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Mobilising magma in the largest eruptions: Quantifying critical processes using in situ real time x-ray tomography

在最大规模的喷发中调动岩浆：使用原位实时 X 射线断层扫描量化关键过程

基本信息

批准号：
NE/M018687/2
负责人：
Katherine Dobson
金额：
$ 31.9万
依托单位：
University of Strathclyde
依托单位国家：
英国
项目类别：
Fellowship
财政年份：
2019
资助国家：
英国
起止时间：
2019 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=NE%2FM018687%2F2
关键词：
Mobilising magma largest eruptions Quantifying

项目摘要

Volcanic eruptions are one the most powerful and impressive natural phenomena, and even relatively small eruptions can have major global impacts. The magma stored beneath volcanoes is an evolving mixture of molten rock (liquid), crystals (solid) and bubbles (gas). As magma cools the number of crystals increases and in principle, when magma reaches ~45% crystals the crystals jam together, 'locking up' and making it too stiff to move: the magma becomes 'uneruptible'. However, some of the most devastating explosive eruptions (including the largest super-eruption ever known) erupt large volumes (100-5000 km3) of this 'uneruptible' crystal-rich (45-60%) magma. So how do these crystal-rich eruptions happen? What lets the magma move?As we cannot visit a magma chamber, laboratory experiments with natural rock samples and synthetic approximations (analogues) are used to simulate what is happening beneath the volcano. From these experiments, we have developed models that describe how crystal-poor magma will flow when a force is applied (its rheology). However, these rheological models fail for more crystal-rich magma (concentrated suspensions). It is thought that in crystal-rich systems the magmas ability to move is critically controlled by the crystal-crystal, crystal-bubble and bubble-bubble interactions, and the variable spatial distribution of the crystals, bubbles and melt within the sample. In one hypothesis a build-up of pressure drives bubbles through the crystal network, and causes the network to break into pieces. Despite still having the same high crystal content, deformation can then occur in the crystal-poor regions between the pieces, and the magma becomes mobile. Crystal-rich magmas and their analogues are opaque, and conventional experimental methods do not allow us to observe the internal micro-scale processes. Therefore we have only been able to quantify the average behaviour of a volume of magma. While many possible microstructural interaction processes have been hypothesised, they remain untested. In this project the equipment used for conventional rheological experiments will be modified to allow the collection of 3D images in real time using X-ray computed Micro-Tomography (XMT). At the Diamond Light Source synchrotron facility this revolutionising imaging technology can capture the 3D internal structure of a sample (i.e. the distribution of crystals, bubbles and melt in a magma) in as little as a few seconds: producing a 3D 'movie' of what happens when the magma is deformed. By applying standard image analysis techniques to the 3D images captured over the course of an experiment, the distribution of bubbles, crystals, and melt can be quantified; every crystal and bubble can be tracked through time; and the nature of every interaction can be identified. For the first time we will be able to see what is happening inside the magma in 4D (3D + time).By working with analogue materials, and systematically testing the microstructural behaviour as we change the crystal content, crystal shape, bubble volume and a range of other parameters known to vary in magma chambers (e.g. temperature, pressure) the high speed 4D data will be used to map out the nature and importance of the different interactions, and define the role of micro-scale variability (phase distributions and interactions) on flow. These data will be used to build a new generation of rheological models that describe the mobility of complex two- and three-phase concentrated magmatic suspensions based on an accurate understanding of the microstructural physics and micro-scale variability. By running 4D experiments on natural samples and testing the model against the results, the project will identify the conditions under which crystal-rich magmas can erupt, and begin to identify the magmatic processes that lead to the most devastating eruptions.

火山喷发是最强大和最令人印象深刻的自然现象之一，即使是相对较小的喷发也可以对全球产生重大影响。储存在火山下的岩浆是熔岩(液体)、晶体(固体)和气泡(气体)的不断演化的混合物。随着岩浆冷却，晶体的数量增加，原则上，当岩浆达到~45%的晶体时，晶体会挤在一起，锁定起来，使其变得太硬而无法移动：岩浆变得不能喷发。然而，一些最具破坏性的爆炸性喷发(包括迄今已知的最大的超级喷发)喷发出大量(100-5000千米)这种富含晶体(45%-60%)的不能喷发的岩浆。那么这些富含水晶的喷发是如何发生的呢？是什么让岩浆移动？因为我们不能参观岩浆室，所以使用天然岩石样本和合成近似(类似物)的实验室实验来模拟火山下面发生的事情。从这些实验中，我们开发了描述当施加一个力(其流变学)时，贫晶岩浆将如何流动的模型。然而，这些流变模型不适用于更富含晶体的岩浆(浓缩悬浮液)。在富含晶体的体系中，岩浆的运移能力受到晶体-晶体、晶体-气泡和气泡-气泡相互作用以及样品中晶体、气泡和熔体的可变空间分布的关键控制。在一种假设中，压力的积累驱动气泡穿过晶体网络，导致网络破碎。尽管仍然具有同样高的晶体含量，但在碎片之间的贫晶区域可能会发生变形，岩浆变得可移动。富含晶体的岩浆及其类似物是不透明的，常规的实验方法不允许我们观察内部的微尺度过程。因此，我们只能量化一定体积岩浆的平均行为。虽然许多可能的微结构相互作用过程已经被假设，但它们仍然没有得到测试。在该项目中，将对用于常规流变学实验的设备进行改造，以允许使用X射线计算机微层析(XMT)实时采集3D图像。在钻石光源同步加速器设施中，这项革命性的成像技术可以在短短几秒钟内捕捉到样品的3D内部结构(即晶体、气泡和熔体在岩浆中的分布)：生成岩浆变形时发生的3D电影。通过对实验过程中捕获的3D图像应用标准图像分析技术，可以量化气泡、晶体和熔体的分布；可以跟踪每个晶体和气泡的时间；可以识别每个相互作用的性质。我们将首次能够在4D(3D+时间)中看到岩浆内部发生的事情。通过使用模拟材料，并系统地测试随着我们改变晶体含量、晶体形状、气泡体积和一系列已知在岩浆室中变化的其他参数(例如温度、压力)时的微观结构行为，高速4D数据将被用于绘制不同相互作用的性质和重要性，并定义微观尺度变化(相分布和相互作用)对流动的作用。这些数据将被用来建立新一代流变学模型，描述复杂的两相和三相浓缩岩浆悬浮液的流动性，其基础是对微结构物理和微尺度变异性的准确理解。通过对自然样品进行4D实验，并根据结果测试该模型，该项目将确定富含晶体的岩浆可以喷发的条件，并开始识别导致最具破坏性的喷发的岩浆过程。