Evidence emerges of ancient lake in California’s Eel River

A catastrophic landslide 22,500 years ago dammed the upper reaches of northern California’s Eel River, forming a 30-mile-long lake which has since disappeared. It left a living legacy found today in the genes of the region’s steelhead trout.

Using remote-sensing technology known as airborne Light Detection and Ranging (LiDAR) and hand-held global-positioning-systems (GPS) units, scientists recently found evidence for a late Pleistocene, landslide-dammed lake along the river.

Today the Eel river is 200 miles long, carved into the ground from high in the California Coast Ranges to the river’s mouth in the Pacific Ocean in Humboldt County.

The evidence for the ancient landslide, which, scientists say, blocked the river with a 400-foot-wall of loose rock and debris, is detailed this week in a paper appearing on-line in the journal Proceedings of the National Academy of Sciences.


The research provides a rare glimpse into the geological history of this rapidly evolving mountainous region.

“This study reminds us that there are still significant surprises to be unearthed about past landscape dynamics and their broad impacts,” said Paul Cutler, program director in the National Science Foundation’s Division of Earth Sciences, which funded the research. “For example, it provides valuable information for assessing modern landslide hazard potential in this region.”

It also helps to explain emerging evidence from other studies that show a dramatic decrease in the amount of sediment deposited from the river in the ocean just offshore at about the same time period, says lead author of the paper Benjamin Mackey of the California Institute of Technology.

“Perhaps of most interest, the presence of this landslide dam also provides an explanation for the results of previous research on the genetics of steelhead trout in the Eel River,” Mackey said.

In that study, scientists found a striking relationship between two types of ocean-going steelhead in the river–a genetic similarity not seen among summer-run and winter-run steelhead in other nearby waterways.

An interbreeding of the two fish, in a process known as genetic introgression, may have occurred among the fish brought together while the river was dammed, Mackey said.

“The dam likely would have been impassable to the fish migrating upstream, meaning both ecotypes would have been forced to spawn and inadvertently breed downstream of the dam. This period of gene flow between the two types of steelhead can explain the genetic similarity observed today.”

Once the dam burst, the fish would have reoccupied their preferred spawning grounds and resumed different genetic trajectories.

“The damming of the river was a dramatic, punctuated event that greatly altered the landscape,” said co-author Joshua Roering, a geologist at the University of Oregon.

“Although current physical evidence for the landslide dam and ancient lake is subtle, its effects are recorded in the Pacific Ocean and persist in the genetic make-up of today’s Eel River steelhead,” said Roering. “It’s rare for scientists to be able to connect the dots between such diverse phenomena.”

The lake formed by the landslide, the researchers theorize, covered about 18 square miles.

After the dam was breached, the flow of water would have generated one of North America’s largest landslide-dam outburst floods.

Landslide activity and erosion have erased much of the evidence for the now-gone lake. Without the acquisition of LiDAR mapping, the lake’s existence may have never been discovered, the scientists said.

The area affected by the landslide-caused dam accounts for about 58 percent of the modern Eel River watershed. Based on today’s general erosion rates, the geologists believe that the lake could have filled in with sediment within about 600 years.

“The presence of a dam of this size was unexpected in the Eel River, given the abundance of easily eroded sandstone and mudstone, which are generally not considered strong enough to form long-lived dams,” Mackey said.

He and colleagues were drawn to the Eel River–among the most-studied erosion systems in the world–to study large, slow-moving landslides.

“While analyzing the elevation of terraces along the river, we discovered they clustered at a common elevation rather than decreased in elevation downstream paralleling the river profile, as would be expected for river terraces,” said Mackey.

“That was the first sign of something unusual, and it clued us into the possibility of an ancient lake.”

Heavy metal — in and around the lakes

Heavy metal pollution of lakes has a seriously detrimental impact on people and ecosystems that rely on such bodies of water. According to a study published in the current issue of Interdisciplinary Environmental Review, researchers have focused on the physicochemical properties and toxicology of water from and around Thane City of Maharashtra.

