“ Hawaiian Islands” by NASA’s Earth Observatory is licensed under Public Domain. These areas include hot spots, mid-ocean ridges, and continental rift zones. We typically observe shield volcanoes in areas where the upper mantle rises to meet the crust. Shield volcanoes are sourced from low- viscosity mafic magma, and they typically have basaltic lava that has reached far distances along the volcanic slope. The word “shield” refers to the shield-like shape of the volcano when it is viewed from the side. These are characterized by very broad, shallow slopes, and small vents. The largest type of volcano is a shield volcano. The Sierra Grande shield volcano at Capulin Volcano National Monument, New Mexico. Click this image to go to an interactive model of the volcano and surrounding landscape by Sara Carena, CC BY-N-SA. Check out the interactive model of Mt St Helens, below Fig. There, an ancient subduction zone used to exist between the North American plate and Farallon plate which formed the Cascade Mountain range and deadly stratovolcanoes including Mount Rainier and Mount St Helens. A good example of these volcanoes can be found along the Pacific Northwest. Stratovolcanoes usually form along subduction zones between oceanic-oceanic or continental-oceanic lithosphere. Stratovolcanoes can have magma that is anywhere from felsic to mafic in composition, although most of these volcanoes tend to be intermediate in composition. These are called “composite” or “strato” because of the different layers of volcanic materials (such as ash) and lava that build up the volcano. Stratovolcanoes (also called composite volcanoes) have steep sides and a symmetrical cone shape with an easily identifiable crater on top. Helens, Mount Vesuvius, Mount Fuji, Mount Pinatubo, Krakatoa-all of these infamous volcanoes belong to a frightening class of volcanoes that are historically known for their destruction and hazards. Helens, Mammoth Mountain in California, and Chaiten in Chile (see above image). The dome-like structure is the result of the high- viscosity of the felsic to intermediate lava, which is too sticky to move long distances. These domes are made of extrusive rocks such as rhyolite, pumice, and obsidian that are piled around the vent. Lava Domes are fairly small structures made of felsic rocks that form within the collapsed craters of stratovolcanoes. A rounded dome of lava above a central volcanic crater of Volcán Chaitén, Chile. Because they are usually mafic in composition, they produce extrusive igneous rock deposits such as scoria. Larger tephra rocks (over 2.5 inches) are called volcanic bombs, which are potentially deadly to anyone within range.Ĭinder cone volcanoes do not last relatively long, but they are common in the United States and Mexico. Cinders are smaller pieces of tephra, or molten rock, that will erupt with lava from the volcano and rapidly cool and solidify in the air. Cinders themselves are composed primarily of mafic lava with more volatile gases than average. Schematic of a typical cinder cone volcano.Ĭinder cones are small volcanoes with steep sides, made of tephra and volcanic bombs ejected from a clear central vent. Below, we will explore the different types of volcanoes on our planet. However, that is where the similarities end. Magma chambers, cones, craters, chimneys, and lava are features that are diagnostic of volcanoes. When the magma reaches the surface, it is called lava, even though the composition does not change. The molten rock and volatile gases explode upward through a pipe-like column called a chimney. When the magma chamber experiences too much pressure, it will erupt. The composition of this magma can vary from felsic to mafic depending on factors such as region, overlying crust composition, and tectonic setting. All active volcanoes sit atop a plume of magma called a magma chamber. At the very top of this cone is a crater. Volcanoes have a cone-shaped structure that has been built over long periods of geologic time after multiple eruptions. “ Volcano Structure” is licensed under Creative Commons Attribution-ShareAlike 4.0 International. However, all volcanoes should be regarded as potentially deadly! Fig. There are several broad types of volcanoes based on their shape, eruption style, magma composition, and other aspects. There are all types of volcanoes on our planet: some are huge, some are no bigger than hills, some are explosive, and some are less so.

Shield volcanoes diagrams