Studies offer new picture of Lake Tahoe’s earthquake potential

Scripps researchers deploy a CHIRP instrument to survey the
faults below Lake Tahoe. -  Scripps Institution of Oceanography, UC San Diego
Scripps researchers deploy a CHIRP instrument to survey the
faults below Lake Tahoe. – Scripps Institution of Oceanography, UC San Diego

For more than a decade, scientists at Scripps Institution of Oceanography at UC San Diego have been unraveling the history of fault ruptures below the cobalt blue waters of Lake Tahoe one earthquake at a time. Two new studies by the Scripps research team offer a more comprehensive analysis of earthquake activity in the Lake Tahoe region, which suggest a magnitude-7 earthquake occurs every 2,000 to 3,000 years in the basin, and that the largest fault in the basin, West Tahoe, appears to have last ruptured between 4,100 and 4,500 years ago.

These studies, led by a team of Scripps researchers including Graham Kent, Neal Driscoll, Jeff Babcock and Alistair Harding, collected new data on earthquake history along three active faults in the region. These new data suggest that the most recent ruptures along the West Tahoe and Incline Village faults each produced nearly 4-meter-high offsets. The most recent event along the Incline Village Fault occurred about 575 years ago.

“These studies taken together show that the West Tahoe Fault is capable of a magnitude-7 earthquake – similar to large earthquakes that have occurred on the nearby Genoa Fault – but with the added danger of nearly 500 m of overlying water, which is capable of spawning a large tsunami wave,” said Kent, a research geophysicist at Scripps.

Jeff Dingler, lead author on a paper in the April online issue of Geological Society of America Bulletin (GSA Bulletin) and former Scripps Oceanography graduate student, used a high-resolution seismic imaging technique, known as CHIRP, to supply a comprehensive view of faulting beneath the lake. Scripps’ Neal Driscoll developed the new digital CHIRP profiler for this study, which provided an unprecedented picture of deformation within the sedimentary layers that blanket the floor of Lake Tahoe, laying the groundwork for more detailed fault studies that continue today.

In a complementary paper, published in the April issue of the Bulletin of the Seismological Society of America (BSSA), Scripps graduate student Danny Brothers investigated the rupture history of the West Tahoe Fault in greater detail. Using comprehensive CHIRP and coring surveys of Fallen Leaf Lake, where the West Tahoe Fault crosses the southern end of the lake, the study confirmed the suspected fault length of over 50 km (31 miles). When combined with the rupture offset size observed across the fault from CHIRP imagery, the analysis suggests an upper limit of a magnitude-7.3 earthquake for the basin’s most dangerous fault.

This new analysis, coupled with a slip-rate approaching 0.8 mm/year and the rupture timeline taking place between 4,100 and 4,500 years ago, places the West Tahoe Fault near the end of its characteristic earthquake cycle. Researchers caution that some degree of variability is to be expected. Such an earthquake could produce tsunami waves some three to 10 meters (10 to 33 feet) high, colleagues at the University of Nevada, Reno, have shown.

Lake Tahoe, which straddles the California and Nevada border in the Sierra Nevada region, is one of the world’s deepest freshwater lakes. At more than 501 meters (1,645 feet) deep, the lake covers 191 square miles in a basin prone to earthquakes and catastrophic landslides. The West Tahoe Fault runs along the west shore of the lake and comes onshore at Baldwin Beach, then passes through the southern third of Fallen Leaf Lake, where it descends into Christmas Valley near Echo Summit.

Geoscientists meet to discuss Rocky Mountain geology

Geoscientists will gather soon for the 61st Annual Meeting of the Rocky Mountain Section of the Geological Society of America, being held 11-13 May 2009 in Orem, Utah. Utah Valley University (UVU) is hosting the meeting in their new library building on the UVU campus. Brigham Young University is co-hosting.

The technical program, presented by academic and industry scientists, and graduate and undergraduate students, will highlight cutting-edge scientific research in themed sessions on a broad range of topics.

TECHNICAL SESSION HIGHLIGHTS

* Quaternary Tectonics and Earthquake-Hazard Characterization in the Rocky Mountain Region *

Topics in this session include kinematics of the Yellowstone Hotspot, and analysis of the 2008-2009 Yellowstone Lake Earthquake swarm, as well as seismic hazard and risk mitigation across the Rocky Mountain region.

