Explosive volcanoes fueled by water

Geologists have tapped water in surface rocks to show how magma forms deep underground and produces explosive volcanoes in the Cascade Range. 

"Water is a key player," says Paul J. Wallace, a professor in the UO's Department of Geological Sciences and coauthor of a paper in the May issue of Nature Geoscience. "It's important not just for understanding how you make magma and volcanoes, but also because the big volcanoes that we have in the Cascades -- like Mount Lassen and Mount St. Helens -- tend to erupt explosively, in part because they have lots of water."

A five-member team, led by UO doctoral student Kristina J. Walowski, methodically examined water and other elements contained in olivine-rich basalt samples that were gathered from cinder cone volcanoes that surround Lassen Peak in Northern California, at the southern edge of the Cascade chain.

The discovery helps solve a puzzle about plate tectonics and Earth's deep water cycle beneath the Pacific Ring of Fire, which scientists began studying in the 1960s to understand the region's propensity for big earthquakes and explosive volcanoes. The ring stretches from New Zealand, along the eastern edge of Asia, north across the Aleutian Islands of Alaska and south along the coast of North and South America. It contains more than 75 percent of the planet's volcanoes.

To understand how water affects subduction of the oceanic plate, in which layers of different rock types sink into the mantle, the UO team studied hydrogen isotopes in water contained in tiny blobs of glass trapped in olivine crystals in basalt.

To do so, the team used equipment in Wallace's lab, CAMCOR, the Carnegie Institution in Washington, D.C., and a lab at Oregon State University. CAMCOR is UO's Advanced Materials Characterization in Oregon, a high-tech extension service located in the underground Lorry I. Lokey Laboratories.

Next, the team fed data gained from the rocks into a complex computer model developed by co-author Ikudo Wada, then of Japan's Tohoku University. She has since joined the University of Minnesota.

That combination opened a window on how rising temperatures during subduction drive water out of different parts of the subducted oceanic crust, Walowski said. Water migrates upwards and causes the top of the subducted oceanic crust to melt, producing magma beneath the Cascade volcanoes.

The key part of the study, Wallace said, involved hydrogen isotopes. "Most of the hydrogen in water contains a single proton," he said. "But there's also a heavy isotope, deuterium, which has a neutron in addition to the proton. It is important to measure the ratio of the two isotopes. We use this ratio as a thermometer, or probe, to study what's happening deep inside the earth."

"Melting of the subducting oceanic crust and the mantle rock above it would not be possible without the addition of water," Walowski said. "Once the melts reach the surface, the water can directly affect the explosiveness of magma. However, evidence for this information is lost to the atmosphere during violent eruptions."

This story is taken from Science Daily

Tidal tugs on 'Teflon' faults drive slow-slipping earthquakes

Teasing out how slow, silent earthquakes respond to tidal forces lets researchers calculate the friction inside the fault, which could help understand when and how the more hazardous earthquakes occur. 

A University of Washington seismologist who studies slow-slip quakes has looked at how they respond to tidal forces from celestial bodies and used the result to make a first direct calculation of friction deep on the fault. Though these events occur much deeper and on a different type of fault than the recent catastrophe in Nepal, the findings could improve general understanding of when and how faults break.

The new study, published online April 27 in Nature Geoscience, shows that the gravitational pull of the sun and the moon affect the Cascadia fault a few days after it has started slipping. The timing of movement suggests that the friction at this depth on the fault is only 0.1, roughly that of two pieces of lubricated metal.

"I was able to tease out the effect of friction and found that it is not the friction of normal rocks in the lab -- it's much lower," said author Heidi Houston, a UW professor of Earth and space sciences. "It's closer to Teflon than to sandpaper."

The surprising results of the new study could help to better model the physics of these systems, and they could even tell us something about the frictional forces in the locked portion of the fault where hazardous earthquakes occur.

The research looked at six recent slow-slip events along the Cascadia subduction zone, one of the best-studied places for these enigmatic slow quakes. The slow quakes are accompanied by tremors, weak seismic vibrations previously thought to be random noise. The tremors begin every 12 to 14 months below Puget Sound, Washington, and then travel north and south at about 5 miles (8 kilometers) per day for several weeks, affecting each section of the fault for about five days.

The paper looks at how the gravitational pull of the sun and moon, which slightly deform Earth and oceans, affect forces along, across and inside the fault, and what that means for the slow-slip seismic activity more than 20 miles (35 kilometers) underground.

Results show that on the first day of tremors, the tidal forces don't matter much. But starting at about 1 1/2 days -- when Houston thinks minerals that had been deposited from the surrounding fluid and that held the fault together may have broken -- the additional pull of the tides does have an effect.

"Three days after the slipping has begun, the fault is very sensitive to the tides, and it almost slips only when the tides are encouraging it," Houston said.

"It implies that something is changing on the fault plane over those five days."

By averaging across many sections of the fault, and over all six events, she found that the amount of the tremor increases exponentially with increasing tidal force.

Regular fast earthquakes are also very slightly affected by the tides, but they are overwhelmed by other forces and the effect is almost too small to detect.

There is no need for worry, Houston says -- even when celestial bodies line up to generate the biggest king tides, the effect would only rarely be enough to actually trigger a slow-slip quake, much less a regular earthquake. But it does tell us something about the physics of a crucial process that can't be easily studied in the lab.

