A mudflow composed of water and volcanic ash. Lahars can be triggered by the flash melting of the snow cap of a volcanic mountain or from heavy rain. Lahars are very dangerous because they can occur suddenly and travel at great speeds.
an Indonesian word that refers to a rapidly flowing mixture of rock debris and water (other than normal water flows) from a volcano. When they overflow their channels, lahars can destroy, erode or bury obstacles in their path. There are various kinds of lahar. A debris flow lahar (the type expected in the current situation) flows like a slurry and contains large amounts of sediment (more than 60 per cent of volume) of varying size (from small particles to boulders). A hyperconcentrated flow lahar contains less sediment, mainly of sand-sized or smaller particles, and flows more like water. Lahars are produced by most eruptions on Ruapehu but also by dam or rim collapse (eg 1953), landslides and heavy rain. Some very recent pre-historic lahars have been very much larger then any seen in historic times.
An Indonesian term for a debris flow containing angular clasts of volcanic material. For the purposes of this report, a lahar is any type of sedimentwater mixture originating on or from the volcano. Most lahars move rapidly down the slopes of a volcano as channelized flows and deliver large amounts of sediment to the rivers and streams that drain the volcano. The flow velocity of some lahars may be as high as 20 to 40 meters per second and sediment concentrations of greater than 750,000 parts per million are not uncommon. Large volume lahars can travel great distances if they have an appreciable clay content (greater than 3 to 5 percent), remain confined to a stream channel, and do not significantly gain sediment while losing water. Thus, they may affect areas many tens to hundreds of kilometers downstream from a volcano.
a massive flood of water mixed with mud and vegetation, triggered by volcanic activity. Can be from the sudden draining of a crater lake, or from volcanic heat suddenly melting snow and ice that previously capped the volcano.
A Lahar is a type of natural disaster closely related to a volcanic eruption, and involves a large amount of material, including mud, rock, and ash sliding down the side of the volcano at a rapid pace. These flows can destroy entire towns in seconds and kill thousands of people. The Tangiwai disaster is an excellent example.
is a mudflow or debris flow originating on a volcano. Jokulhlaups (see above) often become lahars when they incorporate the rock debris that lies within their path. Lateral Moraine A moraine formed at the side of a glacier. Piles of loose unsorted rocks along the side margins of the glacier. The rocks may be pushed there by the moving ice or dumped from the glacier's rounded surface.
A a torrential mudflow of water mixed with volcanic debris.
landslide or mudflow of pyroclastic material on the flank of a volcano; deposit produced by such a landslide. Lahars are described as wet if they are mixed with water derived from heavy rains, escaping from a crater lake or produced by melting snow. Dry lahars may result from tremors of a cone or by accumulating material becoming unstable on a steep slope. If the material retains much heat, they are termed hot lahars. AGI