* Geologic Hazards in the Rocky Mountain Region and Their Impacts on Development *

Topics include geologic hazards mapping to meet the needs of new and evolving geologic-hazard ordinances; seismic vulnerability of public schools along the Wasatch Front, and geological issues along a planned construction route for an electrical transmission line.

Other sessions address structure and tectonics, new discoveries in Paleozoic Stratigraphy and Paleontology, and hydrologic studies in the Rocky Mountains and Basin and Range area.

View the complete technical program at http://gsa.confex.com/gsa/2009RM/finalprogram/

FIELD TRIP HIGHLIGHTS


Utah Valley is located on the eastern edge of the Basin and Range and close to both the Colorado Plateau and Rocky Mountains provinces. The Wasatch Fault, a major crustal feature, forms the eastern margin of the valley. Field trips will include destinations to one of the largest open-pit copper mines in the world; hot springs in Saratoga Springs, Diamond Fork Canyon, Spanish Fork Canyon, and Wasatch Mountain State Park; Brigham Young University’s Museum of Paleontology, housing one of the largest and finest collections of Jurassic dinosaur bones; and various locations providing an in-depth look at the tectonics and stratigraphy of the Western Colorado Plateau.

MEETING, REGISTRATION AND HOUSING INFORMATION

Complete meeting information is available at http://www.geosociety.org/sectdiv/rockymtn/09mtg/index.htm

Information on registration is available at http://www.geosociety.org/sectdiv/rockymtn/09mtg/registration.htm. Information on lodging is available at http://www.geosociety.org/sectdiv/rockymtn/09mtg/lodging.htm.

MEDIA REGISTRATION INFORMATION

Eligibility for media registration is as follows:

  • Working press representing bona fide, recognized news media with a press card, letter or business card from the publication.
  • Freelance science writers, presenting a current membership card from NASW, ISWA, regional affiliates of NASW, ISWA, CSWA, ACS, ABSW, EUSJA, or evidence of work pertaining to science published in 2008 or 2009.
  • PIOs of scientific societies, educational institutions, and government agencies.

Complimentary meeting registration covers attendance at all technical sessions and access to the exhibit hall. Journalists and PIOs must pay regular fees for paid luncheons and any short courses or field trips in which they participate. Representatives of the business side of news media, publishing houses, and for-profit corporations must register at the main registration desk and pay the appropriate fees.

Satellite imagery shows fragile Wilkins Ice Shelf destabilized

The figure displays the Envisat Advanced Synthetic Aperture Radar image from April 27, 2009, superimposed on an image from April 24, 2009. The margins of the collapsed ice bridge that formerly connected Charcot and Latady Islands are outlined in white. The demise of the ice bridge led to a destabilization of the northern ice front of the Wilkins Ice Shelf, where the first icebergs calved off on 20 April 2009 (area denoted in red). -  ESA (Annotations by A. Humbert, Münster University)
The figure displays the Envisat Advanced Synthetic Aperture Radar image from April 27, 2009, superimposed on an image from April 24, 2009. The margins of the collapsed ice bridge that formerly connected Charcot and Latady Islands are outlined in white. The demise of the ice bridge led to a destabilization of the northern ice front of the Wilkins Ice Shelf, where the first icebergs calved off on 20 April 2009 (area denoted in red). – ESA (Annotations by A. Humbert, Münster University)

Satellite images show that icebergs have begun to calve from the northern front of the Wilkins Ice Shelf – indicating that the huge shelf has become unstable. This follows the collapse three weeks ago of the ice bridge that had previously linked the Antarctic mainland to Charcot Island.

The ice bridge, which effectively formed a barrier pinning back the northern ice front of the central Wilkins Ice Shelf, collapsed on 5 April removing about 330 sq km of ice. As a consequence of the collapse, the rifts, which had already featured along the northern ice front, widened and new cracks formed as the ice adjusted in the days that followed.

Dr Angelika Humbert from the Institute of Geophysics, Münster University and Dr Matthias Braun from the Center for Remote Sensing, University of Bonn have been monitoring the ice shelf using a combination of radar images from ESA’s Envisat satellite and the German Aerospace Centre’s TerraSAR-X satellite.

