Geologists shed light on formation of Alaska Range

Syracuse University Professor Paul Fitzgerald and a group of students have been studying the Alaska Range. -  Syracuse University
Syracuse University Professor Paul Fitzgerald and a group of students have been studying the Alaska Range. – Syracuse University

Geologists in Syracuse University’s College of Arts and Sciences have recently figured out what has caused the Alaska Range to form the way it has and why the range boasts such an enigmatic topographic signature. The narrow mountain range is home to some of the world’s most dramatic topography, including 20,320-foot Mount McKinley, North America’s highest mountain.

Professor Paul Fitzgerald and a team of students and fellow scientists have been studying the Alaska Range along the Denali fault. They think they know why the fault is located where it is and what accounts for the alternating asymmetrical, mountain-scale topography along the fault.

Their findings were the subject of a recent paper in the journal Tectonics (American Geophysical Union, 2014).

In 2002, the Denali fault, which cuts across south-central Alaska, was the site of a magnitude-7.9 earthquake and was felt as far away as Texas and Louisiana. It was the largest earthquake of its kind in more than 150 years.

“Following the earthquake, researchers flocked to the area to examine the effects,” says Fitzgerald, who serves as professor of Earth Sciences and an associate dean for the College. “They were fascinated by how the frozen ground behaved; the many landslides [the earthquake] caused; how bridges responded; and how the Trans-Alaska oil pipeline survived, as it was engineered to do so.”

Geologists were also surprised by how the earthquake began on a previously unknown thrust-fault; then propagated eastward, along the Denali fault, and finally jumped onto another fault, hundreds of kilometers away.

“From our perspective, the earthquake has motivated analyses of why the highest mountains in the central Alaska Range occur south of the Denali fault and the highest mountains in the eastern Alaska Range occur north of the fault–something that has puzzled us for years,” Fitzgerald adds. “It’s been an enigma staring us in the face.”

He attributes the Alaska Range’s alternating topographic signatures to a myriad of factors: contrasting lithospheric strength between large terranes (i.e., distinctly different rock units); the location of the curved Denali fault; the transfer of strain inland from southern Alaska’s active plate margin; and the shape of the controlling former continental margin against weaker suture-zone rocks.

It’s no secret that Alaska is one of the most geologically active areas on the planet. For instance, scientists know that the North American Plate is currently overriding the Pacific Plate at the latter’s southern coast, while the Yakutat microplate is colliding with North America.

As a result of plate tectonics, Alaska is an amalgamation of terranes that have collided with the North American craton and have accreted to become part of North America.

Cratons are pieces of continents that have been largely stable for hundreds of millions of years.

Terranes often originate as volcanic islands (like those of Hawaii) and, after colliding with one another or a continent, are separated by large discrete faults. When terranes collide and accrete, they form a suture, also known as a collision zone, which is made up of weak, crushed rock. During deformation, suture-zone rocks usually deform first, especially if they are adjacent to a strong rock body.

“Technically, the Denali fault is what we’d call an ‘intercontinental right-lateral strike-slip fault system,'” says Fitzgerald, adding that a strike-slip fault occurs when rocks move horizontally past one another, usually on a vertical fault. “This motion includes a component of slip along the fault and a component of normal motion against the fault that creates mountains. Hence, the shape of the fault determines which of the two components is predominant and where mountains form.”

In Alaska, the shape of the accreted terranes generally controls the location of the Denali fault and the mountains that form along it, especially at the bends in the trace of the fault.

Fitzgerald: “Mount McKinley and the central Alaska Range lie within the concave curve of the Denali fault. There, higher topography and greater exhumation [uplift of rock] occur south of the Denali fault, exactly where you’d expect a mountain range to form, given the regional tectonics. In the eastern Alaska Range, higher topography and greater exhumation are found north of the fault, on its convex side–not an expected pattern at all and very puzzling.”

Using mapped surface geology, geophysical data, and thermochronology (i.e., time-temperature history of the rocks), Fitzgerald and colleagues have determined that much of Alaska’s uplift and deformation began some 25 million years ago, when the Yakutat microplate first started colliding with North America. The bold, glacier-clad peaks comprising the Alaska Range actually derive from within the aforementioned “weak suture-zone rocks” between the terranes.

While mountains are high and give the impression of strength, they are built largely from previously fractured rock units. Rock movement along the Denali fault drives the uplift of the mountains, which form at bends in the fault, where previously fractured suture-zone rocks are pinned against the stronger former North American continental margin.

“The patterns of deformation help us understand regional tectonics and the formation of the Alaska Range, which is fascinating to geologists and non-geologists alike,” says Fitzgerald. “Being able to determine patterns or how to reveal them, while others see chaos, is often the key to finding the answer to complex problems. … To us scientists, the real significance of this work is that it helps us understand the evolution of our planet, how faults and mountain belts form, and why earthquakes happen. It also provides a number of hypotheses about Alaskan tectonics and rock deformation that we can test, using the Alaska Range as our laboratory.”

In addition to Fitzgerald, the paper was co-authored by Sarah Roeske, a research scientist at the University of California, Davis; Jeff Benowitz, a research scientist at the Geophysical Institute at the University of Alaska Fairbanks; Steven Riccio and Stephanie Perry, graduate students in Earth Sciences at Syracuse; and Phillip Armstrong, professor and chair of geological sciences at California State University, Fullerton.

