Magma chamber behavior beneath a volcanic edifice
Magma chamber behavior beneath a volcanic edifice
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火山大厦下方的岩浆室行为
DOI：
10.1029/2002jb001751
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发表时间：
2003
影响因子：
--
通讯作者：
C. Jaupart
中科院分区：
文献类型：
--
作者：
V. Pinel;C. Jaupart
[1]在地球表面建造一个大型的火山建筑物会在上地壳产生应力，其大小与岩浆房内的构造应力和超压相当。我们研究这如何影响喷发行为。本文对表面有建筑物的弹性半空间中具有内部超压的圆柱形储层进行了二维解析计算。不同的建筑物形状被认为是从盾状火山与缓坡成层火山与陡峭的侧翼。在顶部没有建筑物的情况下，空腔壁处的环向应力在离轴线一定距离的两个对称点处达到最大值，远离空腔顶部。在顶部有一个建筑物，最大值在房间的顶部达到，就在建筑物的顶峰之下。这意味着室壁在轴线处优先失效，因此火山活动通过中央通风系统集中。在岩浆超压的临界值下，空洞壁发生拉伸破坏，该临界值取决于建筑物的尺寸以及空洞的深度和大小。对于一个大的成层火山下面的小岩浆房，在喷发开始时的岩浆超压随着建筑物的增长而增加，并随着建筑物的破坏而减少。这些影响可以解释为什么在圣海伦斯山的斑晶组合记录的压力，在过去的4000年中，随着建筑物经历了连续的增长和破坏阶段而变化。
[1] The construction of a large volcanic edifice at Earth's surface generates stresses in the upper crust whose magnitude is comparable to those of tectonic stresses and overpressures within a magma chamber. We study how this affects eruption behavior. Analytical calculations are carried out in two dimensions for a cylindrical reservoir with an internal overpressure in an elastic half-space with an edifice at the surface. Different edifice shapes are considered, from shield volcanoes with gentle slopes to stratovolcanoes with steeper flanks. Without an edifice at the top, the hoop stress at the cavity walls reaches a maximum at two symmetrical points at some distance from the axis, away from the top of the chamber. With an edifice at the top, the maximum is reached at the top of the chamber, just beneath the edifice summit. This implies preferential failure of chamber walls at the axis and hence the focussing of volcanic activity through a central vent system. Tensile failure of the cavity walls occurs for a critical value of magma overpressure which depends on the dimensions of the edifice and on the depth and size of the cavity. For a small magma chamber beneath a large stratovolcano, the magmatic overpressure at the onset of eruption increases as the edifice grows and decreases following edifice destruction. These effects may explain why pressures recorded in phenocryst assemblages at Mount St. Helens, have varied over the past 4000 years as the edifice went through successive phases of growth and destruction.