Pyroclastic deposits of Ubehebe Crater, Death Valley, California, USA: Ballistics, pyroclastic surges, and dry granular flows

Abstract We describe and interpret deposits associated with the final Ubehebe Crater-forming, phreatomagmatic explosive phase of multivent, monogenetic volcanic center. volcano is located in Death Valley, California, USA. Pyroclastic occur four main facies: (1) lapilli- blockdominated beds, (2) thinly bedded lapilli tuff, (3) laminated cross-laminated ash, (4) massive ash/tuff. Lapilli- block-dominated beds are found mostly within several hundred meters crater transition outward into discontinuous lenses blocks; they interpreted to have been deposited by ballistic processes crater-forming explosions. Thinly tuff mainly meters, ash extends at least 9 km from Dune forms common ~2 center, while finer-grained, distal tend exhibit planar lamination. These two facies (thinly ash) record multiple pyroclastic surges (dilute currents). Repeated couplets coarse layers overlain horizons suggest that many or most were transient, likely recording individual explosions, traveled over complex topography some areas. factors complicate application classical sediment-transport theory quantify surge properties. However, dune-form data provide possible constraints on relationships between suspended load sedimentation bed-load transport consistent using independent approaches. Massive ash/tuff drainages below steep slopes can extend up ~1 onto adjacent valley floors beneath large catchments. Although texture, their grain-size characteristics shared facies, which locally interbedded. concentrated granular flows sourced remobilized deposits, either during shortly after, retained elevated initial pore-gas pressures. similar surge-derived described elsewhere (e.g., Mount St. Helens, Washington, USA, Soufriére Hills, Montserrat, West Indies), our knowledge first case where such identified a maar volcano. followed paths represent potential hazard volcanoes areas terrain.