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Discharge rate of explosive volcanic eruption controls runout distance of pyroclastic density currents

Abstract : We address, through quantitative analysis of results from independent studies, the control of the discharge rate of explosive volcanic eruptions on the runout distance of highly hazardous pyroclastic density currents. We analyze with statistical methods data from 47 well-documented currents with runouts of ∼3–185km and generated by minor eruptions to super-eruptions with discharge rates Q∼107–1012kg/s. Our analysis shows first that the discharge rate during the phase of pyroclastic density currents is on average 13.6 times greater than the rate during the preceding plinian phase. We further find that the runout of both dilute turbulent currents and of two-layer flows with a concentrated base correlates remarkably well with the discharge rate. By applying the power law relationships we infer, we next model the as yet unknown discharge rates of over 53 events, including 27 super-eruptions. At a given rate, dilute currents travel on land generally farther than their concentrated counterparts, and they are even more mobile when propagating over water. We further demonstrate that the runout of dilute current scales with (Q/w)0.5, with w the particle settling velocity, in agreement with theory. Assuming concentrated PDCs obey the same principle we infer particle settling velocities of ∼1–10m/s for these currents. We show also that the classical deposit aspect ratio, AR, allows to discriminate between emplacement from dilute (AR<∼5 ×10−5) and concentrated (AR>∼5 ×10−5) current, which permits us to discuss the dynamics of PDCs produced by the Ito (29 ka) and Taupo (AD 232) eruptions.
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Submitted on : Wednesday, June 16, 2021 - 10:36:45 AM
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Olivier Roche, Nourddine Azzaoui, Arnaud Guillin. Discharge rate of explosive volcanic eruption controls runout distance of pyroclastic density currents. Earth and Planetary Science Letters, Elsevier, 2021, 568, pp.117017. ⟨10.1016/j.epsl.2021.117017⟩. ⟨hal-03254073⟩



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