吉林金龙顶子火山空降堆积物体积估算及其地质意义

Calculation of Fallout Tephra Volumes in Sihai Phase of Jinlongdingzi Volcano of Longgang Volcanic Swarm in Jilin Province

用梯形法、对数坐标直线交叉法、厚度对数-面积平方根法对吉林龙岗金龙顶子火山四海期空降堆积物的体积进行了估算,结果分别为0.096 km3,0.138 km3,0.109 5 km3,与Los Alamos National Laboratory开发的火山喷发模拟软件模拟的结果(0.105 km3)相近。对比分析认为;梯形法存在的主要问题是忽略了最后一条等厚线与零点等厚线间的体积,从而低估了实际喷出量;对数直线交叉法虽然减少了厚度与面积间的非线性相关性,但获得的两条直线具有相当大的主观性;厚度对数-面积平方根法是在空降堆积物随着远离火山口呈指数性减薄的事实基础上提出的,是比较准确的体积估算方法。

Three methods, the trapezoidal rule, the straight lines on log-log plots of area versus thickness and the straight lines on plots of log thickness versus square root of area, of calculating volumes of fallout tephra deposited in Sihai Phase of Jinlongdingzi Volcano of Longgang Volcanic Swarm in Jilin Province are applied in this paper. The calculated results are 0. 096 km^3 ,0. 138 km^3 and 0. 109 5 km^3 respectively. Contrasting with the result （0.105 km^3 ） of volcalic eruption program by Los Alamos National Laboratory, the last method is considered the best calculation, and the problems of the other two methods are discussed. The method using straight lines on plots of log thickness versus square root of area is recognized to be relatively reasonable because volcanic deposits decrease exponentially with distance from volcano center.