlying sediments – the formation of so-called sulfate evaporite minerals. These sulfur-bearing minerals, such as gypsum, settle to the bottom of shallow seas as seawater evaporates. The team found that the formation and burial of sulfate evaporites were highly variable over the last 550 million years, due to changes in shallow sea area, the latitude of ancient continents and sea level. More surprising to Halevy and colleagues was the discovery that only a relatively small fraction of the sulfur cycling through the oceans has exited seawater in this way. Their research showed that the formation and burial of a second sulfur-bearing mineral – pyrite – has apparently been much more important.

Pyrite is an iron-sulfur mineral (also known as fools’ gold), which forms when microbes in seafloor sediments use the sulfur dissolved in seawater to digest organic matter. The microbes take up sulfur in the form of sulfate (bound to four oxygen atoms) and release it as sulfide (with no oxygen). Oxygen is released during this process, thus making it a source of oxygen in the air. But because this part of the sulfur cycle was thought be minor in comparison to sulfate evaporite burial, (which does not release oxygen) its effect on oxygen levels was also thought to be unimportant.

In testing various theoretical models of the sulfur cycle against the Macrostrat data, the team realized that the production and burial of pyrite has been much more significant than previously thought, accounting for more than 80% of all sulfur removed from the ocean (rather than the 30-40% in prior estimates). As opposed to the variability they saw for sulfate evaporite burial, pyrite burial has been relatively stable throughout the period. The analysis also revealed that most of the sulfur entering the ocean washed in from the weathering of pyrite exposed on land. In other words, there is a balance between pyrite formation and burial, which releases oxygen, and the weathering of pyrite on land, which consumes it. The implication of these findings is that the sulfur cycle regulates the atmospheric concentration of oxygen more strongly than previously appreciated.

Fools’ gold found to regulate oxygen

As sulfur cycles through Earth’s atmosphere, oceans and land, it undergoes chemical changes that are often coupled to changes in other such elements as carbon and oxygen. Although this affects the concentration of free oxygen, sulfur has traditionally been portrayed as a secondary factor in regulating atmospheric oxygen, with most of the heavy lifting done by carbon. However, new findings that appeared this week in Science suggest that sulfur’s role may have been underestimated.

Drs. Itay Halevy of the Weizmann Institute’s Environmental Science and Energy Research Department (Faculty of Chemistry), Shanan Peters of the University of Wisconsin and Woodward Fischer of the California Institute of Technology, were interested in better understanding the global sulfur cycle over the last 550 million years – roughly the period in which oxygen has been at its present atmospheric level of around 20%. They used a database developed and maintained by Peters at the University of Wisconsin, called Macrostrat, which contains detailed information on thousands of rock units in North America and beyond.

The researchers used the database to trace one of the ways in which sulfur exits ocean water into the underlying sediments – the formation of so-called sulfate evaporite minerals. These sulfur-bearing minerals, such as gypsum, settle to the bottom of shallow seas as seawater evaporates. The team found that the formation and burial of sulfate evaporites were highly variable over the last 550 million years, due to changes in shallow sea area, the latitude of ancient continents and sea level. More surprising to Halevy and colleagues was the discovery that only a relatively small fraction of the sulfur cycling through the oceans has exited seawater in this way. Their research showed that the formation and burial of a second sulfur-bearing mineral – pyrite – has apparently been much more important.

Pyrite is an iron-sulfur mineral (also known as fools’ gold), which forms when microbes in seafloor sediments use the sulfur dissolved in seawater to digest organic matter. The microbes take up sulfur in the form of sulfate (bound to four oxygen atoms) and release it as sulfide (with no oxygen). Oxygen is released during this process, thus making it a source of oxygen in the air. But because this part of the sulfur cycle was thought be minor in comparison to sulfate evaporite burial, (which does not release oxygen) its effect on oxygen levels was also thought to be unimportant.

In testing various theoretical models of the sulfur cycle against the Macrostrat data, the team realized that the production and burial of pyrite has been much more significant than previously thought, accounting for more than 80% of all sulfur removed from the ocean (rather than the 30-40% in prior estimates). As opposed to the variability they saw for sulfate evaporite burial, pyrite burial has been relatively stable throughout the period. The analysis also revealed that most of the sulfur entering the ocean washed in from the weathering of pyrite exposed on land. In other words, there is a balance between pyrite formation and burial, which releases oxygen, and the weathering of pyrite on land, which consumes it. The implication of these findings is that the sulfur cycle regulates the atmospheric concentration of oxygen more strongly than previously appreciated.