GEOMOPHOLOGICAL CHANGES OF LANDSLIDES DUE TO PHYSICAL WEATHERING AFTER HEAVY RAINS—A CASE IN TAIWAN

This paper attempts to utilize sequence analysis to study the near-surface geomorphological changes of landslides, to better understand the pattern and the evolution of the physical weathering after heavy rains.

Landslide may occur repeatedly at the same place. Sequence analysis of ground penetrating radar data may infer the past unmonitored evolutional geomorphological pattern changes due to physical weathering of landslides after heavy rains in the Suankeng landslides of Taiwan. (1) Abundant surface fissures in the upper part of the original slope and the crown area caused heavy rain to filter easily. The infiltrated water increased the weight of the crown area and enhanced the pressure of the pore water, resulting in an easy slide, due to gravity traction, of the sliding scarp and the related slide block. The time was July 1, 1997. (2) Later, the same precipitation intensity generated mobile soil. The soil moved from the crown area and covered the area between the sliding scarp and the related slide block. Partial colluvial deposits covered the related slide block. (3) Continuous precipitation in late July 1997 caused the sliding of strata and then a small-scale collapse. The depth of the landslide was greater than that of the landslide on July 1, 1997. (4) Heavy rain lasted during the period to the first 10 days of September, causing a relatively small-scale collapse. The slide surface with low dip of the small-scale collapse might be the slide surface generated in the last 10 days of July 1997. However, the slide surface with high dip is located in the upper part of the side slope. The shape of the slide surface generated in the last 10 days of July 1997 changes from a single shape to the multiple type. (5) During the period from the last 10 days of July 1997 to the first 10 days of September, heavy rain caused partially mobile colluvial deposits to accumulate from the upper side slope. Therefore, the slide mass and the sliding scarp in that position were covered with a layer of colluvial deposits. (6) In the following year, the second large-scale landslide occurred on February 20, 1998. After the landslide, a large amount of colluvial deposit was accumulated in the upper side slope.