Housed in Syracuse’s College of Arts and Sciences, the Department of Earth Sciences offers graduate and undergraduate degree opportunities in crustal evolution and tectonics, environmental sciences and climate change, hydrogeology, sedimentology and paleolimnology, geochemistry, and paleobiology.

Prehistoric landslide discovery rivals largest known on surface of Earth

David Hacker, Ph.D., points to pseudotachylyte layers and veins within the Markagunt gravity slide. -  Photo courtesy of David Hacker
David Hacker, Ph.D., points to pseudotachylyte layers and veins within the Markagunt gravity slide. – Photo courtesy of David Hacker

A catastrophic landslide, one of the largest known on the surface of the Earth, took place within minutes in southwestern Utah more than 21 million years ago, reports a Kent State University geologist in a paper being to be published in the November issue of the journal Geology.

The Markagunt gravity slide, the size of three Ohio counties, is one of the two largest known continental landslides (larger slides exist on the ocean floors). David Hacker, Ph.D., associate professor of geology at the Trumbull campus, and two colleagues discovered and mapped the scope of the Markagunt slide over the past two summers.

His colleagues and co-authors are Robert F. Biek of the Utah Geological Survey and Peter D. Rowley of Geologic Mapping, Inc. of New Harmony, Utah.

Geologists had known about smaller portions of the Markagunt slide before the recent mapping showed its enormous extent. Hiking through the wilderness areas of the Dixie National Forest and Bureau of Land Management land, Hacker identified features showing that the Markagunt landslide was much bigger than previously known.

The landslide took place in an area between what is now Bryce Canyon National Park and the town of Beaver, Utah. It covered about 1,300 square miles, an area as big as Ohio’s Cuyahoga, Portage and Summit counties combined.

Its rival in size, the “Heart Mountain slide,” which took place around 50 million years ago in northwest Wyoming, was discovered in the 1940s and is a classic feature in geology textbooks.

The Markagunt could prove to be much larger than the Heart Mountain slide, once it is mapped in greater detail.

“Large-scale catastrophic collapses of volcanic fields such as these are rare but represent the largest known landslides on the surface of the Earth,” the authors wrote.

The length of the landslide – over 55 miles – also shows that it was as fast moving as it was massive, Hacker said. Evidence showing that the slide was catastrophic – occurring within minutes – included the presence of pseudotachylytes, rocks that were melted into glass by the immense friction. Any animals living in its path would have been quickly overrun.

Evidence of the slide is not readily apparent to visitors today. “Looking at it, you wouldn’t even recognize it as a landslide,” he said. But internal features of the slide, exposed in outcrops, yielded evidence such as jigsaw puzzle rock fractures and shear zones, along with the pseudotachylytes.

Hacker, who studies catastrophic geological events, said the slide originated when a volcanic field consisting of many strato-volcanoes, a type similar to Mount St. Helens in the Cascade Mountains, which erupted in 1980, collapsed and produced the massive landslide.

The collapse may have been caused by the vertical inflation of deeper magma chambers that fed the volcanoes. Hacker has spent many summers in Utah mapping geologic features of the Pine Valley Mountains south of the Markagunt where he has found evidence of similar, but smaller slides from magma intrusions called laccoliths.

What is learned about the mega-landslide could help geologists better understand these extreme types of events. The Markagunt and the Heart Mountain slides document for the first time how large portions of ancient volcanic fields have collapsed, Hacker said, representing “a new class of hazards in volcanic fields.”

While the Markagunt landslide was a rare event, it shows the magnitude of what could happen in modern volcanic fields like the Cascades. “We study events from the geologic past to better understand what could happen in the future,” he said.

The next steps in the research, conducted with his co-authors on the Geology paper, will be to continue mapping the slide, collect samples from the base for structural analysis and date the pseudotachylytes.

Hacker, who earned his Ph.D. in geology at Kent State, joined the faculty in 2000 after working for an environmental consulting company. He is co-author of the book “Earth’s Natural Hazards: Understanding Natural Disasters and Catastrophes,” published in 2010.

View the abstract of the Geology paper, available online now.

Learn more about research at Kent State: http://www.kent.edu/research

Syracuse geologist reveals correlation between earthquakes, landslides

Devin McPhillips is a research associate in the Department of Earth Sciences. -  Syracuse University
Devin McPhillips is a research associate in the Department of Earth Sciences. – Syracuse University

A geologist in Syracuse University’s College of Arts and Sciences has demonstrated that earthquakes–not climate change, as previously thought–affect the rate of landslides in Peru.

The finding is the subject of an article in Nature Geoscience (Nature Publishing Group, 2014) by Devin McPhillips, a research associate in the Department of Earth Sciences. He co-wrote the article with Paul Bierman, professor of geology at The University of Vermont; and Dylan Rood, a lecturer at Imperial College London (U.K.).

“Geologic records of landslide activity offer rare glimpses into landscapes evolving under the influence of tectonics and climate,” says McPhillips, whose expertise includes geomorphology and tectonics. “Because deposits from individual landslides are unlikely to be preserved, it’s difficult to reconstruct landslide activity in the geologic past. Therefore, we’ve developed a method that measures landslide activity before and after the last glacial-interglacial climate transition in Peru.”

