THE MARKAGUNT GRAVITY SLIDE, SOUTHWEST UTAH: A LANDSLIDE BIGGER THAN RHODE ISLAND (Invited Presentation)
The MGS is significant because it provides a stunning example of gravity-slide structures so large that they may be mistaken for tectonic features. However, the presence of basal and lateral cataclastic breccias, clastic dikes, jigsaw puzzle fracturing, internal shears, pseudotachylytes, the uniformity of kinematic indicators, breakaway and antithetic faults, and the overall geometry of the MGS show that it represents a single catastrophic emplacement event. That features as large as the MGS can remain undetected despite decades of geologic mapping and research in the area suggests to us that other volcanic fields around the world may hold evidence of as-yet-undiscovered, exceptionally large gravity slides. Furthermore, some modern volcanic fields may possess the conditions capable of generating similarly large slides. Although smaller-scale flank failures have been recognized on hundreds of individual volcanoes worldwide, the MGS catastrophic sector collapse represents a new class of low-frequency but high-impact hazard that may exist in other large volcanic fields.