Geological Characterisation and Failure Analysis of a Catastrophic Landslide in Volcaniclastic Soils – the Banjarnegara–Jemblung Landslide (Indonesia)

The Banjarnegara–Jemblung Landslide was triggered on December 12th 2014 near the village of Jemblung in Central Java (Indonesia). The disaster occurred on the northern slope of Mount Gunung Telagalele and caused more than 100 fatalities, leading to the most disastrous landslide in Indonesia during the last decades. The event is characterized by multiple slope failures forming two landslide events A and B, with two connected scarps but two separated runout paths. According to eyewitnesses, landslide A was mobilized only a few minutes after the initial failure of B. Initially, both landslides began as earth slides which subsequently developed into very to extremely rapid earth flows. Although the failure volume was moderate, both slide-flows reached very high velocities of several m/s and long travel distances, leading to remarkable low travel angles of 14 and 15°. Field investigations confirm that slope failure was favoured by geological predisposition based on a slope-parallel layering of volcaniclastic sediments of different origin and age, as well as intensive tropical weathering generating clay-rich soils. Temporal relationships as well as stability analysis indicate that antecedent rainfall over two months and heavy rainfall the day before was triggering the slope failure. Thematic collection: This article is part of the Leading to innovative engineering geology practices collection available at: https://www.lyellcollection.org/topic/collections/leading-to-innovative-engineering-geology-practices