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Geological and petrological study on phreatomagmatic explosions of the Miyakejima eruption in 2000

2000年三宅岛喷发的岩浆爆发地质和岩石学研究

基本信息

批准号：
16340166
负责人：
NAKADA Setsuya
金额：
$ 8.38万
依托单位：
The University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2004
资助国家：
日本
起止时间：
2004 至 2006
项目状态：
已结题

项目摘要

The mechanisms of phreatomagmatic explosions that occurred during the eruption at Miyakejima in 2000 were investigated based on geological inspection of the products together with the geophysical monitoring data and video footage. Comparative study was also carried out for the eruptions in Anatahan (Northern Mariana Islands) during 2003-2005 and in the Akademy Nauk lake (Kamchatka) in 1996. In Miyakejima, tephra of every explosion events were identified in many places and the depositional times were determined using stratigraphical makers. Eruption volume of tephra of each explosion event gave the precise eruption rates. The fragmentation extents of magma and whole products of each event were estimated by grain analysis. Component analysis gave the proportion of contribution of magma to each explosion event. These data are very valuable parameters to model the explosions of hydrovolcanic eruptions, which nobody could have presented by this study.There is positive correlation between th … More e magma eruption rate and the height of ashy eruption column, and negative correlation between the extent of fragmentation and magma eruption rate. The latter means the highest extent of fragmentation in non-magmatic explosions. Such the high fragmentation may result from (1) repeated fragmentation of coarse grains within the crater, which failed to rise due to the lack of thermal energy and (2) the effect of supercritical water that breaks silicate into pieces immediately. The lines of evidence showing the most effective energy conversion from heat to fragmentation at the mgama-water ration of 0.3, proposed by Wahletz was not confirmed in the present eruption.Large contribution of groundwater into the Miyakejima eruption in 2000 is also verfied by the appearance of erupted products and the isotopic ratios of materials attached to the products. Further investigation including textural comparison of products from the Anatahan and Akadamy Nauk is needed to clarify the circumstance of phreatomagmatic explosions. Less

基于对产品的地质检查以及地球物理监测数据和录像，对2000年三宅岛喷发时发生的岩浆爆发机制进行了调查。还对2003-2005年阿纳塔汉（北马里亚纳群岛）和1996年阿卡德米诺克湖（堪察加半岛）的火山喷发进行了比较研究。在三宅岛，在许多地方识别了每次爆炸事件的火山灰，并使用地层生成器确定了沉积时间。每次爆炸事件的火山灰喷发量给出了精确的喷发率。通过颗粒分析估计了每个事件的岩浆和整个产物的破碎程度。成分分析给出了岩浆对每次爆炸事件的贡献比例。这些数据是模拟水力火山喷发的非常有价值的参数，这是任何人都无法通过这项研究提供的。岩浆喷发速率与火山喷发柱高度呈正相关，破碎程度与岩浆喷发速率呈负相关。后者意味着非岩浆爆炸中破碎程度最高。如此高的破碎可能是由于（1）火山口内的粗颗粒反复破碎，由于缺乏热能而未能上升；（2）超临界水的作用使硅酸盐立即破碎成碎片。 Wahletz 提出的在镁水比为 0.3 时从热量到碎裂的最有效能量转换的证据在本次喷发中并未得到证实。地下水对 2000 年三宅岛喷发的巨大贡献也通过喷发产物的出现和附着在产物上的物质的同位素比率得到了证实。需要进一步调查，包括对阿纳塔汉和阿卡达米诺克的产品进行结构比较，以澄清岩浆爆炸的情况。较少的