New View of Tectonic Plates

PASADENA, Calif.—Computational scientists and geophysicists at the University of Texas at Austin and the California Institute of Technology (Caltech) have developed new computer algorithms that for the first time allow for the simultaneous modeling of the earth's mantle flow, large-scale tectonic plate motions, and the behavior of individual fault zones, to produce an unprecedented view of plate tectonics and the forces that drive it.

A paper describing the whole-earth model and its underlying algorithms will be published in the August 27 issue of the journal Science and also featured on the cover.

The work "illustrates the interplay between making important advances in science and pushing the envelope of computational science," says Michael Gurnis, the John E. and Hazel S. Smits Professor of Geophysics, director of the Caltech Seismological Laboratory, and a coauthor of the Science paper.

To create the new model, computational scientists at Texas's Institute for Computational Engineering and Sciences (ICES)—a team that included Omar Ghattas, the John A. and Katherine G. Jackson Chair in Computational Geosciences and professor of geological sciences and mechanical engineering, and research associates Georg Stadler and Carsten Burstedde—pushed the envelope of a computational technique known as Adaptive Mesh Refinement (AMR).

Partial differential equations such as those describing mantle flow are solved by subdividing the region of interest (such as the mantle) into a computational grid. Ordinarily, the resolution is kept the same throughout the grid. However, many problems feature small-scale dynamics that are found only in limited regions. "AMR methods adaptively create finer resolution only where it's needed," explains Ghattas. "This leads to huge reductions in the number of grid points, making possible simulations that were previously out of reach.”

"The complexity of managing adaptivity among thousands of processors, however, has meant that current AMR algorithms have not scaled well on modern petascale supercomputers," he adds. Petascale computers are capable of one million billion operations per second. To overcome this long-standing problem, the group developed new algorithms that, Burstedde says, "allows for adaptivity in a way that scales to the hundreds of thousands of processor cores of the largest supercomputers available today." 

With the new algorithms, the scientists were able to simulate global mantle flow and how it manifests as plate tectonics and the motion of individual faults. According to Stadler, the AMR algorithms reduced the size of the simulations by a factor of 5,000, permitting them to fit on fewer than 10,000 processors and run overnight on the Ranger supercomputer at the National Science Foundation (NSF)-supported Texas Advanced Computing Center.  

A key to the model was the incorporation of data on a multitude of scales. "Many natural processes display a multitude of phenomena on a wide range of scales, from small to large," Gurnis explains. For example, at the largest scale—that of the whole earth—the movement of the surface tectonic plates is a manifestation of a giant heat engine, driven by the convection of the mantle below. The boundaries between the plates, however, are composed of many hundreds to thousands of individual faults, which together constitute active fault zones. "The individual fault zones play a critical role in how the whole planet works," he says, "and if you can't simulate the fault zones, you can't simulate plate movement"—and, in turn, you can't simulate the dynamics of the whole planet.

In the new model, the researchers were able to resolve the largest fault zones, creating a mesh with a resolution of about one kilometer near the plate boundaries. Included in the simulation were seismological data as well as data pertaining to the temperature of the rocks, their density, and their viscosity—or how strong or weak the rocks are, which affects how easily they deform. That deformation is nonlinear—with simple changes producing unexpected and complex effects.

"Normally, when you hit a baseball with a bat, the properties of the bat don't change—it won't turn to Silly Putty. In the earth, the properties do change, which creates an exciting computational problem," says Gurnis. "If the system is too nonlinear, the earth becomes too mushy; if it's not nonlinear enough, plates won't move. We need to hit the 'sweet spot.'"

After crunching through the data for 100,000 hours of processing time per run, the model returned an estimate of the motion of both large tectonic plates and smaller microplates—including their speed and direction. The results were remarkably close to observed plate movements.

In fact, the investigators discovered that anomalous rapid motion of microplates emerged from the global simulations. "In the western Pacific," Gurnis says, "we have some of the most rapid tectonic motions seen anywhere on Earth, in a process called 'trench rollback.' For the first time, we found that these small-scale tectonic motions emerged from the global models, opening a new frontier in geophysics."

One surprising result from the model relates to the energy released from plates in earthquake zones. "It had been thought that the majority of energy associated with plate tectonics is released when plates bend, but it turns out that's much less important than previously thought," Gurnis says. "Instead, we found that much of the energy dissipation occurs in the earth's deep interior. We never saw this when we looked on smaller scales."

The paper, "The Dynamics of Plate Tectonics and Mantle Flow: From Local to Global Scales," was also coauthored by Lucas C. Wilcox of the University of Texas at Austin and Laura Alisic of Caltech. The work was supported by the NSF, the Department of Energy's Office of Science, and—at the Caltech Tectonics Observatory—by the Gordon and Betty Moore Foundation. 

Kathy Svitil

NRC Recommends Three Astronomy/Astrophysics Projects with Potential Major Caltech Roles

PASADENA, Calif.—In an announcement August 13 at the National Academies in Washington, D.C., the National Research Council (NRC) recommended three space- and ground-based astronomy and astrophysics projects with potential major roles for researchers at the California Institute of Technology (Caltech): CCAT, a submillimeter telescope to be erected in the Chilean Andes, which will help unravel the cosmic origins of stars, planets, and galaxies; the Laser Interferometer Space Antenna (LISA), designed to detect gravitational waves, ripples in the fabric of space and time formed by the most violent events in the universe; and the development of a Giant Segmented Mirrored Telescope (GSMT)—the Thirty Meter Telescope (TMT) being one of two such telescopes under development—which will yield the clearest and deepest view of the universe.

The recommendations were the result of the Astro2010 a decadal survey, in which a panel of experts was convened by the NRC to look at the coming decade and prioritize research activities in astronomy and astrophysics, as well as activities at the interface of these disciplines with physics.

