On Shaky Ground: Geological Faults Threaten Houston

Pictured is a Houston-area map showing the locations of salt domes and known active surface faults interpreted on lidar imagery. (Credit: Shuhab Khan and Richard Engelkemeir)
Pictured is a Houston-area map showing the locations of salt domes and known active surface faults interpreted on lidar imagery. (Credit: Shuhab Khan and Richard Engelkemeir)

After finding more than 300 surface faults in Harris County, a University of Houston geologist now has information that could be vitally useful to the region’s builders and city planners.

This information — the most accurate and comprehensive of its kind — was discovered by Shuhab Khan, assistant professor of geology, and Richard Engelkemeir, a geology Ph.D. student, using advanced radar-like laser technology. Although geologists have long known of the existence of faults in Southeast Texas, only recently have UH researchers produced a comprehensive map pinpointing the locations of the faults.

While the ground moving beneath Houstonians feet is not felt at the magnitude of recent earthquakes in San Antonio and Illinois, this shaky ground could mean trouble for buildings, roads and pipelines located on one of these hundreds of faults traversing the region’s surface.

“These shifting fault lines originated millions of years ago during the formation of the Gulf of Mexico,” Khan said. “While they are not the kinds that wreak havoc in earthquake-prone California and now the Midwest, they can move up to 1 inch a year, causing serious damage over the course of several years to buildings and streets that straddle a fault line. Additionally, structures on the subsiding side of the fault line could be more susceptible to flooding due to the lower elevation over time.”

Khan and Engelkemeir recently presented their findings in Geosphere, a bimonthly online-only journal published by the Geological Society of America that highlights research results from all fields of the geosciences. They began by looking at data compiled during a 2001 study funded by the Federal Emergency Management Administration (FEMA) and the Harris County Flood Control District. That year, Tropical Storm Allison dumped nearly 40 inches of rain on the Houston area during the course of five days, causing nearly two dozen deaths and billions of dollars in property damage.

To update floodplain maps, FEMA and the flood district employed lidar technology — the optical analog of radar meaning ‘light detection and ranging’ — to survey the topography and elevation of the county. From an aircraft flying overhead, laser beams were directed toward the ground. The time between the laser beam pulse and the return reflection from any given point on the ground was used to determine the distance between the instrument and that point on the surface. Buildings and vegetation were then removed from the model to produce a map that recorded even the most subtle surface elevation differences.

Khan and Engelkemeir pored over the data, refining the grids to identify the more than 300 faults. Many were associated with the salt domes in the southeast part of the county. Others were located in the northwest portion of the county near highways Texas 6 and I-10, where there is ongoing subsidence, or sinking, of the ground.

During the summer of 2005, Engelkemeir personally visited about 50 of the faults he located with the lidar data, looking for signs of deformation and displacement where the land on one side of the fault was rising over the other. At many of the faults, he saw cracks in street pavements, with residents living nearby reporting foundation problems. At one home there was about a yard of displacement between the garage and the house. At another site, a building had been so damaged by ground shifts it was condemned.

Geologists are still studying what causes fault movements and the resulting subsidence in the region, with some attributing it to land-use practices such as groundwater and petroleum withdrawal, Engelkemeir said.

Khan is now turning his attention to Fort Bend County. Using lidar data, Cecilia Ramirez, a master’s student working under Khan, has found one potential fault near the Brazos River levee.

“By knowing the location of surface faults, builders and government planners will be able to avoid those areas or accommodate potential ground shifts in their construction plans,” Khan said. “And we must still keep in mind that while lidar has allowed us to identify previously unmapped faults, there still might be faults in the region that have yet to be located.”

Khan has given numerous talks on this work at both scientific meetings for a number of geological and petroleum organizations, as well as at more general meetings attended by the city of Houston and other local and state agencies.

‘New’ Ancient Antarctic Sediment Reveals Climate Change History

Recent additions to the premier collection of Southern Ocean sediment cores at Florida State University’s Antarctic Marine Geology Research Facility will give international scientists a close-up look at fluctuations that occurred in Antarctica’s ice sheet and marine and terrestrial life as the climate cooled considerably between 20 and 14 million years ago.

FSU’s latest Antarctic sediment core acquisition was extracted from deep beneath the sea floor of Antarctica’s western Ross Sea, the Earth’s largest floating ice body. The new samples — segments of a drill core that measures more than 1,100 meters in length — offer an extraordinary stratigraphic record of sedimentary rock from the Antarctic continental margin that documents key developments in the area’s Cenozoic climatic and glacial history.

By correlating that stratigraphic record with existing data and climate and ice sheet models, scientists from FSU and around the world expect to learn how local changes in the Southern Ocean region relate to regional and global climate events.

“Such knowledge will significantly increase our understanding of Antarctica’s potential responses to future global-scale climate changes,” said Sherwood W. Wise, Jr., an FSU geological science professor and co-principal investigator at the Antarctic Marine Geology Research Facility. “This is critical for low-lying regions such as Florida that could be directly affected by the future behavior of the Antarctic Ice Sheets and any resulting sea-level changes. By studying these glacial records of the past, geologists and climatologists seek to better predict the future.”