"We want to understand the physics of what is happening, to understand and predict how the fault is storing stress, and how it's going to relieve stress," Houston said. "Friction is a big piece of that. And it turns out that this part of the fault is much slipperier than previously thought."

Slow-slip earthquakes relieve stress right where they slipped, but the movement actually places more stress on neighboring parts of the fault, including the so-called locked zone, where a rupture can cause the most damaging type of earthquakes.

In Cascadia's slow-slip events the fault will move about an inch (3 centimeters) over several days, with different parts of the fault moving at different times. When the shallower "locked zone" ruptures, by contrast, a large section of the fault can lurch over 60 feet (18 meters) in minutes. When this occurs, as it does about every 500 years in a magnitude 9 on the Cascadia subduction zone, it generates strong damaging seismic waves in Earth's crust.

Still unknown is how slow-slip events are related to the more damaging quakes. A shallower slow-slip event was detected in the weeks before the deadly 2011 Tohoku earthquake and tsunami, on a fault like Cascadia's where an ocean plate plunges below a continental plate.

"Understanding slow slip and tremor could give us some way to monitor what is happening in the shallower, locked part of the fault," Houston said. "Geophysicists started with the picture of just a flat plane of sandpaper, but that picture is evolving."

This story is taken from Science Daily

Aftershock assessment: Buildings collapse during earthquake aftershocks

Earthquakes kill, but their aftershocks can cause the rapid collapse of buildings left standing in the aftermath of the initial quake. Research offers a new approach to predicting which buildings might be most susceptible to potentially devastating collapse due to the ground-shaking aftershock tremors. 

Negar Nazari and John W. van de Lindt of the Department of Civil and Environmental Engineering, at Colorado State University in Fort Collins and Yue Li of Michigan Technological University, in Houghton, USA, point out that it is relatively obvious that buildings that survive a main shock will be at varying degrees of risk of collapse as aftershocks travel through the earthquake zone. Aftershocks are usually several orders of magnitude less intense than the primary earthquake, but can nevertheless have high ground motion intensity, last longer and occur at different vibration frequencies. In addition, changes in the structure of a building and its foundations, whether crippling or not, mean that the different energy content of the ground acceleration can during an aftershock further complicates any analysis. This adds up to a very difficult risk assessment for surviving buildings.
In order to compute the risk of collapse, the probability, for building damaged by a main shock, the team has introduced a logical method based on two key earthquake variables: magnitude and site-to-source distance. They have carried out tests using different site-to-source distances with an incremental dynamic analysis based on simulated ground motions caused by the main shock and aftershocks and applied this to a computer modeled, two-storey, timber-frame building in a hypothetical town in California relatively close to a geological fault line, as a proof of principle. Full-scale structural data was available from an actual building.
The team found that collapse probability increased if there were a sequence of aftershocks following a main shock just 10 kilometers distant from the building. Stronger aftershocks mean greater risk that correlates with the actual magnitude of the shock. As one might also expect if the site-to-source distance is greater, risk is lower. Overall, however, the analysis allows the team to quantify this risk based on the two variables, distance and aftershock magnitude.

This story is taken from Science Daily

New technique harnesses everyday seismic waves to image Earth

Earth researchers have devised a technique that transforms the tiny tremors generated by the everyday hustle and bustle of city life into a tool for probing the subsurface of Earth. 

