10 million years to recover from mass extinction

It took some 10 million years for Earth to recover from the greatest mass extinction of all time, latest research has revealed.

Life was nearly wiped out 250 million years ago, with only 10 per cent of plants and animals surviving. It is currently much debated how life recovered from this cataclysm, whether quickly or slowly.

Recent evidence for a rapid bounce-back is evaluated in a new review article by Dr Zhong-Qiang Chen, from the China University of Geosciences in Wuhan, and Professor Michael Benton from the University of Bristol. They find that recovery from the crisis lasted some 10 million years, as explained today [27 May] in Nature Geoscience.

There were apparently two reasons for the delay, the sheer intensity of the crisis, and continuing grim conditions on Earth after the first wave of extinction.

The end-Permian crisis, by far the most dramatic biological crisis to affect life on Earth, was triggered by a number of physical environmental shocks – global warming, acid rain, ocean acidification and ocean anoxia. These were enough to kill off 90 per cent of living things on land and in the sea.

Dr Chen said: “It is hard to imagine how so much of life could have been killed, but there is no doubt from some of the fantastic rock sections in China and elsewhere round the world that this was the biggest crisis ever faced by life.

Current research shows that the grim conditions continued in bursts for some five to six million years after the initial crisis, with repeated carbon and oxygen crises, warming and other ill effects.

Some groups of animals on the sea and land did recover quickly and began to rebuild their ecosystems, but they suffered further setbacks. Life had not really recovered in these early phases because permanent ecosystems were not established.

Professor Benton, Professor of Vertebrate Palaeontology at the University of Bristol, said: “Life seemed to be getting back to normal when another crisis hit and set it back again. The carbon crises were repeated many times, and then finally conditions became normal again after five million years or so.”

Finally, after the environmental crises ceased to be so severe, more complex ecosystems emerged. In the sea, new groups, such as ancestral crabs and lobsters, as well as the first marine reptiles, came on the scene, and they formed the basis of future modern-style ecosystems.

Professor Benton added: “We often see mass extinctions as entirely negative but in this most devastating case, life did recover, after many millions of years, and new groups emerged. The event had re-set evolution. However, the causes of the killing – global warming, acid rain, ocean acidification – sound eerily familiar to us today. Perhaps we can learn something from these ancient events.”

Geological record shows air up there came from below

The influence of the ground beneath us on the air around us could be greater than scientists had previously thought, according to new research that links the long-ago proliferation of oxygen in Earth’s atmosphere to a sudden change in the inner workings of our planet.

Princeton University researchers report in the journal Nature that rocks preserved in the Earth’s crust reveal that a steep decline in the intensity of melting within the planet’s mantle – the hot, heat-transferring rock layer between the crust and molten outer core – brought about ideal conditions for the period known as the Great Oxygenation Event (GOE) that occurred roughly 2.5 billion years ago.

During the GOE – which may have lasted up to 900 million years – oxygen levels in the atmosphere exploded and eventually gave rise to our present atmosphere.

Blair Schoene, a Princeton assistant professor of geosciences, and lead author C. Brenhin Keller, a Princeton geosciences doctoral student, compiled a database of more than 70,000 geological samples to construct a 4-billion-year geochemical timeline. Their analysis uncovered a sharp drop in mantle melting 2.5 billion years ago that coincides with existing rock evidence of atmospheric changes related to the GOE.

Based on this correlation, the researchers suggest in Nature that diminished melting in the mantle decreased the depth of melting in the Earth’s crust, which in turn reduced the output of reactive, iron oxide-based volcanic gases into the atmosphere. A lower concentration of these gases – which react with and remove oxygen from the atmosphere – allowed free oxygen molecules to proliferate.

The Princeton research offers the strongest data-driven correlation yet between deep Earth processes and the GOE, Schoene said. Previous hypotheses are largely based on qualitative observations of the rock record and computational models that simulate how this rapid oxygenation might have occurred. The Princeton research, however, is based on a statistical analysis of the geologic record and the chemical traces of deep-Earth activity it has preserved, Schoene said.

“The perspective behind past efforts to connect geologic processes to the Great Oxygenation Event has been hypothetical, saying that ‘If the Earth had been X, there would have been reaction Y,'” Schoene said. “But these ideas cannot be tested experimentally because they are largely notional. In our paper, we have the evidence to say, ‘The Earth was like this,’ and then propose a hypothesis that can be tested by examining the same rich database of mantle and deep-crust changes we used in our work.”