The new cores came to FSU compliments of ANDRILL (ANtarctic geological DRILLing), an international collaboration among more than 120 scientists — plus drillers, engineers, educators and technicians — from Germany, Italy, New Zealand and the United States. FSU’s Antarctic Marine Geology Research Facility and its staff and associated geological science faculty play a key ANDRILL role, providing both on-the-ice curatorial services during the drilling season and a permanent repository for the core samples recovered during the project.

In fact, from April 29 through May 3, some 100 ANDRILL scientists and educators, including seven from the FSU “on-ice” curatorial team, will converge at the Antarctic Marine Geology Research Facility core repository. They will re-examine the latest core acquisitions to refine their descriptions of the material and take additional samples for tests to extract even more information about their history and the conditions under which the sediments were deposited.

Those hard-won, deep-sea sediment cores may be millions of years old, but the scientists will find them in mint condition at FSU. The Antarctic research facility carefully curates the samples in its large, 6,000-square-foot refrigerated “Cold Room,” which is maintained at 34 F. (i.e., sea-bottom temperatures).

“The sediment cores recovered during this year’s successful ANDRILL expedition have filled in a major gap in the most direct record of the ice activity yet recovered from the period of about 20 to 14 million years ago,” said Wise, who serves ANDRILL as a participating (off-ice) scientist and member of its U.S. advisory committee. “The 1,139 meters of core retrieved, 98 percent intact, records the critical transition from times warmer than today to the onset of major cooling between about 14 to 13 million years ago when a semi-permanent ice sheet formed across most of Antarctica.”

That record was created, said Wise, because sediments deposited close to or beneath grounded glaciers alternate with marine sediments, providing clear evidence of cyclical ice advances followed by substantial retreats and reflecting variations in sea-level, glacial and climate fluctuations. The new stratigraphic section housed at FSU will allow scientists to devise more accurate models of the timing of past ice-sheet movements, volume changes and variability, and paleotemperature fluctuations, and will enable a better understanding of the development of Antarctica’s terrestrial and marine life.

The Antarctic Marine Geology Research Facility was established at FSU in 1963 through the National Science Foundation’s Office of Polar Programs and now serves as the national repository for geological material from the Southern ocean. It functions as one of the university’s two user facilities (the National High Magnetic Field Laboratory is the other) for visiting researchers from around the globe.

ANDRILL’s meeting April 29-May 3 will take place throughout FSU’s Carraway Building — home to the Department of Geological Sciences and the annex that houses the Antarctic Marine Geology Research Facility. During the workshop one of the two chief scientists of the second ANDRILL expedition, David M. Harwood, an FSU master’s graduate (1982) and a geology professor at the University of Nebraska-Lincoln, will be honored with a special alumni award.

Visiting ANDRILL researchers who attended last May’s inaugural post-drilling workshop at FSU will notice that since then the Antarctic research facility’s core repository has undergone a major renovation to make room for recent acquisitions and future ones. Funding for those improvements to one of the coolest places on campus came from the National Science Foundation.

Formation of ice sheets 34 million years ago changed ocean acidity

Before ice first began to form in Antarctica around 34 million years ago, the Earth was a very different place – but then greenhouse conditions swiftly gave way to an icehouse climate, causing the oceans to become less acidic.

Scientists at the University of Southampton’s School of Ocean and Earth Science, based at the National Oceanography Centre, Southampton UK and Germany’s GKSS Research Centre have been piecing together how Earth’s changing climate affected ocean chemistry during this period of transition. Their work sheds light on the links between glaciation and the ocean carbon cycle.

Their research, published in Nature (24 April 2008), confirms the connection between two separate phenomena that occurred at the same time: a fall in sea-level caused by Antarctic glaciation and a change in ocean acidity – revealed by a change in the depth at which calcium carbonate shells start dissolving on the sea floor.

Dr Toby Tyrrell of the National Oceanography Centre, Southampton said:

“We were keen to discover why the oceans became suddenly less acidic – the reverse of what is happening today. Although the changes took place 34 million years ago, by understanding how the Earth System operated at this time of dramatic change we can gain insights as to how Earth will respond as we modify it by adding carbon dioxide from burning fuels.”

The team used a global biogeochemical ocean model to test different explanations as to what was happening during the transition from the Eocene period – a time of warm greenhouse conditions with higher ocean acidity, to the Oligocene period – characterised by ice, cooler temperatures and lower ocean acidity.

Dr Tyrrell continued:

“This work has advanced our understanding of how the Earth System worked during this critical period. When most explanations were incorporated into our computer model, it produced results in conflict with the available data. Only one scenario was found to be compatible with the data.”

Dr Tyrrell’s colleague, Professor Paul Wilson also of the University of Southampton’s School of Ocean and Earth Science said:

“Our work suggests that a fall in sea-level had the effect of leaving coral reefs stranded above the high-tide level where they were then eroded by wind and rain. Corals are composed of calcium carbonate – chalk – which reduces the acidity when it dissolves in seawater.”

