High-temperature fracture mechanics of dome lava

正如美国圣海伦斯火山过去25年的活动所证明的那样，喷发高粘性熔岩穹顶的火山是最危险、最具研究价值和最具新闻价值的地质现象之一。地质科学中的一个关键挑战是如何可靠地预测这种穹顶典型的行为突然变化，从温和的熔岩喷出到毁灭性的爆炸性喷发。近年来，在喷发行为的研究方面取得了很大进展，认识到岩浆对外加应力的物质响应在很大程度上控制着喷发机制，在浅层脱气和结晶过程中，穹顶熔岩的流变性发生了很大变化。当前一代穹顶增长模型的一个目标是确定与变形岩浆是否会破裂或流动的基本物理行为密切相关的行为阈值(例如，爆炸性/喷发、内源性/外源性穹隆生长)。我们建议在实验室里对最近圣海伦斯火山喷发的熔岩穹顶材料进行模拟火山条件下的实验。这些实验将为穹顶的扩大和爆炸性喷发设定门槛。在这些实验室实验期间，还将测量声发射，以便实验室实验可以与观测到的火山地震有关。这些实验室研究将为开发当前一代火山穹顶行为模型提供直接投入。

Volcanoes that erupt highly-viscous lava domes are amongst the most hazardous, intensely studied and newsworthy of geological phenomena, as the past twenty-five years of activity at Mount St Helens, USA have demonstrated. A key challenge in geological science is how to predict reliably the sudden changes in behaviour that are typical of such domes, from gentle lava effusion to devastating explosive eruptions. Much progress has been made in recent years in studying eruptive behaviour, with the realisation that the material response of magma to applied stresses largely controls eruption mechanisms and the rheology of dome lava changes greatly during shallow degassing and crystallisation. A goal of the current generation of models for dome growth is to identify thresholds in behaviour (e.g. explosive/effusive eruptions, endogenous/exogenous dome growth) that are closely related to the fundamental physical behaviour of whether deforming magma will fracture or flow. We propose to do experiments in the laboratory on lava dome material from the recent eruption of Mt St Helens under simulated volcanic conditions. These expriments will establish the thresholds for dome growth and explosive eruptions. Acoustic emissions will also be measured during these laboratory experiments, so that the laboratory experiments can be related to observed volcano seismicity.These laboratory studies will provide direct input into the development of the current generation of models of volcanic dome behaviour.