The lava effusive processes and transport system of Laoheishan volcano,Wudalianchi,NE China
The Laoheishan volcano in Heilongjiang Province,NE China,erupted in 1720-1721 AD.The eruption of Laoheishan volcano show typical Hawaiian and Strombolian eruptive styles.The lava flow field of Laoheishan volcano covers an area of 60.19 km2.Due to it preserves the newest lava flows in China,it is an ideal case to investigate the lava surface morphologies,lava transport system,and lava-flow-hazard processes of monogenetic basaltic volcanism.We use 0.05～0.92m/pix image data acquiring from small Unoccupied Aircraft Systems(UAS)and 12.5m/pix satellite image,to create a 1∶1000 scale flow processes map that was ground-truthed by field observations.In order to understand the flow process,we defined six lava flow fields as the products of the corresponding lava outlets.Moreover,we distinguished the sub-flow field,lava flow sets(a set of lava flows originated from the same bocca of their parent flow)and flow units within each lava flow field.In this paper,two criteria for the boundary demarcation of lava flows at different scales summarized as below.(1)The boundary of the flow field(i.e.,lava from the same outlet)mostly defined by the large topographic depression and valley.The distribution and stratigraphic contact of lava toes provide evidences for the demarcation work.(2)The demarcation of the flow units within a flow field depends more on the assembly of lava surface facies,and the boundary is determined with the assistance of small topographic features.We concluded that there are three types of lava transportation in Laoheishan lava flow field:'a'ā flow,pāhoehoe flow and inflation behaviors,by analyzing the surface facie of specific lava flows.We found the'a'ā flow behavior dominated in Laoheishan lava flow field.In this way,a large portion of the Laoheishan lava flow field(s)were divided into relative small units,by a model that pāhoehoe toes developed from its'a'ā parent.In addition,significant pāhoehoe and inflation processes also taken place in somewhere.We propose a layer-by-layer and set-by-set estimation method for quantitative values of area,volume for demarcated flow fields and flow sets,based on the lava surface facies,their transportation behaviors and measurable thicknesses.This method rooted on the fact that the propagation of lava flows(especially'a'ā flow)tend to both laterally to widen and vertically to thicken(near-vent)the flow field.Furthermore,we estimated the volume of tephra is 70 × 106m3 and gives a VEI=1～2.The volume of lava is 290 × 106m3,which gives out the eruptive magnitude of 4.9.The intensity of this eruptive shows low to medium(intensity=4～8),which is speculated from eruption(s)of another volcano,i.e.,the 1983-84 eruption of Puu Oo.
万方数据
维普