"It is particularly gratifying to see that Caltech faculty are prepared to play leading roles in three of the major projects identified by the Astro2010 study," says Tom Soifer, professor of physics, director of the Spitzer Science Center, and chair of the Division of Physics, Mathematics and Astronomy at Caltech. "Many of the important discoveries in the coming decades will be based on CCAT, TMT, and LISA, and our deep involvement in these projects will ensure that Caltech remains a vibrant, exciting center for astrophysics."


CCAT was recommended for an immediate start. CCAT is a collaboration between Caltech and the Jet Propulsion Laboratory (JPL), managed by Caltech for NASA; Cornell University; the University of Colorado; and consortia in both Germany and Canada. It will be a 25-meter telescope located on a mountain site in Chile at an elevation of 18,500 feet above sea level. Taking advantage of recent advances in detector technology, CCAT will employ cameras and spectrometers to survey the sky at millimeter and submillimeter wavelengths, providing an unprecedented combination of sensitivity and resolution across a wide field of view. CCAT will reveal young galaxies, stars, and solar systems enshrouded in clouds of dust that make these objects very faint or invisible at other wavelengths.

"We are making rapid progress on all fronts—in detectors, instruments, and new facilities—and this is leading to important scientific discoveries," says Jonas Zmuidzinas, Merle Kingsley Professor of Physics at Caltech, director of the Microdevices Laboratory at JPL, and a CCAT project scientist. "With CCAT, we will gain real insight into the evolution of stars and galaxies."

According to Riccardo Giovanelli, CCAT director and professor of astronomy at Cornell University, "CCAT will allow us to explore the process of formation of galaxies, which saw its heyday about a billion years after the Big Bang, some 13 billion years ago; to peek into the interior of the dusty molecular clouds within which stars and planets form; and to survey the pristine chunks of material left intact for billions of years on the outskirts of our solar system." 

CCAT is a natural complement to the international Atacama Large Millimeter Array (ALMA) project now under construction in Chile, which will provide detailed, high-resolution images of individual objects over narrow fields of view. This complementarity provides a strong impetus to begin construction of CCAT as soon as possible. Indeed, as Nobel Laureate and CCAT Design Review Committee Chair Robert W. Wilson noted, "CCAT is very timely and cannot wait."

This sentiment was echoed in the Decadal Review Committee's report, which stated that "CCAT is called out to progress promptly to the next step in its development because of its strong science case, its importance to ALMA, and its readiness." The Committee recommended federal support for 33 percent of the construction cost for CCAT, as well as support in the operations phase.


The decadal survey recommended LISA as one of NASA's next major space missions, to start in 2016 in collaboration with the European Space Agency (ESA). In the U.S. the LISA project is managed by the NASA Goddard Space Flight Center and includes significant participation by JPL, which is managed by Caltech for NASA.

LISA is designed to be complementary to the ground-based observatories (such as the Laser Interferometer Gravitational Wave Observatory, or LIGO) that currently are actively searching for signs of gravitational waves, which carry with them information about their origins and about the nature of gravity that cannot be obtained using conventional astronomical tools.

The LISA instrument will consist of three spacecraft in a triangular configuration with 5-million-kilometer arms moving in an Earth-like orbit around the sun. Gravitational waves from sources throughout the universe will produce slight oscillations in the arm lengths (changes as small as about 10 picometers, or 10 million millionths of a meter). LISA will capture these motions using laser links to monitor the displacements of gold–platinum test masses floating inside the spacecraft. It is slated for launch in the early 2020s. The instrument will observe gravitational waves in a lower frequency band (0.1 milliHertz to 1 Hertz) than that detectable by LIGO and other ground-based instruments and will sense ripples coming simultaneously from tens of thousands of sources in every direction.

The survey recommended LISA because of the expectation that observations of gravitational waves in space will answer key scientific questions about the astrophysics of the cosmic dawn and the physics of the universe.

"We are very pleased with the NRC's recognition of LISA's revolutionary research opportunities in astrophysics and fundamental physics and we are looking forward to unveiling a new window on the universe by observing thousands of gravitational wave sources," says Tom Prince, professor of physics at Caltech, senior research scientist at the Jet Propulsion Laboratory (JPL), and the U.S. chair of the LISA International Science Team.


The decadal survey rated the development of a Giant Segmented Mirrored Telescope as a high priority. The TMT is one of two such telescopes under development by consortia with major involvement by private and public entities in the U.S., including Caltech.

Building on the success of the twin Keck telescopes, the core technology of TMT will be a 30-meter segmented primary mirror. This will give TMT nine times the collecting area of today's largest optical telescopes and three-times-sharper images. The TMT has begun full-scale polishing of the 1.4-meter mirror blanks that will make up the primary mirror. TMT also has developed many of the essential prototype components for the telescope, including key adaptive optics technologies and the support and control elements for the 492 mirror segments.

The TMT project is an international partnership among Caltech, the University of California, and the Association of Canadian Universities for Research in Astronomy, joined by the National Astronomical Observatory of Japan, the National Astronomical Observatories of the Chinese Academy of Sciences, and the Department of Science and Technology of India.

Kathy Svitil

Caltech, Canadian Space Agency Awarded NASA Project to Develop Spectrometer Headed to Mars

Instrument will look for evidence of life and volcanic activity on Mars; will fly aboard ExoMars Trace Gas Orbiter in 2016

PASADENA, Calif.—The California Institute of Technology (Caltech) and the Canadian Space Agency (CSA) announced today that they will be partnering on the development of the Mars Atmospheric Trace Molecule Occultation Spectrometer (MATMOS) instrument to be flown aboard the ExoMars Trace Gas Orbiter when it launches in 2016.

The project will be funded by a grant from NASA, with additional support coming from the CSA.

NASA participation in the ExoMars Trace Gas Orbiter is managed by the Jet Propulsion Laboratory, a division of Caltech, in partnership with the European Space Agency.

"The ExoMars investigation is designed to study the composition of Mars's atmosphere, with a focus on biogenically or volcanically derived trace gases," says Paul Wennberg, the R. Stanton Avery Professor of Atmospheric Chemistry and Environmental Science and Engineering at Caltech and director of the Ronald and Maxine Linde Center for Global Environmental Science. Wennberg is the principal investigator on the MATMOS team.

