The photo above is of Krafla Volcano on the island of Iceland. It covers almost 100,000 square miles and is almost a mile thick in places. The Columbia Plateau of the western United States is the largest lava plateau in the world. The Deccan Plateau of India was formed this way and covers 100,000 square miles (A little smaller than the state of Montana). These volcanoes erupt many times over the same area forming huge, and thick lava plateaus. Shield cones are very low and very broad shaped volcanoes. The type of cone produced from icelandic eruptions is a shield cone. Some of these fissures can be up to 15 miles long. The lava comes out of the ground through long cracks in the surface called fissures. Icelandic, flood, or fissure eruptions are all terms for volcanic eruptions that flood the surface of the Earth with massive amounts of very hot, very thin, runny lava. You will read about these volcanic types in more depth later in the lesson. Notice how, as the eruptions become more violent, the cone shapes become more steeply constructed. The six eruption types are in order from least explosive to the most explosive Icelandic, Hawaiian, Strombolian, Vulcanian, Pelean, and Plinian. The three cone shapes are cinder cones, shield cones, and composite cones or stratovolcanoes. There are three basic cone shapes and six eruption types. Volcanoes are classified by the eruption type and by the volcanic cone shape. When you open the pop can the pressure is released so quickly that the gas that is dissolved in the pop comes rushing out along with some of the pop. Have you ever had a can of soda pop explode all over the room? This "eruption" of pop is caused by the same scientific principle that causes a volcano to erupt violently. As the magma approaches the surface of the Earth the gas that is in the magma will come bubbling out because the pressure surrounding the magma will decrease nearer the surface. The magma deep under the crust is less dense than the surrounding rock causing it to rise.Ģ. The thickness and thinness of the magma will determine how a volcano will erupt and what kind of a cone will form.ġ. The eruption that occurred was a Plinian eruption, which is the most violent eruption classification.Īs you learned in the last lesson, different magmas have varying amounts of silica and gas that cause the lava to either be thick and pasty or thin and runny. This once beautiful mountain was changed dramatically on May 18, 1980. In this manner of collapsing and filling, calderas come and go throughout the active lifetime of a basaltic volcano.The photo above is of Mt. Collapse since then has produced the present caldera. This is an indication that they erupted from the volcano summit when the caldera was full. Notice also that many of the lava flows (dark and light are 'a'a and pahoehoe, respectively) have been truncated by the caldera margin. Notice that the caldera is composed of numerous smaller "cookie-cutter" collapses which have coalesced to form the main caldera. This is a vertical air photo of the summit caldera of Mauna Loa volcano (North is to the left). These are the largest volcanoes on Earth. The photo was taken from near the summit of East Maui volcano (EM). They are Mauna Kea (MK), Mauna Loa (ML), Hualalai (H), and Kohala (K). Here are 4 of the volcanoes that comprise the big island of Hawai'i. Examples of shield volcanoes are Kilauea and Mauna Loa (and their Hawaiian friends), Fernandina (and its Galápagos friends), Karthala, Erta Ale, Tolbachik, Masaya, and many others. Shield volcanoes are the common product of hotspot volcanism but they can also be found along subduction-related volcanic arcs or all by themselves. Shield volcanoes are the result of high magma supply rates the lava is hot and little-changed since the time it was generated. Eruptions at shield volcanoes are only explosive if water somehow gets into the vent, otherwise they are characterized by low-explosivity fountaining that forms cinder cones and spatter cones at the vent, however, 90% of the volcano is lava rather than pyroclastic material. For this reason these volcanoes are not steep (you can't pile up a fluid that easily runs downhill). Shield volcanoes are almost exclusively basalt, a type of lava that is very fluid when erupted. The Hawaiian shield volcanoes are the most famous examples. Shield volcanoes are the largest volcanoes on Earth that actually look like volcanoes (i.e.
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