The Relationship of Lithology with Landslide Occurrences in Banyumanik and Tembalang Districts, Semarang City

Abstract

Movement of soil and rock masses down the slope or known as landslide is a natural activity that can pose a danger to humans. Generally, landslide can be influenced by the slope, slope materials (rock/soil), and rainfall. Morphologically, the study area, which is located in the borders of Tembalang and Banyumanik Districts, Semarang City, is a hill that is quite steep. It has a potential to experience landslides. Landslide occurences at the study area do not always occur on steep slopes. Therefore, the aim of this study is to determine the relationship between the slope materials and the occurrences of landslide. Data was obtained through mapping to determine geological conditions and enlisting landslide occurrences at the study area. Furthermore, the correlation between the number of occurrences and the type of slope materials at the location of the ground motion was carried out using information value method. Based on geological mapping, 5 types of lithology were obtained, namely: alluvium, breccia, sandstone, siltstone, and claystone. Out of 10 landslides that were found, 6 of them occurred in claystone lithology. We interpret that landslide occurrences in study area are relating to the lithology claystone with information value 0.416. The claystone, a part of the Kerek Formation, physically were easily degraded. In addition, this lithology mostly found in open slopes, where the process of erosion by water is more intense.