A change in subsurface activity around the time of the GOE has been noted before, Keller explained. But evidence of that shift is geochemically subtle, especially after billions of years. The database he and Schoene created allowed them to show more precisely how the geochemical makeup of the crust changed through time, resulting in a more detailed hypotheses about how this would affect the atmosphere, Keller said.

“Research in this area has been largely qualitative, but with this much data, we can pick up finer features in the geologic record, particularly a level of detail related to this sudden change 2.5 billion years ago that people had not seen with such clarity before,” Keller said.

A missing piece of the GOE puzzle?

Woodward Fischer, an assistant professor of geobiology at the California Institute of Technology who specializes in the GOE, said that the Princeton research could help shed more light on an important factor in Earth’s oxygenation that is not well understood. Fischer is familiar with the paper but had no role in it.

The dominant theory of oxygenation is that an abundance of photosynthetic life emerged some hundreds of millions of years before the GOE and began producing oxygen via photosynthesis, Fischer said. The problem is that this output would not have been enough to overcome “sinks” that were absorbing more oxygen from the atmosphere than was being put into it. So, a lingering question is what happened to those sinks to bring about oxygenation.

Keller and Schoene show how one of the primary sinks – volcanic gases – might have suddenly been neutralized, Fischer said. The exact effect this would have had on atmospheric oxygen levels is difficult to know – even recent fluctuations are hard to gauge, he said. Nonetheless, the clear and objective data the researchers use strongly suggests that a quick reduction in volcanic gases brought about by a drop in mantle-melt intensity was an important precursor to oxygenation, Fischer said.

“This paper offers a really striking assessment of changes occurring in the solid Earth that greatly helped set the stage for one of the most marked environmental transitions in Earth history,” Fischer said.

“And their methodology precludes a strong tendency that researchers, as humans invested in our work, have to look for anecdotal geological evidence and conclude based on coincidence that events co-occurring in time must have been related,” Fischer said. “The statistical approach taken by the authors in this paper really lets the data shine and reveals that there were important secular changes in the way the Earth made igneous rocks, and that these changes were possibly part of an interplay between life and deep-Earth processes.”

Keller and Schoene fashioned their expansive database from previously reported rock and trace element analyses, which are increasingly available through online databases. They focused on changes in the chemical composition of basalt, a byproduct of melting in the Earth’s mantle.

When melting in the mantle is high, Keller said, basalt contains greater concentrations of “compatible” elements such as chromium and magnesium that are ordinarily found in the mantle. Less intense melting, on the other hand, results in basalt with a higher content of incompatible elements such as sodium and potassium that are found closer to the Earth’s surface.

From their examination, Keller and Schoene saw that the Earth’s mantle has undergone a gradual cooling since the planet’s early history, which is consistent with scientists’ expectations based on heat loss at the Earth’s surface. Around 2.5 billion years ago, however, the levels of compatible elements in the sampled basalt plummeted, indicating that the magnitude of melting deep in the mantle dropped off suddenly.

Keller and Schoene confirmed their findings by checking them against existing analyses of crust-level “felsic” rocks such as granite, which form when hot basalt merges with other minerals. Heightened melt activity in the mantle leads to deeper melting in the Earth’s crust, and felsic rocks can indicate the intensity of mantle melting, Keller said.

The researchers conclude that when melting happens at a great depth in the crust then the concentration of the iron-oxide gases in magma increases. When emitted into the air by volcanoes, these gases bond with free oxygen and essentially remove it from the air. On the other hand, when crust melting becomes shallower, as they observed, atmospheric levels of those volcanic gases drop and free oxygen molecules can flourish.

Connecting the Earth’s systems

In a broader sense, said Schoene, his and Keller’s research depicts a close interaction between the Earth’s geologic and biological systems that is becoming more apparent. “In science, it is becoming increasingly obvious that seemingly different systems act together and the question is how,” Schoene said.

“Overall, this analysis strengthens emerging arguments that interaction between the solid Earth and biosphere are very intimate and important,” he said. “This is strong evidence of how biological and geological systems might work together, and it suggests that important planetary change is not simply the result of life dragging the rest of the planet along.”

Fischer of Caltech added that this interplay of systems applies to various events in the planet’s history – such as mass extinctions – that are the result of multiple factors both above and below the Earth’s surface. Decidedly more difficult is tracing how these events influenced one another and ultimately led to a greater planetary change, he said.

“Because of the complicated questions of how solid Earth changes lead to biological innovations, scientists now have to start thinking deeply and working across the boundaries of what have traditionally been pretty rigid subdisciplines in the Earth sciences,” Fischer said.

“It’s clear from research like this,” he said, “that there is hay to be made by interdisciplinary efforts to connect processes and mechanisms from the solid to the fluid Earth, and to understand that interplay with an ever-evolving biology.”

