Roche O, Buesch D C, Valentine G A
Laboratoire Magmas et Volcans, Université Blaise Pascal-CNRS-IRD, OPGC, 6 Avenue Blaise Pascal, TSA 60026-CS 60026, F-63178 Aubière, France.
United States Geological Survey, 345 Middlefield Road, MS 973, Menlo Park, California 94025, USA.
Nat Commun. 2016 Mar 7;7:10890. doi: 10.1038/ncomms10890.
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.
数百立方千米甚至更大规模的火山超级爆发会产生长距离的火山碎屑密度流，其动力学机制尚不清楚且存在争议。美国西南部一次此类事件形成的1880万年前的桃泉凝灰岩，是由火山碎屑流形成的，这些火山碎屑流从喷发中心流动超过170千米，并在流动路径上夹带了直径达70 - 90厘米的岩块。在这里，我们将这些数据与新的实验结果相结合，以表明该火山碎屑流底部具有高颗粒浓度，速度相对适中，约为5 - 20米/秒，由一次喷发供给岩浆，喷发速率高达约10⁷ - 10⁸立方米/秒，持续至少2.5 - 10小时。我们得出结论，在促进火山碎屑流长距离流动方面，持续的高喷发流量和致密颗粒分散体中长时间的高孔隙压力可能比大的初始速度和稀悬浮体中的湍流输运更为重要。
