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Background On 21 February 2005 the Leuwigajah dumpsite, Bandung (Java, Indonesia) was affected by a large slide after heavy rainfalls. Second deadliest waste slide in history, it buried 71 houses and killed 143 people. Amongst the contemporary disastrous events of this type, only a few have been documented. We explored failure preconditions, triggering mechanisms and local context that conducted to this disaster. We carried on four field investigations on the site. A series of aerial photographs were acquired and completed by topographical measures on the ground. The morphology of the slide and its trajectory were reconstructed. To constrain the movement condition, we studied the internal structure of the source area and realized surveys among stakeholders of the dumpsite and citizen. Results 2.7 × 10 6  m 3 of waste materials spread 1000 m from the source in a rice field with an average thickness of 10 m. The material displays a preferential fabric parallel to the previous topography. Numerous internal slip surfaces, underlined by plastic bags explain the low friction coefficient. The presence of methane within the waste dump was responsible for explosions prior to sliding and for the fire that affects whole sliding mass. Conclusions Resulting of a combination of heavy rainfall and consecutive explosions due to biogas sudden release, this disaster was predictable in reason of i) a front slope of the dump of about 100% before the failure; ii) a poor dumpsite management; iii) the extreme vulnerability of the marginalized scavengers living at risk at the foot of the instable dump.

Cilengkrang is a sub-village in the north of Ujung Berung and Cijambe sub-District Bandung Regency, Indonesia. It is located on the west of Cikeruh sub-watershed. This subwatershed is part of greater upstream Citarum watershed. This area has been developed rapidly by new settlement and villa. However, the available data of erosion potential in this area is less convenient. The erosion is a severe problem that has a strong relation to flood potential. This study starts with collected engineering geological data from 14 samples. These samples were taken from different soil types from its engineering characteristics. Based on the field and laboratory observation, this area is form by fine-grained soils as a result of residual soils from young volcanic rocks - the silt and very fine sand content range from 49 to 70 % of the total soil. The erodibility value (K) in this area is from 0.03 to 0.06. These values are indicating moderate soil erodibility class. The plasticity index (PI) also shows value from 9 to 48 %. This value is pointing low to high plasticity behavior of this soil. The regression linear shows strong correlation between PI and K with r = 0.7. This correlation is interpreted that the cohesion controls the soil characteristic in Cilengkrang area and affect the moderate erodibility value. This study hopefully giving new insight that soil mechanic data is can also support data on erosion potential.

A multivariate statistical technique of principal component analysis (PCA) and hierarchical cluster analysis (HCA) has been applied to identify and classify the various water sources that comprise the Rawadanau Basin. The data collection includes 60 samples taken during the dry (29 samples) and the rainy season (31 samples) in tropical regions. Sources of sampled water include dug wells, rivers, cold springs, and hot springs. Water chemistry measurable variables include field data (T, pH, EC), major ions (Na+, K+, Ca2+, Mg2+, Cl-, HCO3 -, SO4 2-), SiO2 , Fetotal, Mn, and stable isotopes of water (δ2H, and δ18O). The correlation of the concentration of water chemistry shows changes in the rainy season to Fetotal and Mn. Interpretation based on HCA using the dendrogram based on the chemical elements of water produces two clusters. Cluster A reflects an unconfined aquifer and bicarbonate type. Meanwhile, cluster B is a chloride type from the confined aquifer and does not change in different seasons. The PCA results show that the three-component matrix accounts for 86.12% of the data structure describing the Rawadanau Basin water sources that volcanic rocks affect and strongly correlate with Na+, K+, Ca2+, and Mg2+. PC1 has a high positive value for hydrochemical composition, indicating that lithology influences the kind of water. PC2 has a positive value for the stable isotope (δ18O and δ2H), meaning it is the main water source in Rawadanau. PC3 has a positive value for elevation and a negative for longitude, indicating a recharge area influenced by geological factors and is correlated with geothermal influences and volcanic rocks. This multivariate analysis can identify components and clusters of hydrochemical variables that have not been determined in previous studies.