LiDAR technology reveals faults near Lake Tahoe

Results of a new U.S. Geological Survey study conclude that faults west of Lake Tahoe, Calif., referred to as the Tahoe-Sierra frontal fault zone, pose a substantial increase in the seismic hazard assessment for the Lake Tahoe region of California and Nevada, and could potentially generate earthquakes with magnitudes ranging from 6.3 to 6.9. A close association of landslide deposits and active faults also suggests that there is an earthquake-induced landslide hazard along the steep fault-formed range front west of Lake Tahoe.

Using a new high-resolution imaging technology, known as bare-earth airborne LiDAR (Light Detection And Ranging), combined with field observations and modern geochronology, USGS scientists, and their colleagues from the University of Nevada, Reno; the University of California, Berkeley; and the U.S. Army Corps of Engineers, have confirmed the existence of previously suspected faults.

LiDAR imagery allows scientists to “see” through dense forest cover and recognize earthquake faults that are not detectable with conventional aerial photography.

“This study is yet one more stunning example of how the availability of LiDAR information to precisely and accurately map the shape of the solid Earth surface beneath vegetation is revolutionizing the geosciences,” said USGS Director Marcia McNutt. “From investigations of geologic hazards to calculations of carbon stored in the forest canopy to simply making the most accurate maps possible, LiDAR returns its investment many times over.”

Motion on the faults has offset linear moraines (the boulders, cobbles, gravel, and sand deposited by an advancing glacier) providing a record of tectonic deformation since the moraines were deposited. The authors developed new three-dimensional techniques to measure the amount of tectonic displacement of moraine crests caused by repeated earthquakes. Dating of the moraines from the last two glaciations in the Tahoe basin, around 21 thousand and 70 thousand years ago, allowed the study authors to calculate the rates of tectonic displacement.

“Although the Tahoe-Sierra frontal fault zone has long been recognized as forming the tectonic boundary between the Sierra Nevada to the west, and the Basin and Range Province to the east, its level of activity and hence seismic hazard was not fully recognized because dense vegetation obscured the surface expressions of the faults,” said USGS scientist and lead author, James Howle. “Using the new LiDAR technology has improved and clarified previous field mapping, has provided visualization of the surface expressions of the faults, and has allowed for accurate measurement of the amount of motion that has occurred on the faults. The results of the study demonstrate that the Tahoe-Sierra frontal fault zone is an important seismic source for the region.”

Autopsy of an eruption: Linking crystal growth to volcano seismicity

How processes below a volcano are linked to seismic signals at the surface is described by scientists from the petrology group of the Ruhr-Universität Bochum and their colleagues from Bristol in a paper published today in Science. They analyzed the growth of crystals in the magma chamber and used results obtained from the monitoring of seismic signals. The research could ultimately help to predict future volcanic eruptions with greater accuracy.

Like tree rings: Crystals in a magma chamber

A few kilometers below the volcano a liquid reservoir exists, the magma chamber, which feeds volcanic eruptions. Zoned crystals grow concentrically like tree rings within the magma body and contain critical information. Individual zones have subtly different chemical compositions, reflecting the changes in physical conditions (for example the temperature) within the magma chamber and thus give an indication of volcanic processes and the timescales over which they occur. During a volcanic eruption, crystals are thrown to the surface in conjunction with the liquid parts of the magma, which quickly petrifies and thus can be sampled.

Mount St. Helens

The researchers analyzed the chemical composition of crystals from Mount St. Helens and linked these data to seismic observations of the deadly 1980 Mount St. Helens eruption. The peaks in crystal growth were found to correlate with increased seismicity and gas emissions in the months prior to the eruption. An increase in crystal growth is also evidence of pulses of magma entering a growing chamber within the volcano, which finally triggers the eruption. In this way, the researchers confirmed what has long been anticipated: a clear evidence of the correlation between crystal growth (fresh magma input) and volcanic seismicity.

Time scales: An expertise of Bochum

The extraction of time scales of different kinds of processes from zoned crystals is an expertise of the petrology group at the Institute for Geology, Mineralogy, and Geophysics in Bochum. A similar study on eruptions from another active volcano, Mt. Etna in Italy, was carried out by Bochum scientists in collaboration with scientists from Singapore and Pisa (published in Earth and Planetary Science Letters, 2011). For these kinds of studies the researchers use information on how fast certain elements move through minerals (diffusion). The determination of diffusion rates in minerals is another research focus of the petrologists in Bochum.