Using tiny ground tremors generated by the rumble of cars and trucks across highways, the activities within offices and homes, pedestrians crossing the street and even airplanes flying overhead, a team led by Nakata created detailed three-dimensional subsurface maps of the California port city of Long Beach.
The maps, detailed in a recent issue of the Journal of Geophysical Research, marks the first successful demonstration of an elusive Earth-imaging technique, called ambient noise body wave tomography. "It's a technique that scientists have been trying to develop for more than 15 years," said Nakata, who is the Thompson Postdoctoral Fellow at the School of Earth, Energy & Environmental Sciences.
The subsurface maps were created by applying a new signal processing technique to a particular type of seismic waves -- energy waves that travel across the Earth's surface and through its interior. Seismic waves can be generated naturally, during earthquakes and volcanic eruptions, for example, or by artificial means such as explosions.
There are two major types of seismic waves: surface waves and body waves. As their name suggests, surface waves travel along the surface of the Earth. Scientists have long been able to harness surface waves to study the upper layers of the planet's crust, and recently they have even been able to extract surface waves from the so-called ambient seismic field. Also known as ambient noise, these are very weak but continuous seismic waves that are generated by colliding ocean waves, among other things.
Body waves, in contrast, travel through the Earth, and as a result can provide much better spatial resolution of the planet's interior than surface waves. "Scientists have been performing body-wave tomography with signals from earthquakes and explosives for decades," said study coauthor Jesse Lawrence, an assistant professor of geophysics at Stanford. "But you can't control when and where an earthquake happens, and explosives are expensive and often damaging."
For this reason, geophysicists have long sought to develop a way to perform body wave tomography without relying on earthquakes or resorting to explosives. This has proven challenging, however, because body waves have lower amplitudes than surface waves, and are therefore harder to observe.
"Usually you need to combine and average lots and lots of data to even see them," Lawrence said.
In the new study, the Stanford team applied a new software processing technique, called a body-wave extraction filter. Nakata developed the filter to analyze ambient noise data gathered from a network of thousands of sensors that had been installed across Long Beach to monitor existing oil reservoirs beneath the city.
While experimenting with different types of filters for parsing and analyzing ambient noise, Nakata came up with an idea for a filter of his own that focused specifically on body waves. "When I saw the Long Beach data, I realized I had all of the pieces in my hand to isolate body- wave energy from ambient noise," Nakata said. "I was excited, but at the same time I was skeptical my idea would work."
The filter Nakata developed and then refined with help from his Stanford colleagues represents a new way of processing the ambient noise by comparing each observation to every other observation, which boosts the body-wave signal while reducing the noise.
Using its filter, the team was able to create maps that revealed details about the subsurface of Long Beach down to a depth of more than half a mile (1.1. kilometers). The body-wave maps were comparable to, and in some cases better than, existing imaging techniques.
One map, for example, clearly revealed the Newport-Inglewood fault, an active geological fault that cuts through Long Beach. This fault also shows up in surface-wave maps, but the spatial resolution of the body-wave velocity map was much higher, and revealed new information about the velocity of seismic waves traveling through the fault's surrounding rocks, which in turn provides valuable clues about their composition and organization.
"This has been something of a holy grail in Earth imaging, and Nori's work is a first-of-its-kind study," said geophysicist Greg Beroza, the Wayne Loel Professor at Stanford, who was not involved in the study. "His groundbreaking achievement is sure to be widely emulated."
Lawrence says the real power of the new technique will come when it is combined with surface wave tomography. "Primary waves, which are a type of body wave, are sensitive to compressional forces, whereas surface waves are more sensitive to shear, or sliding, forces," Lawrence said. "To characterize the subsurface properly, one must measure both shear and compressional properties. Using one wave type and not the other is like trying to study a painting by looking at it through a frosted window."
Now that ambient-noise body wave tomography has been shown to work, Nakata says he plans to apply his technique to much larger test areas.

This story is taken from Science Daily

Location matters in the lowland Amazon

You know the old saying: Location, location, location? It turns out that it applies to the Amazon rainforest, too. New work illustrates a hidden tapestry of chemical variation across the lowland Peruvian Amazon, with plants in different areas producing an array of chemicals that changes across the region's topography. 

"Our findings tell us that lowland Amazon forests are far more geographically sorted than we once thought," Asner explained. "It is not simply a swath of green that occurs with everything strewn randomly. Place does matter, even if it all appears to be flat and green monotony at first glance."
The Amazonian forest occupies more than five million square kilometers, stretching from the Atlantic coast to the foothills of the Andes. Thousands of tree and other plant species are found throughout this area, each synthesizing a complex portfolio of chemicals to accomplish a variety of functions from capturing sunlight to fighting off herbivores, to attracting pollinators, not to mention the chemical processes involved in adapting to climate change.
The lowland forests of the Amazon rest on a hidden, underlying mosaic of geologic and hydrologic variation. It turns out that this mosaic affects the diversity of chemical functions that forest plants undertake, because the varying topography affects water, nutrients, and other plant resources. Understanding how the chemical activity of plants varies geographically is crucial to understanding the way an ecosystem functions on a large scale.
To figure it out, Asner and his team took a high-tech approach based on data collected from their Carnegie Airborne Observatory, or CAO, and developed the first high-resolution maps of the forest's canopy chemistry. A novel combination of instruments onboard the CAO, including a high-fidelity imaging spectrometer and a laser scanner, was used to map four huge forested landscapes along two Amazonian river systems. The instruments enabled the team to capture previously hidden chemical fingerprints of rainforest canopy species.
"This is the first time that so many chemicals have been measured and mapped in any forest ecosystem on Earth," Asner said. "No one has done the mapping we have achieved here, which enabled a discovery that the lowland Amazon is anything but monotonous or similar everywhere."
Their results reveal that the pattern of chemical properties in canopy trees changes along the paths of the two rivers--the Madre de Dios River and the Tambopata River--as well as across the landscape's topography on a 'microscale', with very small changes in elevation making all the difference to the plants living there. CAO's laser-guided spectroscopic mapping is unsurpassed in its ability to connect biological and geological processes. Studies of this kind help scientists to better understand Earth's tremendous diversity and its geographic patterning, both of which are required to understand evolution or the future of species in a changing world.
"Looking at the lowland Amazon with this kind of detail, you can see back in time, from the way the topography was shaped millions of years ago, which still affects soils and mineral availability today, to the way that different species evolved to take advantage of this great variety of subtly changing conditions," Asner explained. "And we can peer into the future and see how quickly human activity is changing the kaleidoscope of diversity that has been uniquely shaped over millions of years."

This story is taken from  Science Daily

Signs of ancient earthquakes may raise risks for New Zealand

Researchers have uncovered the first geologic evidence that New Zealand's southern Hikurangi margin can rupture during large earthquakes. The two earthquakes took place within the last 1000 years, and one was accompanied by a tsunami, according to the study. 

