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Ancient landslide could be record breaker

Nov. 21, 2014
Courtesy of Kent State University
and World Science staff

An enor­mous land­slide more than 21 mil­lion years ago in what is now Utah could be the larg­est known in all of Earth’s land ar­eas, ge­ol­o­gists are re­port­ing.

The so-called Mark­a­gunt gra­vity slide cov­ered an ar­ea great­er than the state of Rho­de Is­land with­in min­utes—mov­ing fast enough to melt rock in­to glass due to the im­mense fric­tion, the re­search­ers said. Any an­i­mals in the way would have been quickly mowed down.

Ge­ol­o­gists pre­vi­ously knew about parts of the land­slide, but in new work, ge­ol­o­gist Da­vid Hack­er of Kent State Uni­vers­ity in Ohio hiked through wil­der­ness to find fea­tures in­di­cat­ing the slide was much big­ger than pre­vi­ously real­ized. The find­ings are pub­lished in the No­vem­ber is­sue of the jour­nal Ge­ol­o­gy.

The land­slide took place in an ar­ea be­tween what is now Bryce Can­yon Na­t­ional Park and the town of Bea­ver, Utah, Hack­er and col­leagues said, and cov­ered about 1,300 square miles (3,400 square km). That would make it one of the two larg­est known con­ti­nen­tal land­slides (larg­er slides ex­ist on the ocean floors).

Its ri­val in size, the “Heart Moun­tain slide,” which took place around 50 mil­lion years ago in north­west Wy­o­ming, was discov­ered in the 1940s. The Mark­a­gunt slide could prove to be much larg­er, once it is bet­ter mapped, Hack­er and col­leagues said.

They sug­gest it oc­curred when not just one moun­tain­side gave way, but a whole por­tion of a vol­can­ic moun­tain range whose base had been pushed up high­er and high­er by mol­ten rock, or mag­ma, gath­er­ing be­neath.

“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 land­slide was over 55 miles (90 km) long, Hack­er added, though to­day, “look­ing at it, you would­n’t even rec­og­nize it as a land­slide.”

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

Such events could the­o­ret­ic­ally hap­pen in mod­ern vol­can­ic fields, or groups of vol­can­ic moun­tains, such as the Cas­cade Moun­tains, which in­clude Mt. St. Hel­ens in Wash­ing­ton, he added. But many con­di­tions must come to­geth­er to pro­duce a land­slide. “We study events from the ge­o­log­ic past to bet­ter un­der­stand what could hap­pen in the fu­ture,” said Hack­er, who plans to con­tin­ue map­ping and an­a­lyz­ing the slide.


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An enormous landslide more than 21 million years ago in what is now Utah could be the largest known in all of Earth’s land areas, geologists are reporting. The so-called Markagunt gravity slide covered an area greater than the state of Rhode Island within minutes—moving fast enough to melt rock into glass due to the immense friction, the researchers said. Any animals in the way would have been quickly mowed down. Geologists previously knew about parts of the landslide, but in new work, geologist David Hacker of Kent State University in Ohio hiked through wilderness to find features indicating the slide was much bigger than previously realized. The findings are published in the November issue of the journal Geology. The landslide took place in an area between what is now Bryce Canyon National Park and the town of Beaver, Utah, Hacker and colleagues said, and covered about 1,300 square miles (3,400 square km). That would make it one of the two largest known continental landslides (larger slides exist on the ocean floors). Its rival in size, the “Heart Mountain slide,” which took place around 50 million years ago in northwest Wyoming, was discovered in the 1940s. The Markagunt slide could prove to be much larger, once it is better mapped, Hacker and colleagues said. They suggest it occurred when not just one mountainside gave way, but a whole portion of a volcanic mountain range whose base had been pushed up higher and higher by molten rock, or magma, gathering beneath. “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 landslide was over 55 miles (90 km) long, Hacker added, though today, “looking at it, you wouldn’t even recognize it as a landslide.” Understanding the mega-landslide could help geologists better understand these extreme types of events, he said. The Markagunt and the Heart Mountain slides document for the first time how large portions of ancient volcanic fields have collapsed, Hacker explained, representing “a new class of hazards in volcanic fields.” Such events could theoretically happen in modern volcanic fields, or groups of volcanic mountains, such as the Cascade Mountains, which include Mt. St. Helens in Washington, he added. But many conditions must come together to produce a landslide. “We study events from the geologic past to better understand what could happen in the future,” said Hacker, who plans to continue mapping and analyzing the slide.