A relevant study for millions of people

Over 500 million people live close to volcanoes which may erupt with little or no clear warning, causing widespread devastation, disruption to aviation and even global effects on climate. Many of the world’s volcanoes are monitored for changes such as increases in seismicity or ground deformation. However, an on-going problem for volcanologists is linking observations at the surface to processes occurring underground. This forensic approach applied by the English-German team can be also applied to other active volcanoes to shed new light upon the nature and timescale of pre-eruptive activity. This will help scientists to evaluate monitoring signals at restless volcanoes and enable better forecasting of future eruptions.

Visualizing the imprints of past and present Earth dynamics

New Lithosphere articles posted online 16 May 2012 report on (1) seismic anisotropy measured beneath 14 broadband stations in southeastern India; (2) why geoscientists should persist in their efforts to reach and study such spectacular sub-sea geologic features as the Mariana Trench (recently explored by film director James Cameron) and how “land geologists” can help this effort by studying on-land equivalents like ophiolites; and (3) pressures and melting temperatures of sediments deeply buried in Earth’s mantle.


Seismic anisotropy beneath the eastern Dharwar Craton
Sunil Kumar Roy et al., National Geophysical Research Institute, Seismic Hazard Group, Hyderabad 500007, India. Posted online 16 May 2012; doi: 10.1130/L198.1.

Seismic anisotropy is an intrinsic property of the Earth that imparts a directional dependence to the velocity of elastic waves and carries imprints of past and present deformation. Due to this phenomenon, a shear wave passing through an anisotropic medium gets polarized in a particular direction and splits into two orthogonal waves, with one wave traveling faster than the other. Analysis of the nature and difference in the arrival times of the fast and slow waves registered at a seismic station enables Sunil Kumar Roy and colleagues to parameterize anisotropy in terms of the delay time and fast polarization direction. They estimate the nature of anisotropy beneath 14 broadband stations in southeastern India, utilizing the core refracted (SKS, SKKS) and direct S waves to obtain a total of 113 high-quality measurements of delay time and fast polarization direction. The delay time between the fast and slow axes tend to cluster around 0.8 s, slightly lower than that observed globally for continental shield regions (~1 s). The fast directions at a majority of stations are in accordance with the present-day motion of the Indian plate, suggesting that the shear at the base of the Indian lithosphere is the primary cause of anisotropy. Interestingly, this study also brings out the effect of anisotropy frozen in the lithosphere due to past tectonic episodes. For example, stations in the vicinity of the east coast of India reveal a coast parallel trend, suggesting that anisotropy in the underlying medium may be the imprint of continental rifting that separated India from the rest of Gondwana.


To understand subduction initiation, study forearc crust: To understand forearc crust, study ophiolites
R.J. Stern et al., Geosciences Dept., The University of Texas at Dallas, Richardson, Texas 75083-0688, USA. Posted online 16 May 2012; doi: 10.1130/L183.1.

Subduction is the process by which seafloor (oceanic crust and upper mantle) is returned to Earth’s interior. Subduction is what powers the plates and thus may be the most important solid Earth process. Subduction results in spectacular geologic features, including “island arc” volcanoes like those of the U.S. Cascades and trenches like the Mariana Trench, which has recently been explored by film director James Cameron. As a result of studying many convergent plate margins around the world, geoscientists have a good understanding of how mature subduction zones operate but know far less about how new subduction zones form. In this paper, R.J. Stern and colleagues emphasize the importance of studying the igneous rocks of the ~100-mile-wide “forearc” region, which lies between the arc volcanoes and the trench, for understanding how new subduction zones are generated. Forearc igneous rocks preserve an outstanding record of how new subduction zones form, but direct study is difficult because forearcs are buried beneath younger sediments and often lie in the deepest parts of the ocean, where deep-sea studies require expensive research vessels and submersibles. This article explores why geoscientists must continue to study in situ forearcs and how land geologists can help this effort by studying on-land equivalents of forearc crust known as “ophiolites.” Ophiolites are found on all continents, and they are important targets for geoscientific study because they present an opportunity for better understanding of the composition and origin of forearc crust and how new subduction zones form.


Melting of metasedimentary Rocks at Ultrahigh Pressure — Insights from Experiments and Thermodynamic Calculations
H.-J. Massonne and T. Fockenberg, Institut für Mineralogie und Kristallchemie, Universität Stuttgart, Azenbergstrasse 18, D-70174 Stuttgart, Germany. Posted online 16 May 2012; doi: 10.1130/L185.1.

