Reference Terms
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Volcanic ash

Volcanic ash consists of very fine rock and mineral particles less than 2 mm in diameter that are ejected from a volcanic vent.

Ash is created when solid rock shatters and magma separates into minute particles during explosive volcanic activity.

The usually violent nature of an eruption involving steam results in the magma and perhaps solid rock surrounding the vent, being torn into particles of clay to sand size.

The plume that is often seen above an erupting volcano is composed primarily of ash and steam.

The very fine particles may be carried for many miles, settling out as a dust-like layer across the landscape.

This is known as an "ash fall".

Unlike the ash that forms from burning wood or other combustible materials, volcanic ash is hard and abrasive, rather than soft and fluffy.

Note:   The above text is excerpted from the Wikipedia article "Volcanic ash", which has been released under the GNU Free Documentation License.
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October 6, 2015

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