The earthquakes took place roughly 350 years apart, according to the analysis by Kate Clark of GNS Science and colleagues. This may mean that the time between large earthquakes in this region is shorter than scientists have thought. The current seismic models account for these types of earthquakes every 500 to 1000 years.
A worst-case, M8.9 Hikurangi earthquake could cause about 3350 deaths and 7000 injuries, and lead to $13 billion in costs in New Zealand's capital Wellington alone, according to a calculation made in 2013 by a different set of scientists. The Hikurangi margin marks the area where the Pacific and Australian tectonic plates collide to the east of New Zealand. The margin is one of the few places around the Pacific where a major subduction interface earthquake--which occurs deep in the crust where one plate is thrust under another--has not occurred in historic times.
However, "subduction earthquakes are not a 'new' risk for New Zealand, as we have always assumed they can occur, and they are accounted for in our seismic hazard models," Clark said. "This study is significant in that it confirms that risk.
"We have a record of three to five past earthquakes on most of the major upper plate faults in the [New Zealand] lower North Island and upper South Island, but there was previously no evidence of past subduction earthquakes on the southern Hikurangi margin," Clark explained. "Subduction earthquakes have the potential to be significantly larger in magnitude than upper plate fault ruptures, affect a much larger spatial area and are much more likely to trigger tsunami."
To look for evidence of past earthquakes on the margin, the researchers performed a painstaking examination of the geologic layers contained within a salt marsh at Big Lagoon in the southeastern Wairau River valley on South Island. They analyzed cores drilled from the marsh to look at differences in the kinds of sediment and the shells from tiny marine animals called foraminifera, deposited throughout a stretch of the lagoon's history.
These data revealed that the lagoon sank relatively suddenly twice during the past 1000 years, suggesting that the land was subsiding as a result of significant earthquakes. The more recent earthquake occurred between 520 and 470 years ago.
Another earlier earthquake probably took place between 880 and 800 years ago. Judging by the sedimentary debris found at that time, this earthquake was accompanied by a tsunami that swept more than 360 meters inland at the study site.
Clark said the findings will help researchers better understand the risks posed by large subduction interface earthquakes in the region. Studies have shown, for example, that there have been subduction earthquakes on the central Hikurangi margin, "and we wanted to understand if the central and southern Hikurangi margins are likely to rupture in the same earthquake," said Clark.
"We can see that the [southern Hikurangi margin] subduction earthquake at about 500 years before present possibly correlates with a central Hikurangi margin earthquake, implying both segments may have ruptured in the same earthquake," she continued, "but the radiocarbon dating is not yet precise enough to be certain--possibly there were two earthquake closely spaced in time."
Clark said that she and other scientists are looking at other locations in the lower North Island to find evidence of the same paleoearthquakes, which could help provide a better picture of how big these quakes might have been and how they impacted the region.
"In addition we would like to go further back in time and find evidence of older subduction earthquakes," Clark said."With a longer record of past subduction earthquakes we can get a better constraint on the recurrence of such earthquakes, which will help to forecast future subduction earthquakes."

This story is taken from Science Daily

Study highlights ways to boost weather, climate predictions

Long range weather forecasts and climate change projections could be significantly boosted by advances in our understanding of the relationship between layers of the Earth's atmosphere -- the stratosphere and troposphere. 

A team of UK scientists have studied how a circulation changes in the stratosphere (above 10 km) can influence both weather and climate conditions on the surface of Earth.
The experts, who include Professor Mark Baldwin from the University of Exeter, argue that the predictability and persistence of stratospheric events could help scientists enhance both short term, and seasonal, forecast skills.
They also suggest that some of the uncertainties that currently restrict the effectiveness of regional climate projections could be reduced through developing a better understanding of the stratosphere influence on surface-level jet streams, storm tracks and weather.
The review article, produced by experts from the University of Exeter, the Met Office and the University Of Oxford, is published online in the leading scientific journal, Nature Geoscience.
Professor Mark Baldwin, from the University of Exeter Mathematics department and co-author of the study, said: "We have known for about 15 years that the stratosphere affects surface weather and climate, but only recently have we made significant progress in understanding why."
The research review studied the mechanisms whereby an event occurring in the stratosphere -- which is found 10-50km above Earth's surface -- can influence ground-level climatic conditions.
It highlighted a series of global weather phenomena that resulted from this stratosphere-troposphere 'coupling' -- such as the cold European winters and occurrences of extreme temperatures over eastern North America. The scientists also showed that events in the stratosphere could affect weather patterns over much of the Southern Hemisphere including Australia and New Zealand, the Antarctic Peninsula and Patagonia during the summer months.
The experts suggest that, by using sophisticated computer modelling, scientists could develop a greater understanding of the relationship between events in the upper part of the atmosphere, and the effect they have on the weather experienced across the globe.
Professor Adam Scaife from the Met Office said "The stratosphere is now included in our computer models and is already helping to deliver improved climate predictions."
Professor Baldwin added: "Natural large pressure fluctuations in the polar stratosphere tend to last a long time -- at least a month, and we see this reflected as surface pressure changes that look very much like the North Atlantic Oscillation -- which has significant effects on weather and extreme events across Europe."
The research comes just months after a team of experts from The University of Exeter received a £1.1 million grant to fund pioneering new research that will significantly improve crucial long-term weather forecasts across Europe.
The team, which includes Professor Baldwin, will lead innovative new research, which aims to advance current understanding of three key conditions that influence seasonal weather across the continent -- the North Atlantic upper-ocean heat content, Arctic sea-ice, and the stratosphere. They will exploit a combination of state-of-the-art climate model experiments, advanced statistical techniques and idealised dynamical frameworks to accomplish the project.
The motivation behind developing consistently reliable long-ranging forecasting is clear. With almost every aspect of modern society reliant on improved predictions of both weather and climate both by decade and season -- whether it be agriculture, energy, civil and military defence, urban planning or even commodity trading -- the project has the potential to offer marked benefits to both UK and European businesses and communities.