H.-J. Massonne and T. Fockenberg use high pressure experiments at temperatures of 950 to 1400 degrees Celsius to simulate the melting of sediments deeply buried into Earth’s mantle by geodynamic processes. Experimental pressures were at and above 3 GPa (greater than or equal to 100 km Earth depths). Temperatures close to 1000 and 1100 degrees Celsius at 3 GPa and 5 GPa, respectively, were sufficient to produce initial melts from the selected rocks. At a temperature of about 350 degrees Celsius above these temperatures, the rocks were completely molten. In addition, the melting was modeled by complex calculations using thermodynamic data for minerals and melt. Both methods resulted in initial melt compositions rich in water and potassium. With rising temperatures the melts become granitic with garnet plus coesite plus or minus kyanite as remaining solid phases. The new data were applied to natural diamondiferous rocks with sedimentary whole-rock compositions from the Erzgebirge in central Europe and the Kokchetav Massif in northern Kazakhstan. According to previously reported microfabrics etc. of these rocks, pointing to their partial melting and crystallization of diamond from the melt, the rocks would have been as hot as 1400 degrees Celsius (Erzgebirge) and 1200 degrees Celsius (Kokchetav Massif) once, probably at pressures of around 7 GPa. Furthermore, Massonne and Fockenberg conclude that granitic melts could also have been produced in deep mantle regions and not exclusively in lower portions of Earth’s crust in the past.

Sumatra faces yet another risk — major volcanic eruptions

The early April earthquake of magnitude 8.6 that shook Sumatra was a grim reminder of the devastating earthquakes and tsunami that killed tens of thousands of people in 2004 and 2005.

Now a new study, funded by the National Science Foundation, shows that the residents of that region are at risk from yet another potentially deadly natural phenomenon – major volcanic eruptions.

Researchers from Oregon State University working with colleagues in Indonesia have documented six major volcanic eruptions in Sumatra over the past 35,000 years – most equaling or surpassing in explosive intensity the eruption of Washington’s Mount St. Helens in 1980.

Results of the research have just been published in the Journal of Volcanology and Geothermal Research.

“Sumatra has a number of active and potentially explosive volcanoes and many show evidence of recent activity,” said Morgan Salisbury, lead author on the study, who recently completed his doctoral studies in OSU’s College of Earth, Ocean, and Atmospheric Sciences. “Most of the eruptions are small, so little attention has been paid to the potential for a catastrophic eruption.

“But our study found some of the first evidence that the region has a much more explosive history than perhaps has been appreciated,” he added.

Until this study, little was known about Sumatra’s volcanic history – in part because few western scientists have been allowed access to the region. The most visible evidence of recent volcanic activity among the estimated 33-35 potentially active volcanoes are their steep-sided cones and lack of vegetation, indicating at least some minor eruptive processes.

But in 2007, an expedition led by OSU’s Chris Goldfinger was permitted into the region and the Oregon State researchers and their Indonesian colleagues set out to explore the earthquake history of the region by studying sediment cores from the Indian Ocean. Funded by the National Science Foundation, it was the first research ship from the United States allowed into Indonesia/Sumatran waters in nearly 30 years.

While searching the deep-sea sediment cores for “turbidites” – coarse gravel deposits that can act as a signature for earthquakes – they noticed unmistakable evidence of volcanic ash and began conducting a parallel investigation into the region’s volcanic history.

“The ash was located only in certain cores, so the activity was localized,” said Adam Kent, a professor of geosciences at OSU and an author on the study. “Yet the eruptions still were capable of spreading the ash for 300 kilometers or more, which gave us an indication of how powerful the explosive activity might have been.”

Salisbury and his colleagues found evidence of six major eruptions and estimated them to be at least from 3.0 to 5.0 on the Volcanic Explosivity Index. Mount St. Helens, by comparison, was 5.0.

The Indian Ocean region is certainly known to have a violent volcanic history. The 1883 eruption of Krakatoa between Sumatra and Java is perhaps the most violent volcanic explosion in recorded history, measuring 6.0 on the VEI and generating what many scientists believe to have been one of the loudest noises ever heard on Earth.

Sumatra’s own Toba volcano exploded about 74,000 years ago, generating a major lake – not unlike Oregon’s own Crater Lake, but much larger. “It looks like a giant doughnut in the middle of Sumatra,” said Jason “Jay” Patton, another OSU doctoral student and author on the study.

Sumatra’s volcanoes occasionally belch some ash and smoke, and provide comparatively minor eruptions, but residents there may not be fully aware of the potential catastrophic nature of some of its resident volcanoes, Goldfinger said.

“Prior to 2004, the risk from a major earthquake were not widely appreciated except, perhaps, in some of the more rural areas,” Goldfinger said. “And earthquakes happen more frequently than major volcanic eruptions. If it hasn’t happened in recent memory?”

