长白山天池地区全新世以来火山活动及其特征

新生代以来,强烈而频繁的火山活动铸成了长白山火山的主体——白头山火山锥。近几年来,从火山学和火山灾害学角度在该区进行研究和调查所获得的资料发现,长白山天池地区在全新世至少有六期火山活动在地表留下了记录。除白云峰期和八卦庙期喷发出大量碱流岩质浮岩形成的火山碎屑流造成了严重的火山灾害之外,其他四次喷发的规模均较小、影响面不大。老虎洞期活动发生在浮岩喷发之前,主要产物为玄武质火山渣和熔岩;气象站期喷发可能是该火山近期活动的表现,以碱流岩喷溢为主。这些喷发活动证实,该区近代火山活动不仅从未停止过,相反,活动的频度却逐渐加大。

HOLOCENE VOLCANIC ACTIVITIES AND THEIR FEATURES IN TIANCHI AREA, CHANGBAISHAN MOUNTAINS

Volcanic calamity would have a great impact on the mankind and the environment. There have been frequent and intense Cenozoic volcanic activities in Changbaishan region, which is a part of the Circum-Pacific volcanic belt. Recent investigations on the Baitoushan volcano, Tianchi area of Changbaishan region provide many new information about Holocene volcanic activities in this region. Before Holocene, intense and frequent eruptions of basaltic lavas constructed the base of the Baitoushan volcano in Tianchi area. The shield base of the Baitoushan volcano was constructed by the Junjianshan basalt in Late Pliocene. Recent information from volcanologic and volcano calamity investigations had shown that since the beginning of Holocene the Baitoushan volcano had gradually entered another hightide of activities. At least six eruption stages in Tianchi area have been distinguished based on the residual materials on land surface, geological relationship and some chronological datings. The basaltic lavas and scorias of Laohudong stage had constructed several small cones which are scattered on the slope of the Baitoushan volcano. New discovery of the basaltic rocks in Holocene shows that the volcanic activities and the magmatic evolution process might be more complex than that discussed before. Pyroclastic Pumice Flow of Baiyunfeng stage began with an intensive explosion of gasified magma, which broke through the Tianchi crater and produced a very high and huge explosion column. Alkali trachytic clastic rocks of Baguamiao stage outcropped on the inner side of the crater, hillside of cone and valleys were erupted from the Tianchi crater. The Qixiangzhan pantelleritic lavas have been determined with some new investigations, that is, the forming age of the pantelleritic lavas and breccia is Holocene instead of Pleistocene suggested by Liu Xiang (1989). The Tianchi Weather Observatory is located just at the center of a small crater which was blocked by Pantellerites. New geological datings show that tuff breccia of Nangou stage is probably the products of several limited intermittent eruptions. Some black coke-like cinder and soil scattered in the ditches nearby the sixth boundary tablet between China and Korea (Liuhaojie), might be the relict of another limited volcanic activity. Based on the above information it can be seen that in Holocene, the most important ac- tivities in Changbaishan region are the strong explosions of Baiyunfeng and Baguamiao stages, which caused pyroclastic flows and brought great suffering to this area. Another limited eruption in Holocene also shows the potential dangers in Tianchi arta in the near future. People should pay close attention to the possibility of short term volcanic hazard.