Environmental chemist Pravin Singare of Bhavan’s College, in Mumbai, and colleagues highlight the fact that fresh water bodies all over the world are becoming increasingly polluted day by day and that this represents a growing problem in the developing world and beyond. They suggest that regular monitoring is crucial for the well-being and health of the surrounding population and as such, the team has carried out a systematic study to estimate the physico-chemical parameters and level of toxic heavy metal content in the Jail Talav and Kalwa Lakes of Thane City, as perhaps being indicative of similar problems with other bodies of water.

The team’s measurements suggest that the presence of heavy metals such as iron, copper, nickel and zinc, which are essential for life at trace levels are well above permissible concentrations making them a significant threat to ecosystems and a problem for those who rely on the lakes for drinking water or crop irrigation. In addition mercury, arsenic and cadmium were all present at much higher than acceptable concentrations.

South Asia is home to more a fifth of the world’s population, the researchers say, and is facing a serious water crisis. “This region, which is in the grip of flood and drought cycles, needs a long-term strategy for management of its water resources,” the team says. Unfortunately, strategies adopted so far have all failed in India, the team asserts, this is obvious given the poor quality of the water revealed by their measurements of Jail Talav and Kalwa Lakes assuming these are typical of the region as a whole.

Food chain contamination by heavy metals has become an important issue partly because of the potential accumulation in biosystems, through contaminated water, the team adds. “A better understanding of heavy metal sources, their accumulation in water and the effect of their presence in water on plant systems are particularly impertinent in ongoing risk assessments,” the researchers say.

Researchers test cutting-edge technology for underwater mapping at Tahoe basin

A borrowed boat, a small mountain lake and the inaugural run of a half-a-million dollar state-of-the-art multi-beam sonar system made history this month with the successful high-definition mapping by University of Nevada, Reno, and Scripps Institution of Oceanography researchers of the bottom of Fallen Leaf Lake, a tributary lake just upstream from Lake Tahoe. -  Photo by Mike Wolterbeek, University of Nevada, Reno
A borrowed boat, a small mountain lake and the inaugural run of a half-a-million dollar state-of-the-art multi-beam sonar system made history this month with the successful high-definition mapping by University of Nevada, Reno, and Scripps Institution of Oceanography researchers of the bottom of Fallen Leaf Lake, a tributary lake just upstream from Lake Tahoe. – Photo by Mike Wolterbeek, University of Nevada, Reno

A borrowed boat, a small mountain lake and the inaugural run of a half-a-million dollar state-of-the-art multi-beam sonar system made history this month with the successful high-definition mapping of the bottom of Fallen Leaf Lake, a tributary lake just upstream from Lake Tahoe.

“The clarity of the images we produced is unmatched in detail,” said University of Nevada, Reno Seismology Lab Director Graham Kent and co-lead investigator of the project. “We can clearly see 1,000-year-old trees standing upright under 100 feet of water and remnants of earthquake activity along the West Tahoe Fault line. This is a valuable tool for a number of scientific pursuits.”

What the scientists can see:

  • Fault mapping such as the West Tahoe Fault which runs through Fallen Leaf Lake – it’s a magnitude 7.3 capable normal fault that’s approaching the end its characteristic earthquake cycle (almost overdue)
  • The effects of drought, including the Medieval Warm Period (approximately 950-1250 AD); features include: old shorelines at 80- to140-feet underwater; and standing, rooted trees at 110-foot level below the lake’s current surface
  • Substrate identification that has potential uses for biohabitat mapping of various aquatic species, both native and invasive

“The centerpiece of the system comes from rocket technology, with an inertial guidance/gyro system, which allows image stability even as the boat rocks back and forth in the waves,” said Kent, also a professor in the University’s College of Science. “It’s also positioned with a phased GPS array and sound velocity corrections to align or properly register lake-floor pixels. It’s a half-million dollar acoustic system, but mo
st of the cost is in the guidance system.”

