Laharid

Laharid is a term used in volcanology and sedimentology to describe phenomena and deposits associated with lahars, i.e., volcanic mudflows composed of water-saturated volcanic debris that travel down the slopes of a volcano. The term is typically used adjectivally to refer to materials or processes that resemble or are produced by lahars.

Lahars form when volcanic ash and other debris mix with sufficient water, often as a result of eruptions melting snow and ice, heavy rainfall, or lake outburst; this mixture behaves as a fluid and can move rapidly downslope.

Typical laharid deposits are poorly to moderately sorted and range widely in grain size from clay to boulder, commonly displaying a matrix-supported fabric and bedforms that indicate rapid flow, such as cross-bedding, graded bedding, or levees along channel deposits. They can occur as cohesive flows or as more dilute currents depending on water content.

Laharid events can devastate river valleys and populated areas and may occur during or after eruptions. Modern hazard assessment relies on monitoring volcanic activity, rainfall, and snowmelt, with early warning systems, lahar channels, and barriers to reduce impact.

See also: Lahar, Volcanic hazard, Debris flow