On 24 April, the satellite data showed that the first icebergs had started to break away from the fragile ice shelf. A very rough estimate suggests that, so far, about 700 sq km of ice has been lost from the Wilkins Ice Shelf.

In contrast to the ice bridge, which shattered very quickly, it is expected that the discharge of ice will continue for some weeks. The icebergs are calving as a result of fracture zones that have formed over the last 15 years and which turned Wilkins into a fragile and vulnerable ice shelf.

“The retreat of Wilkins Ice Shelf is the latest and the largest of its kind. Eight separate ice shelves along the Antarctic Peninsula have shown signs of retreat over the last few decades. There is little doubt that these changes are the result of atmospheric warming on the Antarctic Peninsula, which has been the most rapid in the Southern Hemisphere,” explained David Vaughan from the British Antarctic Survey.

“The changes to Wilkins Ice Shelf provide a fabulous natural laboratory that will allow us to understand how ice shelves respond to climate change and what the future will hold for the rest of Antarctica,” Vaughan commented. “The quality and frequency of images acquired by ESA satellites mean that the break-up of Wilkins Ice Shelf can be analysed far more effectively than any previous event. For the first time, I think, we can really begin to see the processes that have brought about the demise of the ice shelf.”

However, it is still unclear how the situation will evolve. Humbert noted that, “We are not sure if a new stable ice front will now form between Latady Island, Petrie Ice Rises and Dorsey Island. If the connection to Latady Island is lost, the projected loss of 3370 sq km of ice might be greater – though we have no indication that this will happen in the near future.”

The combination of high resolution TerraSAR-X images and the more frequently acquired Envisat images, increases the understanding of ice shelf break-up more than ever before.

ESA’s Webcam from Space is available to the public and features the latest Envisat images, documenting the break-up of Antarctica’s Wilkins Ice Shelf.

New blow for dinosaur-killing asteroid theory

Computer generated gravity map image of the Chixulub Crater in Mexico.- Credit: NASA
Computer generated gravity map image of the Chixulub Crater in Mexico.- Credit: NASA

The enduringly popular theory that the Chicxulub crater holds the clue to the demise of the dinosaurs, along with some 65 percent of all species 65 million years ago, is challenged in a paper to be published in the Journal of the Geological Society on April 27, 2009.

The crater, discovered in 1978 in northern Yucutan and measuring about 180 kilometers (112 miles) in diameter, records a massive extra-terrestrial impact.

When spherules from the impact were found just below the Cretaceous-Tertiary (K-T) boundary, it was quickly identified as the “smoking gun” responsible for the mass extinction event that took place 65 million years ago.

It was this event which saw the demise of dinosaurs, along with countless other plant and animal species.

However, a number of scientists have since disagreed with this interpretation.

The newest research, led by Gerta Keller of Princeton University in New Jersey, and Thierry Adatte of the University of Lausanne, Switzerland, uses evidence from Mexico to suggest that the Chicxulub impact predates the K-T boundary by as much as 300,000 years.

“Keller and colleagues continue to amass detailed stratigraphic information supporting new thinking about the Chicxulub impact, and the mass extinction at the end of the Cretaceous,” says H. Richard Lane, program director in the National Science Foundation (NSF)’s Division of Earth Sciences, which funded the research. “The two may not be linked after all.”

From El Penon and other localities in Mexico, says Keller, “we know that between four and nine meters of sediments were deposited at about two to three centimeters per thousand years after the impact. The mass extinction level can be seen in the sediments above this interval.”

Advocates of the Chicxulub impact theory suggest that the impact crater and the mass extinction event only appear far apart in the sedimentary record because of earthquake or tsunami disturbance that resulted from the impact of the asteroid.

“The problem with the tsunami interpretation,” says Keller, “is that this sandstone complex was not deposited over hours or days by a tsunami. Deposition occurred over a very long time period.”

The study found that the sediments separating the two events were characteristic of normal sedimentation, with burrows formed by creatures colonizing the ocean floor, erosion and transportation of sediments, and no evidence of structural disturbance.

The scientists also found evidence that the Chicxulub impact didn’t have the dramatic impact on species diversity that has been suggested.

At one site at El Penon, the researchers found 52 species present in sediments below the impact spherule layer, and counted all 52 still present in layers above the spherules.

