Secondary hydroeruptions in pyroclastic-flow deposits: Examples from Mount St. Helens

The 2008 phreatomagmatic eruption of Okmok Volcano, Aleutian Islands, Alaska: Chronology, deposits, and landform changes

“…3). Because the pits cut through and exposed sections of the 1958 lava flow beneath 2008 tephra, they were first interpreted as phreatic explosion craters formed in response to heated groundwater, similar to those at Mount St. Helens where on May 18, 1980, hot pyroclastic flows were deposited on wet ground (for example, Moyer and Swanson, 1987). However, the absence of raised rims or ejecta from the 1958 'a'a flow discounts an explosive origin.…”

Resedimentation of the 1.8 ka Taupo ignimbrite in the Mohaka and Ngaruroro river catchments, Hawke's Bay, New Zealand

“…Pyroclastic surge deposits in the Ripia valley interbedded with and overlying debris-flow deposits (Fig. 5) are interpreted to have been formed by secondary hydroeruptions, probably triggered by rain or entrapment of water underneath the hot ignimbrite (e.g., Moyer & Swanson 1987;Pierson et al 1992). Lacustrine association deposits preserved in Middle phase of response A transition from debris-flow to hyperconcentrated-flow deposits towards the top of laharic remobilisation association deposits in the middle reaches of the Mohaka River implies a decrease in the sediment:water ratio of the parent flows (Fig.…”

“…Pinatubo (Umbal & Rodolfo 1996;Montgomery et al 1999), Mount St. Helens (Collins & Dunne 1986;Moyer & Swanson 1987;Meyer & Martinson 1989;Major et al 2000), Irazti (Waldron 1967), Mayon (Rodolfo 1989;Rodolfo & Arguden 1991), and Paricutin (Segerstrom 1950(Segerstrom , 1960). In comparing the post-Taupo deposits with those of modern eruptions, consideration was given to differences in climatic conditions, geomorphic settings, and the nature of the source material, such as the grain-size distribution and density of the pyroclasts and their spatial distribution and emplacement style (e.g., pyroclastic flow or fall deposits).…”

Widespread crater-related pitted materials on Mars: Further evidence for the role of target volatiles during the impact process

“…Among the alternatives, impact-related pitted material exhibits the greatest morphological and geospatial similarities to dense populations of craters formed during explosive lava-water interactions (e.g., Hamilton et al, 2010aHamilton et al, , 2010b and crater groups formed within hot debris flows that have interacted with near surface water (e.g., Moyer and Swanson, 1987). Crater-related pitted materials are morphological similar to secondary explosion craters formed by rapid escape of heated volatiles, but their mechanisms are likely to be fundamentally different in that volatile sources would be different.…”