This story is staken from Science Daily

Probing iron chemistry in the deep mantle

Upper mantle carbonates are magnesium-rich and iron-poor. Under lower mantle conditions, it is thought that the arrangement of electrons in carbonate minerals changes under the pressure stress in such a way that iron may be significantly redistributed. A research team has now focused on the high-pressure chemistry of a carbonate mineral called siderite, FeCO3, commonly found in hydrothermal vents. Their findings help resolve questions about the presence of iron-containing lower mantle carbonates. 

Carbonates were known to exist in the upper mantle due to their role in the deep carbon cycle. But it was thought that they could not withstand the more-extreme conditions of the lower mantle. Laboratory experiments and the discovery of tiny bits of carbonate impurities in lower mantle diamonds indicated that carbonates could withstand the extreme pressures and temperatures of not only the upper mantle, but the lower mantle as well.
Previous research had shown that upper mantle carbonates are magnesium-rich and iron-poor. Under lower mantle conditions, it is thought that the arrangement of electrons in carbonate minerals changes under the pressure stress in such a way that iron may be significantly redistributed. However, accurate observations of lower mantle carbonates' chemical composition are not possible yet.
A research team--Carnegie's Sergey Lobanov and Alexander Goncharov, along with Konstantin Litasov of the Russian Academy of Science and Novosibirsk State University in Russia--focused on the high-pressure chemistry of a carbonate mineral called siderite, which is an iron carbonate, FeCO3, commonly found in hydrothermal vents. Their findings help resolve questions about the presence of iron-containing lower mantle carbonates, and are published by American Mineralogist.
Until recently the electron-arrangement change responsible for iron redistribution in the lower mantle had not been measured in the lab. It was previously discovered that this change, a phenomenon called a spin transition, took place between about 424,000 and 484,000 times normal atmospheric pressure (43 to 49 gigapascals).The team was able to pinpoint that spin transition was occurring in iron carbonates under about 434,000 times normal atmospheric pressure (44 gigapascals), typical of the lower mantle.
A spin transition is a rearrangement of electrons in a molecule or a mineral. Electrons hold a compound's atoms together by bonding. Certain fundamental rules of chemistry govern this bonding process, which have to do with the energy it takes to form the bonds. Pressure-induced spin transitions rearrange electrons and change the energy of the chemical bonds. If the change in chemical bond energy is high enough, the spin transition may trigger iron redistribution between coexisting minerals.
To quantify the energy change, siderite's spin transition was examined using highly sensitive spectroscopic techniques at pressures ranging from zero to about 711,000 times normal atmospheric pressure (72 gigapascals), and also revealed by a visible color change after the transition, indicating rearrangement of electrons. The obtained spectroscopic data provided the key ingredient to estimating the carbonate composition at pressures exceeding the spin transition-pressure. It turned out that lower mantle carbonates should be iron-rich, unlike upper mantle carbonates. Similar effects may exist in other lower mantle minerals, if they also undergo spin transitions.
"As we learn more about how the spin transition affects chemical composition in carbonates, we improve our understanding of all iron-bearing minerals, enhancing our knowledge about lower mantle chemistry," said Lobanov.

This story is taken from Science Daily

Raising groundwater keeps valleys from sinking: Santa Clara Valley, Callifornia, USA

California and other parts of the western U.S. are experiencing extended severe drought conditions. The Santa Clara Valley in California underwent extensive groundwater development from the early 1900s through the mid-1960s. This development caused groundwater level declines of more than 200 feet. 