McPhillips and his team have spent the past several years in the Western Andes Mountains, studying cobbles in the Quebrada Veladera river channel and in an adjacent fill terrace. By measuring the amount of a nuclide known as Beryllium-10 (Be-10) in each area’s cobble population, they’ve been able to calculate erosion rates over tens of thousands of years.

The result? The range of Be concentrations in terrace cobbles from a relatively wet period, more than 16,000 years ago, was no different from those found in river channel cobbles from more recent arid periods.

“This suggests that the amount of erosion from landslides has not changed in response to climatic changes,” McPhillips says. “Our integrated millennial-scale record of landslides implies that earthquakes may be the primary landslide trigger.”

McPhillips says the study is the first to study landslides by measuring individual particles of river sediment, as opposed to amalgamating all the particles and then measuring a single concentration.

“These concentrations provide a robust record of hill-slope behavior over long timescales,” he adds. “Millennial-scale records of landslide activity, especially in settings without preserved landslide deposits, are an important complement to studies documenting modern landslide inventories.”

Earthquakes are a regular occurrence in Peru, which is located at the nexus of the small Nazca oceanic plate and the larger South American crustal plate. The ongoing subduction, or sliding, of the Nazca Plate under the South American Plate has spawned considerable tectonic activity.

“Peru is rife with earthquakes, landslides, volcanic eruptions, and tectonic uplift,” McPhillips adds. “By studying its past, we may be able to better predict and prepare for future calamities.”

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Housed in Syracuse’s College of Arts and Sciences, the Department of Earth Sciences offers graduate and undergraduate degree opportunities in environmental geology, wetland hydrogeology, crustal evolution, sedimentology, isotope geochemistry, paleobiology, paleolimnology, and global environmental change.

Predicting landslides with light

Optical fiber sensors are used around the world to monitor the condition of difficult-to-access segments of infrastructure-such as the underbellies of bridges, the exterior walls of tunnels, the feet of dams, long pipelines and railways in remote rural areas.

Now, a team of researchers in Italy are expanding the reach of optical fiber sensors “to the hills” by embedding them in shallow trenches within slopes to detect and monitor both large landslides and slow slope movements. The team will present their research at The Optical Society’s (OSA) 98th Annual Meeting, Frontiers in Optics, being held Oct. 19-23 in Tucson, Arizona, USA.

As major disasters around the world this year have shown, landslides can be stark examples of nature at her most unforgiving. Within seconds, a major landslide can completely erase houses and structures that have stood for years, and the catastrophic toll they inflict on communities is felt not just in that destructive loss of property but in the devastating loss of life. The 1999 Vargus tragedy in Venezuela, for instance, killed tens of thousands of people and erased whole towns from the map without warning.

The motivation for an early warning technology, like the one the Italian team has devised, is to find a way to mitigate such losses -just as hurricane tracking can prompt coastal evacuations and save lives.

Predicting Landslides by Detecting Land Strains


Landslides are failures of a rock or soil mass, and are always preceded by various types of “pre-failure” strains-known technically as elastic, plastic and viscous volumetric and shear strains. While the magnitude of these pre-failure strains depends on the rock or soil involved-ranging from fractured rock debris and pyroclastic flows to fine-grained soils-they are measurable. This new technology can detect small shifts in soil slopes, and thus can detect the onset of landslides. Usually, electrical sensors have been used for monitoring landslides, but these sensors are easily damaged. Optical fiber sensors are more robust, economical and sensitive. This is where the new technology could make a difference.

“Distributed optical fiber sensors can act as a ‘nervous system’ of slopes by measuring the tensile strain of the soil they’re embedded within,” explained Professor Luigi Zeni, who is in the Department of Industrial & Information Engineering at the Second University of Naples.

Taking it a step further, Zeni and his colleagues worked out a way of combining several types of optical fiber sensors into a plastic tube that twists and moves under the forces of pre-failure strains. Researchers are then able to monitor the movement and bending of the optical fiber remotely to determine if a landslide is imminent.

The use of novel fiber optic sensors “allows us to overcome some limitations of traditional inclinometers, because fiber-based ones have no moving parts and can withstand larger soil deformations,” Zeni said. “These sensors can be used to cover very large areas-several square kilometers-and interrogated in a time-continuous way to pinpoint any critical zones.”

The findings clearly demonstrate the potential of distributed optical fiber sensors as an entirely new tool to monitor areas subject to landslide risk, Zeni said, and to develop early warning systems based on geo-indicators-early deformations-of slope failures.

New Oso report, rockfall in Yosemite, and earthquake models

From AGU’s blogs: Oso disaster had its roots in earlier landslides

A research team tasked with being some of the first scientists and engineers to evaluate extreme events has issued its findings on disastrous Oso, Washington, landslide. The report studies the conditions and causes related to the March 22 mudslide that killed 43 people and destroyed the Steelhead Haven neighborhood in Oso, Washington. The team from the Geotechnical Extreme Events Reconnaissance (GEER) Association, funded by the National Science Foundation, determined that intense rainfall in the three weeks before the slide likely was a major issue, but factors such as altered groundwater migration, weakened soil consistency because of previous landslides and changes in hillside stresses played key roles.

From this week’s Eos: Reducing Rockfall Risk in Yosemite National Park

The glacially sculpted granite walls of Yosemite Valley attract 4 million visitors a year, but rockfalls from these cliffs pose substantial hazards. Responding to new studies, the National Park Service recently took actions to reduce the human risk posed by rockfalls in Yosemite National Park.