While there are many commercial applications of this type of mapping, this system is owned by only a handful of academic institutions worldwide. The technology allows for several centimeter depth resolution (with less than one-meter spatial resolution), giving definition similar to airborne lidar.

“This system helps document the best estimate of how severe the Medieval Warm Period drought was, with perhaps 40 percent less precipitation than we get today, for more than two centuries,” Kent said. “It’s disturbing to think it could happen again. This is possibly the best estimate of medieval drought anywhere in the Sierra.”

Kent and his colleagues from Scripps Institution of Oceanography in San Diego, Calif., geophysicists Jeff Babcock and Neal Driscoll, have been studying the glacially carved lake bottom in conjunction with seismic studies at Lake Tahoe for nearly a decade, and they are excited to use the new tool they have developed to continue and enhance those studies.

“Not only are we using this cutting-edge system to map the geologic substrate but we can use this, for example, to quickly find potential habitat for invasive species at Lake Tahoe such as the Asian Clam,” Kent said.

These expeditions also provide an ideal environment to train the next generation of research scientists; two graduate students, one from the University and one from SIO, participated in the mapping. The team has also been joined by Emeritus Professor John Kleppe from the University’s College of Engineering, who was one of the first to document the submerged trees beneath Fallen Leaf, and his involvement has been significant in both the science and educational aspects of this project.

The Fallen Leaf Lake area was the largest unmapped region of the Tahoe Basin. The lake is three miles long and one mile wide, and the surface is about 150 feet higher in elevation than Lake Tahoe. The lake is about 415 feet deep at its deepest point.

The team has mapped lakes and shallow-seas such as Pyramid Lake, Lake Tahoe, Salton Sea and the Great Salt Lake to name a few of their latest endeavors.

Geologists show unprecedented warming in Lake Tanganyika

Jessica Tierney is a geologist at Brown University. -  Brown University
Jessica Tierney is a geologist at Brown University. – Brown University

Lake Tanganyika, the second oldest and the second-deepest lake in the world, could be in for some rough waters.

Geologists led by Brown University have determined the east African rift lake has experienced unprecedented warming during the last century, and its surface waters are the warmest on record. That finding is important, the scientists write in the journal Nature Geoscience, because the warm surface waters likely will affect fish stocks upon which millions of people in the region depend.

The team took core samples from the lakebed that laid out a 1,500-year history of the lake’s surface temperature. The data showed the lake’s surface temperature, 26 degrees Celsius (78.8°F), last measured in 2003, is the warmest the lake has been for a millennium and a half. The team also documented that Lake Tanganyika experienced its biggest temperature change in the 20th century, which has affected its unique ecosystem that relies upon the natural conveyance of nutrients from the depths to jumpstart the food chain upon which the fish survive.

“Our data show a consistent relationship between lake surface temperature and productivity (such as fish stocks),” said Jessica Tierney, a Brown graduate student who this spring earned her Ph.D. and is the paper’s lead author. “As the lake gets warmer, we expect productivity to decline, and we expect that it will affect the [fishing] industry.”

The research grew out of two coring expeditions sponsored by the Nyanza Project in 2001 and 2004. Cores were taken by Andrew Cohen, professor of geological sciences at the University of Arizona and director of the Nyanza project, and James Russell, professor of geological sciences at Brown, who is also Tierney’s adviser.

Lake Tanganyika is bordered by Burundi, the Democratic Republic of Congo, Tanzania, and Zambia – four of the poorest countries in the world, according to the United Nations Human Development Index. An estimated 10 million people live near the lake, and they depend upon it for drinking water and for food. Fishing is a crucial component for the region’s diet and livelihood: Up to 200,000 tons of sardines and four other fish species are harvested annually from Lake Tanganyika, a haul that makes up a significant portion of local residents’ diets, according to a 2001 report by the Lake Tanganyika Biodiversity Project.