In the introduction to his paper, Hanson provides a succinct history of the area, as paraphrased here: Santa Clara Valley is a long, narrow (240 square miles), trough-like coastal watershed that borders the southern end of San Francisco Bay, extending about 35 miles southeast from there. The watershed principally drains parts of Santa Clara and San Mateo counties. Santa Clara Valley has experienced the typical evolution of land- and water-use development in the western United States, with a transition from an agricultural and ranching economy to one based on urban services and industry. In the first half of the twentieth century, the valley was intensively cultivated for fruit and truck crops, but subsequent development has included urbanization and industrialization, so that the area is now commonly known as "Silicon Valley."
Hanson says that the valley underwent extensive groundwater development from the early 1900s through the mid-1960s. This development caused groundwater level declines of more than 200 feet and induced regional subsidence of as much as 12.7 feet from the early 1900s to the mid-1960s. As with other coastal aquifer systems, Hanson notes, "the possibility exists that the combined effects of land subsidence and seawater intrusion will result in large water-level declines."
The San Francisco Water Department started delivering imported water to several north county cities in the early 1950s. In the 1960s, the Santa Clara Valley Water District (SCVWD) began importing surface water into the valley to help meet growing demands and to reduce the area's dependence on groundwater. The combination of reduced groundwater pumping and this artificial recharge has caused groundwater levels to recover to near their predevelopment levels, and this, in turn, has arrested the land subsidence, says Hanson, noting, "Currently, the water purveyors in the Santa Clara Valley, in conjunction with SCVWD, would like to meet the water demand in the basin while limiting any potential for additional land subsidence."
Even though extensive studies have been completed in the Santa Clara Valley, there were no comprehensive three-dimensional hydrologic, geologic, and geochemical data that would allow the delineation of the hydrologic framework that controls the distribution and movement of the water resources in the Santa Clara Valley. Hanson's article summarizes the hydrologic framework of the valley using data obtained from nine new monitoring-well sites and various supply wells in combination with a detailed groundwater-surface-water model.
The synthesis of this framework is based on a sequence of interdisciplinary studies between the U.S. Geological Survey and the Santa Clara Valley Water District. The framework components, as summarized in Hanson's article, include the hydrogeologic structure of the valley, groundwater budgets, the role of climate cycles, the nature of stream-aquifer interactions, distribution and nature of groundwater pumpage, effects of land subsidence, the distribution of artificial recharge, geochemical characteristics of the aquifers and wells, and the overall water-resource management issues relevant to the sustainable and conjunctive use of the groundwater and surface water resources of the Santa Clara Valley.

This story is taken from Science Daily

How rivers regulate global carbon cycle

River transport of carbon to the ocean is not on a scale that will solve our carbon dioxide problem, but we haven't known how much carbon the world's rivers routinely flush into the ocean, until now. Scientists calculated the first direct estimate of how much and in what form organic carbon is exported by rivers. The estimate will help modelers predict how this export may shift as Earth's climate changes.

While river transport of carbon to the ocean is not on a scale that will bail humans out of our CO₂ problem, we don't actually know how much carbon the world's rivers routinely flush into the ocean -- an important piece of the global carbon cycle.
But in a study published May 14 in the journal Nature, scientists from Woods Hole Oceanographic Institution (WHOI) calculated the first direct estimate of how much and in what form organic carbon is exported to the ocean by rivers. The estimate will help modelers predict how the carbon export from global rivers may shift as Earth's climate changes.
"The world's rivers act as Earth's circulatory system, flushing carbon from land to the ocean and helping reduce the amount that returns to the atmosphere in the form of heat-trapping carbon dioxide," said lead author and geochemist Valier Galy. "Some of that carbon--'new' carbon--is from decomposed plant and soil material that is washed into the river and then out to sea. But some of it comes from carbon that has long been stored in the environment in the form of rocks-- 'old' carbon--that have been eroded by weather and the force of the river."
The scientists, who included Bernhard Peucker-Ehrenbrink, and Timothy Eglinton (now at ETH Zürich), amassed data on sediments flowing out of 43 river systems all over the world, which cumulatively account for 20 percent of the total sediments discharged by rivers. The representative rivers also encompassed a broad range of climates, vegetation, geological conditions, and levels of disturbance by people.
From these river sediment flow measurements, the research team calculated amounts of particles of carbon-containing plant and rock debris that each river exported. They estimated that the world's rivers annually transport 200 megatons (200 million tons) of carbon to the ocean. The total equals about .02 percent of the total mass of carbon in the atmosphere. That may not seem like a lot, but over 1000 to 10,000 years, it continues to add up to significant amounts of carbon (20 and 200 percent) extracted from the atmosphere.
Generally, plants convert CO₂ from the atmosphere into organic carbon via photosynthesis. But most of this carbon eventually returns to the atmosphere when plant material (or animals that eat plants) decompose. A small fraction of this material, however, ends up in rivers. They carry it out to sea, where some settles to the seafloor and is buried and disconnected from the atmosphere for millions of years and eventually makes its way back to the surface in the form of rocks.
At the same time, rivers also erode carbon-containing rocks into particles carried downstream. The process exposes carbon to air, oxidizing the previously locked-up carbon into carbon dioxide that can leak back out to the atmosphere. Until now, scientists had no way to distinguish how much of the carbon whisked away by rivers comes from either the biospheric or petrogenic (rock) sources. Without this information, scientists' ability to model or quantitatively predict carbon sequestration under different scenarios was limited.
To solve this dilemma, the scientists found a novel way to distinguish for the first time the sources of that carbon--either from eroded rocks or from decomposed plant and soil material. They analyzed the amounts of carbon-14, a radioactive isotope, in the river particles. Carbon-14 decays away within about 60,000 years, so it is present only in material that came from living things, and not rocks. Subtracting the portion of particles that did not contain carbon-14, the scientists calculated the percentage that was derived from the terrestrial biosphere: about 80 percent.
But even though biospheric carbon is the major source of carbon exported by rivers, the scientists also discovered that rivers surrounded by greater amounts of vegetation didn't necessarily transport more carbon to the ocean. Instead, the export was "primarily controlled by the capacity of rivers to mobilize and transport" particles. Erosion is the key factor--the more erosion occurs along the river, the more carbon it transfers to sea and sequesters from the air.
"The atmosphere is a small reservoir of carbon compared to rocks, soils, the biosphere, and the ocean," the scientists wrote in Nature. "As such, its size is sensitive to small imbalances in the exchange with and between these larger reservoirs."
The new study gives scientists a firmer handle on measuring the important, and heretofore elusive, role of global rivers in the planetary carbon cycle and enhances their ability to predict how riverine carbon export may shift as Earth's climate changes.
"This study will provide geochemical modelers with new insights on an important link between the global carbon and water cycles," says Don Rice, program director in the National Science Foundation's Division of Ocean Sciences, a major funder of the research.