The ExoMars Orbiter's circular path around Mars will point the MATMOS telescope at the center of the sun as the spacecraft goes into orbital sunrise and sunset. During these periods, as the sun sets and rises through the atmosphere, MATMOS will take spectra of the sunlight, recording the absorption of numerous gases. The sun's long path length through the Martian atmosphere will allow MATMOS to measure the trace gases with very high sensitivity, notes Wennberg.

"If you take the spectra fast," says Geoffrey Toon, senior research scientist at JPL and a visiting associate in planetary sciences at Caltech, "you can measure the gas abundance at many different heights above the planet —70 measurements as the sun rises, and 70 as it sets."

Among the gases of interest to the team are those "diagnostic of active geological and biogenic activity," says Wennberg—gases like methane, as well as carbon, sulfur, and nitrogen-containing molecules, sulfur dioxide, and hydrogen sulfide.

MATMOS will be so exquisitely sensitive, says Wennberg, that it will be able to measure the concentrations of these gases down to parts per trillion.

"We did a calculation which shows that the microbial community found in three cows' bellies would produce an amount of methane that, in the Mars atmosphere, would be observable by MATMOS," says Mark Allen, principal scientist at JPL and a visiting associate in planetary sciences at Caltech.

MATMOS is based on the Atmospheric Trace Molecule Spectroscopy (ATMOS) experiment, developed by JPL, and the Atmospheric Chemistry Experiment–Fourier Transform Spectrometer (ACE–FTS), pioneered by University of Waterloo and the Canadian Space Agency. The ATMOS instrument has flown four times on the Space Shuttle since 1985. ACE–FTS was launched in 2003 and is still operational.

"MATMOS is an excellent instrument and an opportunity for a great partnership," says CSA Senior Planetary Scientist Victoria Hipkin, co-principal investigator on the MATMOS project. "We have taken the optical systems of one of Canada's flagship satellite instruments (Scisat ACE–FTS) and combined it with state-of-the-art data processing from the US (JPL's ATMOS and MrkIV). Our team—with US and Canadian leadership and Canadian, US, French, and UK members—is looking forward to providing fundamental data about this fascinating planet."

Lori Oliwenstein

Caltech Team Finds Evidence of Water in Moon Minerals

PASADENA, Calif.-That dry, dusty moon overhead? Seems it isn't quite as dry as it's long been thought to be. Although you won't find oceans, lakes, or even a shallow puddle on its surface, a team of geologists at the California Institute of Technology (Caltech), working with colleagues at the University of Tennessee, has found structurally bound hydroxyl groups (i.e., water) in a mineral in a lunar rock returned to Earth by the Apollo program.

Their findings are detailed in this week's issue of the journal Nature.

"The moon, which has generally been thought to be devoid of hydrous materials, has water," says John Eiler, the Robert P. Sharp Professor of Geology and professor of geochemistry at Caltech, and a coauthor on the paper.

"The fact that we were able to quantitatively measure significant amounts of water in a lunar mineral is truly surprising," adds lead author Jeremy Boyce, a visitor in geochemistry at Caltech, and a research scientist at the University of California, Los Angeles.

The team found the water in a calcium phosphate mineral, apatite, within a basalt collected from the moon's surface by the Apollo 14 astronauts.

To be precise, they didn't find "water"-the molecule H2O. Rather, they found hydrogen in the form of a hydroxyl anion, OH-, bound in the apatite mineral lattice.

"Hydroxide is a close chemical relative of water," explains coauthor George Rossman, Caltech's Eleanor and John R. McMillan Professor of Mineralogy. "If you heat up the apatite, the hydroxyl ions will 'decompose' and come out as water."

The lunar basalt sample in which the hydrogen was found had been collected by the Apollo 14 moon mission in 1971; the idea to focus the search for water on this particular sample was promoted by Larry Taylor, a professor at the University of Tennessee in Knoxville, who sent the samples to the Caltech scientists last year.

"The moon has been considered to be bone dry ever since the return of the first Apollo rocks," Taylor notes. However, there are lunar volcanic deposits interpreted as having been erupted by expanding vapor. Although carbon dioxide and sulfur gases have generally been thought to dominate the expanding vapor, recent evidence from the study of the these deposits has suggested that water could also play a role in powering lunar volcanic eruptions.  The discovery of hydroxyl in apatite from lunar volcanic rocks is consistent with this suggestion.

The idea of looking for water in lunar apatite isn't new, Boyce notes. "Charles B. Sclar and Jon F. Bauer, geoscientists at Lehigh University, first noted that something was missing from the results of chemical analyses of apatite in 1975," he says. "Now, 35 years later, we have quantitative measurements-and it turns out, they were right. The missing piece was OH."

The Caltech team analyzed the lunar apatite for hydrogen, sulfur, and chlorine using an ion microprobe, which is capable of analyzing mineral grains with sizes much smaller than the width of a human hair. This instrument fires a focused beam of high-energy ions at the sample surface, sputtering away target atoms that are collected and then analyzed in a mass spectrometer. Ion microprobe measurements demonstrated that in terms of its hydrogen, sulfur, and chlorine contents, the lunar apatite in this sample is indistinguishable from apatites from terrestrial volcanic rocks. 

"We realized that the moon and the earth were able to make the same kind of apatite, relatively rich in hydrogen, sulfur and chlorine," Boyce says.

Does that mean the moon is as awash in water as our planet? Almost certainly not, say the scientists. In fact, the amount of water the moon must contain to be capable of generating hydroxyl-rich apatite remains an open question. After all, it's hard to scale up the amount of water found in the apatite-1600 parts per million or 0.16 percent by weight-to determine just how much water there is on the lunar landscape. The apatite that was studied is not abundant, and is formed by processes that tend to concentrate hydrogen to much higher levels than are present in its host rocks or the moon as a whole.

"There's more water on the moon than people suspected," says Eiler, "but there's still likely orders of magnitude less than there is on the earth."