Lake Tanganyika, one of the richest freshwater ecosystems in the world, is divided into two general levels. Most of the animal species live in the upper 100 meters, including the valuable sardines. Below that, the lake holds less and less oxygen, and at certain depths, it is anoxic, meaning it has no oxygen at all. What this all means is the lake is highly stratified and depends on wind to churn the waters and send nutrients from the depths toward the surface as food for algae, which supports the entire food web of the lake. But as Lake Tanganyika warms, the mixing of waters is lessened, the scientists find, meaning less nutrients are funneled from the depths toward the surface. Worse, more warming at the surface magnifies the difference in density between the two levels; even more wind is needed to churn the waters enough to ferry the nutrients toward the fish-dwelling upper layer.

The researchers’ data show that during the last 1,500 years, intervals of prolonged warming and cooling are linked with low and high algal productivity, respectively, indicating a clear link between past temperature changes and biological productivity in the lake.

“The people throughout southcentral Africa depend on the fish from Lake Tanganyika as a crucial source of protein,” Cohen noted. “This resource is likely threatened by the lake’s unprecedented warming since the late 19th century and the associated loss of lake productivity.”

Climate change models show a general warming in the region, which, if accurate, would cause even greater warming of the Lake Tanganyika’s surface waters and more stratification in the lake as a whole. “So, as you move forward, you can imagine that density gradient increasing,” Russell said.

Some researchers have posited that the declining fish stocks in Lake Tanganyika can be attributed mainly to overfishing, and Tierney and Russell say that may be a reason. But they note that the warming in the lake, and the lessened mixing of critical nutrients is exacerbating the stocks’ decline, if not causing it in the first place. “It’s almost impossible for it not to,” Russell said.

Were short warm periods typical for transitions between interglacial and glacial epochs?

Russian and German researchers took sediment probes of four silted up lakes in Central and Eastern Europe in order to reconstruct the climate of the Eemian Interglacial 115,000 years ago. At this time the Eemian Interglacial ended and was followed by the Weichselian Glacial which ended 15,000 years ago. -  Frank W. Junge/SAW
Russian and German researchers took sediment probes of four silted up lakes in Central and Eastern Europe in order to reconstruct the climate of the Eemian Interglacial 115,000 years ago. At this time the Eemian Interglacial ended and was followed by the Weichselian Glacial which ended 15,000 years ago. – Frank W. Junge/SAW

At the end of the last interglacial epoch, around 115,000 years ago, there were significant climate fluctuations. In Central and Eastern Europe, the slow transition from the Eemian Interglacial to the Weichselian Glacial was marked by a growing instability in vegetation trends with possibly at least two warming events. This is the finding of German and Russian climate researchers who have evaluated geochemical and pollen analysis of lake sediments in Saxony-Anhalt, Brandenburg and Russia. Writing in Quaternary International, scientists from the Helmholtz Centre for Environmental Research (UFZ), the Saxon Academy of Sciences (SAW) in Leipzig and the Russian Academy of Sciences say that a short warming event at the very end of the last interglacial period marked the final transition to the ice age.

The Eemian Interglacial was the last interglacial epoch before the current one, the Holocene. It began around 126,000 years ago, ended around 115,000 years ago and is named after the river Eem in the Netherlands. The followed Weichselian Glacial ended around 15,000 years ago is the most recent glacial epoch named after the Polish river Weichsel. At its peak around 21,000 years ago, the glaciers stretched as far as the south of Berlin (Brandenburg Stadium).

The researchers studied lake sediments to reconstruct the climate history of the Eemian Interglacial, since deposits on river and lake beds can build up a climate archive over the years. The sediment samples came from lakes that existed at the time, but which have since silted up and been uncovered in the former open cast mines at Gröbern near Bitterfeld, Neumark-Nord in the Geiseltal valley near Merseburg, and Klinge near Cottbus and at Ples on the upper reaches of the Volga, around 400 kilometres north-east of Moscow. Gröbern in Saxony-Anhalt is now seen by experts as one of the most studied places for Eemian Interglacial climate history in Germany. As well as pollen concentrations, the researchers analyzed the level and ratios of stable carbon (13C/12C) and oxygen isotopes (18O/16O) in carbonates and organic matter from sediment layers, since these provide information about the vegetation development and an indication of the climate.