From AGU’s journals: A new earthquake model may explain discrepancies in San Andreas fault slip

Investigating the earthquake hazards of the San Andreas Fault System requires an accurate understanding of accumulating stresses and the history of past earthquakes. Faults tend to go through an “earthquake cycle”-locking and accumulating stress, rupturing in an earthquake, and locking again in a well-accepted process known as “elastic rebound.” One of the key factors in preparing for California’s next “Big One” is estimating the fault slip rate, the speed at which one side of the San Andreas Fault is moving past the other.

Broadly speaking, there are two ways geoscientists study fault slip. Geologists formulate estimates by studying geologic features at key locations to study slip rates through time. Geodesists, scientists who measure the size and shape of the planet, use technologies like GPS and satellite radar interferometry to estimate the slip rate, estimates which often differ from the geologists’ estimations.

In a recent study by Tong et al., the authors develop a new three-dimensional viscoelastic earthquake cycle model that represents 41 major fault segments of the San Andreas Fault System. While previous research has suggested that there are discrepancies between the fault slip rates along the San Andreas as measured by geologic and geodetic means, the authors find that there are no significant differences between the two measures if the thickness of the tectonic plate and viscoelasticity are taken into account. The authors find that the geodetic slip rate depends on the plate thickness over the San Andreas, a variable lacking in previous research.

The team notes that of the 41 studied faults within the San Andreas Fault system, a small number do in fact have disagreements between the geologic and geodetic slip rates. These differences could be attributed to inadequate data coverage or to incomplete knowledge of the fault structures or the chronological sequence of past events.

Against the current with lava flows

<IMG SRC="/Images/38239538.jpg" WIDTH="350" HEIGHT="233" BORDER="0" ALT="A pit chain marks a subterranean lava tunnel. Its roof collapsed partially. – Image: Mars Image Explorer / asu.edu“>
A pit chain marks a subterranean lava tunnel. Its roof collapsed partially. – Image: Mars Image Explorer / asu.edu

An Italian astronomer in the 19th century first described them as ‘canali’ – on Mars’ equatorial region, a conspicuous net-like system of deep gorges known as the Noctis Labyrinthus is clearly visible. The gorge system, in turn, leads into another massive canyon, the Valles Marineris, which is 4,000 km long, 200 km wide and 7 km deep. Both of these together would span the US completely from east to west.

As these gorges, when observed from orbit, resemble terrestrial canyons formed by water, most researchers assumed that immense flows of water must have carved the Noctis Labyrinthus and the Valles Marineris into the surface of Mars. Another possibility was that tectonic activity had created the largest rift valley on a planet in our solar system.

Lava flows caused the gorges

These assumptions were far from the mark, says Giovanni Leone, a specialist in planetary volcanism in the research group of ETH professor Paul Tackley. Only lava flows would have had the force and mass required to carve these gigantic gorges into the surface of Mars. The study was recently published in the Journal of Volcanology and Geothermal Research.

In recent years, Leone has examined intensively the structure of these canyons and their outlets into the Ares Vallis and the Chryse Planitia, a massive plain on Mars’ low northern latitude. He examined thousands of high-resolution surface images taken by numerous Mars probes, including the latest from the Mars Reconnaissance Orbiter, and which are available on the image databases of the US Geological Survey.

No discernible evidence of erosion by water

His conclusion is unequivocal: “Everything that I observed on those images were structures of lava flows as we know them on Earth,” he emphasises. “The typical indicators of erosion by water were not visible on any of them.” Leone therefore does not completely rules out water as final formative force. Evidence of water, such as salt deposits in locations where water evaporated from the ground or signs of erosion on the alluvial fans of the landslides, are scarce but still existing. “One must therefore ask oneself seriously how Valles Marineris could have been created by water if one can not find any massive and widespread evidence of it.” The Italian volcanologist similarly could find no explanation as to where the massive amounts of water that would be required to form such canyons might have originated.

Source region of lava flows identified

The explanatory model presented by Leone in his study illustrates the formation history from the source to the outlet of the gorge system. He identifies the volcanic region of Tharsis as the source region of the lava flows and from there initial lava tubes stretched to the edge of the Noctis Labyrinthus. When the pressure from an eruption subsided, some of the tube ceilings collapsed, leading to the formation of a chain of almost circular holes, the ‘pit chains’.

When lava flowed again through the tubes, the ceilings collapsed entirely, forming deep V-shaped troughs. Due to the melting of ground and rim material, and through mechanical erosion, the mass of lava carved an ever-deeper and broader bed to form canyons. The destabilised rims then slipped and subsequent lava flows carried away the debris from the landslides or covered it. “The more lava that flowed, the wider the canyon became,” says Leone.

Leone supported his explanatory model with height measurements from various Mars probes. The valleys of the Noctis Labyrinthus manifest the typical V-shape of ‘young’ lava valleys where the tube ceilings have completely collapsed. The upper rims of these valleys, however, have the same height. If tectonic forces had been at work, they would not be on the same level, he says. The notion of water as the formative force, in turn, is undermined by the fact that it would have taken tens of millions of cubic kilometres of water to carve such deep gorges and canyons. Practically all the atmospheric water of all the ages of Mars should have been concentrated only on Labyrinthus Noctis. Moreover, the atmosphere on Mars is too thin and the temperatures too cold. Water that came to the surface wouldn’t stay liquid, he notes: “How could a river of sufficient force and size even form?”

