The failure mode of lava—dilatant or compactant—depends on the physical attributes of the lava, primarily the porosity and pore size, and the conditions under which it deforms. The failure mode for edifice host rock has attendant implications for the structural stability of the edifice and the efficiency of the sidewall outgassing of the volcanic conduit. In this contribution, we present a systematic experimental study on the failure mode of edifice-forming andesitic rocks (porosity from 7 to 25 %) from Volcán de Colima, Mexico. The experiments show that, at shallow depths (<1 km), both low- and high-porosity lavas dilate and fail by shear fracturing. However, deeper in the edifice (>1 km), while low-porosity (<10 %) lava remains dilatant, the failure of high-porosity lava is compactant and driven by cataclastic pore collapse. Although inelastic compaction is typically characterised by the absence of strain localisation, we observe compactive localisation features in our porous andesite lavas manifest as subplanar surfaces of collapsed pores. In terms of volcano stability, faulting in the upper edifice could destabilise the volcano, leading to an increased risk of flank or large-scale dome collapse, while compactant deformation deeper in the edifice may emerge as a viable mechanism driving volcano subsidence, spreading and destabilisation. The failure mode influences the evolution of rock physical properties: permeability measurements demonstrate that a throughgoing tensile fracture increases sample permeability (i.e. equivalent permeability) by about a factor of two, and that inelastic compaction to an axial strain of 4.5 % reduces sample permeability by an order of magnitude. The implication of these data is that sidewall outgassing may therefore be efficient in the shallow edifice, where rock can fracture, but may be impeded deeper in the edifice due to compaction. The explosive potential of a volcano may therefore be subject to increase over time if the progressive compaction and permeability reduction in the lower edifice cannot be offset by the formation of permeable fracture pathways in the upper edifice. The mode of failure of the edifice host rock is therefore likely to be an important factor controlling lateral outgassing and thus eruption style (effusive versus explosive) at stratovolcanoes.

中文翻译：

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火山结构中安山岩的断裂和压实

熔岩的破坏模式——膨胀或致密——取决于熔岩的物理属性，主要是孔隙度和孔径，以及它变形的条件。建筑物主岩的破坏模式对建筑物的结构稳定性和火山管道的侧壁除气效率具有伴随的影响。在这篇文章中，我们对墨西哥科利马火山形成的安山岩（孔隙度为 7% 至 25%）的破坏模式进行了系统的实验研究。实验表明，在较浅的深度（<1 公里），低孔隙度和高孔隙度的熔岩都会膨胀并通过剪切压裂而破裂。然而，在建筑物更深处（> 1 公里），虽然低孔隙度（<10 %）熔岩仍然膨胀，但高孔隙度熔岩的破坏是致密的，并由碎裂孔隙坍塌驱动。尽管非弹性压实的典型特征是不存在应变局部化，但我们观察到多孔安山岩熔岩中的压实局部化特征表现为塌陷孔隙的亚平面表面。在火山稳定性方面，上层结构的断层可能会破坏火山的稳定性，导致侧翼或大规模穹顶坍塌的风险增加，而结构较深的压实变形可能会成为推动火山下沉、扩张和不稳定的可行机制. 破坏模式影响岩石物理性质的演变：渗透率测量表明，贯穿的拉伸裂缝使样品渗透率（即等效渗透率）增加了大约 2 倍，并且非弹性压实使轴向应变为 4。5% 将样品渗透率降低一个数量级。这些数据的含义是侧壁除气因此在浅层建筑物中可能是有效的，在那里岩石可以破裂，但可能由于压实而在建筑物更深处受到阻碍。因此，如果下部建筑物的逐渐压实和渗透性降低不能被上部建筑物中可渗透裂缝路径的形成所抵消，那么火山的爆炸潜力可能会随着时间的推移而增加。因此，建筑物主岩的破坏模式很可能是控制层状火山横向释气和喷发方式（喷发式与爆炸式）的重要因素。但由于压实，可能会在建筑物中更深地受到阻碍。因此，如果下部建筑物的逐渐压实和渗透性降低不能被上部建筑物中可渗透裂缝路径的形成所抵消，那么火山的爆炸潜力可能会随着时间的推移而增加。因此，建筑物主岩的破坏模式很可能是控制层状火山横向释气和喷发方式（喷发式与爆炸式）的重要因素。但由于压实，可能会在建筑物中更深地受到阻碍。因此，如果下部建筑物的逐渐压实和渗透性降低不能被上部建筑物中可渗透裂缝路径的形成所抵消，那么火山的爆炸潜力可能会随着时间的推移而增加。因此，建筑物主岩的破坏模式很可能是控制层状火山横向释气和喷发方式（喷发式与爆炸式）的重要因素。