[HGM03-08] A sinkhole emerged at the foot of the scarp of Matoishi Bokujo I Fault, northwest of outer rim of Aso caldera
Keywords:sinkhole, outer rim of Aso caldera, pyroclastic flow deposit surface, fault scarp
In November 2019, it was discovered that a new sinkhole with a diameter of about 3 m had been formed at the foot of the Matoishi Bokujo I fault. The depth was about 4 m, the inside was about 5 m wide, and the length was at least 10 m, gently dipping to the south. No clear channel was found in the hole. On the inner wall of the hole, a sandy and muddy black ash containing a lot of breccia appeared at the upper part, and a white sediment likely to originate from pyroclastic flow deposits appeared at the lower part. The white sediment is cut into a south-drop fault, and the black ash layer is deformed to increase the slope to the north. These characteristics were consistent with observations from a pit survey conducted approximately 200 m east of this site (Une et al., 2019).
In this report, we will discuss the geomorphology of the sinkhole, its origin, and its relation to fault activity, including the results of subsequent surveys.