Life less likely

Leone’s study could have far-reaching consequences. “If we suppose that lava formed the Noctis Labyrinthus and the Valles Marineris, then there has always been much less water on Mars than the research community has believed to date,” he says. Mars received very little rain in the past and it would not have been sufficient to erode such deep and large gorges. He adds that the shallow ocean north of the equator was probably much smaller than imagined – or hoped for; it would have existed only around the North Pole. The likelihood that life existed, or indeed still exists, on Mars is accordingly much lower.

Leone can imagine that the lava tubes still in existence are possible habitats for living organisms, as they would offer protection from the powerful UV rays that pummel the Martian surface. He therefore proposes a Mars mission to explore the lava tubes. He considers it feasible to send a rover through a hole in the ceiling of a tube and search for evidence of life. “Suitable locations could be determined using my data,” he says.

Swimming against the current

With his study, the Italian is swimming against the current and perhaps dismantling a dogma in the process. Most studies of the past 20 years have been concerned with the question of water on Mars and how it could have formed the canyons. Back in 1977, a researcher first posited the idea that the Valles Marineris may have been formed by lava, but the idea failed to gain traction. Leone says this was due to the tunnel vision that the red planet engenders and the prevailing mainstream research. The same story has been told for decades, with research targeted to that end, without achieving a breakthrough. Leone believes that in any case science would only benefit in considering other approaches. “I expect a spirited debate,” he says. “But my evidence is strong.”

Mega-landslide in giant Utah copper mine may have triggered earthquakes

This is Figure 1 from K.L. Pankow et al. of megalandslide at the Bingham Canyon Mine, Utah. Landslide image copyright Kennecott Utah Copper. -  Seismic/Infrasound image by K.L. Pankow et al. Landslide image copyright Kennecott Utah Copper.
This is Figure 1 from K.L. Pankow et al. of megalandslide at the Bingham Canyon Mine, Utah. Landslide image copyright Kennecott Utah Copper. – Seismic/Infrasound image by K.L. Pankow et al. Landslide image copyright Kennecott Utah Copper.

Landslides are one of the most hazardous aspects of our planet, causing billions of dollars in damage and thousands of deaths each year. Most large landslides strike with little warning — and thus geologists do not often have the ability to collect important data that can be used to better understand the behavior of these dangerous events. The 10 April 2013 collapse at Kennecott’s Bingham Canyon open-pit copper mine in Utah is an important exception.

Careful and constant monitoring of the conditions of the Bingham Canyon mine identified slow ground displacement prior to the landslide. This allowed the successful evacuation of the mine area prior to the landslide and also alerted geologists at the University of Utah to enable them to successfully monitor and study this unique event.

The landslide — the largest non-volcanic landslide in the recorded history of North America — took place during two episodes of collapse, each lasting less than two minutes. During these events about 65 million cubic meters of rock — with a total mass of 165 million tons — collapsed and slid nearly 3 km (1.8 miles) into the open pit floor.

In the January 2014 issue of GSA Today, University of Utah geologists, led by Dr. Kristine Pankow, report the initial findings of their study of the seismic and sound-waves generated by this massive mega-landslide. Pankow and her colleagues found that the landslide generated seismic waves that were recorded by both nearby seismic instruments, but also instruments located over 400 km from the mine. Examining the details of these seismic signals, they found that each of the two landslide events produced seismic waves equivalent to a magnitude 2 to 3 earthquake.

Interestingly, while there were no measurable seismic events prior to the start of the landslide, the team did measure up to 16 different seismic events with characteristics very much like normal “tectonic” earthquakes beneath the mine. These small (magnitude less than 2) earthquakes happened over a span of 10 days following the massive landslide and appear to be a rare case of seismic activity triggered by a landslide, rather than the more common case where an earthquake serves as the trigger to the landslide.

Later studies of both the seismic and sound waves produced by this landslide will allow Pankow and her team to characterize the failure and displacement of the landslide material in much more detail.

Mine landslide triggered quakes

The April 10, 2013, landslide at Rio Tinto-Kennecott Utah Copper's Bingham Canyon mine contains enough debris to bury New York City's Central Park 66 feet deep, according to a new University of Utah study. The slide happened in the form of two rock avalanches 95 minutes apart. The first rock avalanche included grayer bedrock material seen around the margins of the lower half of the slide. The second rock avalanche is orange in color, both from bedrock and from waste rock from mining. The new study found the landslide triggered 16 small quakes. Such triggering has not been noted previously. The slide likely was the largest nonvolcanic landslide in North America's modern history. -  Kennecott Utah Copper.
The April 10, 2013, landslide at Rio Tinto-Kennecott Utah Copper’s Bingham Canyon mine contains enough debris to bury New York City’s Central Park 66 feet deep, according to a new University of Utah study. The slide happened in the form of two rock avalanches 95 minutes apart. The first rock avalanche included grayer bedrock material seen around the margins of the lower half of the slide. The second rock avalanche is orange in color, both from bedrock and from waste rock from mining. The new study found the landslide triggered 16 small quakes. Such triggering has not been noted previously. The slide likely was the largest nonvolcanic landslide in North America’s modern history. – Kennecott Utah Copper.