The third member of the team, Dr Agostino Merico, who is a former postdoctoral researcher at the National Oceanography Centre, Southampton and is now with the GKSS Research Centre in Geesthacht, said:

“With this powerful tool we can peer into the deep past to gain insights into arguably the most important climatic transition of the last 100 million years. With this work we have been able to put together different components and complex processes of the Earth System, and to relate them to each other. The whole point of a model is to abstract core ideas or hypothesis in a way that enables us to learn about them.”

Twenty years of the Alaska Volcano Observatory

AVO's John Paskievitch and John Power at the remains of a seismic station on Mount Spurr, the nearest active volcano to Anchorage. The late June 1992 eruption from Crater Peak blasted 44 million cubic meters of ash, blocks, and gas into the atmosphere.  - Photo by Bill Bolling, courtesy of Alaska Volcano Observatory
AVO’s John Paskievitch and John Power at the remains of a seismic station on Mount Spurr, the nearest active volcano to Anchorage. The late June 1992 eruption from Crater Peak blasted 44 million cubic meters of ash, blocks, and gas into the atmosphere. – Photo by Bill Bolling, courtesy of Alaska Volcano Observatory

Twenty summers ago, earthquakes rocked the town of King Cove on the Alaska Peninsula. Some people were so worried that the nearby volcano, Mt. Dutton, was going to erupt that they caught flights out of town. Others called in the cavalry–members of the fledgling Alaska Volcano Observatory.

In 1988, John Power had just finished his master’s degree when he became the observatory’s first full-time employee. He flew out to King Cove with a few colleagues to check on the volcano.

“I remember that the biggest earthquake happened in August, on 8/8/88,” said Power, a geophysicist with the USGS Alaska Science Center who still works for AVO in Anchorage. “It happened right at the peak of salmon season, so there were a lot of people in town.”

After installing a few seismometers on the flanks of 4,800-foot Mt. Dutton, eight miles from King Cove, Power and his comrades saw that the character and the size of the earthquakes didn’t suggest that Mt. Dutton was going to explosively erupt that August.

“We told people, ‘we’ll watch it, but evacuation doesn’t make sense right now,'” Power said.

While spending a few weeks in King Cove and bunking at the Peter Pan cannery, Power noticed the earthquake activity waning, showing that the volcanologists had made the right call. The brand-new Alaska Volcano Observatory was one-for-one in advising people what to do, or, in the case of Mt. Dutton, what not to do.

Since that first response in 1988, the Alaska Volcano Observatory has grown from a good idea lobbied for by scientists–including John Davies, Syun-Ichi Akasofu, John Filson, and Tom Miller–into a team of people in Anchorage and Fairbanks who have their fingers on the pulse of more than 30 volcanoes in Alaska. The observatory is a cooperative program of the Geophysical Institute, the USGS and the Alaska Division of Geological and Geophysical Surveys. The job of the experts there is to monitor volcanoes and give Alaskans information when they need it most.

“Alaska has more explosive eruptions than any other state,” said Jon Dehn, an associate research professor at the Geophysical Institute, “It’s AVO’s responsibility to be prepared so the average person doesn’t have to worry about it.”

Like other AVO scientists tuned into Alaska’s volcanoes, Dehn is never far from his cellphone, which rings with Jimmy Buffett’s “Volcano” when an Alaska volcano shows signs of unrest. He and other AVO scientists now monitor an impressive data stream, which was just a trickle in 1988.

The last two decades have seen the development of satellite sensors that allow people to check for volcano hotspots several times a day, precise GPS receivers that enable scientists to watch volcanoes inflate and deflate, infrasound sensors that record sudden changes in air pressure during explosive eruptions, and the advent of a helpful tool called the Internet.

“When AVO was founded, there was no e-mail,” Power said.

“We were really kind of winging it in 1988,” Dehn said. “But in ’08, our game is pretty tight.”

Nowhere was that more evident than during the 2006 eruption of Augustine Volcano, across Cook Inlet from Homer. AVO not only predicted the eruption, but also forecast the migration of ash clouds (which can shut down aircraft engines).

“We ended up with the best dataset we’ve had so far,” said Steve McNutt, coordinating scientist at AVO and a research professor at UAF’s Geophysical Institute.

Other improvements to the volcano observatory include the late 1990s instrumentation of volcanoes in the Aleutians. Right now, scientists are monitoring most of the potentially dangerous volcanoes that make up the remote islands, which about 80,000 large jets fly over each year. That wasn’t the case when McNutt joined AVO in the early ’90s, when a volcano named Westdahl was spewing ash into the sky.

“The first report was from a pilot who said Shishaldin (a nearby volcano) was erupting,” said McNutt. “That’s what happened 16 or 17 years ago. Nowadays, we catch it first. We’re the ones telling airline pilots, not the other way around.”

Earthquake in Illinois could portend an emerging threat

A map of the surrounding area and aftershocks felt from the April 18 earthquake. - Image courtesy of CERI
A map of the surrounding area and aftershocks felt from the April 18 earthquake. – Image courtesy of CERI

To the surprise of many, the earthquake on April 18, 2008, about 120 miles east of St. Louis, originated in the Wabash Valley Fault and not the better-known and more-dreaded New Madrid Fault in Missouri’s bootheel.

