Eruptions occur along rift zones because they are areas of weakness, hence allow pathways for magma to travel within the volcanoes. Kīlauea’s rift zones are oriented parallel to the mobile southern flank that accommodates spreading and widening since Kīlauea is buttressed against Mauna Loa on its northern flank. The rift zones on Mauna Loa and Kīlauea contain vents, fissures, pit craters, spatter cones, cinder cones, and grabens. Rift zones and summit vents typically share the same magmatic source with magma moving laterally from the shallow magma chamber beneath the summit to feed rift eruptions. The island of Ambae, in Vanuatu, is a large basaltic shield volcano that lies along the subduction zone between Fiji and Papua New Guinea in the South Pacific. The presence of rift zones are responsible for these shield’s elongated shapes. There are other large shield volcanoes found along subduction zones rimming the Pacific Ocean, but they can behave very differently from Klauea and Mauna Loa. Learn MoreĮruptions that occur along rift (fissure) zones are a major feature of some shield volcanoes, particularly the shield volcanoes that make up Hawai‘i. The first formed the broad tholeiitic shield. It was formed in two volcanic phases during the Pleistocene epoch of the Quaternary period in the Cenozoic Era. The snow-capped Mauna Loa behind the active lava lake in the Halemaʻumaʻu pit crater in the Kīlauea caldera. West Molokai Volcano, sometimes called Mauna Loa for the census-designated place, is an extinct shield volcano comprising the western half of Molokai island in the U.S. They are built by repeated eruptions that occurred intermittently over vast periods of time (up to a million years or longer). Shield volcanoes are usually constructed almost entirely of basaltic and/or andesitic lava flows which were very fluid when erupted. Shield volcanoes are truly massive with volumes that dwarf other types of volcanoes, even large composite volcanoes. Case Study 3 Shield Volcano Mauna Loa, Hawaii They form like this, because the lava is runnier, and it travels further from the crater before it cools. Shield volcanoes have a convex shape as they are flatter near the summit. Instead, they are broad volcanoes with gentle slopes and are shaped somewhat like a warrior’s shield lying flat on the Earth. With a summit elevation of 13,677 feet (4169 m) above sea level, Mauna Loa is more than 7,500 feet (2,280 m) in elevation higher than Kīlauea (4,091 feet 1,247 m).Īlthough shield volcanoes are the largest volcanoes on Earth, they do not form soaring mountains with conical peaks like composite volcanoes. The broad shield of Mauna Loa (in the background) rising above the Kīlauea caldera in the foreground.
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