Landforms

Volcanoes

An example of the complexity of landforms can be found in the processes that develop volcanoes and volcanic landforms. The tectonic setting determines the chemistry of the lavas and largely the shape of the ensuing volcano. Along colliding ocean plates or ocean and continental plate subduction zones, composite volcanoes are formed, which are often cone shaped and produced by a combination of variably explosive and flowing types of eruption. The classic example of the type of tectonic setting containing composite volcanoes can be found in the Cascade Range in the United States, with Mount St. Helens perhaps [Page 1688]being the most famous volcano. The chemistry of hot spot volcanoes, such as those found on the Big Island of Hawaii, is very different from that of composite volcanoes, and the flowing eruptions most often produce large, low-angled, shield-type volcanoes when the hot spot occurs within ocean plates. Hot spots that develop within continental plates can produce subtle volcanoes such as the Yellowstone (Figure 1) or the Long Valley Caldera in California. These landforms do not look like the classic volcano but are capable of producing tremendous climate-changing eruptions and large-scale landforms such as calderas and pyroclastic deposits that can cover large areas. The chemistry of rift zone volcanism produces flowing eruptions, which often flow over and cover large swaths of land. An example of rift zone volcanics in the United States can be found within the large basalt flows of the Columbia River Basalt Province.

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