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Study of Lava Lake at Nyiragongo Volcano

尼拉贡戈火山熔岩湖研究

基本信息

批准号：
08454116
负责人：
HAMAGUCHI Hiroyuki
金额：
$ 3.26万
依托单位：
Tohoku University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1996
资助国家：
日本
起止时间：
1996 至 1997
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-08454116/
关键词：
Volcanic Activity Eruption Lava lake Nyiragongo Volcano East African Rift Valley Basaltic lava Magma Volcano マグマ供給系

项目摘要

The Nyiragongo volcano in the western rift valley of the East African Rift System had a long-lived lava lake in the summit crater for about 100 years. We reviewed this lava lake actibities based on the old documents and the recent our field observations. Some results of the present study is summarized as follows ;(1) Based on the old documents and our field observations, the temporal variations of lava lake activity in the summit crater are summarized for the last 100 years.(2) Based on the observatin of temporal changes of lava-lake elevation, the average magma supply rate is estimated to be 7,000 kg/day. Total magma suplly is 86 million cubic meters in the period of 1994-1996.(3) the volcanic earthquakes were classified into two types on the basis of their waveform. The seismic activity of the A-type events shows ratherconcentrated features at the depth of about 15 km just beneath the Nyiragongo crater.(4) Whenever volcanic tremors are observed the eruptive activity in the lava-lake has been always reognized by an eye-witness. After the initial episode of eruption in the lava-lake, we observed at least 36 eruptive episodes in 1994 - 1996. We found that there is a dear reverse correlation between the occurrence of the A-type earthquakes at a depth and the lava fountain on the surface of lava lake. This feature can be interpreted by the increase of advective overpressure in the conduit system.

位于东非裂谷系西部裂谷的尼拉贡戈火山在山顶火山口有一个寿命约100年的熔岩湖。本文根据前人的研究资料和我们最近的野外观察，对这一熔岩湖活动进行了综述。主要研究结果如下：（1）根据文献资料和野外观测资料，总结了近百年来山顶火山口熔岩湖活动的时间变化规律。(2)根据熔岩湖高程随时间变化的观察，估计平均岩浆供应量为7，000公斤/天。1994 ~ 1996年，岩浆供应总量为8600万m3。(3)根据火山地震的波形，将其分为两类。A型地震活动在尼拉贡戈火山口下约15公里处有较集中的特征。(4)每当观察到火山震动时，熔岩湖中的喷发活动总是被目击者识别出来。在熔岩湖中的喷发的第一幕之后，我们观察到至少36喷发事件在1994 - 1996年。研究发现，A型地震在一定深度上的发生与熔岩湖表面的熔岩喷泉有很好的反相关性。这一特征可以用管道系统中平流超压的增加来解释。