The results show a relatively stable climate over most of the time, but with instabilities at the beginning and end of the Eemian Interglacial. “The observed instability with the proven occurrence of short warming events during the transition from the last interglacial to the last glacial epoch could be, when viewed carefully, a general, naturally occurring characteristic of such transition phases,” concludes Dr Tatjana Boettger of the UFZ, who analyzed the sediment profiles at the UFZ’s isotope laboratory in Halle. “Detailed studies of these phenomena are important for understanding the current controversial discussed climate trend so that we can assess the human contribution to climate change with more certainty,” explains Dr Frank W. Junge of the SAW.

From reconstructions of climate history, we know that in the Earth’s recent history, interglacial epochs occurred only once every 100,000 years or so and lasted for an average of around 10,000 years. The current interglacial epoch – the Holocene – has already lasted more than 10,000 years and reached its highest point so far around 6000 years ago. From a climate history perspective, we are currently at the end of the Holocene and could therefore expect to see a cooling-down in a few thousand years if there had been no human influence on the atmosphere and the resulting global warming.

Digging deeper below Antarctica’s Lake Vida

Antarctica’s Lake Vida, a geologic curiosity that is essentially an ice bottle of brine, is home to some of the oldest and coldest living organisms on Earth. Perpetually covered by more than 60 feet of ice, the brine below — water that is five to seven times more salty than seawater — has been found to be home to cryobiological microbes some 2,800 years old which were revived after a gradual thaw.

That widely reported finding came in 2002 from Peter Doran, associate professor of earth and environmental sciences at the University of Illinois at Chicago. But the discovery raised many new questions. Now, Doran and his department colleague Fabien Kenig with collaborators from the Nevada-based Desert Research Institute will return to Lake Vida late next year for more exploration, funded by a $1.1 million National Science Foundation grant.

Doran and Kenig plan to perform the first-ever drilling entirely through Lake Vida’s thick ice cap, into the brine, and down into sediment below, retrieving about 10 feet or more of core sample for analysis.

“The main goal is to get into that brine pocket and the sediment beneath it to both document and define the ecosystem that’s there today, and the history of that ecosystem,” Doran said.

The sediment samples could yield clues about life in such an extreme environment dating back thousands of years, which could help geoscientists draw a better picture of processes that occur as the Earth moves into colder periods.

“If we took, for example, a Wisconsin lake and started turning the temperatures down during a climatic downturn, what is the impact on the lake’s ecosystem and what strategies are used by living things to survive this extremely cold brine?” Doran said of the salty liquid that hovers around 10 degrees Fahrenheit year-round. “There are few examples on Earth of things shown to live in that water temperature.”

A University of Wisconsin group will drill the ice hole, but special care will be required in preparing the site. A tent will be partitioned to provide both a drilling site cover and adjacent laboratory to analyze samples. It will be sort of like setting up a hospital operating room in the Antarctic cold, with the drill requiring the sanitary cleanliness of a surgeon’s scalpel to prevent any surface contaminants from ruining samples.

Kenig, an organic geochemist, will study the lake’s carbon and organic chemistry as well as molecular fossils in the sediment core. These preserved organic compounds will point to changes in the ecosystem as the lake froze.

“As this environment was isolated for some time, we need to be very cautious not to introduce any external elements that could bias our samples,” Kenig said. To assure sample purity, nothing plastic or rubber will be used in the drilling and all equipment penetrating the lake water and sediment will be sterilized.

While specially preserved samples will be shipped back to UIC and the Desert Research Institute for later analysis, some work, such as microbial counts, will be done on site. Doran’s previous on-site research at Lake Vida found in the ice the highest concentration of nitrous oxide — “laughing gas” — of any ecosystem on Earth. It was a clue that would make any scientist smile.

