Clarke A B, Voight B, Neri A, Macedonio G
Department of Geosciences, Penn State University, University Park, Pennsylvania 16802, USA.
Nature. 2002 Feb 21;415(6874):897-901. doi: 10.1038/415897a.
Several analytical and numerical eruption models have provided insight into volcanic eruption behaviour, but most address plinian-type eruptions where vent conditions are quasi-steady. Only a few studies have explored the physics of short-duration vulcanian explosions with unsteady vent conditions and blast events. Here we present a technique that links unsteady vent flux of vulcanian explosions to the resulting dispersal of volcanic ejecta, using a numerical, axisymmetric model with multiple particle sizes. We use observational data from well documented explosions in 1997 at the Soufrière Hills volcano in Montserrat, West Indies, to constrain pre-eruptive subsurface initial conditions and to compare with our simulation results. The resulting simulations duplicate many features of the observed explosions, showing transitional behaviour where mass is divided between a buoyant plume and hazardous radial pyroclastic currents fed by a collapsing fountain. We find that leakage of volcanic gas from the conduit through surrounding rocks over a short period (of the order of 10 hours) or retarded exsolution can dictate the style of explosion. Our simulations also reveal the internal plume dynamics and particle-size segregation mechanisms that may occur in such eruptions.
几个分析和数值喷发模型已经为火山喷发行为提供了见解，但大多数模型针对的是喷口条件近似稳定的普林尼式喷发。只有少数研究探讨了喷口条件不稳定的短持续时间武尔卡诺式爆炸和爆炸事件的物理过程。在此，我们提出一种技术，利用一个具有多种粒径的轴对称数值模型，将武尔卡诺式爆炸的不稳定喷口通量与火山喷出物的扩散联系起来。我们使用了来自1997年西印度群岛蒙特塞拉特苏弗里耶尔火山记录完备的爆炸的观测数据，来约束喷发前的地下初始条件，并与我们的模拟结果进行比较。模拟结果重现了观测到的爆炸的许多特征，显示出在由坍塌的喷泉供给的浮力羽流和危险的径向火山碎屑流之间进行质量分配的过渡行为。我们发现，在短时间内（约10小时）通过周围岩石从管道中泄漏的火山气体或延迟的脱溶作用可以决定爆炸的形式。我们的模拟还揭示了此类喷发中可能发生的内部羽流动力学和粒径分选机制。