Nonetheless, the finding is significant for what it implies about our moon's composition and its history. "These findings tell us that the geological processes on the moon are capable of creating at least one hydrous mineral," Eiler says. "Recent spectroscopic observations of the moon showed that hydrogen is present on its surface, maybe even as water ice.  But that could be a thin veneer, possibly hydrogen brought to the moon's surface by comets or solar wind. Our findings show that hydrogen is also part of the rock record of the moon, and has been since early in its history."

Beyond that, Eiler continues, "it's all a great big question mark. We don't know whether these were igneous processes,"-in which rocks are formed by solidification of molten lava-"or metamorphic"-in which minerals re-crystallize or change in change in chemistry without melting. "They're both on the table as possible players."

In addition to Boyce, Eiler, Rossman, and Taylor, other authors on the Nature paper, "Lunar apatite with terrestrial volatile abundances," include Research Assistant Professor Yang Liu from the University of Tennessee in Knoxville; Edward Stolper, Caltech's William E. Leonhard Professor of Geology, and Yunbin Guan, manager of Caltech's ion microprobe laboratory. 

Their work was funded by grants from NASA's Cosmochemistry Program, the National Science Foundation, and the Gordon and Betty Moore Foundation.

Lori Oliwenstein
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Caltech Scientists Measure Changing Lake Depths on Titan

PASADENA, Calif.—On Earth, lake levels rise and fall with the seasons and with longer-term climate changes, as precipitation, evaporation, and runoff add and remove liquid. Now, for the first time, scientists have found compelling evidence for similar lake-level changes on Saturn's largest moon, Titan—the only other place in the solar system seen to have a hydrological cycle with standing liquid on the surface.

Using data gathered by NASA's Cassini spacecraft over a span of four years, the researchers—led by graduate student Alexander G. Hayes of the California Institute of Technology (Caltech) and Oded Aharonson, associate professor of planetary science at Caltech—have obtained two separate lines of evidence showing roughly a 1 meter per year drop in the levels of lakes in Titan's southern hemisphere. The decrease is the result of the seasonal evaporation of liquid methane from the lakes—which, because of Titan's frigid temperatures (roughly minus 300 degrees Fahrenheit at the poles), are composed largely of liquid methane, ethane, and propane.

"It's really exciting because, on this distant object, we're able to see this meter-scale drop in lake depth," says Hayes. "We didn't know Cassini would even be able to see these things."

One of the lakes—Ontario Lacus (named after Earth's Lake Ontario, which is of comparable size) —is the southern hemisphere's largest lake, and was the first lake to be observed on the moon. In a paper submitted to the journal Icarus, Hayes, Aharonson, and their colleagues report that the shoreline of Ontario Lacus receded by about 10 kilometers (6 miles) from June 2005 to July 2009, a period of time that represents mid-summer to fall in Titan's southern hemisphere. (One Titan year lasts 29.5 Earth years.)

Ontario Lacus and other southern-hemisphere lakes were analyzed using Synthetic Aperture Radar (SAR) image data from the Cassini spacecraft. In radar data, smooth features—such as lakes—appear as dark areas, while rougher features—such as mountain belts—appear bright. The intensity of the radar backscatter provides information about the composition and roughness of surface features. In addition to the SAR data, radar altimetry—which measures the time it takes for microwave signals bouncing off a surface to arrive back at the spacecraft—was collected across a transect of Ontario Lacus in December 2008.

"The combination of SAR and altimetry measurements across the transect gave information about the absorptive properties of the liquid, and argues that the liquids are relatively pure hydrocarbons made up of methane and ethane and not a gunky tar," Aharonson says.

"The liquid is not highly attenuating," explains Hayes, "which means it is fairly clear to radar energy—that is, transparent, like liquid natural gas." Because of this, radar can see through the liquid in Titan's lakes to a depth of several meters. "Then the radar hits the floor, and bounces back," he says. "Or, if the lake is deeper than a few meters, the radar is completely absorbed, producing a 'black' signature."

Once the liquid's optical properties were known, the researchers could use the radar data to "see" the lakebed underneath the liquid—at least, down to the depth where the signal is completely attenuated. "How far offshore you can see is determined by the local slope of the lakebed, or bathymetry," says Hayes. "This gave us the ability to take changes in radar signals and convert them to depths," and thus to calculate the slope of the lakebed around the entire lake.

"We were able to determine the bathymetry of the lake out to a depth of about 8 meters," he says. The lake is shallowest and most gently sloped along its southern edge, in areas where sediment is accumulating. Along its eastern shore, the slope of the lake is somewhat steeper. "This is what we are calling the 'beachhead,'" Hayes says. The slope is very steep along the lake's northern boundary, where it butts up against a range of mountains.

"The slope changes we see are consistent with the geology around the lake," Hayes says. The bathymetry measurements and their geologic correlations are discussed in a separate paper by Hayes, Aharonson, and colleagues, which has been accepted for publication in the Journal of Geophysical Research (JGR).

The researchers compared lake images obtained four years apart, and found that Ontario had shrunk. "The extent to which the lake has receded is related to the slope—i.e., where the lake is shallow, the liquid will have receded more," Hayes says. "This allows us to deduce the vertical height by which the lake depth has dropped, which is about 1 meter per year."

The researchers also analyzed the evaporation of methane from nearby lakes by comparing the radar signatures of these lakes as measured in December 2007 with data obtained in May 2009. Over that period, the "apparent darkness" of the lakes—indicating the presence of a radar-attenuating liquid—either decreased or disappeared entirely, which means that their liquid levels had been reduced. The researchers were able to calculate the drop in lake depth, "and we got the same result: 1 meter per year of liquid loss," Aharonson says.

Lakes in Titan's northern hemisphere—which is now entering spring—have also been covered multiple times by radar instruments, but so far no analogous changes have been conclusively detected.

That doesn't mean the changes haven't occurred, however. "We would expect it will happen, but we don't know how it would manifest in the data if the lakes in the north are significantly deeper. We'll continue to look for this effect with future radar images, to disentangle the seasonal variations from longer-term climate variations we previously have proposed." Aharonson says.

