The primary cause of the large landslide in Hachimantai, Akita Prefecture on May 11, 1997 is considered to be heavy rainfall of 110 mm/day on the 8 th three days prior to the landslide. However, the occurrence of this landslide cannot be explained by this rainfall alone because such events occur every 7 to 8 years, according to the Gambel-Chow method for the last 19 years meteorological data. In addition to the heavy rainfall , continuously supplied meltwater from snow pack is also thought to

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... ve played an important role in the occurrence of this landslide. Therefore, we estimated the rate of meltwater flow by the heat balance method using the AMeDAS data set of the Meteorological Agency to clarify the meltwater conditions prior to the landslide . Our calculations showed that the 30 -50 mm/day of meltwater in late April rose to 40 -60 mm/day in the beginning of May due to the seasonal increase of heat fluxes. On May 8, 170 mm of water which consisted of 110 mm of rainfall and 60 mm of meltwater was assumed to have flowed out from the snow pack to the ground . As a result of calculations of meltwater for 19 years and subsequent comparision between meltwater and rainfall of each year and analysis of probable distribution of the annual maximum daily values, it was revealed that the 170 mm of [meltwater+rainfall] flow on May 8 occurs only once every 70 -80 years.