Last year’s gigantic landslide at a Utah copper mine probably was the biggest nonvolcanic slide in North America’s modern history, and included two rock avalanches that happened 90 minutes apart and surprisingly triggered 16 small earthquakes, University of Utah scientists discovered.

The landslide – which moved at an average of almost 70 mph and reached estimated speeds of at least 100 mph – left a deposit so large it “would cover New York’s Central Park with about 20 meters (66 feet) of debris,” the researchers report in the January 2014 cover study in the Geological Society of America magazine GSA Today.

While earthquakes regularly trigger landslides, the gigantic landslide the night of April 10, 2013, is the first known to have triggered quakes. The slide occurred in the form of two huge rock avalanches at 9:30 p.m. and 11:05 p.m. MDT at Rio Tinto-Kennecott Utah Copper’s open-pit Bingham Canyon Mine, 20 miles southwest of downtown Salt Lake City. Each rock avalanche lasted about 90 seconds.

While the slides were not quakes, they were measured by seismic scales as having magnitudes up to 5.1 and 4.9, respectively. The subsequent real quakes were smaller.

Kennecott officials closely monitor movements in the 107-year-old mine – which produces 25 percent of the copper used in the United States – and they recognized signs of increasing instability in the months before the slide, closing and removing a visitor center on the south edge of the 2.8-mile-wide, 3,182-foot-deep open pit, which the company claims is the world’s largest manmade excavation.

Landslides – including those at open-pit mines but excluding quake-triggered slides – killed more than 32,000 people during 2004-2011, the researchers say. But no one was hurt or died in the Bingham Canyon slide. The slide damaged or destroyed 14 haul trucks and three shovels and closed the mine’s main access ramp until November.

“This is really a geotechnical monitoring success story,” says the new study’s first author, Kris Pankow, associate director of the University of Utah Seismograph Stations and a research associate professor of geology and geophysics. “No one was killed, and yet now we have this rich dataset to learn more about landslides.”

There have been much bigger human-caused landslides on other continents, and much bigger prehistoric slides in North America, including one about five times larger than Bingham Canyon some 8,000 years ago at the mouth of Utah’s Zion Canyon.

But the Bingham Canyon Mine slide “is probably the largest nonvolcanic landslide in modern North American history,” said study co-author Jeff Moore, an assistant professor of geology and geophysics at the University of Utah.

There have been numerous larger, mostly prehistoric slides – some hundreds of times larger. Even the landslide portion of the 1980 Mount St. Helens eruption was 57 times larger than the Bingham Canyon slide.

News reports initially put the landslide cost at close to $1 billion, but that may end up lower because Kennecott has gotten the mine back in operation faster than expected.

Until now, the most expensive U.S. landslide was the 1983 Thistle slide in Utah, which cost an estimated $460 million to $940 million because the town of Thistle was abandoned, train tracks and highways were relocated and a drainage tunnel built.

Pankow and Moore conducted the study with several colleagues from the university’s College of Mines and Earth Sciences: J. Mark Hale, an information specialist at the Seismograph Stations; Keith Koper, director of the Seismograph Stations; Tex Kubacki, a graduate student in mining engineering; Katherine Whidden, a research seismologist; and Michael K. McCarter, professor of mining engineering.

The study was funded by state of Utah support of the University of Utah Seismograph Stations and by the U.S. Geological Survey.

Rockslides Measured up to 5.1 and 4.9 in Magnitude, but Felt Smaller

The University of Utah researchers say the Bingham Canyon slide was among the best-recorded in history, making it a treasure trove of data for studying slides.

Kennecott has estimated the landslide weighed 165 million tons. The new study estimated the slide came from a volume of rock roughly 55 million cubic meters (1.9 billion cubic feet). Rock in a landslide breaks up and expands, so Moore estimated the landslide deposit had a volume of 65 million cubic meters (2.3 billion cubic feet).

Moore calculated that not only would bury Central Park 66 feet deep, but also is equivalent to the amount of material in 21 of Egypt’s great pyramids of Giza.

The landslide’s two rock avalanches were not earthquakes but, like mine collapses and nuclear explosions, they were recorded on seismographs and had magnitudes that were calculated on three different scales:

  • The first slide at 9:30 p.m. MDT measured 5.1 in surface-wave magnitude, 2.5 in local or Richter magnitude, and 4.2 in duration or “coda” magnitude.

  • The second slide at 11:05 p.m. MDT measured 4.9 in surface-wave magnitude, 2.4 in Richter magnitude and 3.5 in coda magnitude.

Pankow says the larger magnitudes more accurately reflect the energy released by the rock avalanches, but the smaller Richter magnitudes better reflect what people felt – or didn’t feel, since the Seismograph Stations didn’t receive any such reports. That’s because the larger surface-wave magnitudes record low-frequency energy, while Richter and coda magnitudes are based on high-frequency seismic waves that people usually feel during real quakes.

So in terms of ground movements people might feel, the rock avalanches “felt like 2.5,” Pankow says. “If this was a normal tectonic earthquake of magnitude 5, all three magnitude scales would give us similar answers.”

The slides were detected throughout the Utah seismic network, including its most distant station some 250 miles south on the Utah-Arizona border, Pankow says.

The Landslide Triggered 16 Tremors

The second rock avalanche was followed immediately by a real earthquake measuring 2.5 in Richter magnitude and 3.0 in coda magnitude, then three smaller quakes – all less than one-half mile below the bottom of the mine pit.