“We found that not a single species went extinct as a result of the Chicxulub impact,” says Keller.

This conclusion should not come as too great a surprise, she says. None of the other great mass extinctions are associated with an impact, and no other large craters are known to have caused a significant extinction event.

Keller suggests that the massive volcanic eruptions at the Deccan Traps in India may be responsible for the extinction, releasing huge amounts of dust and gases that could have blocked out sunlight and brought about a significant greenhouse effect.

Critical turning point can trigger abrupt climate change

Ice ages are the greatest natural climate changes in recent geological times. Their rise and fall are caused by slight changes in the Earth’s orbit around the Sun due to the influence of the other planets. But we do not know the exact relationship between the changes in the Earth’s orbit and the changes in climate. New research from the Niels Bohr Institute indicates that there can be changes in the CO2 levels in the atmosphere that suddenly reach a critical turning point and with that trigger the dramatic climate changes. The results are published in the American journal Paleoceanography.

The Earth’s climate is essentially contolled by three different cycles (Milankovitch). All three cycles are caused by the pull of the other planets in the solar system on the Earth, and one could say that they control the Earth’s climate by causing changes in the Sun’s radiation.

1: The Earth’s orbit around the sun is not completely circular, but slightly elliptical. The orbit is ‘elastic’ and contracts and expands in a cycle of 100.000 years. And the closer we are to the Sun, the more solar radiation and the more heat we receive.

2: The Earth’s axis has a tilt in relation to the Sun and that is why we have summer and winter. But the tilt is not constant, it swings between 22 degrees and 24 degrees, and the greater the tilt, the greater the difference between summer and winter. This cycle takes 40.000 years.

3: The Earth rotates around on its axis like a top – this gives day and night. But due to the tilt of the Earth and the elliptical orbit the direction changes with a cycle of 20.000 years. This results in varation in to whether the Earth is nearest the Sun during the summer or during the winter.

Solar radiation varies in the two hemispheres during the summer due to these cycles in the Earth’s tilt and the elliptical orbit and this has profound implications for whether ice caps can build up in the northern hemisphere, where the largest land areas are.

Mysterious changes in ice ages


The ice ages have come and gone the last 20 million years and for the last few million years we know with reasonable accuracy how often they come. In the period before about 1 million years ago the ice ages occured around every 40.000 years, then it happened suddenly that the period changed so that it became circa 100.000 years between ice ages. It is a mystery because nothing changed in the behaviour of the Earth’s orbit 1 million years ago. It is therefore due to a change that comes from the climate itself.

The conventional wisdom around the 100.000 year cycle of the last 10 ice ages is that the 100.000 years variation in the Earth’s orbital eccentricity (the measure for how elliptical the orbit is and the half-yearly variation in the Earth’s distance from the sun). This variation is still weaker than the variation that occurs with the 40.000 year cycle, so that in itself is a mystery.

Warm, half cold, ice cold



With completely new research results geophysicist Peter Ditlevsen, Centre for Ice and Climate at the Niels Bohr Institute, has found part of the explanation for the mystery of the sudden change of the ice ages. He has made model calculations of the climate of the past and compared it to the concrete data from seabed cores, which tell us about the climatic fluctuations of the past.

From the results he has been able to construct a diagram over the possible climatic conditions resulting from the variation in solar radiation. It appears that the ice ages and interglacial periods are not a gradual fluctuation between cold and warm climates.

What happened 1 million years ago was that the climate system went from a situation where it fluctuated between two states (cold and warm) with a 40.000 year cycle, corresponding to the dominant change in the Sun’s radiation. After this period the dynamic changed so that the climate jumped between 3 states, that is to say between a warm interglacial climate like our present climate, a colder climate and a very cold ice age climate. It is still the 40.000 year variation in solar radiation which controls our current fluctuations, but it results in changing climate periods of 80.000 and 120.000 years.

Chaotic dynamic climate
The climate does not become gradually colder or warmer – it jumps from the one state to the other. That which gets the climate to jump is that when the solar radiation changes and reaches a certain threshold – a ‘tipping point’, the existing climate state, e.g. an ice age, is no longer viable and so the climate jumps over into another state, e.g. a warm interglacial period. In chaos dynamics this phenomenon is called a bifurcation or a ‘catastrophe’.

