关键词: 天池火山, 熔岩流, 流动速度, 溢流性灾害

Abstract: The Tianchi volcano is the most important active volcano in China for its largest magnitude, complicate history and the most potential hazards. Tianchi volcano experienced the stages of an early basalt shield, a middle trachyte composite-cone and a late ignimbrite-forming. Junjianshan Formation was first introduced for the Neocene thick confined or unconfined basaltic lava flows around the Tianchi Cone and has been divided into three parts as, from early to late, Toudao F, Baishan F and Laofangzixiaoshan F, composing the Tianchi basalt shield. The Tianchi shield basalts flowed a distance of a few to dozens kilometers with a width of hundreds to thousands meters and a thickness of a few to dozens meters, comprising the composite flow units in confined or unconfined mechanism. The Laofangzixiaoshan basalt, composed of the uppermost part of the shield, flowed much a less distance than the earlier Toudao and Baishan basalts in a lower aspect ratio. It shows that the basalt shield was formed between 4.26Ma and 0.31Ma. We calculated the flow velocity of Tianchi basaltic lava flow and the time duration of lava reaching its distal localities. The calculated velocity of the lava flow with 0.5m thickness and 5% crystal content is less than 1m/s, while it reaches up to 10m/s when the flow thickness increases to 2m. But if the crystal content in a 0.5m thick lava flow increases to 30%, the lava flow velocity will decrease sharply to less than 0.12m/s. The 2m thick lava flow of Tianchi volcano in the northeast can reach its distal part in less than a day, but it needs ten days if the flow thickness is 0.5m. The lava flow of Tianchi volcano may have a distance up to 50km in the future eruption. Volcanic hazards due to lava flows from the Tianchi volcano in the future are destructive to buildings, farm lands, roads and power stations and may cause some fire disasters.

Key words: Changbaishan Tianchi volcano, lava flow, velocity, effusive hazards