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Dig into Montana Before History: 11K Years of Hunter-Gatherers in the Rockies and Plains by D. H. MacDonald, Ph.D. See our online store book collection.
Redoubt Volcano, Alaska (USA) during a continuous, low-level eruption of steam and ash on December 18, 1989.
Courtesy of USGS

Volcanic Ash

Ash is made of millions of tiny fragments of rock and glass formed during a volcanic eruption. Volcanic ash particles are less than 2 mm in size and can be much smaller.

Volcanic ash forms in several ways during eruptions. Sometimes gas is released from the underground magma chamber which shatters rock into the tiny pieces that make up ash. Sometimes, newly-formed volcanic rock shatters into ash when it comes into contact with water or ice and cools quickly.

Falling ash can sometimes cause more damage than flowing lava because ash can be carried great distances through the atmosphere. Volcanoes have a cooling effect on weather because the ash remains in the sky and reduces the amount of sunlight reaching the surface. Ash however, also carries important nutrients to the soil on which it finally lands.


Last modified April 19, 2010 by Lisa Gardiner.

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Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA