Pan B.,China Earthquake Administration |
Fan Q.-C.,China Earthquake Administration |
Zhong G.-P.,Changbaishan Tianchi Volcano Observatory |
Xu J.-D.,China Earthquake Administration |
Wan Y.,China Earthquake Administration
Dizhen Dizhi | Year: 2013
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 5.4 km in length and 400~800 m 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.
Liu G.-M.,Changbaishan Tianchi Volcano Observatory |
Yang J.K.,China Earthquake Administration |
Wang L.-J.,China Earthquake Administration |
Sun J.-C.,Changbaishan Tianchi Volcano Observatory
Bulletin of Mineralogy Petrology and Geochemistry | Year: 2011
Seismic monitoring has been conducted in the area of the Tianchi active volcano during every June to September since 1985. The volcanic seismic events were recorded about 40 times each year from 1985 to 1994. According to our observation data, it was found that the volcanic seismic events obviously increased since July, 2002. The times of recorded seismic events increased to 1293 for the year 2002, the seismic events decreased in year 2004, but the released seismic energy remained increasing. This paper evaluated the ability of Changbaishan volcanic seismic monitoring, discussed the current volcano active level of Changbaishan, and presented our predictions for future active level of the Tianchi active volcano, Changbai Mountain.