Презентация на тему: Volcanoes

Volcanoes Structure and formation of volcanoes Active and extinct volcanoes

Structure of volcanoes Volcanoes are mountains, which have a regular shape. A volcano consists of a magma’s source, where the lava originates, a conduit, via which the lava arises, a crater, where the lava goes from on the ground.

Formation of volcanoes Sometimes volcanoes arise on person’s eyes. Parikutin's origin is described in many books. On February 20th, 1943 one Mexican peasant saw a crack, which was steaming.The peasant closed the crack with a stone but the steam went out much stronger. By the end of the day there were started explosions. Volcanic bombs and ashes began to fly out as the heated flow of lava. In a year the mountain grew up to 430 meters height. What was the reason of Parikutin's origin?

The Earth's crust has cracks. The magma’s pressure is less near cracks. Magma fuses to forming a magma’s source. Gases, dissolved in magma displace the lava from a magma’s source to a crater. Magma, effused on the ground, is the lava. The temperature of the new lava reaches 1000 C.

The new lava effuses easily. Gases emission out of the viscous lava is accompanied by explosions. The very viscous lava is thrown out like volcanic bombs and ash.

Active and extinct volcanoes Active volcanoes are volcanoes erupted in the humans history. Majority of active volcanoes are located on the bank of the Pacific Ocean. There are a lot of volcanoes under the ocean. A volcano top over the water surface forms the volcanic island. E.g., Hawaiian Islands have volcanic origin. Volcanoes of Hawaian Islands, such as Mauna-Loa, Kilauea, are erupted without explosions. In the craters of these volcanoes there are lakes of liquid lava, which is thrown up on the huge height up to 280 meters during the eruption, and then is speeded over slopes. Because of liquid lava's outpouring, these volcanoes have the shield shape that is why they are called shield-shaped volcanoes.

Extinct volcanoes are volcanoes never erupted in the human’s history. They are located on each continent (Kilimanjaro).

Some of volcanoes, which were considered as dormant, become active. The example of such a volcano is Vesuvius, which was "sleeping" hundreds of years and suddenly began erupting in 79 A.D., and ruined the roman cities like Pompea, Herculanium and Stabia.

Mauna Loa is the largest volcano on the Earth. It is an active shield volcano, with a volume estimated at approximately 18,000 cubic miles (75,000 km3), although its peak is about 120 feet (37 m) lower than that of its neighbor, Mauna Kea, another of five volcanos that from the Islands Of Hawaii. The Hawaiian name "Mauna Loa" means "Long Mountain". Lava eruptions from it are silica-poor, thus very fluid: and as a result eruptions tend to be non-explosive and the volcano has extremely shallow slopes. The volcano has probably been erupting for at least 700,000 years and may have emerged above sea level about 400,000 years ago, although the oldest-known dated rocks do not extend beyond 200,000 years. Its magma comes from the Hawaii hotspot, which has been responsible for the creation of the Hawaiian island chain for tens of millions of years. The slow drift of the Pacific Plate will eventually carry the volcano away from the hotspot, and the volcano will thus become extinct within 500,000 to one million years from now. Mauna Loa's most recent eruption occurred from March 24, 1984, to April 15, 1984. No recent eruptions of the volcano have caused fatalities, but eruptions in 1926 and 1950 destroyed villages, and the city of Hilo is partly built on lava flows from the late nineteenth century. In view of the hazards it poses to population centers, Mauna Loa is part of the Decade Volcanoes program, which encourages studies of the most dangerous volcanoes. Mauna Loa has been intensively monitored by the Hawaiian Volcano Observatory (HVO) since 1912. Observations of the atmosphere are undertaken at the Mauna Loa Observatory, and of the Sun at the Mauna Loa Solar Observatory, both located near its summit. Hawaii Volcanoes National Park covers the summit and the southeastern flank of the volcano, including a separate volcano, Kilauea.

Maun-Loa

Kilauea is an active volcano in the Hawai’ian Islands, one of five shield volcanoes that together form the Island of Hawai’i. In Hawai’ian, the word kīlauea means "spewing" or "much spreading", in reference to the mountain's frequent outpouring of lava. Issuing lava continuously since January 1983, Kīlauea is currently the most active volcano on the planet, an invaluable resource for volcanologists, and also the planet's most visited active volcano. Kīlauea is the most recent of a series of volcanoes that have created the Hawai’ian Archipelago, as the Pacific Plate has moved and is moving over the Hawai’i hotspot. Kīlauea is located on Hawai’i Island, Hawai’i, in the United States. It lies against the southeast flank of much larger Mauna Loa volcano. Mauna Loa's massive size and elevation (13,677 feet or 4,169 m) is a stark contrast to Kīlauea, which rises only 4,091 feet (1,247 m) above sea level, and thus from the summit caldera appears as a broad shelf of uplands well beneath the long profile of occasionally snow-capped Mauna Loa, 15 miles distant. Kīlauea is a very low, flat shield volcano — vastly different in profile from the high, sharply sloping peaks of stratovolcanoes like Mt. Fuji, Mount Hood, and Mount St. Helens.