A hydrochemical study of Hungtsaiping landslide area, Nantou, Taiwan

The Hungtsaiping landslide was triggered by the Chi-Chi earthquake (Mw?=?7.6), which occurred on September 20, 1999 near the town of Chi-Chi in Nantou County in central Taiwan. The purpose of this study is to understand the relationship between geochemical characteristics and the landslide in the Hungtsaiping area. Water samples were collected from springs, creeks, ponds, groundwater and the Yonglu stream once every month from May 2008 to May 2009. Oxygen and hydrogen stable isotopes, ionic concentrations, electrical conductivities, and pH values were analyzed. The results show that the ionic concentrations display a significant spatial variation. For instance, calcium and magnesium bicarbonate-rich water was found on the top and the middle part of the slope. In addition, sodium bicarbonate-rich water with exceptionally high sulfate concentration was found on the foot of the slope. The sulfate content decreased with increasing elevation along the slope. Finally, a conceptual model was established by summarizing the hydrogeochemical analyses. After a scientific understanding of the mechanism of the Hungtsaiping landslide, all of the analytical information can be integrated for hazard prevention in the future.