“This gas is produced by microbes,” Doran said. “That was a hint that we had a viable ecosystem there.”

Map characterizes active lakes below Antarctic ice

Lakes in Antarctica, concealed under miles of ice, require scientists to come up with creative ways to identify and analyze these hidden features. Now, researchers using space-based lasers on a NASA satellite have created the most comprehensive inventory of lakes that actively drain or fill under Antarctica’s ice. They have revealed a continental plumbing system that is more dynamic than scientists thought.

“Even though Antarctica’s ice sheet looks static, the more we watch it, the more we see there is activity going on there all the time,” said Benjamin Smith of the University of Washington in Seattle, who led the study.

Unlike most lakes, Antarctic lakes are under pressure from the ice above. That pressure can push melt water from place to place like water in a squeezed balloon. The water moves under the ice in a broad, thin layer, but also through a linked cavity system. This flow can resupply other lakes near and far.

Understanding this plumbing is important, as it can lubricate glacier flow and send the ice speeding toward the ocean, where it can melt and contribute to sea level change. But figuring out what’s happening beneath miles of ice is a challenge.

Researchers led by Smith analyzed 4.5 years of ice elevation data from NASA’s Ice, Cloud and land Elevation satellite (ICESat) to create the most complete inventory to date of changes in the Antarctic plumbing system. The team has mapped the location of 124 active lakes, estimated how fast they drain or fill, and described the implications for lake and ice-sheet dynamics in the Journal of Glaciology.

What Lies Beneath


For decades, researchers flew ice-penetrating radar on airplanes to “see” below the ice and infer the presence of lakes. In the 1990s, researchers began to combine airborne- and satellite-based data to observe lake locations on a continent-wide scale.

Scientists have since established the existence of about 280 “subglacial” lakes, most located below the East Antarctic ice sheet. But those measurements were a snapshot in time, and the question remained as to whether lakes are static or dynamic features. Were they simply sitting there collecting water?

In 2006 Helen Fricker, a geophysicist at the Scripps Institution of Oceanography, La Jolla, Calif., used satellite data to first observe subglacial lakes on the move. Working on a project to map the outline of Antarctica’s land mass, Fricker needed to differentiate floating ice from grounded ice. This time it was laser technology that was up to the task. Fricker used ICESat’s Geoscience Laser Altimeter System and measured how long it took a pulse of laser light to bounce of the ice and return to the satellite, from which she could infer ice elevation. Repeating the measurement over a course of time revealed elevation changes.

Fricker noticed, however, a sudden dramatic elevation change — over land. It turned out this elevation change was caused by the filling and draining of some of Antarctica’s biggest lakes.

“Sub-ice-sheet hydrology is a whole new field that opened up through the discovery of lakes filling and draining on relatively short timescales and involving large volumes of water,” said Robert Bindschadler, a glaciologist at NASA’s Goddard Space Flight Center in Greenbelt, Md., who has used ICESat data in other studies of Antarctica. “ICESat gets the credit for enabling that discovery.”

Networking in the Antarctic


But were active lakes under the ice a common occurrence or a fluke?

To find out, Ben Smith, Fricker and colleagues extended their elevation analysis to cover most of the Antarctic continent and 4.5 years of data from ICESat’s Geoscience Laser Altimeter System (GLAS). By observing how ice sheet elevation changed between the two or three times the satellite flew over a section every year, researchers could determine which lakes were active. They also used the elevation changes and the properties of water and ice to estimate the volume change.

Only a few of the more than 200 previously identified lakes were confirmed active, implying that lakes in East Antarctica’s high-density “Lakes District” are mostly inactive and do not contribute much to ice sheet changes.

Most of the 124 newly observed active lakes turned up in coastal areas, at the head of large drainage systems, which have the largest potential to contribute to sea level change.