The work described in the two papers—"Transient Surface Liquid in Titan's Polar Regions from Cassini," which was submitted to Icarus, and "Bathymetry and Absorptivity of Titan's Ontario Lacus," which was accepted by JGR—was supported by the Cassini Project and NASA's Graduate Student Researchers Program, and was carried out in collaboration with members of the Cassini RADAR Science Team. The Cassini mission is managed by the Jet Propulsion Laboratory in Pasadena, California.

Kathy Svitil

Caltech Geologist Investigates Canyon Carved in Just Three Days in Texas Flood

Study of how canyon formed offers insight into ancient flood events on Earth and Mars

PASADENA, Calif.—In the summer of 2002, a week of heavy rains in Central Texas caused Canyon Lake—the reservoir of the Canyon Dam—to flood over its spillway and down the Guadalupe River Valley in a planned diversion to save the dam from catastrophic failure. The flood, which continued for six weeks, stripped the valley of mesquite, oak trees, and soil; destroyed a bridge; and plucked meter-wide boulders from the ground. And, in a remarkable demonstration of the power of raging waters, the flood excavated a 2.2-kilometer-long, 7-meter-deep canyon in the bedrock.

According to a new analysis of the flood and its aftermath—performed by Michael Lamb, assistant professor of geology at the California Institute of Technology (Caltech), and Mark Fonstad of Texas State University—the canyon formed in just three days. 

A paper about the research appears in the June 20 advance online edition of the journal Nature Geoscience

Our traditional view of deep river canyons, such as the Grand Canyon, is that they are carved slowly, as the regular flow and occasionally moderate rushing of rivers erodes rock over periods of millions of years. 

Such is not always the case, however. "We know that some big canyons have been cut by large catastrophic flood events during Earth's history," Lamb says.

Streamlined islands sculpted by the flood and large boulders transported by the flood.
Credit: Michael Lamb/Caltech

Unfortunately, these catastrophic megafloods—which also may have chiseled out spectacular canyons on Mars—generally leave few telltale signs to distinguish them from slower events. "There are very few modern examples of megafloods," Lamb says, "and these events are not normally witnessed, so the process by which such erosion happens is not well understood." Nevertheless, he adds, "the evidence that is left behind, like boulders and streamlined sediment islands, suggests the presence of fast water"—although it reveals nothing about the time frame over which the water flowed.

This is why the Canyon Lake flood is so significant. "Here, we know that all of the erosion occurred during the flood," Lamb says. "Flood waters flowed for several weeks, but the highest discharge—during which the bulk of the erosion took place—was over a period of just three days." 

Boulders transported by the 2002 Canyon Lake flood.
Credit: Michael Lamb/Caltech

Lamb and Fonstad reached this conclusion using aerial photographs of the region taken both before and after the flood, along with field measurements of the topography of the region and measurements of the flood discharge. Then they applied an empirical model of the sediment-carrying capacity of the flood—that is, the amount of soil, rocks, boulders, and other debris carried by the flood to produce the canyon.

The analysis revealed that the rate of the canyon erosion was so rapid that it was limited only by the amount of sediment the floodwaters could carry. This is in contrast to models normally applied to rivers where the erosion is limited by the rate at which the underlying rock breaks and is abraded. 

The researchers argue that the rate of erosion was rapid because the flood was able to pop out and cart away massive boulders (a process called "plucking")—producing several 10- to 12-meter-high waterfalls that propagated upstream toward the dam, along with channels and terraces. The flood was able to pluck these boulders because the bedrock below the soil surface of the valley was already fractured and broken. 

The abrasion of rock by sediment-loaded waters—while less significant in terms of the overall formation of the canyon—produced other features, like sculpted walls, plunge pools at the bases of the waterfalls, and teardrop-shaped sediment islands. The sediment islands are particularly significant, Lamb says, because "these are features we see on Earth and on Mars in areas where we think large flow events have occurred. It's nice that here we're seeing some of the same features that we've interpreted elsewhere as evidence of large flow events."

The results, Lamb says, offer useful insight into ancient megafloods, both on Earth and on Mars, and the deep canyons they left behind. "We're trying to build models of erosion rates so we can go to places like Mars and make quantitative reconstructions of how much water was there, how long it lasted, and how quickly it moved," Lamb says. In addition, he says, "this is one of a few places where models for canyon formation can be tested because we know the flood conditions under which this canyon formed."

Kathy Svitil

Edwin S. Munger, 88

Noted Caltech geographer was an expert on Africa, ethnic relations

PASADENA, Calif.-Edwin S. Munger, professor of geography, emeritus, at the California Institute of Technology (Caltech), passed away peacefully June 15 at his home in Pasadena, California. He was 88 years old.

Munger was a renowned specialist on Africa, particularly race and ethnic relations. He made dozens of trips to the continent, visited every country on it, and lived there for a decade.

Born in La Grange, Illinois, Munger received his BS, MS, and PhD degrees from the University of Chicago. He was a visiting lecturer at Caltech throughout the 1950s before becoming professor of geography in 1961. He became professor emeritus in 1988.

Munger took his first trip to Africa in 1947-financed by his Army poker winnings-and his second in 1949 as the first Fulbright Fellow to Africa, attending Makerere University, Kampala, Uganda. He was an Institute of Current World Affairs (ICWA) fellow in Africa from 1950 to 1954, and from 1955 to 1961 was an American Universities Field Staff member, during which time he lived a year each in Ghana, Nigeria, Kenya, and South Africa, while at the same time serving on the faculty of the University of Chicago.

He was an evaluator for the Peace Corps in Uganda (1966) and Botswana (1967) and chairman of the U.S. State Department Evaluation Team in South Africa (1971).

Munger once said, "One of the joys of being a geographer is that the world is my oyster, world travel my most stimulating teacher."

