A Sequence of the 1997 Sumikawa Landslides and its Indused Debris Flows Ocurred on May 11 at Hachimantai, Kazuno City, Akita Prefecture, Japan

Abstract

In this paper we describe the reasons related to the landslide and debris flow events that occurred in May 11 th of 1997 in Sumikawa area located Hachimantai, Kazuno city, Akita Prefecture, Japan.The environmental factors for these events can be explained on the fact that the area is located in a geothermal field where hydrothermally alteredrocks can be found together with the development of a cap rock conforming the geothermal structure. The topogoraphy of the area give also indications that landslide events occurred several times in the past.The main reasons that triggerd the landslide are considered to be due to a considerable amount of snow that rapidly melted in May of 1997 together with heavy rainfalls with a precipitation of about 110 mm during 24 hours from around 8 pm of May 7 th. These two factors caused an unusual increase in the underground water level with in turn originated the landslide.It is remarkable to mention here that the landslide event that occurred about 8 AM in May 11 th of 1997, triggered debris flow and steam oruptions within several minutes.