In addition to the change in solar radiation there can be random changes in the Earth’s weather variations, that contribute to triggering the bifurcation or the ‘catastrophe’. Such variations are called ‘noise’, and a theory is, that the atmosphere’s CO2 level can be an important noise-factor. This means that there is the possibility that the ‘noise’ is a decisive factor for very large climate changes, which can therefore be unpredictable.

There is still no explanation for the change in the climate system 1 million years ago, but one theory is that the atmosphere’s CO2-level fell to the lowest level ever. If so, the manmade increase in CO2 may result in a return to 40.000 year ice age cycles.

“The new results are an important piece of the puzzle for understanding the ice ages and their climate dynamics. In the manmade climate changes, that we are possibly in the middle of now, one worries a lot about the possible so-called ‘tipping points’. The bifurcations that are now identified in the natural climate fluctuations are tipping points, so this is of course an important step in our understanding of climate changes”, explains Peter Ditlevsen.


Reference: (log-on required)



The bifurcation structure and noise assisted transitions in the Pleistocene glacial cycles, Paleoceanography, doi:10.1029/2008PA001673

Fingerprinting slow earthquakes

The most powerful earthquakes happen at the junction of two converging tectonic plates, where one plate is sliding (or subducting) beneath the other. Now a team of researchers, led by Teh-Ru Alex Song of the Carnegie Institution’s Department of Terrestrial Magnetism, has found that an anomalous layer at the top of a subducting plate coincides with the locations of slow earthquakes and non-volcanic tremors. The presence of such a layer in similar settings elsewhere could point to other regions of slow quakes. Slow earthquakes, also called silent earthquakes, take days, weeks, or even months to release pent-up energy instead of seconds or minutes as in normal earthquakes. The research is published in the April 24th issue of Science.

The scientists analyzed 20 years of seismic data for southern Mexico, where the Cocos plate is slipping beneath the North American plate. “We can tell a lot about the material inside the Earth by the speed, strength, and interferences of different seismic waves,” explained Song. “Typically, P-waves are the fastest, followed by scattered waves associated with variations in seismic wave speed within the medium. We used local observations recorded within 100 to 150 miles to map the structures at the top of the subducting plate.”

From observations and modeling, the researchers found that 30 events had similar waveforms and thus provided reinforcing information on structural details in the source region. In particular, they found a layer on top of the subducted plate where the speed of S-waves-which do not travel through liquids and are slower than P-waves-was some 30% to 50% slower than typical water-laden oceanic crust. The anomalous layer, dubbed the ultra-slow-velocity layer by the researchers, is found at depths of 15 to 30 miles (25 to 50 kilometers), somewhat deeper than the portion of the plate interface zone that is strongly coupled and is the site of great earthquakes in this region. The spatial distribution of such a structure is also confirmed by observations recorded by stations located more than 3,000 miles away in Canada.

The scientists also examined the locations where slow earthquakes and non-volcanic tremors have occurred. They found that slow earthquake areas and the ultra-slow-velocity layers cluster together, and that regions of non-volcanic tremors are adjacent to those clusters.

But what is this layer and what does it have to do with these seismic events? Song and team believe that it may be subducted oceanic crust at unusually high levels of water saturation. The cause of such anomalously high pore pressures is unknown, but a clue might come from the fact that non-volcanic tremors are concentrated in areas with temperatures around 840°F (450°C). The researchers think that at such temperature and under ambient pressures a combination of fluid release and reduction in permeability may give rise both to the high pore pressures and the stimulation of tremor activities.

“The ultra-slow-velocity layer may be the fingerprint that shows us where these slow quakes are active elsewhere in the world,” remarked Song. “It is extremely important to learn more about slow quakes and how they are temporally and spatially associated with more powerful and destructive earthquakes. Mapping these structures is a first step toward this goal, and the study provides observational data that can be used in numerical simulations on stress interactions between slow earthquakes and megaearthquakes.”

