夏威夷火山高喷9千米的启示

岳中琦

今天下午拜读了新华网“夏威夷火山再度猛烈喷发火山灰柱最高逾9000米”等新闻http://www.xinhuanet.com/world/2018-05/19/c_129876056.htm。当地时间17日大约凌晨4时，位于夏威夷群岛的基拉韦Kilauea火山再次猛烈喷发，持续数分钟。火山灰柱最高超过9100米。美国地质勘探局夏威夷火山观测站发布的视频显示，火山灰遮天蔽日。

基拉韦火山这轮喷发与1924年喷发类似。它在1790年的巨大喷发导致十多人死亡，这是美国死亡人数最多的一次火山喷发。

美国USGS相关火山专家介绍了,导致这次高耸喷发原因可能是，火山熔浆湖下沉到达或低于地下水位深度，地下水流进入熔浆柱，而形成了蒸汽爆发：“Kilauea’s falling lava lake has likely descended to a level at or below the water table, allowing water to run on to the top of its lava column and create steam-driven blasts.”。http://yp.scmp.com/news/international/article/109372/hawaii%E2%80%99s-kilauea-volcano-erupts-spewing-9-kilometre-high-plume-ash

《Nature》在2018年5月17日新闻“Kilauea holds clues to predicting eruptions”中也介绍了这种地下水成因机理。“The first hint of an impending eruption came with a series of earthquakes on 3 May. Soon after, fissures opened up in the ground as far as 40 kilometres away from the volcano’s rim — oozing lava that forced about 2,000 people to evacuate. The openings also depressurized the network of underground channels beneath Kilauea, including its lava chamber. As a result, the lava level within the volcano's crater quickly dropped by more than 30 metres. It was, Poland says, “like someone pulled the plug in a bathtub”.

That caused the walls of the volcano to begin crumbling into the crater, creating a layer of rock atop the surface of the remaining lava. And once the surface of the still-draining lava dropped below the water table, water began to seep into the crater, creating steam and pressure beneath the freshly formed rock cap.” https://www.nature.com/articles/d41586-018-05206-w?utm_source=briefing-wk&utm_medium=email&utm_campaign=briefing&utm_content=20180518

我认为值得质疑，这个地下水流入熔浆、高温熔浆将水加温，形成大量水蒸气而导致这场巨大喷发成因机理。原因在于，熔浆区是高温高压和低渗透率区域，地下水在自重作用下是难以流入其中。

基拉韦火山这次、1924年和1790年的喷发证明了，夏威夷群岛（红色岩浆）火山同环太平洋等地的爆发型喷发火山（灰色火山）有类似的成因机理。它们的共同成因机理可参见科学网博文“世界上第二个火山成因假说的出世” http://blog.sciencenet.cn/blog-240687-950841.html。

2018年5月19日14：30写成于港大602办公室