Phreatomagmatic and phreatic fall and surge deposits from explosions at Kilauea volcano, Hawaii, 1790 a.d.: Keanakakoi Ash Member
Phreatomagmatic and phreatic fall and surge deposits from explosions at Kilauea volcano, Hawaii, 1790 a.d.: Keanakakoi Ash Member
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公元 1790 年夏威夷基拉韦厄火山爆炸产生的岩浆、潜水和涌流沉积物：Keanakakoi Ash 成员
DOI：
10.1007/bf00302047
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发表时间：
1990
影响因子：
3.5
通讯作者：
R. L. Christiansen
中科院分区：
文献类型：
--
作者：
J. McPhie;G. Walker;R. L. Christiansen
大约在公元1790年，基拉韦厄盾状火山的最高破火山口发生了一次爆炸性喷发。当时，一群靠近火山口的夏威夷战士被爆炸的影响所杀害。基拉韦厄周围火山碎屑沉积的地层学（即，Keanakakoi火山灰段）表明，历史记录中提到的爆炸是由三个主要阶段组成的长期水火山喷发的高潮。第一阶段是蒸汽岩浆和产生良好的层状，罚款落灰丰富的玻璃状，微泡，少年岩浆和致密，岩屑火山碎屑。火山灰主要被东北信风吹向破火山口西南部。第二阶段产生了一个Strombolian风格的火山渣下降存款，其次是类似于第一阶段的蒸汽岩浆灰，但更丰富的加积火山砾和岩屑。第三阶段和最终阶段是潜水和沉积的富含岩石的火山砾和块落层，与交错层浪涌沉积物和增生的富含火山砾的细灰层互层。这些最后的爆炸可能是造成战士死亡的原因。这三个阶段被分开的静止法术期间，初级存款被侵蚀和运输顺风沙丘迁移西南和当地挖掘的河流径流靠近边缘。整个水火山喷发可能持续了数周或数月。大约在同一时间，熔岩从基拉韦厄的东部裂谷带喷发出来，很可能把山顶储存的岩浆吸走了。对基拉韦厄的最早描述（Keanakakoi火山爆发后30年）强调了底部的巨大深度（边缘以下300-500米）和阶梯状壁架的存在。因此，基阿纳卡柯伊火山的爆炸很可能是在基拉韦厄火山深处发生的，而且火山口的边缘比破火山口的边缘低得多。从潜水岩浆相到潜水相的变化可能反映了岩浆在深退过程中的逐步脱气和冷却：在整个潜水岩浆相中，岩浆泡形成通过启动碎裂过程而促进了与水的爆炸性相互作用：此后，下沉岩浆柱的主要作用是为蒸汽生产提供热量，从而驱动了最后阶段的潜水爆炸。
In or around 1790 a.d. an explosive eruption took place in the summit caldera of Kilauea shield volcano. A group of Hawaiian warriors close to the caldera at the time were killed by the effects of the explosions. The stratigraphy of pyroclastic deposits surrounding Kilauea (i.e., the Keanakakoi Ash Member) suggests that the explosions referred to in the historic record were the culmination of a prolonged hydrovolcanic eruption consisting of three main phases. The first phase was phreatomagmatic and generated well-bedded, fine fallout ash rich in glassy, variably vesiculated, juvenile magmatic and dense, lithic pyroclasts. The ash was mainly dispersed to the southwest of the caldera by the northeasterly trade winds. The second phase produced a Strombolian-style scoria fall deposit followed by phreatomagmatic ash similar to that of the first phase, though richer in accretionary lapilli and lithics. The third and culminating phase was phreatic and deposited lithic-rich lapilli and block fall layers, interbedded with cross-bedded surge deposits, and accretionary lapilli-rich, fine ash beds. These final explosions may have been responsible for the deaths of the warriors. The three phases were separated by quiescent spells during which the primary deposits were eroded and transported downwind in dunes migrating southwestward and locally excavated by fluvial runoff close to the rim. The entire hydrovolcanic eruption may have lasted for weeks or perhaps months. At around the same time, lava erupted from Kilauea's East Rift Zone and probably drained magma from the summit storage. The earliest descriptions of Kilauea (30 years after the Keanakakoi eruption) emphasize the great depth of the floor (300–500 m below the rim) and the presence of stepped ledges. It is therefore likely that the Keanakakoi explosions were deepseated within Kilauea, and that the vent rim was substantially lower than the caldera rim. The change from phreatomagmatic to phreatic phases may reflect the progressive degassing and cooling of the magma during deep withdrawal: throughout the phreatomagmatic phases magma vesiculation contributed to the explosive interaction with water by initiating the fragmentation process: thereafter, the principal role of the subsiding magma column was to supply heat for steam production that drove the phreatic explosions of the final phase.