Woitischek Julia, Edmonds Marie, Woods Andrew W
Department of Earth Sciences, University of Cambridge, Downing St, Cambridge, CB2 3EQ, UK.
BP Institute, University of Cambridge, Madingley Rd, Cambridge, UK.
Sci Rep. 2020 Sep 10;10(1):14862. doi: 10.1038/s41598-020-71667-7.
Basaltic open vent volcanoes are major global sources of volcanic gases. Many of these volcanoes outgas via intermittent Strombolian-type explosions separated by periods of passive degassing. The gas emitted during the explosions has high molar CO/SO and SO/HCl ratios, while during the passive degassing these ratios are lower. We present new laboratory experiments in a model volcanic conduit, which suggest that these differences in gas geochemistry are a consequence of gas migration through crystal-rich magma. We show that gas may flow along channels through the particle-laden liquid and, at a critical depth, the gas may displace an overlying crystal-rich plug en masse, producing a growing slug of gas. Owing to the friction on the walls of the conduit, this plug becomes progressively sheared and weakened until gas enriched in the least soluble volatiles breaks through, causing an explosion at the surface. When the gas slug bursts, liquid is drawn up in its wake, which exsolves the more soluble volatile components, which then vent passively at the surface until the next explosive slug-bursting event.
玄武质开放喷口火山是全球主要的火山气体来源。其中许多火山通过间歇性的斯特龙博利式爆炸排气，爆炸之间为被动排气阶段。爆炸期间释放的气体具有较高的摩尔CO/SO和SO/HCl比值，而在被动排气期间这些比值较低。我们在一个模拟火山管道中进行了新的实验室实验，结果表明这些气体地球化学差异是气体在富含晶体的岩浆中迁移的结果。我们发现气体可能沿着通道在充满颗粒的液体中流动，在一个临界深度，气体可能会整体置换上覆的富含晶体的堵塞物，产生不断增长的气柱。由于管道壁的摩擦，这个堵塞物逐渐被剪切并弱化，直到富含最难溶挥发物的气体突破，导致地表发生爆炸。当气柱破裂时，液体在其后被抽吸上来，使更易溶的挥发成分逸出，然后在地表被动排出，直到下一次爆炸气柱破裂事件发生。