Ancient Greenland methane study good news for planet

CU-Boulder postdoctoral researcher Vasilii Petrenko, foreground, cleans a sample ice block from Greenland while Scripps Institution of Oceanography Professor Jeff Severinghaus loads another ice block into a vacuum melting tank. -  Photo courtesy Hinrich Schaefer
CU-Boulder postdoctoral researcher Vasilii Petrenko, foreground, cleans a sample ice block from Greenland while Scripps Institution of Oceanography Professor Jeff Severinghaus loads another ice block into a vacuum melting tank. – Photo courtesy Hinrich Schaefer

An analysis of ancient Greenland ice suggests a spike in the greenhouse gas methane about 11,600 years ago originated from wetlands rather than the ocean floor or from permafrost, a finding that is good news according to the University of Colorado at Boulder scientist who led the study.

Methane bound up in ocean sediments and permafrost, called methane clathrate, has been a concern to scientists because of its huge volume, greenhouse gas potency and potential for release during periods of warming, said Vasilii Petrenko, a CU-Boulder postdoctoral fellow and lead study author. If just 10 percent of methane from clathrates — an ice-like substance composed of methane and water — were suddenly released into Earth’s atmosphere, the resulting increase in the greenhouse effect would be equivalent to a 10-fold increase in atmospheric carbon dioxide, he said.

Using carbon 14 as a “tracer” to date and distinguish wetland methane from methane clathrates, an international team determined the methane jump 11,600 years ago likely emanated primarily from Earth’s wetlands. “From a global warming standpoint, this appears to be good news,” said Petrenko of CU-Boulder’s Institute of Arctic and Alpine Research, lead author on a paper that was published in Science on April 24.

Methane is the third most powerful greenhouse gas behind water vapor and CO2 and accounts for roughly 20 percent of the human-caused increase in the greenhouse effect.

As Earth emerged from the last ice age, temperatures in some places in the Northern Hemisphere shot up about 18 degrees Fahrenheit in just 20 years, said Petrenko. Scientists have been concerned that such abrupt warming events could trigger huge oceanic methane “burps” caused by the dissociation of seafloor clathrates, providing a positive climate feedback mechanism that could drive up Earth’s temperatures still further.

“If we found that clathrates release a lot of methane to the atmosphere during abrupt episodes of warming, that could signal big trouble for the planet, ” said Petrenko. “But even though wetlands appear be the primary source, it’s still something to be concerned about.”

Methane emitted from human activities like rice cultivation, livestock, the burning of grasslands, forests and wood fuels, gas leaks from fossil fuel production and waste management activities have nearly tripled methane concentrations in Earth’s atmosphere in the past 250 years, Petrenko said. The amount of carbon held in methane clathrate deposits on Earth may equal the amount of carbon in all oil, coal and gas reserves on the planet, he said.

Study co-authors were from the Scripps Institution of Oceanography, Oregon State University, the Australian Nuclear Science and Technology Organisation, the National Institute of Water and Atmospheric Research in New Zealand, Danish Technical University and the Commonwealth Scientific and Industrial Research Organisation in Australia. Petrenko conducted most of the research as part of his doctoral thesis at the Scripps Institution of Oceanography under Professor Jeffrey Severinghaus.

The research team extracted several tons of ancient ice from the western margin of the Greenland ice sheet at a site called Pakitsoq, the largest ice samples ever recovered for a climate change study. The researchers cut the ice into blocks with electric chain saws, dumped 17 cubic feet at a time into a vacuum melting tank heated by powerful propane torches, and transferred ancient air released from bubbles in the ice into cylinders for subsequent laboratory analysis, Petrenko said.

The effort, which lasted five field-seasons, was “an undertaking of epic proportions,” said Petrenko. “This was the first measurement of its kind, and we really pushed the envelope,” he said. “It represents a major advance in analytical methods for studying ancient ice.”

Methane clathrates are only stable in conditions that combine cold temperatures and high pressures. Some scientists suspect that a swift and massive warming in the early Cenozoic era about 56 million years ago may have been triggered by huge methane releases from clathrates into the atmosphere, Petrenko said.

Methane levels in Earth’s atmosphere increased about 2 percent from about A.D. 1 to 1000 and decreased by 2 percent from 1000 to 1700, which may have been due in part to decreased landscape burning by indigenous people in the Americas devastated by introduced diseases, according to a 2005 CU-Boulder study. About 60 percent of atmospheric methane is now generated from human-related activities, according to the International Panel on Climate Change.

Measuring snow with a bucket, a windmill, and the sun?

