SEISMOLOGY AND GEOLOGY ›› 2013, Vol. 35 ›› Issue (3): 542-552.DOI: 10.3969/j.issn.0253-4967.2013.03.008

• CONTENTS • Previous Articles     Next Articles

A DISCUSSION ON THE TYPE OF THE QIXIANGZHAN ERUPTION OF CHANGBAISHAN TIANCHI VOLCANO, NORTHEAST CHINA

PAN Bo1, FAN Qi-cheng1, ZHONG Guang-pei2, XU Jian-dong1, WAN Yuan1   

  1. 1. Key Laboratory of Active Tectonics and Volcano, Institute of Geology, China Earthquake Administration, Beijing 100029, China;
    2. Changbaishan Tianchi Volcano Observatory, Antu, Jilin Province 133613, China
  • Received:2013-02-20 Revised:2013-06-27 Online:2013-09-30 Published:2013-10-12

长白山天池火山气象站期喷发类型研究

潘波1, 樊祺诚1, 仲广培2, 许建东1, 万园1   

  1. 1. 中国地震局地质研究所, 活动构造与火山重点实验室, 北京 100029;
    2. 长白山天池火山监测站, 吉林安图 133613
  • 作者简介:潘波,男,1981年生,中国地震局地质研究所在读博士研究生,助理研究员,主要从事火山地质与灾害研究,电话:010-62009071,E-mail:dujushi1981@163.com。
  • 基金资助:

    中国地震局地质研究所基本科研业务专项(IGCEA1103)和国家自然科学基金(41302267)共同资助

Abstract:

Changbaishan Tianchi volcano is one of the most dangerous active volcanoes in Northeast Asia. It experienced three periods of large-scale eruptions since the Holocene,i.e.the Tianwenfeng period at about 5,000 years ago,the Qixiangzhan period at about 4,000 years ago and the Millennium eruption at about 1,100 years ago,respectively. The type of Tianwenfeng and Millennium eruptions is commonly accepted to be a typical Plinian eruption. However,there arises a considerable debate about the type of Qixiangzhan eruption as whether it is effusive or explosive. In high-resolution remote-sensing images,the morphology of the products of Qixiangzhan eruption looks like a lava flow,which erupts from Qixiangzhan parasitic crater,and flows along the northern slope of the volcanic cone about 5.4km in length and 400~800m in width. However,the recent researches by the author have revealed that the Qixiangzhan eruption should be a small-scale pulsed explosive eruption. The main evidence is as follows: 1)The bulk-rock composition of Qixiangzhan eruption products is characterized by high SiO2(≥71%)and Na2O+K2O(≥10%)contents representative of alkaline magma,which has high viscosity,low flowing ability and extremely high potential of explosive eruption; 2)Field observations show that the Qixinagzhan eruption products appear as thin layers about 2~5cm in thickness,the central part of which is welded stronger than the edge,significantly different from the massive or slaggy structures of lava flow. In addition,flame structures indicative of explosive eruption are well developed in the volcanic deposits around parasitic crater; 3)Microscopic observation reveals that most of the phenocrysts in the Qixiangzhan eruption products were severely broken by explosion to form angular grains with well developed micro-cracks. The vesicles in the Qixiangzhan eruption products are irregular in shape and have rough margin,different significantly from the elliptical and smooth margin vesicles commonly observed in lava flow; 4)Stereomicroscopic observation shows that the Qixiangzhan eruption products are composed of clastic particles and exhibit grain-supported texture with well developed irregular vesicles. Based on the above analyses,we may conclude that the Qixiangzhan eruption can be assigned to a small-scale pulsed explosive eruption. During the explosive eruption,a large number of fine pyroclastic particles flowed down the mountain slope as a high speed pyroclasstic flow to form thin layer of ignimbrite under the action of high temperature and strong shear forces. Over many times of explosive eruptions,layer upon layer of ignimbrite were accumulated,resulting in a shape just like lava flow. Therefore,all the three large eruptions of Changbaishan Tianchi volcano in Holocene can be assigned to explosive eruption,rather than the previously proposed model of explosive-effusive-explosive explosions.

Key words: the type of volcano eruption, Qixiangzhan eruption, explosive, effusive, ignimbrite

摘要:

全面系统地了解一座活火山的喷发特征与历史,对于预测其未来喷发形式及灾害性具有重要意义。长白山天池火山晚更新世或全新世以来存在3期大规模的喷发活动,天文峰期喷发与千年大喷发皆为典型的大规模的布里尼式爆炸喷发,而气象站期喷发方式却在爆炸式或溢流式的喷发类型上存在着激烈的争论。气象站期喷发物在遥感影像上表现为以气象站为寄生火口,向北流动长约5.4km,形貌上似一条熔岩流,但文中研究认为是小规模的脉冲式爆炸喷发而形成的岩层形态。主要依据为: 1)岩石成分为高黏度的酸性岩浆; 2)野外露头与剖面的薄层状堆积特征; 3)晶屑的棱角状破碎形态; 4)岩石的颗粒支撑结构。研究结果表明,气象站期的堆积物是爆炸喷发产生的碎屑物沿山坡以火山灰流的形式快速流动,在高温与高流速的剪切力作用下,火山灰流形成1套薄层状的熔结凝灰岩。因此,长白山天池火山晚更新世或全新世以来3期喷发活动均为爆炸式喷发,而非以前认为的爆炸—溢流—爆炸式喷发。

关键词: 火山喷发类型, 气象站期喷发, 爆炸式喷发, 溢流式喷发, 熔结凝灰岩

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