Mud Flow

Unique identifier / Notation

MH0051

Synonyms

Hyperconcentrated flow,

Land slide,

Debris flow.

A mud flow is a flow of water so heavily charged with sediment and debris that the flowing mass is thick and viscous (WMO and UNESCO, 2012).

Primary reference(s)

WMO and UNESCO, 2012. International Glossary of Hydrology. WMO-No.385. World Meteorological Organization (WMO) and United Nations Educational, Scientific and Cultural Organization (UNESCO). Accessed 13 October 2020.

Additional scientific description

A flow is a spatially continuous movement in which the surfaces of shear are short-lived, closely spaced, and usually not preserved. The component velocities in the displacing mass of a flow resemble those in a viscous liquid. Often, there is a gradation of change from slides to flows, depending on the water content, mobility, and evolution of the movement. Debris flows and mudflows usually occur in small, steep stream channels and are commonly mistaken for floods (Highland and Bobrowsky, 2008). Metrics and numeric limits Not available.

Metrics and numeric limits

Not available.

Key relevant UN convention / multilateral treaty

Not identified.

Examples of drivers, outcomes and risk management

Possibly one of the most significant mudflow events in recent times was reported from Indonesia.

On 29 May 2006, hot mud and gas began gushing from a rice field near a gas exploration well in East Java. More than a decade later, the Lusi mud flow continues on the Indonesian island (NASA, 2019).

Over the years, flows of boiling mud from the Lusi Mud Flow have displaced more than 40,000 people, destroyed 15 villages, and caused nearly USD 3 billion in damage (NASA, 2019).

The Lusi eruption has become one of the most dramatic and damaging eruptions of its type. Some villages have been buried by layers of mud 40 metres (130 feet) thick. The mud, which has a consistency similar to porridge, pours constantly from Lusi’s main vent. Every thirty minutes or so, surges in the flow send plumes of water vapour, carbon dioxide, and methane shooting tens of meters into the air (NASA, 2019).

In the early years of the eruption, mud oozed over homes, factories, highways, and farmland. Now it spreads within a network of earthen levees, retention ponds, and distribution channels that form a rectangular grid around the main eruptive vents. Channels direct the mud into holding ponds to the north and south. Large volumes of mud get flushed into the Porong River, which flows east toward the Bali Sea (NASA, 2019).