Mudflow

A mudflow or mud flow is a form of mass wasting involving "very rapid to extremely rapid surging flow" of debris that has become partially or fully liquified by the addition of significant amounts of water to the source material.

Mudflows contain a significant proportion of clay, which makes them more fluid than debris flows; thus, they are able to travel farther and across lower slope angles. Both types are generally mixtures of various kinds of materials of different sizes, which are typically sorted by size upon deposition.

Mudflows are often called mudslides, a term applied indiscriminately by the mass media to a variety of mass wasting events. Mudflows often start as slides, becoming flows as water is entrained along the flow path; such events are often called flow slides.

Other types of mudflows include lahars (involving fine-grained pyroclastic deposits on the flanks of volcanoes) and jökulhlaups (outbursts from under glaciers or icecaps).

A statutory definition of "flood-related mudslide" appears in the United States' National Flood Insurance Act of 1968, as amended, codified at 42 USC Sections 4001 and following.

Heavy rainfall, snowmelt, or high levels of ground water flowing through cracked bedrock may trigger a movement of soil or sediments. Floods and debris flows may also occur when strong rains on hill or mountain slopes cause extensive erosion and/or what is known as "channel scour". The 2006 Sidoarjo mud flow may have been caused by rogue drilling.

Some broad mudflows are rather viscous and therefore slow; others begin very quickly and continue like an avalanche. If large enough, they can devastate villages and countrysides. They are composed of at least 50% silt and clay-sized materials and up to 30% water. Mudflows are common even in the hills around Los Angeles, California, where they have destroyed many homes built on hillsides without sufficient support after fires destroy vegetation holding the land.

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