Abstract
Relationship between Beppu-Shimabara graben and Kagoshima graben with cauldrons in them are examined with special reference to uplifting preceding collapse. Collapse style of cauldrons in Kyushu is similar to Motojuku double collapse type cauldrons that occurred before and after the volcanism. In scale model experiments radial fracture system at the central uplift area and "tilted topography" surrounding the collapse were observed. "Connecting fractures" were formed at the same site if uplift areas are more than one. With rise of magma, collapse seems to occur but if the conduit of magma is not reached to the surface, no collapse after eruption occurs. Therefore, whether or not two-stage collapse is formed depends on the volume of magma outpouring to the surface. When multiple large-scale calderas are formed, large depression surrounding the calderas would be created. The shape of the depression is controlled by the arrangement of magma chambers. When the chambers are formed as chain, elongated depression like Kagoshima graben is formed. If cluster of chambers are created wide depression like Beppu-Shimabara graben is formed.