The Utah researchers sped up recorded seismic data by 30 times to create an audio file in which the second part of the slide is heard as a deep rumbling, followed by sharp gunshot-like bangs from three of the subsequent quakes.

Later analysis revealed another 12 tiny quakes – measuring from 0.5 to minus 0.8 Richter magnitude. (A minus 1 magnitude has one-tenth the power of a hand grenade.) Six of these tiny tremors occurred between the two parts of the landslide, five happened during the two days after the slide, and one was detected 10 days later, on April 20. No quakes were detected during the 10 days before the double landslide.

“We don’t know of any case until now where landslides have been shown to trigger earthquakes,” Moore says. “It’s quite commonly the reverse.”

A Long, Fast Landslide Runout

The landslide, from top to bottom, fell 2,790 vertical feet, but its runout – the distance the slide traveled – was almost 10,072 feet, or just less than two miles.

“It was a bedrock landslide that had a characteristically fast and long runout – much longer than we would see for smaller rockfalls and rockslides,” Moore says.

While no one was present to measure the speed, rock avalanches typically move about 70 mph to 110 mph, while the fastest moved a quickly as 220 mph.

So at Bingham Canyon, “we can safely say the material was probably traveling at least 100 mph as it fell down the steepest part of the slope,” Moore says.

The researchers don’t know why the slide happened as two rock avalanches instead of one, but Moore says, “A huge volume like this can fail in one episode or in 10 episodes over hours.”

The Seismograph Stations also recorded infrasound waves from the landslide, which Pankow says are “sound waves traveling through the atmosphere that we don’t hear” because their frequencies are so low.

Both seismic and infrasound recordings detected differences between the landslide’s two rock avalanches. For example, the first avalanche had stronger peak energy at the end that was lacking in the second slide, Pankow says.

“We’d like to be able to use data like this to understand the physics of these large landslides,” Moore says.

The seismic and infrasound recordings suggest the two rock avalanches were similar in volume, but photos indicate the first slide contained more bedrock, while the second slide contained a higher proportion of mined waste rock – although both avalanches were predominantly bedrock.

Study uncovers new evidence for assessing tsunami risk from very large volcanic island landslides

A core is extracted from the seabed. -  Russell Wynn
A core is extracted from the seabed. – Russell Wynn

The risk posed by tsunami waves generated by Canary Island landslides may need to be re-evaluated, according to researchers at the National Oceanography Centre. Their findings suggest that these landslides result in smaller tsunami waves than previously thought by some authors, because of the processes involved.

The researchers used the geological record from deep marine sediment cores to build a history of regional landslide activity over the last 1.5 million years. They found that each large-scale landslide event released material into the ocean in stages, rather than simultaneously as previously thought.

The findings – reported recently in the scientific journal Geochemistry Geophysics Geosystems – can be used to inform risk assessment from landslide-generated tsunamis in the area, as well as mitigation strategies to defend human populations and infrastructure against these natural hazards. The study also concluded that volcanic activity could be a pre-condition to major landslide events in the region.

The main factor influencing the amplitude of a landslide-generated tsunami is the volume of material sliding into the ocean. Previous efforts, which have assessed landslide volumes, have assumed that the entire landslide volume breaks away and enters the ocean as a single block. Such studies – and subsequent media coverage – have suggested an event could generate a ‘megatsunami’ so big that it would travel across the Atlantic Ocean and devastate the east coast of the US, as well as parts of southern England.

The recent findings shed doubt on this theory. Instead of a single block failure, the landslides in the past have occurred in multiple stages, reducing the volumes entering the sea, and thereby producing smaller tsunami waves. Lead author Dr James Hunt explains: “If you drop a block of soap into a bath full of water, it makes a relatively big splash. But if you break it up into smaller pieces and drop it in bit by bit, the ripples in the bath water are smaller.”

The scientists were able to identify this mechanism from the deposits of underwater sediment flows called turbidity currents, which form as the landslide mixes with surrounding seawater. Their deposits, known as ‘turbidites’, were collected from an area of the seafloor hundreds of miles away from the islands. Turbidites provide a record of landslide history because they form from the material that slides down the island slopes into the ocean, breaks up and eventually settles on this flatter, deeper part of the seafloor.

However, the scientists could not assume that multistage failure necessarily results in less devastating tsunamis – the stages need to occur with enough time in between so that the resulting waves do not compound each other. “If you drop the smaller pieces of soap in one by one but in very quick succession, you can still generate a large wave,” says Dr Hunt.

Between the layers of sand deposited by the landslides, the team found mud, providing evidence that the stages of failure occurred some time apart. This is because mud particles are so fine that they most likely take weeks to settle out in the ocean, and even longer to form a layer that would be resistant enough to withstand a layer of sand moving over the top of it.

While the authors suggest that the tsunamis were not as big as originally thought, they state that tsunamis are a threat that the UK should be taking seriously. The Natural Environment Research Council (NERC) is investing in a major programme looking at the risk of tsunamis from Arctic landslides as part of the Arctic Research Programme, of which NOC is the lead collaborator. The EU have also just funded a £6 million FP7 project called ASTARTE, looking at tsunami risk and resilience on the European North Atlantic and Mediterranean coasts, of which NOC is a partner.