This is  taken from Science Daily

Watch invisible gravity waves rumble through the atmosphere

Just as waves ripple across a pond when a tossed stone disturbs the water's surface, gravity waves ripple toward space from disturbances in the lower atmosphere. 

Gravity waves are born when air masses are pushed up or down -- by a thunderstorm, perhaps, or when wind is forced up and over a mountain range -- but in the lower atmosphere, their impacts usually remain regional. By the time they reach the upper atmosphere, however, the waves have built in amplitude and extent. There, they can dominate atmospheric processes on a much larger scale, sometimes threatening the reliability of Earth-based communication systems.

For the first time, scientists have found a way to "watch" the propagation of gravity waves toward space -- and the view is captivating. The trick, according to a team of researchers led by NCAR Senior Scientist Hanli Liu, was to push the NCAR-based Whole Atmosphere Community Climate Model to a resolution that is fine enough to pick up gravity waves at their source, when they're still relatively small.

"We've never seen a global picture of gravity waves in the upper atmosphere before, either from observations or simulations, even though we have suspected their importance up there," said Liu, who studies the upper atmosphere at NCAR's High Altitude Observatory. "This is the first time we have been able to capture these waves with a computer model of the whole atmosphere."

The standard version of the model gets only a blurry look at phenomena that take place on scales less than 2,000 km (about 1,243 miles) across -- and it's blind to anything smaller than 200 km. The higher-resolution model has much sharper vision all the way down to 200 km. The intense computing power of the NCAR-Wyoming Supercomputing Center's Yellowstone system made the higher-resolution runs possible.

In a study published in the journal Geophysical Research Letters, Liu and his colleagues demonstrated the finer-scaled model's abilities by showing how gravity waves such as those created by a tropical cyclone east of Australia grew as they traveled upwards. The model shows that what starts out as a localized phenomenon extends across the entire Pacific Region at 100 km above Earth's surface.

"For the middle and lower atmosphere, if you miss the gravity wave, you're not missing too much," Liu said. "But it's a different story in the upper atmosphere."

Disturbances in the upper atmosphere -- which can endanger satellites, skew GPS readings, and shut down radio transmissions -- are often thought about as originating from the Sun, where solar storms can kick off geomagnetic storms around Earth. But the ionosphere, the upper reaches of the atmosphere affected by this kind of space weather, is also influenced by disturbances originating on Earth.

These Earth-born disturbances can be difficult for scientists to disentangle when solar storm activity is strong, but the relative tranquility of the Sun during the last solar cycle has given scientists an opportunity to home in on the disturbances reaching the ionosphere from below, creating a fuller picture of processes in the ionosphere.

"When gravity waves propagate to the bottom side of the ionosphere, they can kick off instabilities," Liu said. "If you want to have a better understanding of space weather -- the ionosphere -- you need this kind of modeling capability.

This is taken from Science Daily

New trigger for volcanic eruptions discovered using jelly and lasers

Scientists have made an important step towards understanding how volcanic eruptions happen, after identifying a previously unrecognized potential trigger. Researchers think their findings could lead to new ways of interpreting signs of volcanic unrest measured by satellites and surface observations. 

An international team of researchers from the University of Liverpool, Monash University and the University of Newcastle (Australia) think their findings could lead to new ways of interpreting signs of volcanic unrest measured by satellites and surface observations.
Dr Janine Kavanagh, from the University of Liverpool's School of Environmental Sciences and lead author of the research paper, said: "Understanding the triggers for volcanic eruptions is vital for forecasting efforts, hazard assessment and risk mitigation.
"With more than 600 million people worldwide living near a volcano at risk of eruptive activity, it is more important than ever that our understanding of these complex systems and their triggering mechanisms is improved.
"There is also a strong economic incentive to understand the causes of volcanic activity -- as demonstrated in 2010 by the eruption of Eyjafjallajökull, Iceland, which caused air-traffic disruption across Europe for more than one month, with an estimated US$1.8 billion loss in revenue to the airline industry."
Studying volcanic processes in nature can be challenging because of the remoteness of many volcanoes, the dangers to scientists wanting to study destructive eruptions up close, and the fact that they are often obscured from direct observation by volcanic ash or rock.
To get around this difficulty, the researchers recreated a scaled down version in labs at Monash University.
They studied the plumbing systems of volcanoes by modelling how magma ascends from great depths to the surface through a series of connected fractures (called dykes and sills).
The scientists used a tank filled with gelatine (jelly) into which coloured water was injected to mimic ascending magma. A high-speed camera and a synchronised laser was used to observe what was going on inside the tank as the ascending magma moved upwards.
Professor Sandy Cruden, from the School of Earth, Atmosphere and Environment at Monash University, said: "It was at this point that we discovered a significant and previously unknown drop in pressure when the ascending vertical dyke stalled to form a horizontal sill."
"Sills often form in nature as part of a developing volcanic plumbing system, and a pressure drop can drive the release of dissolved gasses, potentially causing the magma to explode and erupt."
"It's similar to removing a cap from a bottle of shaken fizzy drink -- the pressure drop causes bubbles to form and the associated increase in volume results in a fountain of foam erupting from the bottle."
Volcano-monitoring systems around the world rely on the interpretation of signals of Earth's surface and subsurface measured by satellites, ground deformation devices and seismometers. These record when and how magma moves at depth and they are used to help determine the likelihood of an eruption occurring.
The new results will aid this effort by adding a previously unknown potential eruption triggering mechanism and by helping to improve understanding of the dynamics of magma ascent, which leads to eruptions.

