A drastic change of landforms caused by a huge pyroclastic flow in the hida district, central japan

Six huge pyroclastic flow eruptions from the Hida Mountains occurred in and around the Takayama Basin during the Plio-Pleistocene. These eruptions were related to the uplift of the Hida Mountains and it was expected that these would have markedly changed the landforms of the area. However, there is a scarcity of information on the details of this. In this study, we describe the landforms of the area before and after the eruption of the Kamitakara Pyroclastic Flow during the Middle Pleistocene in the southwest of the Hida Mountains. In the northeast of the Takayama Basin, the Uwano Mudflow Deposit and the Kiriyama Gravel Bed which show the flow path of the "paleo-Ausa River", are covered with the Kamitakara Pyroclastic Flow Deposit. We searched for corresponding deposits to these from the Takayama Basin to the Hida Mountains. There was a valley through which the "paleo-Azusa River" flowed from Kamikochi into the Takayama Basin before the eruption of the Kamitakara Pyroclastic Flow. The cross section of this valley was very wide. The "paleo-Azusa River" was later forced to change its path by the deposition of the Kamitakara Pyroclastic Flow