In Maine, government scientists have figured out how to measure snowfall in remote areas with a bucket, a small windmill, and the sun – all the while saving money, energy, and, ultimately helping to save lives.

What led to this energy-efficient ingenuity was the need to help the National Weather Service forecast and predict the risk of floods from spring snowmelt.

The problem was this: While the USGS has about 15 snowmelt measurement sites in Maine, they also needed a way to measure snowfall in remote areas where power grids are scarce. Emergency managers need accurate information to prepare for forthcoming hazards and energy companies need to plan ahead for how much water to expect in reservoirs.

“We needed to find an alternative power source,” said Bob Lent, chief of the USGS Maine Water Science Center in Augusta. “So we cobbled together a small-scale commercial windmill to replace commercial AC power, and supplemented the windmill with solar panels. What we ended up with is a windmill that powers our measurements on windy and cloudy days, and solar panels that power them on calm, sunny days,” said Lent. “And,” he added, “not only will we get more accurate information, but the systems will pay for themselves in about 3 to 4 years since using the electricity-dependent devices cost between $200 and $400 a year.”

A prototype system has been housed in use at the USGS office in Augusta for the past winter. It has proved so accurate, said Lent, that the USGS plans to install four snowfall sites around the state this summer using the same system.

Basically, the system looks like this: a gage is attached to a 5-gallon bucket that sits atop a simple wooden platform on a metal pole. The gage has a heating element to melt the snow as it collects in the cone of the bucket. The gage only turns on when snow is detected. Nearby is a data-collection box that is linked to the windmill and solar panels. When the bucket fills up with melted snow it tips over and empties. Each tip of the bucket measures 0.01 inches of precipitation and is recorded to the data recorder, which transmits the data and is updated on the web every hour.

“We are very optimistic about the utility of this system in other remote areas in the country and not just for snowfall measurements. It would be good for any remote site that needs more power than solar alone can deliver. For example, this could be used to measure water quality in the swamps of Florida as well as snowfall in Maine,” Lent noted.

“It’s a very small step in a very long journey of helping this country become greener, but this embodies what we need to be doing and the direction in which we need to be going,” said Lent.

Increasing Antarctic sea ice extent linked to the ozone hole

Increased growth in Antarctic sea ice during the past 30 years is a result of changing weather patterns caused by the ozone hole according to new research published this week (Thurs 23 April 2009).

Reporting in the journal Geophysical Research Letters scientists from British Antarctic Survey (BAS) and NASA say that while there has been a dramatic loss of Arctic sea ice, Antarctic sea ice has increased by a small amount as a result of the ozone hole delaying the impact of greenhouse gas increases on the climate of the continent.

Sea ice plays a key role in the global environment – reflecting heat from the sun and providing a habitat for marine life. At both poles sea ice cover is at its minimum during summer. However, during the winter freeze in Antarctica this ice cover expands to an area roughly twice the size of Europe. Ranging in thickness from less than a metre to several metres, the ice insulates the warm ocean from the frigid atmosphere above. Satellite images show that since the 1970s the extent of Antarctic sea ice has increased at a rate of 100,000 square kilometres a decade.

The new research helps explain why observed changes in the amount of sea-ice cover are so different in both polar regions.

Lead author Professor John Turner of BAS says,

“Our results show the complexity of climate change across the Earth. While there is increasing evidence that the loss of sea ice in the Arctic has occurred due to human activity, in the Antarctic human influence through the ozone hole has had the reverse effect and resulted in more ice. Although the ozone hole is in many ways holding back the effects of greenhouse gas increases on the Antarctic, this will not last, as we expect ozone levels to recover by the end of the 21st Century. By then there is likely to be around one third less Antarctic sea ice.”

Using satellite images of sea ice and computer models the scientists discovered that the ozone hole has strengthened surface winds around Antarctica and deepened the storms in the South Pacific area of the Southern Ocean that surrounds the continent. This resulted in greater flow of cold air over the Ross Sea (West Antarctica) leading to more ice production in this region.

The satellite data reveal the variation in sea ice cover around the entire Antarctic continent. Whilst there has been a small increase of sea ice during the autumn around the coast of East Antarctica, the largest changes are observed in West Antarctica. Sea ice has been lost to the west of the Antarctic Peninsula – a region that has warmed by almost 3ºC in the past 50 years. Further west sea ice cover over the Ross Sea has increased.

