Syn- and Post-caldera Eruptive History of Izu Oshima Volcano based on Tephra and Loess Stratigraphy
Syn- and Post-caldera Eruptive History of Izu Oshima Volcano based on Tephra and Loess Stratigraphy
复制标题
基于火山灰和黄土地层的伊豆大岛火山同期和破火山口后喷发历史
DOI：
--
复制
发表时间：
1996
期刊：
影响因子：
--
通讯作者：
Y. Hayakawa
中科院分区：
文献类型：
--
作者：
M. Koyama;Y. Hayakawa
通过火山灰和黄土地层学的研究，揭示了日本伊豆大岛火山的同期喷发史和后火山口喷发史。覆盖在火山口外斜坡上的24个火山灰岩层表明，自火山口形成以来(约1450年前)发生了24次喷发。这些喷发之间有10-200年的明显休眠期，可以通过风尘(黄土)与特弗拉岩层的夹层来识别。这24次喷发可分为3种类型：1)有蝎子和灰降的喷发(12次)，2)只有蝎子的喷发(7次)，3)只有灰落的喷发(5次)。类型1的Tephra流量一般较大(1.5×1010~7×1011 kg)，类型2或类型3的Tephra流量较小(0.6×109~1×1011 kg)。1986年的火山喷发被归类为第二类。就在火山口形成之前发生的碎片雪崩几乎覆盖了伊豆大岛岛的全部，表明现在的火山口墙是由一座旧建筑的斜坡破坏形成的。火山喷发时间与岩浆累计排泄量/质量的关系图表明：1)火山喷发的平均喷发速率是恒定的(N1.0喷发前为92 kg/S，N1.0喷发后为25 kg/S)，N1.0喷发发生在约900年前，是过去1450年来规模最大的喷发；2)N1.0喷发前后，1型喷发都具有体积可预测性，即：可以预测下一次1型喷发的排泄量/质量，3)未来某个时候应该再次发生1型喷发，当它发生时，火山灰的排泄量应达到2×1011公斤或更多。
We reveal the detailed syn-and post-caldera eruptive history of Izu Oshima Volcano, Japan, by tephra and loess stratigraphy. Twenty-four tephra layers, which overlie the slope outside the caldera, show that 24 eruptions occurred since the formation of the caldera (about 1, 450 years ago). These eruptions are separated by 10-200 years clear dormant periods, which can be identified by eolian dust (loess) interbedded with tephra layers. The 24 eruptions can be classified into three types : 1) eruption with scoria and ash falls (12 eruptions), 2) eruption only with scoria falls (7 eruptions), and 3) eruption only with ash falls (5 eruptions). While tephra discharge mass of the type 1 is generally large (1.5×1010 to 7×1011 kg), that of the type 2 or 3 is small (0.6 ×109 to 1 ×1011 kg). The 1986 eruption is classified into the type 2. Debris avalanches, which occurred just before the caldera formation and covered almost all of the Izu Oshima island, demonstrate that the present caldera wall was formed by slope failure of an old edifice. The tephra-discharge stepdiagram, which shows a relationship between time and cumulative discharge volume / mass of magma, shows : 1) the average tephra-discharge rate is constant (92 kg/ s before the N1.0 eruption and 25 kg/s after the N1.0 eruption), showing an abrupt decrease of the rate at about the time of the N1.0 eruption, which occurred about 900 years ago and was the most voluminous eruption for the past 1, 450 years, 2) both before and after the N1.0 eruption, the type 1 eruption shows volume-predictability, that is, the discharge volume / mass of a next type 1 eruption can be predicted, 3) a type 1 eruption should occur sometime in the future again, and when it occurs, the discharge mass of tephra should attain to as much as 2×1011 kg or more.