Chapter 4 Volcanism
4.3 Types of Volcanoes
There are numerous types of volcanoes or volcanic sources; some of the more common ones are summarized in Table 4.1.
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| Type | Tectonic Setting | Size and Shape | Magma and Eruption Characteristics | Example |
|---|---|---|---|---|
| Cinder cone | Various; some form on the flanks of larger volcanoes | Small (10s to 100s of metres) and steep (Greater than 20°) | Most are mafic and form from the gas-rich early stages of a shield- or rift-associated eruption | Eve Cone, northern B.C. |
| Composite volcano | Almost all are at subduction zones | Medium size (1000s of metres high and up to 20 km across) and moderate steepness (10° to 30°) | Magma composition varies from felsic to mafic, and from explosive to effusive | Mount St. Helens |
| Shield volcano | Most are at mantle plumes; some are on spreading ridges | Large (up to several 1,000 metres high and up to 200 kilometres across), not steep (typically 2° to 10°) | Magma is almost always mafic, and eruptions are typically effusive, although cinder cones are common on the flanks of shield volcanoes | Kilauea, Hawaii |
| Large igneous provinces | Associated with “super” mantle plumes | Enormous (up to millions of square kiometres) and 100s of metres thick | Magma is always mafic and individual flows can be 10s of metres thick | Columbia River basalts |
| Sea-floor volcanism | Generally associated with spreading ridges but also with mantle plumes | Large areas of the sea floor associated with spreading ridges | Pillows form at typical eruption rates; lava flows develop if the rare of flow is faster | Juan de Fuca ridge |
| Kimberlite | Upper-mantle sourced | The remnants are typically 10s to 100s of metres across | Most appear to have had explosive eruptions forming cinder cones; the youngest one is dated at about 10 ka, and all others are at least 30 Ma | Lac de Gras Kimberlite Field, N.W.T. |
The sizes and shapes of typical shield, composite, and cinder-cone volcanoes are compared in Figure 4.3.1, although, to be fair, Mauna Loa is the largest shield volcano on Earth; all others are smaller. Mauna Loa rises from the surrounding flat sea floor, and its diameter is in the order of 200 km. Its elevation is 4,169 m above sea level. Mount St. Helens, a composite volcano of average size, rises above the surrounding hills of the Cascade Range. Its diameter is about 6 km, and its height is 2,550 m above sea level. Cinder cones are much smaller. On this drawing, even a large cinder cone is just a dot.
Cinder Cones
Cinder cones, like Eve Cone in northern B.C. (Figure 4.3.2), are typically only a few hundred metres in diameter, and few are more than 200 m high. Most are made up of fragments of vesicular mafic rock (scoria) that were expelled as the magma boiled when it approached the surface, creating fire fountains. In many cases, these later became the sites of effusive lava flows when the gases were depleted. Most cinder cones are monogenetic, m