Emplacement age of the Markagunt gravity slide in southwestern Utah, USA

The Markagunt gravity slide (MGS) is a large-volume landslide in southwestern Utah that originated within the Oligocene-Miocene Marysvale volcanic field. Gravity slides are single emplacement events with long runout distances and are now recognized as a new class of volcanic hazard. Accumulation of volcanic material on a structurally weak substrate along with voluminous shallow intrusive events led to collapse. Here, Ar-40/Ar-39 data for landslide-generated pseudotachylyte, the landslide-capping Haycock Mountain Tuff and the deformed Osiris Tuff are combined with a Bayesian age model to determine an emplacement age of 23.05 + 0.22/-0.20 Ma for the MGS. The results suggest a lag time of < 200 kyr between the caldera-forming eruption of the Osiris Tuff, additional buildup of the unstable volcanic pile and subsequent mass movement.