Is the Onioshidashi Lava Flow, Asama Volcano, Formed by a secondary Flowage of Pyroclastic Materials after the Landing?

Abstract

The ‘Onioshidashi lava flow’ has been considered a typical block andesitic lava flow, which gently flowed over the crater rim of Asama volcano in the 1873 eruption. But the lava flow is mainly composed of secondary-flowage products derived from welded-pyroclastic fall deposits in the climax phase of eruptive cycle. The fact subjest that the lava flow occuered explosive eruption. The eruptive sequence ‘Plinian eruption→pyroclastic flow→lava flow’ must be reconsidered. The method of the aerial photograph interpretation also for volcanic land forms(lava levee etc.)shoud be reexamined.