West Java Mudflows: Natural Dam Collapse – Geologist Report

Bandung, W Java – A series of destructive mudflows that impacted West Bandung on Saturday, January 24, weren’t typical landslides, but the result of a natural dam bursting upstream, a geologist warns. The disaster, which struck pasirkuning, Pasirkuda, and Sukadami hamlets, underscores a continuing threat as similar blockages remain in the region’s river systems.

Mudflow Triggered by Dam Collapse in West bandung

The mudflows were initiated by the collapse of a landslide dam on Mount Burangrang,a sudden release of water and debris from a landslide dam,not conventional slope failures.

• The mudflows were initiated by the collapse of a landslide dam on Mount Burangrang.
• Prolonged rainfall saturated the soil, reducing slope stability and contributing to the dam formation.
• Residents shoudl monitor river flow for sudden changes, like a river disappearing during heavy rain.
• mitigation efforts should focus on debris-flow barriers and monitoring systems,not just reforestation.

Imam Achmad Sadisun, from the Bandung Institute of Technology (ITB), explained that homes weren’t sliding from slopes, but being impacted by a surge of material carried through river channels. “The houses did not slide from the slopes where they stood, instead, they were hit by landslide material delivered from upstream through river channels,” Sadisun told reporters in Bandung on Sunday.

How the Disaster unfolded

The primary cause, according to Sadisun, was a landslide dam on the southern slopes of Mount Burangrang. Collapsed material blocked upstream river channels,creating a natural reservoir. This blockage trapped a notable volume of water, which built up until the saturation point was reached, causing a catastrophic burst. The resulting surge of mud, sand, and large rocks traveled downstream with immense force.

The disaster wasn’t solely attributable to changes in land use. The interaction of old volcanic terrain, thick weathered layers, and sustained rainfall played a crucial role in reducing the soil’s shear strength, allowing the landslide and subsequent dam formation.

Sadisun cautioned that the danger hasn’t passed. Expert teams have identified other potential blockages in upstream sections of the river system. Should heavy rainfall return, these could also fail, sending new waves of debris toward settlements.

Recognizing the Warning Signs

A critical, frequently enough-overlooked warning sign is a change in river flow. Sadisun urged residents along riverbanks to closely monitor water levels. “If a river that usually flows suddenly recedes or disappears during intense rain, it signals upstream damming,” he said, emphasizing the need for immediate evacuation from river channels.

He concluded that effective mitigation requires a multi-faceted approach. Beyond reforestation, he advocates for debris-flow barriers and monitoring systems, such as geophones, stressing that sediment-not just water-causes the greatest damage.

Q: What caused the West Bandung mudflows? A: The mudflows were triggered by the collapse of a natural landslide dam on Mount Burangrang, releasing a surge of water, mud, and debris downstream.