The concern of Douglas Wiens, Ph.D., and Michael Wysession, Ph.D., seismologists at Washington University in St. Louis, is that the New Madrid Fault may have seen its day and the Wabash Fault is the new kid on the block.

The earthquake registered 5.2 on the Richter scale and hit at 4:40 a.m. with a strong aftershock occurring at approximately 10:15 a.m. that morning, followed by lesser ones in subsequent days. The initial earthquake was felt in parts of 16 states.

“I think everyone’s interested in the Wabash Valley Fault because a lot of the attention has been on the New Madrid Fault, but the Wabash Valley Fault could be the more dangerous one, at least for St. Louis and Illinois,” said Wiens, professor of earth and planetary sciences in Arts & Sciences. “The strongest earthquakes in the last few years have come from the Wabash Valley Fault, which needs more investigation.”

Wiens said that seismologist Robert Hermann of Saint Louis University, Gary Pavils of Indiana University, and several geologists including Steven Obermeir of the U.S. Geological Survey (USGS), have made studies of the Wabash Valley Fault. Pavils also has run a dense local array of stations and recorded many very small earthquakes at the Wabash Valley Fault. Hermann has studied the 1968 magnitude 5.5 earthquake, the largest ever recorded there. Obermeir and others have found disturbed sediments from previous earthquakes along the fault with estimated magnitudes of about 7 on the Richter scale over the past several thousand years.

According to Wysession, there are 200,000 earthquakes recorded every year, with a magnitude 6 earthquake happening every three days somewhere in the world.

“There hasn’t been a magnitude 6 earthquake on the New Madrid zone in more than 100 years, yet in 20 years there have been three magnitude 5 or better earthquakes on the Wabash Valley Fault,” said Wyssession, associate professor of earth and planetary sciences. “There is evidence that sometime in the past the Wabash Valley Fault has produced as strong as magnitude 7 earthquakes. On the other hand, the New Madrid Fault has been very quiet for a long time now. Clearly, the Wabash Valley Fault has gotten our deserved attention.”

Wysession said a recent re-analysis of data by USGS shows that the New Madrid fault risk is much less than was thought three decades ago. The three notable earthquakes that occurred at the end of 1811 and the beginning of 1812 were not magnitude 8s, rather magnitude 7s. A magnitude 8 is 30 times more energetic than a magnitude 7.

“The damage to the region by those earthquakes has been exaggerated,” Wysession said. “St. Louis was here at the time, and all that happened was some chimneys fell in East St. Louis. The little village of St. Genevieve, closer to the fault zone, had no damage at all. But, let’s face it, St. Louis is the biggest city in the region of both faults, and the Wabash Valley Fault is closer to us. If the big one does occur, it’s looking more like it will come out of Illinois.”

Wysession said that the North American Earth’s crust is filled with cracks and faults, and that an earthquake can occur anywhere on the continent. Many of the faults are undetected.

“As the continents bang into each other, sometimes they pull apart, and the crust cracks and ruptures, causing earthquakes,” he explained. “This whole region of New Madrid and the Wabash Valley seismic zone became a rift zone about 750 million years ago when the continent almost broke apart. There was a lot of volcanic activity, a lot of seismic activity. The crust got stretched and thinned. By looking at seismometers, we can actually see many of these faults in the thinning of crusts underground.”

Wysession said that an earthquake in the Midwest will be felt ten times farther away than one occurring in the western United States because the crust beneath the Midwest is very old, stiff and cold. The rock is about 1.7 billion years old and the seismic waves can travel very long distances through this type of crust. It can be felt hundreds of miles away, even if it was a smaller earthquake. In the western United States, the rock is hotter, and thus it dampens the shock waves and they are not felt as far away.

Despite the fact that most seismologists, including Wysession and Wiens, don’t think it likely that earthquakes ever will be predicted – which inevitably dredges up memories of the 1990 Midwest earthquake scare sparked by Iben Browning – Wysession says that there are some precursory phenomena that have been observed right before some earthquakes. Radon or helium gas may leak out of the ground as the ground cracks. Sometimes water well pressure changes, or there’s a change in the magnetic field. Electrical resistivity changes have been noted, too.

“These are changes we can measure with instruments, but we can’t sense them as humans,” he said. “Many people think that animals sense atmospheric changes. You always get stories about Rover going bananas right before an earthquake. But until Rover learns to tell us what he’s barking about, we won’t be able to employ animals in any predictive way.”

Refining the date of dinosaur extinction

At Zumaia in the Basque country of northern Spain, sediments laid down around the end of the Cretaceous period show layers of light limestone and dark marl reflecting warm and cool periods, respectively, in Earth's climate. These alternating climatic periods are caused by 100,000-year and 405,000-year cycles in Earth's orbital eccentricity. Because Earth's orbit, and thus the relative ages of the sediment layers, can be precisely calculated, dating of the sediments by the argon-argon method provided a much-needed recalibration of the method and made it possible to pinpoint the Cretaceous/Tertiary boundary at 65.95 million years ago. (Image courtesy of Science)
At Zumaia in the Basque country of northern Spain, sediments laid down around the end of the Cretaceous period show layers of light limestone and dark marl reflecting warm and cool periods, respectively, in Earth’s climate. These alternating climatic periods are caused by 100,000-year and 405,000-year cycles in Earth’s orbital eccentricity. Because Earth’s orbit, and thus the relative ages of the sediment layers, can be precisely calculated, dating of the sediments by the argon-argon method provided a much-needed recalibration of the method and made it possible to pinpoint the Cretaceous/Tertiary boundary at 65.95 million years ago. (Image courtesy of Science)

Improved rock-dating method pinpoints dinosaur demise with unprecedented precision

Scientists at the University of California, Berkeley, and the Berkeley Geochronology Center have pinpointed the date of the dinosaurs’ extinction more precisely than ever thanks to refinements to a common technique for dating rocks and fossils.