Kent said the next step in the research is to work with scientists from the region to collect ash and volcanic rock from the island’s volcanoes, and then match their chemical signature to the ash they discovered in the sediment cores.

“Each volcano has a subtly different fingerprint,” Kent said, “so if we can get the terrestrial data, we should be able to link the six major eruptions to individual volcanoes to determine the ones that provide the greatest risk factors.”

Chocolate and diamonds: Why volcanoes could be a girl’s best friend

Kimberlite volcanoes, the primary source of diamonds, contain pelletal lapilli -- enigmatic magma-coated clasts. These are generated deep in the volcanic vent by a granulation process analogous to that commonly used in coating chocolates, drugs and fertilizers. -  University of Southampton
Kimberlite volcanoes, the primary source of diamonds, contain pelletal lapilli — enigmatic magma-coated clasts. These are generated deep in the volcanic vent by a granulation process analogous to that commonly used in coating chocolates, drugs and fertilizers. – University of Southampton

Scientists from the University of Southampton have discovered a previously unrecognized volcanic process, similar to one that is used in chocolate manufacturing, which gives important new insights into the dynamics of volcanic eruptions.

The scientists investigated how a process called ‘fluidized spray granulation’ can occur during kimberlite eruptions to produce well-rounded particles containing fragments from the Earth’s mantle, most notably diamonds. This physical process is similar to the gas injection and spraying process used to form smooth coatings on confectionary, and layered and delayed-release coatings in the manufacture of pharmaceuticals and fertilizers.

Kimberlite volcanoes are the primary source of diamonds on Earth, and are formed by gas-rich magmas from mantle depths of over 150 km. Kimberlite volcanism involves high-intensity explosive eruptions, forming diverging pipes or ‘diatremes’, which can be several hundred metres wide and several kilometers deep. A conspicuous and previously mysterious feature of these pipes are ‘pelletal lapilli ‘ – well-rounded magma coated fragments of rock consisting of an inner ‘seed’ particle with a complex rim, thought to represent quenched magma.

These pelletal lapilli form by spray granulation when kimberlite magma intrudes into earlier volcaniclastic infill close to the diatreme root zone. Intensive degassing produces a gas jet in which the seed particles are simultaneously fluidized and coated by a spray of low-viscosity melt.

In kimberlites, the occurrence of pelletal lapilli is linked to diamond grade (carats per tonne), size and quality, and therefore has economic as well as academic significance.

Dr Thomas Gernon, Lecturer in Earth Science at the University of Southampton, says: “The origin of pelletal lapilli is important for understanding how magmatic pyroclasts are transported to the surface during explosive eruptions, offering fundamental new insights into eruption dynamics and constraints on vent conditions, notably gas velocity.”

“The ability to tightly constrain gas velocities is significant, as it enables estimation of the maximum diamond size transported in the flow. Gas fluidisation and magma-coating processes are also likely to affect the diamond surface properties.”

Dr Gernon and colleagues studied two of the world’s largest diamond mines in South Africa and Lesotho. In the Letseng pipe in Lesotho, pelletal lapilli have been found in association with concentrations of large diamonds (up to 215 carat), which individually can fetch up to tens of millions of pounds. Knowledge of flow dynamics will inform models of mineral transport, and ultimately could improve resource assessments.

Dr Gernon, who is based at the National Oceanography Centre at Southampton’s waterfront campus, says: “This multidisciplinary research, incorporating Earth sciences, chemical and mechanical engineering, provides evidence for fluidised granulation in natural systems which will be of considerable interest to engineers and chemical, pharmaceutical and food scientists who use this process routinely. The scale and complexity of this granulation process is unique, as it has not previously been recognised in natural systems.”

The paper ‘The origin of pelletal lapilli in explosive kimberlite eruptions’ is published in the latest issue of Nature Communications.

Researchers gain greater insight into earthquake cycles

This image shows an array of geodetic instruments at the surface of Earth and activity that was modeled on the fault below. The yellow colors indicate the highest speeds of slippage between plates along the San Andreas Fault. The reddish colors represent slower seismic speeds and the bluish colors indicate slippage at velocity close to the long-term advance of the San Andreas Fault. The dark color indicates a portion of the fault where the velocity is so small that it appears completely locked. -  Sylvain Barbot / Caltech
This image shows an array of geodetic instruments at the surface of Earth and activity that was modeled on the fault below. The yellow colors indicate the highest speeds of slippage between plates along the San Andreas Fault. The reddish colors represent slower seismic speeds and the bluish colors indicate slippage at velocity close to the long-term advance of the San Andreas Fault. The dark color indicates a portion of the fault where the velocity is so small that it appears completely locked. – Sylvain Barbot / Caltech

For those who study earthquakes, one major challenge has been trying to understand all the physics of a fault-both during an earthquake and at times of “rest”-in order to know more about how a particular region may behave in the future. Now, researchers at the California Institute of Technology (Caltech) have developed the first computer model of an earthquake-producing fault segment that reproduces, in a single physical framework, the available observations of both the fault’s seismic (fast) and aseismic (slow) behavior.

