Figure 7.3.2 Eve Cone, Which Rises About 170 m Above the Surrounding Plateau, Formed Approximately 700 Years Ago. Because cinder cones are made up almost exclusively of loose fragments, they have very little strength and can be easily, and relatively quickly, eroded away. Most cinder cones are monogenetic, meaning that they were created during a single eruptive phase that might have lasted weeks or months. Most are comprised of fragments of vesicular mafic volcanic rock that were blasted out during a high-gas-pressure early phase of an eruption that may have subsequently become effusive (lava flows). Helens), and a Large Cinder Cone Cinder ConesĬinder cones, like Eve Cone in northern BC (Figure 7.3.2), are typically only a few hundred metres in diameter and few are more than 200 m high. Figure 7.3.1 Profiles of a Shield Volcano (Mauna Loa and Kilauea), a Composite Volcano (Mt. On this drawing even a large cinder cone is just a dot. It is about 6 km across at the base, and its height is 2550 m above sea level. Helens, a composite volcano, rises above the surrounding hills of the Cascade Range.
#Shield volcanoes diagrams full#
Mauna Loa rises from the surrounding flat sea floor, and its full diameter is in the order of 200 km, with a diameter of about 100 km above sea level. The sizes and shapes of typical shield, composite and cinder-cone volcanoes are compared on Figure 7.3.1, although, to be fair, Mauna Loa is the largest shield volcano on Earth, all others are smaller. The youngest one is over 10 ka, and all others are over 30 Ma. Most appear to have had explosive eruptions forming cinder cones. The remnants are typically 10s to 100s of m across Most of the oceanic crust formed at spreading ridgesĪt normal eruption rates pillows form. Generally associated with spreading ridges but also mantle plumes Individual flows can be 10s of metres thick Magma is almost always mafic, and eruptions are typically effusive, although cinder cones are common on the flanks of shield volcanoesĮnormous (up to millions of km2) and 100s of m thick Large (up to several 1000 m high and 200 km across), not steep (typically 2 to 10°) Most are at mantle plumes, some on spreading ridges Magma composition varies from felsic to mafic, and from explosive to effusive Medium size (1000s of m) and moderate steepness (10 to 30°) Most are mafic and form from the gas-rich early stages of a shield- or rift-associated eruption Small (10s to 100s of m) and steep (>30°) Some form on the flanks of other volcanoes Table 7.3.1 Summary of Common Types of Volcanism Type There are numerous types of volcanism some of the more common ones are summarized in Table 7.3.1.
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