The argon-argon dating method has been widely used to determine the age of rocks, whether they’re thousands or billions of years old. Nevertheless, the technique had systematic errors that produced dates with uncertainties of about 2.5 percent, according to Paul Renne, director of the Berkeley Geochronology Center and an adjunct professor of earth and planetary science at UC Berkeley.

Renne and his colleagues in Berkeley and in the Netherlands now have lowered this uncertainty to 0.25 percent and brought it into agreement with other isotopic methods of dating rocks, such as uranium/lead dating. As a result, argon-argon dating today can provide more precise absolute dates for many geologic events, ranging from volcanic eruptions and earthquakes to the extinction of the dinosaurs and many other creatures at the end of the Cretaceous period and the beginning of the Tertiary period. That boundary had previously been dated at 65.5 million years ago, give or take 300,000 years.

According to a paper by Renne’s team in the April 25 issue of Science, the best date for the Cretaceous-Tertiary, or K/T, boundary is now 65.95 million years, give or take 40,000 years.

“The importance of the argon-argon technique is that it is the only technique that has the dynamic range to cover nearly all of Earth’s history,” Renne said. “What this refinement means is that you can use different chronometers now and get the same answer, whereas, that wasn’t true before.”

Renne noted that the greater precision matters little for recent events, such as the emergence of human ancestors in Africa 6 million years ago, because the uncertainty is only a few tens of thousands of years.

“Where it really adds up is in dating events in the early solar system,” Renne said. “A 1 percent difference at 4.5 billion years is almost 50 million years.”

One major implication of the revision involves the formation of meteorites, planetessimals and planets in the early solar system, he said. Argon-argon dating was giving a lower date than other methods for the formation of meteorites, suggesting that they cooled slowly during the solar system’s infancy.

“The new result implies that many of these meteorites cooled very, very quickly, which is consistent with what is known or suggested from other studies using other isotopic systems,” he said. “The evolution of the early solar system – the accretion of planetessimals, the differentiation of bodies by gravity while still hot – happened very fast. Argon-argon dating is now no longer at odds with that evidence, but is very consistent with it.”

Renne has warned geologists for a decade of uncertainty in the argon-argon method and has been correcting his own data since 2000, but it took a collaboration that he initiated in 1998 with Jan R. Wijbrans of the Free University in the Netherlands to obtain convincing evidence. Wijbrans and his Dutch colleagues were studying a unique series of sediments from the Messinian Melilla-Nador Basin on the coast of Morocco that contain records of cycles in Earth’s climate that reflect changes in Earth’s orbit that can be precisely calculated.

Wijbrans’ colleague Frits Hilgen at the University of Utrecht, a coauthor of the study, has been one of the world’s leaders in translating the record of orbital cycles into a time scale for geologists, according to Renne. Renne’s group had proposed using the astronomical tuning approach to calibrate the argon-argon method as early as 1994, but lacked ideal sedimentary sequences to realize the full power of this approach. The collaboration brought together all the appropriate expertise to bring this approach to fruition, he said.

“The problem with astronomical dating of much older sediments, even when they contain clear records of astronomical cycles, is that you’re talking about a pattern that is not anchored anywhere,” Renne said. “You see a bunch of repetitions of features in sediments, but you don’t know where to start counting.”

Argon-argon dating of volcanic ash, or tephra, in these sediments provided that anchor, he said, synchronizing the methods and making each one more precise. The argon-argon analyses were conducted both in Berkeley and Amsterdam to eliminate interlaboratory bias.

Argon-argon dating, developed at UC Berkeley in the 1960s, is based on the fact that the naturally-occurring isotope potassium-40 decays to argon-40 with a 1.25-billion-year half-life. Single-grain rock samples are irradiated with neutrons to convert potassium-39 to argon-39, which is normally not present in nature. The ratio of argon-40 to argon-39 then provides a measurement of the age of the sample.

“This should be the last big revision of argon-argon dating,” Renne said. “We’ve finally narrowed it down to where we are talking about fractions-of-a-percent revisions in the future, at most.”

Klaudia Kuiper, the lead author of the Science paper, was a Ph.D. student in Amsterdam working with study coauthors Wijbrans, Hilgen and Wout Krijgsman when the study was initiated. She also conducted lab work with Renne and Alan Deino, a geochronologist with Renne at the Berkeley Geochronology Center who was also one of the study’s coauthors.

The work was funded by the U.S. and Dutch National Science Foundations and the Ann and Gordon Getty Foundation.

