2.1 Volcano Shape

After completing the weekly reading on volcanoes, you should already have a general idea of the main types of volcanoes:

Shield

Shield Volcanoes are by far the largest types of volcanoes in size due to their extremely broad slopes that can extend for many tens of kilometers. These volcanoes have shallow slopes that are typically formed by runny lavas that are often basaltic (as is the case of Mauna Loa, the largest volcano, in Hawai’i).

a broad low mountain with gently slopes
Figure 2.1.1 The broad shield of Mauna Loa (in the background) rising above the Kīlauea caldera in the foreground. With a summit elevation of 13,677 feet (4169 m) above sea level, Mauna Loa is more than 7,500 feet (2,280 m) in elevation higher than Kīlauea (4,091 feet; 1,247 m). NPS photo by David Boyle, Public Domain

Stratovolcano (AKA, composite)

Stratovolcanoes are large, steep mountains formed by many alternating layers of ash and volcanic rock with a small crater at the top. These are the stereotypical volcanoes imagined in most media and they are known for their violent eruptions with ash, pyroclastic flows, and lava bombs from a source of magma that is usually intermediate in composition.

snow covered volcanic peak
Figure 2.1.2 Iliamna Volcano in Lake Clark National Park. Image courtesy of AVO/USGS. McGimsey, R. G, Public Domain

Cinder Cone

Cinder Cone volcanoes are small, hill-like collections of basaltic ash and scoria, a volcanic rock that erupted with a lot of escaping gas. These are the smallest types of volcanoes, but like stratovolcanoes, they tend to have steep slopes.

cinder cone with trail and few trees
Figure 2.1.3 Cinder Cone volcano in Lassen Volcanic National Park, California (2018). Cinder Cone erupted in approximately 1650 CE (Common Era). NPS photo, Public Domain

and

Caldera

Calderas were once steep volcanoes with a central crater at the top, but they were so explosive due to the rhyolitic magma in their chambers, that a violent eruption caused the volcano dome to collapse inward forming a huge crater. These craters are often infilled with water or become volcanic crater lakes, but don’t be fooled – they are often still active volcanoes!

aerial photo of a summit caldera, with a deep crater and snow and clouds
Figure 2.1.4 Aniakchak Caldera in Aniakchak National Monument on the Aleutian Peninsula in Alaska was formed by a Colossal (VEI 6) eruption 3,700 years ago at the site of a former composite volcano. The preexisting volcano was largely destroyed when its summit collapsed. NPS photo by M. William, Public Domain

Return to the reading to review these if you forget the difference between them. Otherwise, you will test your knowledge of them in these next exercises!

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