This story is taken from Science Daily

Common mechanism for shallow and deep earthquakes proposed

Geologists report that a universal sliding mechanism operates for earthquakes of all depths -- from the deep ones all the way up to the crustal ones. The physics of the sliding is the self-lubrication of the earthquake fault by flow of a new material consisting of tiny new crystals, the study reports. 

A new study published online in Nature Geoscience today by a research team led by University of California, Riverside geologists now reports that a universal sliding mechanism operates for earthquakes of all depths -- from the deep ones all the way up to the crustal ones.
"Although shallow earthquakes -- the kind that threaten California -- must initiate differently from the very deep ones, our new work shows that, once started, they both slide by the same physics," said deep-earthquake expert Harry W. Green II, a distinguished professor of the Graduate Division in UC Riverside's Department of Earth Sciences, who led the research project. "Our research paper presents a new, unifying model of how earthquakes work. Our results provide a more accurate understanding of what happens during earthquake sliding that can lead to better computer models and could lead to better predictions of seismic shaking danger."
The physics of the sliding is the self-lubrication of the earthquake fault by flow of a new material consisting of tiny new crystals, the study reports. Both shallow earthquakes and deep ones involve phase transformations of rocks that produce tiny crystals of new phases on which sliding occurs.
"Other researchers have suggested that fluids are present in the fault zones or generated there," Green said. "Our study shows fluids are not necessary for fault weakening. As earthquakes get started, local extreme heating takes place in the fault zone. The result of that heating in shallow earthquakes is to initiate reactions like the ones that take place in deep earthquakes so they both end up lubricated in the same way."
Green explained that at 300-700 kilometers depth, the pressure and temperature are so high that rocks in this deep interior of the planet cannot break by the brittle processes seen on Earth's surface. In the case of shallow earthquakes, stresses on the fault increase slowly in response to slow movement of tectonic plates, with sliding beginning when these stresses exceed static friction. While deep earthquakes also get started in response to increasing stresses, the rocks there flow rather than break, except under special conditions.
"Those special conditions of temperature and pressure induce minerals in the rock to break down to other minerals, and in the process of this phase transformation a fault can form and suddenly move, radiating the shaking -- just like at shallow depths," Green said.
The research explains why large faults like the San Andreas Fault in California do not have a heat-flow anomaly around them. Were shallow earthquakes to slide by the grinding and crunching of rock, as geologists once imagined, the process would generate enough heat so that major faults like the San Andreas would be a little warmer along their length than they would be otherwise.
"But such a predicted warm region along such faults has never been found," Green said. "The logical conclusion is that the fault must move more easily than we thought. Extreme heating in a very thin zone along the fault produces the very weak lubricant. The volume of material that is heated is very small and survives for a very short time -- seconds, perhaps -- followed by very little heat generation during sliding because the lubricant is very weak."
The new research also explains why faults with glass on them (reflecting the fact that during the earthquake the fault zone melted) are rare. As shallow earthquakes start, the temperature rises locally until it is hot enough to start a chemical reaction -- usually the breakdown of clays or carbonates or other hydrous phases in the fault zone. The reactions that break down the clays or carbonates stop the temperature from climbing higher, with heat being used up in the reactions that produce the nanocrystalline lubricant.
If the fault zone does not have hydrous phases or carbonates, the sudden heating that begins when sliding starts raises the local temperature on the fault all the way to the melting temperature of the rock. In such cases, the melt behaves like a lubricant and the sliding surface ends up covered with melt (that would quench to a glass) instead of the nanocrystalline lubricant.
"The reason this does not happen often, that is, the reason we do not see lots of faults with glass on them, is that the Earth's crust is made up to a large degree of hydrous and carbonate phases, and even the rocks that don't have such phases usually have feldspars that get crushed up in the fault zone," Green explained. "The feldspars will 'rot' to clays during the hundred years or so between earthquakes as water moves along the fault zone. In that case, when the next earthquake comes, the fault zone is ready with clays and other phases that can break down, and the process repeats itself."
The research involved the study of laboratory earthquakes -- high-pressure earthquakes as well as high-speed ones -- using electron microscopy in friction and faulting experiments. It was Green's laboratory that first conducted a serendipitous series of experiments, in 1989, on the right kind of mantle rocks that give geologists insight into how deep earthquakes work. In the new work, Green and his team also investigated the Punchbowl Fault, an ancestral branch of the San Andreas Fault that has been exhumed by erosion from several kilometers depth, and found nanometric materials within the fault -- as predicted by their model.

This story is taken from Science Daily