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 ΜμΜμ³ΤΉΟ geologist in a paper published in the November issue of the journal Geology.β¨βΆΔ¨
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 ΜμΜμ³ΤΉΟ at Trumbull, and two colleagues discovered and mapped the scope of the Markagunt slide over the past two summers.
β¨β¨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.
β¨β¨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.β¨βΆΔ¨
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 Ohioβs Cuyahoga, Portage and Summit counties combined.β¨βΆΔ¨
Its rival in size, the βHeart Mountain slide,β which took place around 50 million years ago in northwest Wyoming, was discovered in the 1940s and is a classic feature in geology textbooks.
β¨β¨The Markagunt could prove to be much larger than the Heart Mountain slide, once it is mapped in greater detail.β¨βΆΔ¨
βLarge-scale catastrophic collapses of volcanic fields such as these are rare but represent the largest known landslides on the surface of the Earth,β the authors wrote.β¨βΆΔ¨The length of the landslide β over 55 miles β also shows that it was as fast moving as it was massive, Hacker said.
Evidence showing that the slide was catastrophic β occurring within minutes β 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.β¨βΆΔ¨Evidence of the slide is not readily apparent to visitors today.β¨βΆΔ¨βLooking at it, you wouldnβt even recognize it as a landslide,β Hacker 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. β¨β¨
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.β¨βΆΔ¨
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.β¨βΆΔ¨
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 βa new class of hazards in volcanic fields.β
β¨β¨While the Markagunt landslide was a rare event, it shows the magnitude of what could happen in modern volcanic fields like the Cascades.β¨βΆΔ¨
βWe study events from the geologic past to better understand what could happen in the future,β he said.β¨βΆΔ¨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.β¨βΆΔ¨
Hacker, who earned his Ph.D. in geology at ΜμΜμ³ΤΉΟ State, joined the faculty in 2000 after working for an environmental consulting company. He is co-author of the book Earthβs Natural Hazards: Understanding Natural Disasters and Catastrophes, published in 2010.β¨βΆΔ¨
of the Geology paper, available online now.
β¨β¨Learn more about research at ΜμΜμ³ΤΉΟ State at www.kent.edu/research.
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Photo Caption:
David Hacker, Ph.D., ΜμΜμ³ΤΉΟ associate professor of geology, points to pseudotachylyte layers and veins within the Markagunt gravity slide.
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