“The survey identified quite a few more subglacial lakes, but the locations are the intriguing part,” Bindschadler said. “The survey shows that most active subglacial lakes are located where the ice is moving fast, which implies a relationship.”

Connections between lakes are apparent when one lake drains and another simultaneously fills. Some lakes were found to be connected to nearby lakes, likely through a network of subglacial tunnels. Others appeared to be linked to lakes hundreds of miles away.

The team found that the rate at which lake water drains and fills varies widely. Some lakes drained or filled for periods of three to four years in steady, rather than episodic, changes. But water flow rates beneath the ice sheet can also be as fast as small rivers and can rapidly supply a lubricating film beneath fast-flowing glaciers.

“Most places we looked show something happening on short timescales,” Smith said. “It turns out that those are fairly typical examples of things that go on under the ice sheet and are happening all the time all over Antarctica.”

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.

Great Basin’s Bear Lake reveals records of past climate

This is the cover of 'Paleoenvironments of Bear Lake, Utah and Idaho, and Its Catchment,'
by Joseph G. Rosenbaum and Darrell S. Kaufman. -  Geological Society or America
This is the cover of ‘Paleoenvironments of Bear Lake, Utah and Idaho, and Its Catchment,’
by Joseph G. Rosenbaum and Darrell S. Kaufman. – Geological Society or America

The Geological Society of America presents a new Special Paper, Paleoenvironments of Bear Lake, Utah and Idaho, and Its Catchment. This volume is the culmination of more than a decade of coordinated investigations aimed at a holistic understanding of the long-lived Bear Lake, which is located 100 km northeast of Salt Lake City, along the course of the Bear River, the largest river in the Great Basin of the western United States.

One of the oldest existing lakes in North America, Bear Lake lies within an asymmetric, tectonically active basin that contains hundreds of meters of sediment accumulated over the past several million years. This volume’s 14 chapters, with 20 contributing authors, contain geological, mineralogical, geochemical, paleontological, and limnological studies extending from the drainage basin to the depocenter. The studies span both modern and paleoenvironments, including a 120-m-long sediment core that captures a continuous record of the last two glacial-interglacial cycles.

According to editors Joseph Rosenbaum of the U.S. Geological Survey in Denver and Darrell S. Kaufman of Northern Arizona University, understanding Bear Lake and the paleorecords revealed there yields information about past climate for the larger region, including the Upper Colorado River Basin, the source of much of the water for the southwestern United States.

Cardiac fibrillation of the climate

In the current issue of the Scientific Journal Nature Geoscience a group of Norwegian, Swiss and German geoscientists prove that before the set-in of the Holocene very rapid climate changes already existed. The transition from the stable cold period took place about 12 150 to 11 700 years ago with very rapid fluctations up to the temperatur-threshold at which the Holocene began.

For this study, a group of scientists around J. Bakke, University of Bergen, examined sediments from Lake Kråkenes in Southwest Norway. These micro-layered lake deposits constitute a particularly suitable geological archive, with which scientists are able to analyse the climate volatility. The geochemical determination of titanium in sediments shows that during this phase significant short-term fluctuations in the titanium concentrations in the lake are detectable.

“We ascribe this to the short-term fluctuations in watermelt runoff from the inland glacier which feeds this lake”, explains Professor Gerald Haug from the DFG Leibniz Center for Earth Surface Process and Climate Studies at the University of Potsdam and the ETH Zürich, who carried out the analysis together with his colleague, Peter Dulkski, from the GFZ German Research Centre for Geosciences. “The fluctuating glacialmelt is a result of the intermittent advancement of the Gulf Stream and the resulting successive retreat of the sea-ice coverage.”

This process is closely linked with an equally high-frequence change in the westwind system and the therewith connected heat transport to Europe. This cardiac fibrillation of the climate is reflected again, as shown, in the fast-varying meltwater runoff into the examined lake, which at this point in time actually lay at the most climate-sensitive location of Europe, namely there where the Gulf Stream and the sea-ice coverage transformed.