長野県地附山地すべり地における天然水の化学成分および同位体組成について

Abstract

A large-scale landslide took place at a southeastern slope of Mt. Jizuki, Nagano Prefecture, on July 26, 1985. It has been said that landslide is closely related to the hydrological and hy-drogeochemical nature of groundwater involved.To investigate the weathering mechanism and the origin of groundwater, we collected andanalyzed water samples from the large-scale landslide area. The following facts can be pointedout: (1) weater-rock interaction is remarkably active in the landslide area, (2) most of the watersfrom the landslide area are in equilibrium with Na-montmorillonite (3) immediately after the land-slide occurred bicarbonate and sodium ions are dominant, but sulfate and sodium ions becomedominant with time, and (4) groundwater passing through horizontally drilled holes does noteffectively drain off to stabilize a slope in the landslide area.And our hypothesis on the mechanism for the formation of sodium sulfate type water is alsopresented.