Did a Significant Cool Spell Mark the Demise of Megafauna?

Regents’ Professor Vance Haynes cites a need for more investigation into a mysterious disappearance of Earth’s largest creatures and the humans that pursued them.

The end of the Pleistocene Epoch was marked with steadily warmer temperatures and the great ice age glaciers that covered vast areas of North America were in retreat.

Except for a 1,000-year period when things once again suddenly got remarkably colder, the cause of which is a mystery that researchers of the period have argued over for years.

Geologically, the start of this period is marked by a “black mat” of organically rich soil. Below the mat is the evidence of late Pleistocene flora and fauna, including the very large animals that once roamed across North America: mammoth and mastodons, dire wolves, horses, short-faced bears and others.

Also just below the line is the evidence of the humans who hunted these animals, called Clovis for their large fluted stone spear points first found by archaeologists at Clovis, N.M. Above the line, neither the megafauna nor the Clovis points are anywhere to be found.

C. Vance Haynes Jr., a Regents’ Professor of anthropology and geosciences at The University of Arizona, analyzed the black mats at nearly a hundred archaeological sites in North America. Stratigraphically they represent the beginning of what’s known as the Younger Dryas cooling period that began about 10,900 years ago and lasted until about 9,800 years ago. This also includes sites along Arizona’s San Pedro River that Haynes and others have excavated over the years.

Haynes’ current study (“Younger Dryas ‘black mats’ and the Rancholabrean termination in North America”) is published in the April 21 issue of the Proceedings of the National Academy of Sciences’ Online Early Edition.

The black mats are dark gray or black soil deposits that contain a higher organic carbon content than in either the strata above or below. While not all alike, the mats all represent relatively moist conditions of the time, such as cooler temperatures and rising water tables, which likely signaled an abrupt change in climate as well.

More than two dozen archaeological sites have yielded mammoth bones blanketed by black mat. Some of these sites also contain Clovis artifacts, leftovers of the technology that was developed to kill and process very large animals.

One large species that survived the Younger Dryas extinction period was the American bison. The increased number of bison kill sites and evidence of cultural diversity also point to a significant human population increase following the Clovis period.

What caused this phenomenon is far from settled. About all that is known for certain is that the extinction of the giant Pleistocene mammals came about fairly quickly, possibly in as little as a century.

Paul Martin, a recognized expert on Quaternary geology and a retired UA geoscience professor, has argued that human predation was responsible for the demise of the animals. The Quaternary is the most recent geologic time period and includes the Pleistocene.

Haynes counters that humans would have had to have killed all of these animals everywhere at the same time. Others have suggested the demise of megafauna came from mass epidemics.

One theory suggests a comet or asteroid impact, citing microscopic glass-like carbon particles found at the base of the black mats as evidence. Again, Haynes, based on his work at Murray Springs along the San Pedro River, says these compounds could just as easily be cosmic dust that constantly rains down on Earth.

Haynes says he’s skeptical of an extraterrestrial impact event as the genesis of the Younger Dryas period and the end of North America’s giant animals, but he also acknowledged that “something happened at 10,900 B.P. that we have yet to understand,” adding that the E.T. theory needs further testing.

1600 Eruption Caused Global Disruption

The 1600 eruption of Huaynaputina in Peru had a global impact on human society, according to a new study of contemporary records by geologists at UC Davis.

The eruption is known to have put a large amount of sulfur into the atmosphere, and tree ring studies show that 1601 was a cold year, but no one had looked at the agricultural and social impacts, said Ken Verosub, professor of geology at UC Davis.

“We knew it was a big eruption, we knew it was a cold year, and that’s all we knew,” Verosub said.

Sulfur reacts with water in the air to form droplets of sulfuric acid, which cool the planet by reducing the amount of sunlight reaching the Earth’s surface. But the droplets soon fall back to Earth, so the cooling effects last only a year or so.

Verosub and undergraduate student Jake Lippmann combed through records from the turn of the 17th century from Europe, China and Japan, as well as the Spanish and Portuguese colonies in South America and the Philippines, for information about changes in climate, agriculture and society.

In Russia, 1601-1603 brought the worst famine in the country’s history, leading to the overthrow of the reigning tsar. Records from Switzerland, Latvia and Estonia record exceptionally cold winters in 1600-1602; in France, the 1601 wine harvest was late, and wine production collapsed in Germany and colonial Peru. In China, peach trees bloomed late, and Lake Suwa in Japan had one of its earliest freezing dates in 500 years.

“In one sense, we can’t prove that the volcano was responsible for all this,” Verosub said. “But we hope to show that 1601 was a consistently bad year, connected by this event.”

The previous major eruption that might have affected global climate was in 1452-53, when records were much less complete: in Europe, people began to take more careful note of the natural world after the Renaissance. The 1815 Tambora eruption in Indonesia had a well-documented impact on global agriculture, so such eruptions may occur as often as every 200 years, Verosub noted.

Verosub hopes to expand the study by examining records kept by the Jesuit order in Seville, Spain, and from the Ming Dynasty in China.

The initial results are presented in an article in Eos, the transactions of the American Geophysical Union.

