The Dynamics of Short-Duration, Unsteady Volcanic Eruptions

世界上550多座历史上的活火山中，大约有30座受到了充分的监测，尽管它们对不断入侵的人类构成了威胁。更好地预测火山喷发的时间和规模对于减少这些脆弱人群的风险至关重要。为此，科学家们正试图确定目前尚未认识到的爆发动力学模式，并随后建立可靠的预测模型。大规模持续（普林尼）喷发的计算机模型，如1980年5月18日圣海伦斯火山的喷发，或1991年6月12日菲律宾皮纳图博火山的喷发，构成了我们目前认识的基础。然而，尽管脉动或非定常源特性被认为对喷发行为有重大影响，但这些模型必须通过对密度和速度等关键源特性进行时间平均来简化。为了应对这种明显的脱节，本研究旨在建立不稳定源条件和爆发动力学之间的牢固关系。这项研究将集中在小型、短暂、高度不稳定的火山喷发上，这些火山喷发比普林尼火山喷发频繁得多，因此对于加强对火山喷发动力学的一般理解和改进模型来说，是一个有价值的、可获得的数据来源。塌陷的喷发柱和由此产生的火山碎屑流（热气体、石块和火山灰的雪崩）是爆炸性火山爆发中最致命的现象之一。火山喷发的复杂性和危险性促使实验室进行研究，目的是根据驱动火山喷发的非定常力，确定稳定的上升喷发柱和不稳定的产生火山碎屑流的喷发柱之间的过渡。特别令人感兴趣的是，初始浮力和动量的变化如何影响这些流的灰烬和速度分布的变化。该小组还将测试现有的火山爆发数学模型在捕捉简单实验室实验行为方面的有效性。同时，他们将评估相同的模型是否能有效地反映真实的火山喷发。该项目的最终目标是建立对脉冲非定常源产生的大范围流动的理论认识，包括大规模爆炸性火山喷发、工业爆炸、污染物羽流、森林火灾和许多其他现象。

Approximately 30 of the more than 550 historically active volcanoes in the world are adequately monitored despite the threats they pose to encroaching human populations. Better predictions of volcanic eruption timing and scale are critical for reducing risk to these vulnerable populations. To that end, scientists are attempting to identify currently unrecognized patterns in explosive eruption dynamics and subsequently build reliable predictive models. Computer models of large, sustained (Plinian) eruptions, like the eruption of Mt. St. Helens on May 18, 1980, or the June 12, 1991 eruption of Pinatubo volcano in the Philippines, form the basis of our current understanding. However, despite the fact that pulsating or unsteady source properties are thought to have significant impact on eruption behavior, such models are necessarily simplified by time-averaging key source properties such as density and velocity. In response to this apparent disconnect, this research aims to establish robust relationships between unsteady source conditions and explosive eruption dynamics. The study will focus on small, short-lived, highly unsteady (vulcanian) eruptions, which occur much more frequently than Plinian eruptions, and are thus a valuable and accessible source of data for enhancing general understanding of eruption dynamics and improving models. Collapsing eruption columns and resulting pyroclastic flows (avalanches of hot gas, blocks and ash) are one of the deadliest phenomena produced in explosive volcanic eruptions. The complexity and danger presented by volcanic eruptions motivates the laboratory investigations that will take place with the aim to define the transition between stable, rising eruption columns and unstable, pyroclastic-flow-producing columns in terms of the unsteady forces driving the eruption. Of particular interest is how variations in the initial buoyancy and momentum forces influence changes in the ash and velocity distribution of these flows. The team will also test the effectiveness of existing mathematical models of eruptions in capturing the behavior of simple laboratory experiments. Simultaneously, they will assess whether the same models are valid representations of real volcanic eruptions. The ultimate goal of the project is to establish theoretical understanding of a wide-range of flows generated by impulsive, unsteady sources, including large-scale explosive volcanic eruptions, industrial explosions, contaminant plumes, forest fires and many other phenomena.