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Ecological Types


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Alluvium, Alluvial Fans: Alluvium is soil material, in this case glacial silt and volcanic ash, sand, cinders and gravel, that is carried by streams. It is deposited on the stream's flood plain which is often in the form a fan.

Debris Avalanche: Volcanic eruptions often build deposits of lava or pyroclastic material that are beyond their angle of repose and are unstable. Eventually they will move down slope under the force of gravity often in a catastrophic event where large masses of rock may become dislodged and sweep down the mountainside. These events usually occur during or shortly after a volcanic eruption.

Dissected: When streams flow downslope they create valleys. A dissected slope is one with stream valleys.

Glacial Outwash: Glaciers are constantly moving and grinding rock into sand and silt. The melt water from glaciers carry this material in streams downslope to the streams's flood plain. At the end of the last glacial period, about 10,000 years ago, the glaciers were much larger than they are today and the warming that ended the glacial period led to accelerated melting. Glacial melt waters came down the mountain side in torrents and carried huge volumes of soil material that created the outwash plains that we see today.

Lahar: A lahar is a flow of ash, cinders or pumice that occurs during a volcanic eruption.

Mudflow: Mudflows usually occur when a volcanic eruption melts part of a glacier and the torrent of meltwater rushes down the mountain side carrying ash, sand, cobbles and boulders. It is similar to outwash except that is occurs in a single, catastrophic event. Sometimes climatic causes can trigger mudflows. In 1924 the Konwakiton Glacier experienced unusual melting in the hot weather. The meltwater became dammed behind a landslide. When the dam gave way the torrent of water that was released behaved much like a volcanically triggered mudflow. Whitney Creek experienced a mudflow event in 1998.

Pumice: Pumice is volcanic material that, when it is ejected to the surface, puffs up with air. It is light and cinder-like. It can occur as material that is blown into the air or as material that will flow like lava.

Pyroclastic: Pyroclastic material is a class of materials including ash, cinders and pumice.


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