GEOLOGIC / GEOMORPHIC FRAMEWORK:
Located within a 200 km wide seismically active zone of Neogene left-lateral strike-slip deformation, this is an area of neotectonic landforms.
Bedrock is composed of Cretaceous to Eocene andesitic volcanics, volcaniclastics, and a sequence of thinly bedded shales and mudstones.
Geological map / Landslide inventory map
The geologic structure is controlled by faults.
Hydrothermal alteration and base metal mineralization has been recorded.
Bedrock is deeply weathered and is overlain by a regolith, 1-2 m thick, and is generally clay-silt.
Apart from patches of forest, the slopes are covered by scattered trees and scrub.
Ruinate land is common.
The hillslopes are steep, generally between 20 to 30 degrees and valley alignment is fault controlled.
The relief between the ridge crests and the valley bottoms ranges from 100 to 250 m.
Debris fans are common along the base of short and steep 2nd and 3rd order streams where they soften the relief.
Mass- movement-scarred hillslopes are characteristic.
Landslides are triggered both by earthquakes and rainfall.
Short-duration, high-intensity rainfall (Such as the January 1998 event) causes shallow soil slips and debris flows, whereas long-duration events, such as tropical storms, could be followed additionally by larger and bedrock slides.
Landslides supply a large amount of sediment to the rivers.
Boulder accumulations are common in the channels.