Boudon Georges, Balcone-Boissard Hélène, Villemant Benoît, Morgan Daniel J
Institut de Physique du Globe de Paris, Sorbonne Paris Cité, Univ. Paris Diderot, CNRS, F-75005, Paris, France.
Sorbonne Universités, UPMC Univ Paris 06, CNRS, Institut des Sciences de la Terre de Paris (iSTeP), 4 place Jussieu 75005 Paris, France.
Sci Rep. 2015 Sep 30;5:14551. doi: 10.1038/srep14551.
Dome-forming eruption is a frequent eruptive style and a major hazard on numerous volcanoes worldwide. Lava domes are built by slow extrusion of degassed, viscous magma and may be destroyed by gravitational collapse or explosion. The triggering of lava dome explosions is poorly understood: here we propose a new model of superficial lava-dome explosivity based upon a textural and geochemical study (vesicularity, microcrystallinity, cristobalite distribution, residual water contents, crystal transit times) of clasts produced by key eruptions. Superficial explosion of a growing lava dome may be promoted through porosity reduction caused by both vesicle flattening due to gas escape and syn-eruptive cristobalite precipitation. Both processes generate an impermeable and rigid carapace allowing overpressurisation of the inner parts of the lava dome by the rapid input of vesiculated magma batches. The relative thickness of the cristobalite-rich carapace is an inverse function of the external lava dome surface area. Explosive activity is thus more likely to occur at the onset of lava dome extrusion, in agreement with observations, as the likelihood of superficial lava dome explosions depends inversely on lava dome volume. This new result is of interest for the whole volcanological community and for risk management.
穹顶式喷发是一种常见的喷发方式，也是全球众多火山面临的主要危害。熔岩穹丘是由脱气后的粘性岩浆缓慢挤出形成的，可能会因重力坍塌或爆炸而被破坏。人们对熔岩穹丘爆炸的触发机制了解甚少：在此，我们基于对关键喷发产生的碎屑进行的纹理和地球化学研究（孔隙率、微晶度、方石英分布、残余含水量、晶体运移时间），提出了一种新的表层熔岩穹丘爆炸性模型。正在生长的熔岩穹丘的表层爆炸可能是由于气体逸出导致气泡压扁以及喷发同期方石英沉淀引起的孔隙率降低所促进的。这两个过程都会产生一个不可渗透且坚硬的外壳，使得泡状岩浆批次的快速注入能够使熔岩穹丘内部压力升高。富含方石英的外壳的相对厚度与外部熔岩穹丘表面积呈反比函数关系。因此，正如观测结果所示，爆炸性活动更有可能在熔岩穹丘挤出开始时发生，因为表层熔岩穹丘爆炸的可能性与熔岩穹丘体积呈反比。这一新结果对整个火山学界和风险管理都具有重要意义。
