Kenzo Kiho

Deep-seated rockslide-avalanches preceded by mass rock creep of sedimentary rocks in the Akaishi Mountains, central Japan

Abstract Seven large rockslide-avalanches of sedimentary rocks are known in Japan. Almost all of these major landslides were preceded by gravitational deformation of rocks (mass rock creep, MRC), as inferred from geologic and geomorphic investigations of five rockslide-avalanches in the Akaishi Mountains. The MRC that preceded the rockslide-avalanches in the Akaishi Mountains was characterized by a slow but steady downslope bowing of steeply dipping foliations, which accompanied intensive deformation and fragmentation of the rock mass by shearing along foliations. This deformation and fragmentation of the rock mass provides a basic cause for the occurrence of rockslide-avalanches, which occur when a creeping rock mass has lost its support from the lower part of a slope by stream erosion. This type of MRC continues for a long time after a part of the creeping area has slid and results in longterm generation of debris by the landslide sear of the rockslide-avalanche.

Dynamic changes in hydrogeochemical conditions caused by tunnel excavation at the Aspo Hard Rock Laboratory (HRL), Sweden

Abstract Hydraulic changes caused by tunneling at the Aspo Hard Rock Laboratory (HRL) in Sweden have been investigated over a period of 2a using different hydrochemical approaches, i.e. noble gas content, isotopic measurements and major ion concentrations. The dissolved noble gases (4He and Ne contents, and the ratio of 3He/4He, 40Ar/36Ar), stable isotopes, chemical concentrations of major ions, and 36Cl/Cl ratios, were determined in groundwater samples collected in the tunnel from borehole sections isolated by inflated packers. Groundwater was categorized into 3 groups based on 4He and Cl− contents: undisturbed groundwater (i.e. prior to tunnel construction) with high 4He and Cl− contents, groundwater that has been gradually changed by mixing with Baltic seawater and whose 4He and Cl− contents have gradually increased with increasing depth, and groundwater that has been totally changed due to a rapid mixing of Baltic seawater and/or shallow groundwater and whose 4He and Cl− contents are extremely low compared with other samples collected at the same surrounding depth. The oldest groundwater with a high salinity of more than 14,000xa0mg l−1 of Cl− is estimated to be more than 1.8 Ma old. The groundwater residence time ranges from 0.9 to 900 Ka in the mixing-zone. Groundwater in the disturbed zone where rapid mixing has occurred is hard to date reliably and its primary hydrochemical character has already been lost.

Present status of the Ogachi HDR Project, Japan, and future plans

Abstract CRIEPI initiated the Ogachi project in the northern part of Japan in 1986, to determine the feasibility of an HDR geothermal power plant based on a multi-layer reservoir. During the past eleven years technologies have been developed for surveying underground resources, forming multi-layer reservoirs and evaluating these reservoirs in a 1.4 billion yen study. Future plans include the development of a lifespan evaluation method, the improvement of production rates and finally, the establishment of an actual HDR power plant.