title: Slow-moving and far-travelled dense pyroclastic flows during the Peach Spring super-eruption.
abstract: Explosive volcanic super-eruptions of several hundred cubic kilometres or more generate long run-out pyroclastic density currents the dynamics of which are poorly understood and controversial. Deposits of one such event in the southwestern USA, the 18.8 Ma Peach Spring Tuff, were formed by pyroclastic flows that travelled >170 km from the eruptive centre and entrained blocks up to ∼ 70-90 cm diameter from the substrates along the flow paths. Here we combine these data with new experimental results to show that the flow's base had high-particle concentration and relatively modest speeds of ∼ 5-20 m s(-1), fed by an eruption discharging magma at rates up to ∼ 10(7)-10(8) m(3) s(-1) for a minimum of 2.5-10 h. We conclude that sustained high-eruption discharge and long-lived high-pore pressure in dense granular dispersion can be more important than large initial velocity and turbulent transport with dilute suspension in promoting long pyroclastic flow distance.
authors.affiliation: Laboratoire Magmas et Volcans, Université Blaise Pascal-CNRS-IRD, OPGC, 6 Avenue Blaise Pascal, TSA 60026-CS 60026, F-63178 Aubière, France.
authors.forename: O
authors.initials: O
authors.lastname: Roche
authors.affiliation: United States Geological Survey, 345 Middlefield Road, MS 973, Menlo Park, California 94025, USA.
authors.forename: D C
authors.initials: DC
authors.lastname: Buesch
authors.affiliation: Department of Geology and Center for Geohazards Studies, University at Buffalo, Buffalo, New York 14260, USA.
authors.forename: G A
authors.initials: GA
authors.lastname: Valentine