Robert F. Biek; David B. Hacker; Peter D. Rowley.
Description: We will introduce three gigantic, newly discovered gravity slides in southwestern Utah that exhibit the full range of structural features commonly seen in modern landslides, but on an enormous scale. Each slide is nearly 100 km long with runouts over the former land surface of at least 35 km; collectively, they form a gravity-slide complex covering an area >8000 km2 and are among Earth’s largest terrestrial landslides. These gravity slides resulted from catastrophic failure of the southern flank of the Marysvale volcanic field near the end of its peak magmatic activity about 25 to 18 Ma. Participants will see a variety of extensional, translational, and compressional structures—hallmarks of any small modern landslide—and learn how they relate to the overall gravity slide complex. Each slide is cut longitudinally by post-gravity-slide basin-range faults, revealing stunning basal breccia layers and slip surfaces, clastic dikes, jigsaw-puzzle fracturing, older-on-younger thrust relationships, and rare pseudotachylytes indicative of high-velocity movement aided by overpressured fluids.
NOTE: Thanks to generous support from the Utah Geological Association, we can offer a reduced registration fee of approximately half off to a limited number of students; the difference in cost will be reimbursed once we have a final student count.