His passion for the region led to his founding of the African Studies Association and the U.S.-South African Leader Program, and later, he served as a board member of the South African Institute of Race Relations. For 14 years he served as president of the L.S.B. Leakey Foundation, working to increase scientific knowledge and public understanding of human origins and evolution. He was also instrumental in launching the foundation's Baldwin Fellowships, which have helped more than 40 Africans obtain advanced degrees in archaeology. In 1985, Munger founded the Cape of Good Hope Foundation to help mostly black universities in southern Africa, and subsequently sent more than $3 million dollars worth of books to help those institutions. He edited the Munger Africana Library Notes (1969-1982) and amassed a library of over 60,000 volumes on sub-Saharan Africa, the largest private collection in the United States, and a unique cultural resource.

He was president of the Pasadena Playhouse (1966) and one of the founders of Caltech's Friends of Beckman Auditorium.

A respected teacher, Munger in 1976 received the top teaching prize given by Caltech's student body and in 1980 was made an honorary member of the Caltech Alumni Association. He continued to be a presence on the Caltech campus by joining notable faculty members at the campus faculty club-the Athenaeum-"round table," a lunchtime gathering of scientific leaders from various disciplines who meet to socialize and hold discussions of the highest order.

In 1993 he received the Alumni Citation Award for public service from the University of Chicago, and in 2002 he was the recipient of the Gandhi-King-Ikeda award from Morehouse College for his years of dedication to improving race relations. 

Later in life, he developed an interest in collecting chess sets and at one point had amassed more than 400 ethnic chess sets from the more than 250 countries and islands he had visited.

A prolific author, Munger produced numerous titles, including 1965's Bechuanaland: Pan-African Outpost or Bantu Homeland?, 1967's Afrikaner and African Nationalism, 1983's Touched by Africa, and 1996's Cultures, Chess & Art, A Collector's Odyssey Across Seven Continents, Volume 1: Sub-Saharan Africa, which he followed with volumes 2 and 3.

Munger leaves behind his wife of 40 years, Ann Boyer Munger, daughter Betsy Owens from his first marriage with the late Elizabeth Nelson Munger, nephews Christopher and Roger, and nieces Jennifer, Trudie, and Sarah.

A memorial service will be held at 4:00 p.m. on Thursday, June 24th at the Athenaeum, 551 S. Hill Avenue, Pasadena. In lieu of flowers, the family requests donations in his memory be made to Friends of Beckman Auditorium, Caltech, Pasadena, CA 91125 or to the Institute of Current World Affairs, 4545 42nd St. NW, Suite 311, Washington, D.C. 20016-4623.

Jon Weiner
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East African Human Ancestors Lived in Hot Environments, Says Caltech-led Team

Geochemical findings could help explain facets of early human evolution, including the development of bipedalism

PASADENA, Calif.—East Africa's Turkana Basin has been a hot savanna region for at least the past 4 million years—including the period of time during which early hominids evolved in this area—says a team of researchers led by scientists at the California Institute of Technology (Caltech). These findings may shed light on the evolutionary pressures that led humans to walk upright, lose most of our body hair, develop a more slender physique, and sweat more copiously than other animals.

Their findings—which were based on measurements of the spatial distribution and concentrations of isotopes in carbonate ions—are being reported this week in the early online edition of the Proceedings of the National Academy of Sciences (PNAS).

"When you measure the temperature of the ground, you learn a lot about the environment above it," says John Eiler, Robert P. Sharp Professor of Geology and professor of geochemistry at Caltech. In fact, he says, soil temperature tells you not just about air temperature, but about whether there were trees and plants to shade the soil, keeping temperatures cooler during the hottest part of the day.

Today, northern Kenya—where the Turkana Basin is found—is among the warmest areas on earth. It has little canopy forest, leaving the ground exposed to sunlight. "The question is, was the ground here ever cooler than it is today?" asks Eiler. "And if it was, why? Was it because the air was cooler, or because of more forest shading?"

To find out, the team examined the spatial organization (or "clumping") of rare, naturally occurring isotopes of carbon and oxygen—specifically, carbon-13 and oxygen-18—in the form of carbonate ions that are constituents of minerals found in buried soils from northern Kenya. The clumping of these isotopes, Eiler and his colleagues have demonstrated in previous papers, is dependent on temperature: Hot temperatures lead to less clumping; cold temperatures, more.

"These carbonates are a common constituent of these soils," Eiler explains. "If you have the ability to measure their isotopes, then you have a ground-temperature thermometer."

When the researchers applied that thermometer to various layers of buried soils from East Africa, they found what Eiler says was "such a straightforward answer, it wasn’t obvious how we could talk ourselves out of the conclusion we reached."

That conclusion? "The Turkana Basin region—one of the key places where hominid fossils documenting human evolution are found—has been a really hot place for a really long time," says Benjamin Passey, formerly a postdoctoral scholar at Caltech. Passey, who led the work on this project, is now at Johns Hopkins University.

But why does it matter how hot Africa was millions of years ago? "This is the area where we find the occurrence of some of the earliest hominid species," notes Eiler. "It tells us that this environment, though harsh, was a place where our ancestors could thrive. It tells us that they were probably originally marginal species that lived in difficult-to-survive environments."

The findings also shed some light—and heat—on a longstanding debate over the origin of bipedalism in early humans.

"For a long time, anthropologists have hypothesized that bipedalism and other unique human traits would be advantageous to life in hot savanna environments," says Passey. "For example, by standing upright, we intercept less direct sunlight than if we were on all fours, and in hot, open environments, the ground and near-surface air can be appreciably hotter than the air a few feet above the ground. So, by standing upright, we are avoiding a high-temperature environment."

Of course, Passey adds, this strategy would only be of significant use if the environment in question is indeed a high-temperature one. "In cooler environments, these traits do not really have a thermal advantage," he notes. These considerations led to the team's interest in figuring out just how hot it was in the part of the world where bipedalism is most likely to have first gained a toehold.

Eiler cautions that the team's findings are simply assessments of the area's temperature over time, and have nothing to say about "the importance of ambient temperature in shaping human evolution." But, he notes, they are "consistent with the notion that the heat in the area would have been a selective pressure that could have made bipedalism advantageous."

