The mechanisms responsible for large landslides have been studied for decades, with relatively solid ideas for how slides spurred by heavy rainfalls get going and continue on their path. But understanding similar mechanisms responsible for the movements of dry landslides has been alluding scientists for just as long. Part of the reason why is because it\u2019s impossible to replicate these massive slides in a lab.<\/p>\n
Way back in 1979, Jay Melosh, now a professor in Purdue University\u2019s Department of Earth, Atmospheric and Planetary Sciences, was looking for a way to describe how such dry slides can occur. Since they have been observed on the Moon, Melosh easily ruled out an idea that the slides were floating on a cushion of air.<\/p>\n
\u201cMy approach didn\u2019t come from landslides at all,\u201d said Melosh. \u201cIt came from trying to understand craters on the moon, and the mechanics of rocks in motion.\u201d<\/p>\n
To explain that, he drew on some knowledge he had gained while working part-time at the Los Alamos National Laboratory, where there was plenty of data on the effects of nuclear test explosions on vibrations in the Earth. In addition, it was common knowledge in that area that fault slips could occur thanks to the vibrations, and so he began to consider that in refining a theory to explain how such large slides get going.<\/p>\n
In the theory, Melosh put forth that landslides of sufficient size could generate vibrational waves that could propagate through rock debris and make it possible for the slides to move further than smaller ones because the vibrations could reduce the effects of friction. He called his idea \u201cacoustic fluidization.\u201d<\/p>\n
At the time, it was a pretty complex idea to propose. But now, more than 35 years later, technology has caught up enough to prove that Melosh\u2019s theory was right all along.<\/p>\n
\u201cIt\u2019s been a long, uphill fight to convince the landslide community that the physics solution could solve the equation,\u201d said Melosh. \u201cThey\u2019re familiar with the roles of fluids, but they\u2019re not familiar with vibrations.\u201d<\/p>\n
In 1995, Charles Campbell, a professor of aerospace and mechanical engineering at University of Southern California, led an effort to model the dynamics at play in such large, dry landslides. All the observations made sense, but the computers of the time didn\u2019t have the capabilities to go further. And so pinpointing the mechanisms responsible for the reduction in friction wasn\u2019t possible.<\/p>\n
\u201cHe shared his computer code with me and I had a grad student revive the computer code. We ran it on 2014 computers instead of 1995 computers,\u201d said Melosh. \u201cAnd indeed, what I had described was going on.\u201d The student is Brandon Johnson, who is now an assistant professor in the Department of Earth, Environmental and Planetary Sciences at Brown University. Johnson is the first author on the study and a “leading light in this field,” says Melosh.<\/p>\n
Melosh is glad that there\u2019s finally a way to explain the vibration mechanisms at play in the landslides, and is hopeful that the finding can help in other areas, such as in improving understanding of earthquake processes or disaster response.<\/p>\n
\u201cUnderstanding these landslides gives us more insight into how friction processes work, more insight into how earthquakes work,\u201d said Melosh. For example, some of the forces that are seen when earthquakes occur are still sometimes overestimated. The results could help to remove that uncertainty.<\/p>\n
Full results of the work are published in the Journal of Geophysical Research: Earth Surface.<\/p>\n
Top image:\u00a0A 1994 “long-runout” landslide in Mesa County, Colorado. (Credit: John White \/ Colorado Geological Survey)<\/span><\/em><\/p>\n","protected":false},"excerpt":{"rendered":" A Purdue University professor\u2019s theory on the forces driving dry landslides is proven right after more than 35 years.<\/p>\n","protected":false},"author":13,"featured_media":25161,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[23,5],"tags":[345,60,109,199],"class_list":["post-25167","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-earth-atmosphere","category-featured-articles","tag-earth-atmosphere","tag-featured","tag-news-ticker","tag-purdue-university"],"remote_post_permalink":false,"remote_post_featured_image":false,"yoast_head":"\n