Explosive volcanic eruption processes: from mesoscopic simulations to constitutive laws

火山喷发过程：从介观模拟到本构定律

• 批准号: NE/D009758/1
• 负责人: Edward Llewellin
• 金额: $ 19.19万
• 依托单位: University of Cambridge
• 依托单位国家: 英国
• 项目类别: Fellowship
• 财政年份: 2006
• 资助国家: 英国
• 起止时间: 2006 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FD009758%2F1
• 关键词: Explosive; volcanic; eruption; processes; mesoscopic

When volcanoes erupt explosively, they are amongst the deadliest of all natural hazards. An explosive eruption, like that at Mt St Helens in 1980, occurs when the molten rock, or magma, erupts so violently that the magma is broken into small fragments. These fragments rise into the air as volcanic ash and flow down the sides of the volcano as deadly pyroclastic flows. Not all volcanic eruptions are explosive, however. Kilauea in Hawaii has been erupting continuously for over twenty years, but has not exploded in this time. Rather, lava has flowed gently down the volcano and into the sea, causing little hazard to the local population; this is an effusive eruption. Some volcanoes can show both types of behaviour: sometimes erupting explosively, sometimes effusively. These volcanoes, of which Mt St Helens is an example, are particularly dangerous as it is very hard to predict when the eruption will switch from effusive to explosive. A main aim of volcanology is to understand what controls whether an eruption is explosive or effusive, and what makes it switch between the two. My research will help to answer this question. Magma contains many gas bubbles. Volcanologists believe that explosive eruptions occur when the pressure in the bubbles gets high enough to make the surrounding magma break into fragments. If the bubbles get big enough, they can merge and form networks along which gas can flow, allowing it to escape from the bubbles. This means that the pressure can't build up and the eruption is more likely to be effusive. It is vital for volcanologists to know how easily gas can flow along these bubble networks. I am developing a computer programme, LBFLOW that simulates gas flow through the bubble networks in volcanic rocks. I am using this programme to calculate how rapidly gas can escape from bubbles for different types of bubble network. This information will allow me to work out how rapidly the pressure can escape from magma at different volcanoes. I have already used LBFLOW to look at gas flow through small networks of bubbles. In order to make the result as useful as possible, I want to adapt LBFLOW to run on a 'parallel computer', a type of supercomputer that we have at the BP Institute at Cambridge University, where I will carry out this work. Running LBFLOW on this computer will allow me to simulate much larger networks, making the results more reliable. When using computer models, it is vital to check the results against experiments to ensure that the model gives the correct answer. I am going to use an MRI machine, similar to ones used in hospitals to look inside a patient's body, to look at fluid flowing through networks of bubbles in rock. The MRI scan will show how fast the fluid is flowing in different parts of the network. By running LBFLOW on the same bubble network, I can compare the programme's results with the MRI results and ensure that they are the same. There are a couple of major advantages to using LBFLOW for this research. Firstly, because computers are so fast, I can examine many different types of bubble network rapidly. The other advantage is that I can control exactly what the bubble networks are like: i. e. how big the bubbles are and how much they overlap. This will make my results applicable to a wide range of volcanoes. It is also important for volcanologists to know how sticky, or viscous magma is. If the magma is sticky, it is much more likely to erupt explosively than it if is runny. LBFLOW will also show how bubbles affect the viscosity of the magma. I have already performed experiments in the laboratory to look at this. I will use LBFLOW to look at how crystals affect magma's viscosity. The results of my work will help volcanologists to understand the way volcanoes erupt. It will help us to work out what type of eruption is likely to happen at a volcano, and what would make it switch from effusive to explosive activity.

当火山爆发时，它们是所有自然灾害中最致命的。像1980年圣海伦斯山那样的爆炸性喷发，是当熔岩或岩浆猛烈喷发，导致岩浆破碎成小碎片时发生的。这些碎片以火山灰的形式上升到空气中，并随着致命的火山碎屑流从火山两侧流下。然而，并不是所有的火山爆发都是爆炸性的。夏威夷的基拉韦厄火山已经连续喷发了二十多年，但这次没有爆发。相反，熔岩温和地顺着火山流入大海，对当地居民几乎没有造成任何危害；这是一次热情洋溢的喷发。一些火山可以同时表现出这两种行为：有时是爆发，有时是热情。这些火山特别危险，圣海伦斯火山就是其中的一个例子，因为很难预测喷发什么时候会从热情洋溢的喷发变成爆炸性的。火山学的一个主要目的是了解是什么控制了一次喷发是爆炸性的还是热情洋溢的，以及是什么让它在两者之间切换。我的研究将有助于回答这个问题。岩浆中含有许多气泡。火山学家认为，当气泡中的压力高到足以使周围的岩浆破碎成碎片时，就会发生爆炸性喷发。如果气泡变得足够大，它们可以合并并形成气体可以沿其流动的网络，使其能够从气泡中逃逸。这意味着压力不能累积，喷发更可能是热情洋溢的。对于火山学家来说，了解气体沿着这些气泡网络流动有多容易是至关重要的。我正在开发一个名为LBFLOW的计算机程序，它模拟了火山岩中气体在气泡网络中的流动。我正在使用这个程序来计算不同类型的气泡网络中气体从气泡中逃逸的速度。这些信息将让我计算出压力从不同火山的岩浆中逃逸的速度有多快。我已经用LBFLOW观察了气体在微小的气泡网络中的流动。为了使结果尽可能有用，我想让LBFLOW在一台‘并行计算机’上运行，这是我们剑桥大学BP研究所拥有的一种超级计算机，我将在那里进行这项工作。在这台计算机上运行LBFLOW将允许我模拟更大的网络，使结果更可靠。在使用计算机模型时，将结果与实验进行核对，以确保模型给出正确的答案，这一点至关重要。我将使用一台核磁共振仪，类似于医院用来观察病人身体内部的机器，来观察液体在岩石气泡网络中的流动。核磁共振扫描将显示液体在网络不同部分的流动速度。通过在相同的气泡网络上运行LBFLOW，我可以将程序的结果与MRI结果进行比较，并确保它们是相同的。在这项研究中使用LBFLOW有几个主要优势。首先，由于计算机速度如此之快，我可以快速检查许多不同类型的气泡网络。另一个好处是，我可以准确地控制泡沫网络是什么样子：即泡沫有多大，它们重叠的程度有多大。这将使我的结果适用于广泛的火山。对火山学家来说，了解岩浆的粘性也很重要。如果岩浆是粘性的，它比流动的岩浆更有可能爆炸喷发。LBFLOW还将展示气泡如何影响岩浆的粘度。我已经在实验室里做了实验来观察这一点。我将使用LBFLOW来观察晶体如何影响岩浆的粘度。我的工作结果将帮助火山学家了解火山喷发的方式。它将帮助我们弄清楚火山可能发生哪种类型的喷发，以及是什么使它从热情洋溢的活动转变为爆炸性活动。