In addition to Eiler and Passey, the coauthors on the PNAS paper, "High-temperature environments of human evolution in East Africa based on bond ordering in paleosol carbonates," were former Caltech postdoc Naomi Levin, now at Johns Hopkins University; and Thure Cerling and Francis Brown from the University of Utah. Their work was supported by grants from the Camille & Henry Dreyfus Foundation and the National Science Foundation.

Lori Oliwenstein

Caltech-Led Team First to Directly Measure Body Temperatures of Extinct Vertebrates

Could help scientists track paleoclimate, determine whether dinosaurs and other species were warm- or cold-blooded

PASADENA, Calif.— Was Tyrannosaurus rex cold-blooded? Did birds regulate their body temperatures before or after they began to grow feathers? Why would evolution favor warm-bloodedness when it has such a high energy cost?

Questions like these—about when, why, and how vertebrates stopped relying on external factors to regulate their body temperatures and began heating themselves internally—have long intrigued scientists.

Now, a team led by researchers at the California Institute of Technology (Caltech) has taken a critical step toward providing some answers. Reporting online this week in the early edition of the Proceedings of the National Academy of Sciences (PNAS), they describe the first method for the direct measurement of the body temperatures of large extinct vertebrates—through the analysis of rare isotopes in the animals' bones, teeth, and eggshells.

"This is not quite like going back in time and sticking a thermometer up a creature's back end," says John Eiler, Robert P. Sharp Professor of Geology and professor of geochemistry at Caltech. "But it's close."

Studying the mechanisms of and changes in temperature regulation in long-extinct animals requires knowing what their body temperatures were in the first place. But the only way scientists have had to study temperature regulation in such creatures was to make inferences based on what is known about their anatomy, diet, or behavior. Until now.

The technique the team has developed to measure body temperature in extinct vertebrates looks at the concentrations of two rare isotopes—carbon-13 and oxygen-18. "These heavy isotopes like to bond, or clump together, and this clumping effect is dependent on temperature," says Caltech postdoctoral scholar Robert Eagle, the paper's first author. "At very hot temperatures, you get a more random distribution of these isotopes, less clumping. At low temperatures, you find more clumping."

In living creatures, this clumping can be seen in the crystalline lattice that makes up bioapatite—the mineral from which bone, tooth enamel, eggshells, and other hard body parts are formed. "When the mineral precipitates out of the blood—when you create bone or tooth enamel—the isotopic composition is frozen in place and can be preserved for millions of years," he adds.

In addition, work in Eiler's lab has "defined the relationship between clumping and temperature," says Eagle, "allowing measurements of isotopes in the lab to be converted into body temperature." The method is accurate to within one or two degrees of difference.

"A big part of this paper is an exploration of what sorts of materials preserve temperature information, and where," notes Eiler.

To do this, the team looked at bioapatite from animals whose form of body-temperature regulation is already known. "We know, for instance, that mammals are warm-blooded; all the bioapatite in their bodies was formed at or near 37 degrees centigrade," says Eagle.

After showing proof of concept in living animals, the team looked at those no longer roaming the earth. For instance, the team was able to analyze mammoth teeth, finding body temperatures of between 37 and 38 degrees—exactly as expected.

Going back even further in time, they looked at 12-million-year-old fossils from a relative of the rhinoceros, as well as from a cold-blooded member of the alligator family tree. "We found we could measure the expected body temperature of the rhino-like mammal, and could see a temperature difference between that and the alligator relative, of about 6 degrees centigrade," Eagle says.

There are, however, limitations to this sort of temperature sleuthing. For one, the information that the technique provides is only a snapshot of a particular time and place, Eiler says, and not a lifelong record. "When we look at tooth enamel, for instance, what we get is a record of the head temperature of the animal when the tooth grew," he notes. "If you want to know what his big-toe temperature was two years later, too bad."

And, of course, the technique relies on the quality of the fossils available for testing. While teeth tend to withstand the rigors of burial and time, eggshells are "fragile and prone to recrystallization during burial," says Eiler. Finding good specimens can be difficult.

But the rewards are worth the effort. "The main reason to do this sort of work is because gigantic land animals are intrinsically fascinating," Eiler says. "We want to look at where warm-bloodedness emerged, and where it didn't emerge. And this technique will help us to reconstruct food webs. In the distant past, dinosaurs and other large animals were the crown of the food web; we'll be able to figure out how they went about their business."

Now that they've pinned down an accurate paleothermometer, the research team has gone further back in time, and has begun looking at the body temperatures of vertebrates about whom less is known. "Before mammals and birds," says Eagle, "we have no good idea what physiology these ancient creatures had."

First up? Dinosaurs, of course. "We're looking at eggshells and teeth to see whether the most conspicuous dinosaur species were warm- or cold-blooded," says Eiler.

In addition, he says, the researchers would like to apply their approach to better understand some key evolutionary transitions.

"Take birds, for instance," Eiler says. "Were they warm-blooded before or after they started to fly? Before or after they developed feathers? We want to take small birds and track their body temperature through time to see what we can learn."

Finally, they hope to get a peek at the paleoclimate, through the body-temperature data derived from ancient cold-blooded animals. "With this method, we can track changes in body temperature as a proxy for changes in air or water temperature."

In addition to Eiler and Eagle, the other authors on the PNAS paper, "Body temperatures of modern and extinct vertebrates from 13C-18O bond abundances in bioapatite," are Edwin Schauble of the University of California, Los Angeles (UCLA); Thomas Tütken of the Universität Bonn in Germany; Richard Hulbert of the Florida Museum of Natural History; and Aradhna Tripati, who has appointments at Caltech, UCLA, and the University of Cambridge.

Their work was supported by grants from the National Science Foundation, and by a Caltech Chancellors Postdoctoral Scholarship.

