Pengaruh Alterasi Hidrotermal Terhadap Kestabilan Lereng dan Mekanisme Gerakan Tanah Daerah Patuhawati, Provinsi Jawa Barat

Abstract

Landslide disaster that occured in Dewata Tea Plantation has killed 70 people and more than 50 houses buried. This research project located at Patuhawati area which has a high susceptibility and vulnerability hazard. Most of Patuhawati area are covered by volcanic material of Mount Patuha that have been altered by intensive hydrothermal alteration. This research is carried out to explain about the influences of hydrothermal alteration to slope stability and the mechanism of landslide in such geologic condition.

Research methods consist of several stages. First step are preparing and collecting all secondary data which relate to the research topic, and the second is collecting the primary data by conducting some detail surface mapping, such as observing and measuring the slope of morphology, litology, landslide point scarp, alteration zone, geological structure and land use. The third stage is conducting several laboratory analysis of soil engineering properties, XRD and petrography.

AHP method is used as data analysis. As a semi quantitative method, AHP analysis is conducted by give some variation of weight value on matrix comparison to understand the most influence factor that controlling landslide. The result show that hydrothermal alteration factor is 2,68 times more influential than geological engineering, morphology, and structural geology factor, and 7,03 times more important than landuse factor. Each sub parameter is given score between 1-3 as their influence to landslide. Susceptibility weighted value then multiple by sub parameter score to conduct susceptibility map by using spatial analysis (weighted overlay) in ArcGIS. The verification result show that the most susceptible zone has the highest number of landslide point. The second conclusion is argilic alteration gives more influence than sub propilitic alteration to controlling landslide. It happens because of physical properties of clay mineral of argilic which is decreasing shear strength of slope material. Mechanism of landslide in Cicacing is rotational landslide where high level of rain fall infiltration as a main triggering factor, beside the earthquake.