Mount Wrangell

Mount Wrangell

Mount Wrangell is a massive shield volcano located in Wrangell-St. Elias National Park and Preserve in southeastern Alaska, United States.

An ice-filled caldera 4 by 6 km in diameter lies at the top. The caldera was apparently formed by subsidence rather than large explosive eruptions. The caldera is in turn rimmed by three small craters, which often display fumarolic activity with steam plumes that can sometimes be seen from a distance. The volume of Wrangell is over 900 cubic km, making it about twice as massive as large stratovolcanoes such as Mount Shasta in California. A large cinder cone, Mount Zanetti, lies on the flank of Wrangell and is the source of some lava flows.

Wrangell is unusual in that despite being a shield volcano, it is made mainly of andesite rather than basalt, which forms most shield volcanoes in other parts of the world. A few other volcanoes in the Wrangell Volcanic Belt also share this feature. Andesite is a volcanic rock found mainly in stratovolcanoes and tends to form short, stubby flows. How Wrangell grew into a shield volcano is poorly understood, but its lava flows appear to have been voluminous and were also probably generated by high eruption rates.

Wrangell is the only volcano in the Wrangell Volcanic Belt to have had historically recorded eruptions, generally in the form of small steam and ash explosions. The amount of geothermal heat being emitted by Wrangell has been increasing since the 1950s, raising the possibility of a future eruption. Also, the heat flux has been high enough to melt ice around the craters and create ice caves.

Sources

• Siebert L, Simkin T (2002–present). Volcanoes of the World: an Illustrated Catalog of Holocene Volcanoes and their Eruptions. Smithsonian Institution, Global Volcanism Program Digital Information Series, GVP-3 (http://www.volcano.si.edu).
• Global Volcanism Program entry
• Alaska Volcano Observatory