Turner continues,
“Understanding how polar sea ice responds to global change – whether human induced or as part of a natural process – is really important if we are to make accurate predictions about the Earth’s future climate. This new research helps us solve some of the puzzle of why sea-ice is shrinking is some areas and growing in others.

As world warms, water levels dropping in major rivers

Rivers in some of the world’s most populous regions are losing water, according to a comprehensive study of global stream flows.

The research, led by scientists at the National Center for Atmospheric Research (NCAR) in Boulder, Colo., suggests that the reduced flows in many cases are associated with climate change, and could potentially threaten future supplies of food and water.

The results will be published May 15 in the American Meteorological Society’s Journal of Climate. The research was supported by the National Science Foundation (NSF), NCAR’s sponsor.

“The distribution of the world’s fresh water, already an important topic,” says Cliff Jacobs of NSF’s Division of Atmospheric Sciences, “will occupy front and center stage for years to come in developing adaptation strategies to a changing climate.”

The scientists, who examined stream flows from 1948 to 2004, found significant changes in about one-third of the world’s largest rivers. Of those, rivers with decreased flow outnumbered those with increased flow by a ratio of about 2.5 to 1.

Several of the rivers channeling less water serve large populations, including the Yellow River in northern China, the Ganges in India, the Niger in West Africa and the Colorado in the southwestern United States.

In contrast, the scientists reported greater stream flows over sparsely populated areas near the Arctic Ocean, where snow and ice are rapidly melting.

“Reduced runoff is increasing the pressure on freshwater resources in much of the world, especially with more demand for water as population increases,” says NCAR scientist Aiguo Dai, the lead author of the journal paper. “Freshwater being a vital resource, the downward trends are a great concern.”

Many factors may affect river discharge, including dams and the diversion of water for agriculture and industry.

The researchers found, however, that the reduced flows in many cases appear to be related to global climate change, which is altering precipitation patterns and increasing the rate of evaporation.

The results are consistent with previous research by Dai and others showing widespread drying and increased drought over many land areas.

The study raises wider ecological and climate concerns.

Discharge from the world’s great rivers results in deposits of dissolved nutrients and minerals into the oceans. The freshwater flow also affects global ocean circulation patterns, which are driven by changes in salinity and temperature, and which play a vital role in regulating the world’s climate.

Although the recent changes in freshwater discharge are relatively small and may only have impacts around major river mouths, Dai said the freshwater balance in the global oceans and over land needs to be monitored for long-term changes.

Scientists have been uncertain about the impacts of global warming on the world’s major rivers. Studies with computer models show that many of the rivers outside the Arctic could lose water because of decreased precipitation in the mid- and lower latitudes, and an increase in evaporation caused by higher temperatures.

Earlier, less comprehensive analyses of major rivers had indicated, however, that global stream flow was increasing.

Dai and his co-authors analyzed the flows of 925 of the planet’s largest rivers, combining actual measurements with computer-based stream flow models to fill in data gaps.

The rivers in the study drain water from every major landmass except Antarctica and Greenland and account for 73 percent of the world’s total stream flow.

Overall, the study found that, from 1948 to 2004, annual freshwater discharge into the Pacific Ocean fell by about 6 percent, or 526 cubic kilometers–approximately the same volume of water that flows out of the Mississippi River each year.

The annual flow into the Indian Ocean dropped by about 3 percent, or 140 cubic kilometers. In contrast, annual river discharge into the Arctic Ocean rose about 10 percent, or 460 cubic kilometers.

In the United States, the Columbia River’s flow declined by about 14 percent during the 1948-2004 study period, largely because of reduced precipitation and higher water usage in the West.

The Mississippi River, however, has increased by 22 percent over the same period because of greater precipitation across the Midwest since 1948.

Some rivers, such as the Brahmaputra in South Asia and the Yangtze in China, have shown stable or increasing flows. But they could lose volume in future decades with the gradual disappearance of the Himalayan glaciers feeding them, the scientists say.

“As climate change inevitably continues in coming decades, we are likely to see greater impacts on many rivers and the water resources that society has come to rely on,” says NCAR scientist Kevin Trenberth, a co-author of the paper.