Arctic Ice More Vulnerable to Sunny Weather, New Study Shows

This June 7, 2007 NASA satellite image, taken under mostly cloud-free conditions, shows the beginning of last summer's Arctic sea ice melt. - Image courtesy NASA
This June 7, 2007 NASA satellite image, taken under mostly cloud-free conditions, shows the beginning of last summer’s Arctic sea ice melt. – Image courtesy NASA

The shrinking expanse of Arctic sea ice is increasingly vulnerable to summer sunshine, new research concludes. The study, by scientists at the National Center for Atmospheric Research (NCAR) and Colorado State University (CSU), finds that unusually sunny weather contributed to last summer’s record loss of Arctic ice, while similar weather conditions in past summers do not appear to have had comparable impacts.

The study, which draws on observations from instruments on a new group of NASA satellites known as the “A-Train,” will be published tomorrow in Geophysical Research Letters. It was funded by NASA and the National Science Foundation, which is NCAR’s principal sponsor.

“In a warmer world, the thinner sea ice is becoming increasingly sensitive to year-to-year variations in weather and cloud patterns,” says NCAR’s Jennifer Kay, the lead author. “A single unusually clear summer can now have a dramatic impact.”

The findings indicate that summer sunshine in the Arctic produces more pronounced melting than in the past, largely because there is now less ice to reflect solar radiation back into space. As a result, the presence or absence of clouds now has greater implications for sea ice loss.

Satellite data offer clues to record-shattering 2007 melt

Last summer’s loss of Arctic sea ice set a modern-day record, with the ice extent shrinking to a minimum of about 1.6 million square miles (4.1 million square kilometers) in September. That was 43 percent less ice coverage than in 1979, when accurate satellite observations began.

Looking at the first two years of data from radar and lidar on the A-Train satellites, Kay and her colleagues found that total summertime cloud cover in the Western Arctic was 16 percent less in 2007 than the year before. A strong high-pressure system centered north of Alaska kept skies relatively clear. Over a three-month period in the summer, the increased sunshine was strong enough to melt about a foot of surface ice. Over open water, it was sufficient to increase sea-surface temperatures by 4.3 degrees Fahrenheit (2.4 degrees Celsius). Warmer ocean waters can contribute to sea ice loss by melting the ice from the bottom, thereby thinning it and making it more susceptible to future melt.

“Satellite radar and lidar measurements allow us to observe Arctic clouds in a new way,” says CSU scientist Tristan L’Ecuyer, a co-author of the study. “These new instruments not only provide a very precise view of where clouds exist but also tell us their height and thickness, which are key properties that determine the amount of sunlight clouds reflect back to space.”

The research team also examined longer-term records of Arctic cloud and weather patterns, including a 62-year-long record of cloudiness from surface observations at Barrow, Alaska. They found that the 2007 weather and cloud pattern was unusual but not unprecedented. At Barrow, five other years–1968, 1971, 1976, 1977, and 1991–had less summertime cloud cover than 2007, but without the same impact on sea ice.

A summer feedback cycle

The research suggests that warmth from the Sun will increasingly affect Arctic sea ice loss in the summer. As the ice shrinks, incoming sunshine triggers a spiraling effect: the newly exposed dark ocean waters, much darker than the ice, absorb the Sun’s radiation instead of reflecting it. This warms the water and melts more ice, which in turn leads to more absorption of radiation and still more warming.

“Our research indicates that the relative importance of solar radiation in the summer is changing,” Kay says. “The sunshine reaching the Arctic is increasingly influential, as there is less ice to reflect it back into space. Dry, sunny conditions in a single summer can now act as a potent force to melt sea ice.”

The authors note that, in addition to solar radiation, other factors such as changes in wind patterns and possibly shifts in ocean circulation patterns also influence sea ice loss. In particular, strong winds along regions of sea ice retreat were important to last year’s loss of ice. The relative importance of these factors, and the precise extent to which global climate change is driving them, are not yet known.

Title: “Contribution of cloud and radiation anomalies to the 2007 Arctic sea ice extent minimum”, Geophysical Research Letters

Mountains reached current elevation earlier than thought

The Ruby Mountains, in northeast Nevada, are within the Basin and Range region where Andreas Mulch and his colleagues analyzed samples of volcanic glass. - Photo Credit: Andreas Mulch
The Ruby Mountains, in northeast Nevada, are within the Basin and Range region where Andreas Mulch and his colleagues analyzed samples of volcanic glass. – Photo Credit: Andreas Mulch

Sierra Nevada rose to current height earlier than thought, geologists say

Geologists studying deposits of volcanic glass in the western United States have found that the central Sierra Nevada largely attained its present elevation 12 million years ago, roughly 8 or 9 million years earlier than commonly thought.

The finding has implications not only for understanding the geologic history of the mountain range but for modeling ancient global climates.

“All the global climate models that are currently being used strongly rely on knowing the topography of the Earth,” said Andreas Mulch, who was a postdoctoral scholar at Stanford when he conducted the research. He is the lead author of a paper published this week in the online Early Edition of the Proceedings of the National Academy of Sciences.