Lori Oliwenstein

Aseismic Slip as a Barrier to Earthquake Propagation

Caltech scientists and partners explore the effects of aseismic slip in the aftermath of 2007 Peru earthquake

PASADENA, Calif.—On August 15, 2007, a magnitude 8.0 earthquake struck in Central Peru, killing more than 500 people—primarily in the town of Pisco, which was heavily damaged by the temblor—and triggering a tsunami that flooded Pisco's shore and parts of Lima's Costa Verde highway. The rupture occurred as the Nazca tectonic plate slipped underneath the South American plate in what is known as a subduction zone.

Soon thereafter, Hugo Perfettini—a former postdoctoral scholar with the Tectonics Observatory at the California Institute of Technology (Caltech), now at the Institut de Recherche pour le Développement in France—deployed an array of GPS stations in southern Peru.

They were used to measure the postseismic deformation—the deformation that occurred in the first year after the earthquake.

When the research team—made up of a collaboration of scientists at the Caltech Tectonics Observatory and their partners in Peru and France—looked at the data from these GPS stations and compared them to the distribution of aftershocks in the area, they noticed something "amazing," says Jean-Philippe Avouac, director of the Tectonics Observatory and professor of geology at Caltech

The team's analysis of this data—and the conclusions they were able to draw as a result—are described in a paper in the May 6 issue of the journal Nature.

"After the earthquake, the plate interface slipped quite a bit," Avouac says. "But the aftershocks were tiny compared to the displacement. In other words, there was a lot of deformation, but most of it was aseismic." (Aseismic slippage, or aseismic creep, is movement along a fault that occurs without any accompanying seismic waves.)

This was contrary to what had long been assumed about plate movement in the area. "We used to think the plate interface at a subduction zone—which extends in this case from the surface to a depth of about 40 kilometers—was only slipping during large earthquakes," Avouac explains. "In Peru, 50 percent of the slippage within this range of depth is actually aseismic."

This study shows that the plate interface is a patchwork of areas differing in their frictional properties: areas with seismic, or unstable, slip (dark gray patches) and areas with aseismic, or stable, slip (light gray patches).
Credit: Caltech Tectonics Observatory

When the team mapped this aseismicity, they found that it occurred in a sort of "patchwork" pattern, says Avouac, with areas that "mostly slip aseismically and areas that mostly slip during earthquakes." As it turns out, some of these areas are always aseismic, "creeping continuously," he notes—and therefore act as a sort of permanent barrier to the propagation of an earthquake. Since seismic stress cannot build up in these particular aseismic areas, there is no stress to be released in an earthquake; any seismic rupture traveling through such an area would stop dead in its tracks.

What was perhaps most surprising, Avouac adds, is that one of the largest aseismic areas the researchers found "corresponds with where the Nazca ridge comes into the trench."

"This large area of aseismic slip is good news," he says. "It lowers the seismic hazard in that region, and allows us to be a little bit predictive. We cannot tell you when there will be an earthquake, but we can tell you where there is stress buildup, and where there is no stress buildup. Where there is no stress buildup, there will be no seismic rupture. That is where the earthquakes are going to stop."

The lessons learned in Peru, Avouac says, should be generalizable to just about any subduction zone—Sumatra, for instance, or Chile—and probably to any other kind of fault as well. And so Avouac—along with Nadia Lapusta, associate professor of mechanical engineering and geophysics at Caltech, and postdoctoral scholar Yoshihiro Kaneko from the Scripps Institution of Oceanography, who worked on this project while doing his PhD at Caltech—decided to look at "the long-term evolution of slip on a model fault where two seismogenic, locked segments are separated by an aseismically slipping patch where rupture is impeded," they explain in a paper recently published online in the journal Nature Geoscience.

When the locked segments (i.e., the areas in which stress builds up, and which produce earthquakes when they rupture) are far apart—or if the intervening aseismic area has frictional characteristics that make aseismic slip easy—they "tend to rupture independently," says Avouac. If they are very close together, they tend to interact and eventually break together.

The interesting question, Avouac says, is what we can expect to happen when the two segments are close, but not too close—and are separated by an aseismic area, as was seen in the Peru patchwork. By looking at what geologists call interseismic coupling—"the fraction of sliding that is aseismic and occurs between earthquakes," explains Avouac—and by factoring in distance, time, and the sliding speed, the team was able to determine whether an earthquake that begins in one locked area is likely to stop when it hits an aseismic barrier, or whether it will be able to cross that barrier and rupture the segment on the other side.

"This model demonstrates that, based on geodetic monitoring of a subduction zone, we can not only locate the places that are accommodating plate motion through slow, aseismic slip, but also determine the probability that they will be able to arrest seismic ruptures," says Lapusta.

The hope, Avouac adds, is that this sort of modeling can be applied to data derived from actual subduction zones. "We want to create models that will take into account the physical properties of a fault to produce a scenario of how the system might evolve," he says, in much the same way that meteorologists forecast the weather.

"Our study opens the possibility of predicting patterns of large earthquakes that a fault system could produce on the basis of observations of its coupling," adds Kaneko, "and suggests that regions of low coupling may reveal permanent barriers to large earthquakes."

In addition to Avouac and Perfettini, the other authors on the Nature paper, "Seismic and aseismic slip on the Central Peru megathrust," were Pierre Soler, Francis Bondoux, Mohamed Chlieh, and Laurence Audin of the Institut de Recherche pour le Développement; Hernando Tavera of the Instituto Geofisico del Perú; Andrew Kositsky, a former Caltech undergraduate student, now at Ashima Research in Pasadena; Jean-Mathieu Nocquet of Géoazur in Valbonne, France; Anthony Sladen, a staff seismologist at Caltech; and Daniel Farber of the University of California, Santa Cruz. The work was supported by grants from the Institut de Recherche pour le Développement, the Gordon and Betty Moore Foundation (through the Caltech Tectonics Observatory), and the National Science Foundation (NSF). The paper can be found at

The abstract of the Nature Geoscience paper, "Towards inferring earthquake patterns from geodetic observations of interseismic coupling," can be found at The work was funded by grants from the NSF and the Gordon and Betty Moore Foundation (through the Caltech Tectonics Observatory).

Lori Oliwenstein


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