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

摘要： 天池火山东北侧造盾玄武岩可划分出8个流动单元,熔岩流的流动距离主要集中在30～50km,熔岩流宽度以5km左右为主。通过由野外调查获得的天池火山东北侧不同熔岩流单元的地表坡度、熔岩流厚度等,结合温度、密度与黏度等物理参数,按照熔岩流速度公式恢复的头道组和早白山组0.5m厚晶体含量5%的玄武岩熔岩流流速集中在0～1m/s之间。晶体含量为30%、厚度为0.5m的晚白山组和老房子小山组玄武岩熔岩流的流动速度集中在0～0.12m/s之间。厚度增大至2m左右,晶体含量不变的头道组和早白山组的玄武岩熔岩流流动速度可加快至11m/s。天池火山2m厚的碱性熔岩流在12h内达到或接近了它的最远距离,而各组内2m厚拉斑玄武岩熔岩流在20h内接近了最远距离。0.5m厚的熔岩流在10d内接近最大距离。50km是预计的熔岩流长度,在未来制定减灾措施时,可将此长度作为重要依据之一。天池火山熔岩流灾害主要表现为熔岩流动时对房屋建筑、农田、道路、林地、电站的毁坏,火灾及大量的人口伤亡。

关键词: 天池火山, 熔岩流, 流动速度, 溢流性灾害