Alaska, United States
Mount Wrangell is a massive shield volcano located in Wrangell-St. Elias National Park and Preserve in southeastern Alaska, United States. The shield rises over 12000 feet above the Copper River to its southwest. Its volume is over 220 cubic miles, making it more than twice as massive as Mount Shasta in California, the largest stratovolcano by volume in the Cascades.
An ice-filled caldera 2.5 by 3.7 miles in diameter lies at the top of Wrangell's broad shield. 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 main summit is on the north side of the caldera, while the west summit rises to 14013 feet. The summit region above 13000 feet in elevation is over 2 by 5 miles in size. A very large cinder cone, 13009 feet Mount Zanetti, rises nearly 1000 feet above the northwest 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 Field 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 Field 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.