“Our study describes a methodology to assimilate geologic, seismologic, and geodetic data surrounding a seismic fault to form a physical model of the cycle of earthquakes that has predictive power,” says Sylvain Barbot, a postdoctoral scholar in geology at Caltech and lead author of the study.

A paper describing their model-the result of a Caltech Tectonics Observatory (TO) collaborative study by geologists and geophysicists from the Institute’s Division of Geological and Planetary Sciences and engineers from the Division of Engineering and Applied Science-appears in the May 11 edition of the journal Science.

“Previous research has mostly either concentrated on the dynamic rupture that produces ground shaking or on the long periods between earthquakes, which are characterized by slow tectonic loading and associated slow motions-but not on both at the same time,” explains study coauthor Nadia Lapusta, professor of mechanical engineering and geophysics at Caltech. Her research group developed the numerical methods used in making the new model. “In our study, we model the entire history of an earthquake-producing fault and the interaction between the fast and slow deformation phases.”

Using previous observations and laboratory findings, the team-which also included coauthor Jean-Philippe Avouac, director of the TO-modeled an active region of the San Andreas Fault called the Parkfield segment. Located in central California, Parkfield produces magnitude-6 earthquakes every 20 years on average. They successfully created a series of earthquakes (ranging from magnitude 2 to 6) within the computer model, producing fault slip before, during, and after the earthquakes that closely matched the behavior observed in the past fifty years.

“Our model explains some aspects of the seismic cycle at Parkfield that had eluded us, such as what causes changes in the amount of time between significant earthquakes and the jump in location where earthquakes nucleate, or begin,” says Barbot.

The paper also demonstrates that a physical model of fault-slip evolution, based on laboratory experiments that measure how rock materials deform in the fault core, can explain many aspects of the earthquake cycle-and does so on a range of time scales. “Earthquake science is on the verge of building models that are based on the actual response of the rock materials as measured in the lab-models that can be tailored to reproduce a broad range of available observations for a given region,” says Lapusta. “This implies we are getting closer to understanding the physical laws that govern how earthquakes nucleate, propagate, and arrest.”

She says that they may be able to use models much like the one described in the Science paper to forecast the range of potential earthquakes on a fault segment, which could be used to further assess seismic hazard and improve building designs.

Avouac agrees. “Currently, seismic hazard studies rely on what is known about past earthquakes,” he says. “However, the relatively short recorded history may not be representative of all possibilities, especially rare extreme events. This gap can be filled with physical models that can be continuously improved as we learn more about earthquakes and laws that govern them.”

“As computational resources and methods improve, dynamic simulations of even more realistic earthquake scenarios, with full account for dynamic interactions among faults, will be possible,” adds Barbot.

Scientists ‘read’ the ash from the Icelandic volcano 2 years after its eruption

The models aim to predict the evolution of volcanic ash clouds, like the one emitted by Eyjafjallajökull. -  FLEXPART/NILU.
The models aim to predict the evolution of volcanic ash clouds, like the one emitted by Eyjafjallajökull. – FLEXPART/NILU.

In May 2010, the ash cloud from the Icelandic volcano Eyjafjallajökull reached the Iberian Peninsula and brought airports to a halt all over Europe. At the time, scientists followed its paths using satellites, laser detectors, sun photometers and other instruments. Two years later they have now presented the results and models that will help to prevent the consequences of such natural phenomena.

The eruption of the Eyjafjallajökull in the south of Iceland began on the 20 March, 2010. On the 14 April it began to emit a cloud of ash that moved towards Northern and Central Europe, resulting in the closure of airspace. Hundreds of planes and millions of passengers were grounded.

After a period of calm, volcanic activity intensified once again on the 3 May. This time the winds transported the aerosols (a mixture of particles and gas) towards Spain and Portugal where some airports had to close between the 6 and 12 May. This was also a busy time for scientists who took advantage of the situation to monitor the phenomenon. Their work has now been published in the Atmospheric Environment journal.

“The huge economic impact of this event shows the need to describe with precision how a volcanic plume spreads through the atmosphere. It also highlighted the importance of characterizing in detail its particles composition and establishing its concentration limits to ensure safe air navigation,” explains Arantxa Revuelta, researcher at the Spanish Research Centre for Energy, Environment and Technology (CIEMAT).

