The collapse of a volcanic flank can be destructive and deadly. Hydrothermal alteration is common to volcanoes worldwide and is thought to promote volcano instability by decreasing rock strength. However, some laboratory studies have shown that not all alteration reduces rock strength. Our new laboratory data for altered rhyodacites from Chaos Crags (Lassen volcanic center, California, USA) show that pore- and crack-filling mineral precipitation can reduce porosity and permeability and increase strength, Young's modulus, and cohesion. A significant reduction in permeability, by as much as four orders of magnitude, will inhibit fluid circulation and create zones of high pore fluid pressure. We explored the consequences of pore fluid pressurization on volcano stability using large-scale numerical modeling. Upscaled physical and mechanical properties for hydrothermally altered rocks were used as input parameters in our modeling. Results show that a high-pore-pressure zone within a volcano increases volcano deformation and that increasing the size of this zone increases the observed deformation. Hydrothermal alteration associated with mineral precipitation, and increases to rock strength, can therefore promote pore pressurization and volcano deformation, increasing the likelihood of volcano spreading, flank collapses, and phreatic/phreatomagmatic explosions. We conclude that porosity-decreasing alteration, explored here, and porosity-increasing alteration can both promote volcano instability and collapse, but by different mechanisms. Hydrothermal alteration should therefore be monitored at volcanoes worldwide and incorporated into hazard assessments.

中文翻译：

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热液蚀变会导致孔隙加压和火山不稳定

火山侧翼的坍塌可能具有破坏性和致命性。热液蚀变在世界范围内的火山中很常见，并且被认为通过降低岩石强度来促进火山的不稳定性。然而，一些实验室研究表明，并非所有的蚀变都会降低岩石强度。我们对来自 Chaos Crags（美国加利福尼亚州拉森火山中心）的蚀变流纹岩的新实验室数据表明，孔隙和裂缝填充矿物沉淀可以降低孔隙度和渗透率，并增加强度、杨氏模量和内聚力。渗透率显着降低多达四个数量级，将抑制流体循环并产生高孔隙流体压力区。我们使用大规模数值模拟研究了孔隙流体加压对火山稳定性的影响。在我们的建模中，热液蚀变岩石的升级物理和机械特性被用作输入参数。结果表明，火山内的高孔隙压力带会增加火山变形，而增加该带的大小会增加观察到的变形。与矿物沉淀相关的热液蚀变并增加岩石强度，因此可以促进孔隙加压和火山变形，增加火山扩张、侧翼坍塌和潜水/潜水岩浆爆炸的可能性。我们得出结论，这里探讨的孔隙度减少蚀变和孔隙度增加蚀变都可以促进火山的不稳定和坍塌，但机制不同。因此，应在世界各地的火山中监测热液蚀变，并将其纳入危害评估。