Utah’s Ancient Mega-Landslides: Geology, Discovery, and Guide to Earth’s Largest Terrestrial Landslides

Southwest Utah contains what may be the largest landslide complex on land in the world. This complex includes three ancient side-by-side gigantic slides that cover an area roughly the size of Yellowstone National Park with a volume of slide debris that would nearly fill the Grand Canyon to its rim. Geologists call it the Marysvale gravity slide complex— “Marysvale” for the namesake volcanic field that partly failed catastrophically three separate times, and “gravity slide” to call attention to a special class of extremely large and geologically complex landslides several tens to thousands of square miles in extent. Here we refer to them simply as mega-landslides or slides—they are larger and far more interesting than geologists could ever have imagined.