The team identified the volcanic ash cloud as it passed over Madrid thanks to LIDAR (Light Detection and Ranging), the most effective system for assessing aerosol concentration at a height. The CIEMAT station is one of 27 belonging to the European network EARLINET (European Aerosol Research Lidar Network) that use this instrument. Its members have also published a publicly accessible article on the matter in the Atmospheric Chemistry and Physics journal.

Using LIDAR technology, scientists direct a laser beam towards the sky, like a saber in Star Wars. The signal reflected back from particles provides information on their physical and chemical properties. A maximum aerosol value of 77 micrograms/m3 was estimated, which as a concentration is below the risk value established for air navigation (2 miligrams/m3).

Furthermore, the levels of particles rich in sulphates shot up even though they were fine particles (with a minimum diameter of 1 micra). This meant that they were much smaller than those particles over 20 micra found in countries in Central Europe.

These thicker particles are generally considered to be ‘ash’ and can really damage aircraft motors. The fine matter, like that detected over the Iberian Peninsula, is similar to that commonly found in urban and industrial areas. It is subject to study more for its damaging health effects rather than its impact on air navigation.

NASA’s network of sun photometers

It is important to track the evolution of all the particles in order to provide information to managers responsible for this kind of crisis. Working in this field were members of NASA’s AERONET (AErosol RObotic NETwork) network, which is made up by the different tracking stations in Spain and Portugal (integrated into RIMA) equipped with automatic sun photometers. These instruments focus towards the sun and collect data each hour on the aerosol optical thickness and their distribution by size in the atmospheric column.

The combined use of sun photometers and LIDAR technology boosts data collection. For example, the station in Granada and Évora revealed that the volcanic ash cloud circulated between 3 km and 6 km above the ground.

“Instruments like LIDAR are more powerful on an analytical level but their spatial and weather coverage is low. This means that sun photometers come in very useful in identifying volcanic aerosols when no other measures are available,” outlines the researcher Carlos Toledano from the University of Valladolid and member of the AERONET-RIMA network.

From their stations it was confirmed that “there is great variation between the size and characteristics of the volcanic aerosol particles over successive periods.” This was also verified by members of another European Network, EMEP (European Monitoring and Evaluation Program), which traces atmospheric pollution and is managed in Spain by the National Meteorological Agency. This group confirmed an increase in aerosols and their sulphate concentrations over the Iberian Peninsula and recorded the presence of sulphur dioxide from the Icelandic volcano.

Models and Predictions

The large part of observations of Eyjafjallajökull’s eruption, which were taken from aeroplanes, satellites or from earth, helped scientists validate their prediction and particle dispersion models.

“During the management of the crisis it became evident that there are still no precise models that provide real time data for delimiting an affected airspace, for example,” admits Toledano. Nevertheless, his team put the FLEXPART model to test using empirical data. From the Norwegian Institute for Air Research (NILU), it managed to calculate the arrival of volcanic ash in certain situations.

The powerful equipment available at the Barcelona Supercomputing Center (BSC-CNS) was used on this occasion to validate a model which had been developed at the centre: the Fall3d. As one of the authors Arnau Folch states, “the model can be applied to the dispersion of any type of particle. But, in practice, it has been especially designed for particles of volcanic origin, like ash.”

Volcanologists and metereologists use this model to re-enact past events and, above all, to make predictions. More specifically it predicts the amount of aerosols in the ground and their concentration in the air. It is therefore of “special interest” to civil aviation. The final objective is to make this type of prediction so as to be prepared during the next volcanic eruption.

Volcanoes sparked, and prolonged, the Little Ice Age

Volcanism is often implicated in periods of abrupt cooling. After the 1991 eruption of Mount Pinatubo in the Philippines, for instance, global temperatures dropped by half a degree Celsius due to airborne particulate matter blocking solar radiation. However, these effects don’t normally last more than a few years. Yet, a recent study blames volcanism for a 500-year cold period referred to as the Little Ice Age.

Beginning around the end of the Middle Ages and lasting into the early 19th century, unusually cold conditions blanketed much of the Northern Hemisphere. This period is known as the Little Ice Age. When exactly this period began, and how it was sustained for so long are matters of much debate. The culprit, according to a new study put forth by climate scientist Gifford Miller of the University of Colorado, is volcanism. How can a short-lived event like a volcanic eruption trigger cooling that lasts for centuries? Find out at http://www.earthmagazine.org/article/volcanoes-sparked-and-prolonged-little-ice-age.