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Evidence of erosional self‐channelization of pyroclastic density currents revealed by ground‐penetrating radar imaging at Mount St. Helens, Washington (USA)
Author(s) -
Gase Andrew C.,
Brand Brittany D.,
Bradford John H.
Publication year - 2017
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1002/2016gl072178
Subject(s) - channelized , pyroclastic rock , geology , outcrop , erosion , turbidity current , beach morphodynamics , geomorphology , volcano , seismology , sediment , sedimentary depositional environment , sediment transport , telecommunications , structural basin , computer science
The causes and effects of erosion are among the least understood aspects of pyroclastic density current (PDC) dynamics. Evidence is especially limited for erosional self‐channelization, a process whereby PDCs erode a channel that confines the body of the eroding flow or subsequent flows. We use ground‐penetrating radar imaging to trace a large PDC scour and fill from outcrop to its point of inception and discover a second, larger PDC scour and fill. The scours are among the largest PDC erosional features on record, at >200 m wide and at least 500 m long; estimated eroded volumes are on the order of 10 6 m 3 . The scours are morphologically similar to incipient channels carved by turbidity currents. Erosion may be promoted by a moderate slope (5–15°), substrate pore pressure retention, and pulses of increased flow energy. These findings are the first direct evidence of erosional self‐channelization by PDCs, a phenomenon that may increase flow velocity and runout distance through confinement and substrate erosion.