2013 Volume 58 Issue 1 Pages 291-306
In studies of volcanic tephra, it is usual that the overall volume of tephra is estimated ashfall volumes based on representative locations within the ashfall area. The precision of the volume estimation largely depends on the number of the locations. However, in the case of ongoing eruptions on island volcanoes, such as Sakurajima volcano, the observation locations are usually limited. We therefore have developed a practical method for estimating ashfall volume and distribution in such case. The method approximates the distribution of ashfall as ellipses, with the distribution area (A) and thickness or weight of deposit (T) determined by A=αT-1. The ellipse-approximated isopachs can be determined by using the direction of the ellipse axis and ashfall data at two points. In determing the ellipse axis exactly, we usually need additional ashfall amounts from the other locations. We set 37 samplers around Sakurajima volcano, and retrieved the samplers 15 times, from April to December, 2008. Using the propose method, we are able to determine the volume of ash produced by small, continuous eruptions.