A variety of studies over the last five years have shown that the presence of the Sierra Nevada and Rocky Mountains in the western United States has direct implications for climate patterns extending into Europe, Mulch said.

“If we did not have these mountains, we would completely change the climate on the North American continent, and even change mean annual temperatures in central Europe,” he said. “That’s why we need to have some idea of how mountains were distributed over planet Earth in order to run past climate models reliably.” Mulch is now a professor of tectonics and climate at the University of Hannover in Germany.

Mulch and his colleagues, including Page Chamberlain, a Stanford professor of environmental earth system science, reached their conclusion about the timing of the uplift of the Sierra Nevada by analyzing hydrogen isotopes in water incorporated into volcanic glass.

They analyzed volcanic glass at sites from the Coast Ranges bordering the Pacific Ocean, across the Central Valley and the Sierra Nevada and into the Basin and Range region of Nevada and Utah.

The ratio of hydrogen isotopes in the glass reflects changes that occurred to the water vapor content of air over the Pacific Ocean as it blew onto the continent and crossed the Sierra Nevada. As the air gains elevation, it cools, moisture concentrates and condenses, and it rains. Water containing heavier isotopes of hydrogen tends to fall first, resulting in a systematic decrease in the ratio of heavy water molecules to lighter ones in the remaining water vapor.

Because so much of the airborne moisture falls as rain on the windward side of the mountains, land on the leeward side gets far less rain-an effect called a “rain shadow”-which often produces a desert.

The higher the mountain, the more pronounced the rain shadow effect is and the greater the decrease in the number of heavy hydrogen isotopes in the water that makes it across the mountains and falls on the leeward side of the range. By determining the ratio of heavier to lighter hydrogen isotopes preserved in volcanic glass and comparing it with today’s topography and rainwater, researchers can estimate the elevation of the mountains at the time the ancient water crossed them.

Volcanic glass is an excellent material for preserving ancient rainfall. The glass forms during explosive eruptions, when tiny particles of molten rock are ejected into the air. “These glasses were little melt particles, and they cooled so rapidly when they were blown into the atmosphere that they just froze, basically,” Mulch said. “They couldn’t crystallize and form minerals.”

Because glass has an amorphous structure, as opposed to the ordered crystalline structure of minerals, there are structural vacancies in the glass into which water can diffuse. Once the glass has been deposited on the surface of the Earth, rainwater, runoff and near-surface groundwater are all available to interact with it. Mulch said the diffusion process continues until the glass is effectively saturated with water.

Other researchers have shown that once such volcanic glass is fully hydrated, the water in it does not undergo any significant isotopic exchange with its environment. Thus, the trapped water becomes a reliable record of the isotopic composition of the water in the environment at the time the glass was deposited.

“It takes probably a hundred to a thousand years or so for these glasses to fully hydrate,” Mulch said. But 1,000 years is the blink of an eye in geologic time and, for purposes of estimating the timing of events that occur on scales of millions or tens of millions of years, that degree of resolution is quite sufficient.

Likewise, you need deposits of volcanic ash that were laid down relatively quickly over a broad area. But that’s the norm for explosive eruptions. Though some ash may circulate in the upper atmosphere for a few years after a major eruption, significant quantities are generally deposited over vast areas within days.

The samples they studied ranged from slightly more than 12 million years old to as young as 600,000 years old, a time span when volcanism was rampant in the western United States owing to the ongoing subduction of the Pacific plate under the continental crust of the North American plate.

“As we use these ashes that are present on either side of the mountain range, we can directly compare what the water looked like before and after it had to cross this barrier to atmospheric flow,” Mulch said. “If you just stay behind the mountain range, you see the effect of the rain shadow, but you have to make inferences about where the water vapor is coming from, what happened to the clouds before they traveled across the mountain range.

“For the first time, we were able to document that we can track the [development of the] rain shadow on both sides of the mountain range over very long time scales.”

Until now, researchers have been guided largely by “very good geophysical evidence” indicating that the range reached its present elevation approximately 3 or 4 million years ago, owing to major changes in the subsurface structure of the mountains, Mulch said.

“There was a very dense root of the Sierra Nevada, rock material that became so dense that it actually detached and sank down into the Earth’s mantle, just because of density differences,” Mulch said. “If you remove a very heavy weight at the base of something, the surface will rebound.”

The rebound of the range after losing such a massive amount of material should have been substantial. But, Mulch said, “We do not observe any change in the surface elevation of the Sierra Nevada at that time, and that’s what we were trying to test in this model.”

However, Mulch said he does not think his results refute the geophysical evidence. It could be that the Sierra Nevada did not evolve uniformly along its 400-mile length, he said. The geophysical data indicating the loss of the crustal root is from the southern Sierra Nevada; Mulch’s study focused more on the northern and central part of the range. In the southern Sierra Nevada, the weather patterns are different, and the rain shadow effect that Mulch’s approach hinges on is less pronounced.

“That’s why it’s important to have information that’s coming from deeper parts of the Earth’s crust and from the surface and try to correlate these two,” Mulch said. To really understand periods in the Earth’s past where climate conditions were markedly different from today, he said, “you need to have integrated studies.”

The research was funded by the National Science Foundation.