The current study was funded by NERC, through a NOC studentship.

Quake-triggered landslides pose significant hazard for Seattle, new study details potential damage

Locations of each zoom-in are shown on the map of Seattle at right. A) Coastal bluffs in the northern part of Seattle are most affected when soils are saturated. B) There are several areas along the I-5 corridor that are highly susceptible to landsliding for all soil saturation levels, such as the area shown here near the access point to the West Seattle bridge. C) The hillsides in West Seattle along the Duwamish valley are at risk of seismically induced landsliding, such as the area shown here. There are industrial as well as 59 residential buildings that could be affected by runout from landsliding in these areas. D) The coastal bluffs along Puget Sound in West Seattle on the hanging wall of the fault, such as the area shown here, are the most highly susceptible areas to landsliding in the city; numerous residential structures are at risk from both potential landslide source areas and runout. -  Allstadt/BSSA
Locations of each zoom-in are shown on the map of Seattle at right. A) Coastal bluffs in the northern part of Seattle are most affected when soils are saturated. B) There are several areas along the I-5 corridor that are highly susceptible to landsliding for all soil saturation levels, such as the area shown here near the access point to the West Seattle bridge. C) The hillsides in West Seattle along the Duwamish valley are at risk of seismically induced landsliding, such as the area shown here. There are industrial as well as 59 residential buildings that could be affected by runout from landsliding in these areas. D) The coastal bluffs along Puget Sound in West Seattle on the hanging wall of the fault, such as the area shown here, are the most highly susceptible areas to landsliding in the city; numerous residential structures are at risk from both potential landslide source areas and runout. – Allstadt/BSSA

A new study suggests the next big quake on the Seattle fault may cause devastating damage from landslides, greater than previously thought and beyond the areas currently defined as prone to landslides. Published online Oct. 22 by the Bulletin of the Seismological Society of America (BSSA), the research offers a framework for simulating hundreds of earthquake scenarios for the Seattle area.

“A major quake along the Seattle fault is among the worst case scenarios for the area since the fault runs just south of downtown. Our study shows the need for dedicated studies on seismically induced landsliding” said co-author Kate Allstadt, doctoral student at University of Washington.

Seattle is prone to strong shaking as it sits atop the Seattle Basin – a deep sedimentary basin that amplifies ground motion and generates strong seismic waves that tend to increase the duration of the shaking. The broader region is vulnerable to earthquakes from multiple sources, including deep earthquakes within the subducted Juan de Fuca plate, offshore megathrust earthquakes on Cascadia subduction zone and the shallow crustal earthquakes within the North American Plate.

For Seattle, a shallow crustal earthquake close to the city would be most damaging. The last major quake along the Seattle fault was in 900 AD, long before the city was established, though native people lived in the area. The earthquake triggered giant landslides along Lake Washington, causing entire blocks of forest to slide into the lake.

“There’s a kind of haunting precedence that tells us that we should pay attention to a large earthquake on this fault because it happened in the past,” said Allstadt, who also serves as duty seismologist for the Pacific Northwest Seismic Network. John Vidale of University of Washington and Art Frankel of the U.S. Geological Survey (USGS) are co-authors of the study, which was funded by the USGS.

While landslides triggered by earthquakes have caused damage and casualties worldwide, they have not often been the subject of extensive quantitative study or fully incorporated into seismic hazard assessments, say authors of this study that looks at just one scenario among potentially hundreds for a major earthquake in the Seattle area.

Dividing the area into a grid of 210-meter cells, they simulated ground motion for a magnitude 7 Seattle fault earthquake and then further subdivided into 5-meter cells, applying anticipated amplification of shaking due to the shallow soil layers. This refined framework yielded some surprises.

“One-third of the landslides triggered by our simulation were outside of the areas designated by the city as prone to landsliding,” said Allstadt. “A lot of people assume that all landslides occur in the same areas, but those triggered by rainfall or human behavior have a different triggering mechanism than landslides caused by earthquakes so we need dedicated studies.”

While soil saturation — whether the soil is dry or saturated with water – is the most important factor when analyzing the potential impact of landslides, the details of ground motion rank second. The amplification of ground shaking, directivity of seismic energy and geological features that may affect ground motion are very important to the outcome of ground failure, say authors.

The authors stress that this is just one randomized scenario study of many potential earthquake scenarios that could strike the city. While the results do not delineate the exact areas that will be affected in a future earthquake, they do illustrate the extent of landsliding to expect for a similar event.

The study suggests the southern half of the city and the coastal bluffs, many of which are developed, would be hardest hit. Depending upon the water saturation level of the soil at the time of the earthquake, several hundred to thousands of buildings could be affected citywide. For dry soil conditions, there are more than 1000 buildings that are within all hazard zones, 400 of those in the two highest hazard designation zones. The analysis suggests landslides could also affect some inland slopes, threatening key transit routes and impeding recovery efforts. For saturated soil conditions, it is an order of magnitude worse, with 8000 buildings within all hazard zones, 5000 of those within the two highest hazard zones. These numbers only reflect the number of buildings in high-risk areas, not the number of buildings that would necessarily suffer damage.

“The extra time we took to include the refined ground motion detail was worth it. It made a significant difference to our understanding of the potential damage to Seattle from seismically triggered landslides,” said Allstadt, who would like to use the new framework to run many more scenarios to prepare for future earthquakes in Seattle.