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- 1. Types of Volcanoes As you may have noticed, not all volcanoes are created the same. Some are found on land, while others are found underneath the ocean. Location is just one way of categorizing them, but volcanoes are also differentiated and classified based on their volcanic activity, structure, and explosiveness.
- 2. Types of Volcanoes according to Activity 1. Active volcano 2. Dormant volcano 3. Extinct volcano
- 3. 1. An ACTIVE VOLCANO is one that has erupted at least once since the last Ice Age, or in the last 10 000 years, and is expected to erupt again in the future. Active volcanoes are often regarded as the most dangerous type. Based on the most recent findings of the United States Geological Survey, there are about 1 500 active volcanoes in the world today. In the Philippines, around 23 volcanoes are considered active; one of them is Mayon Volcano. Mayon is the most active volcano in the country. It is found in Albay, Bicol. Its most recent volcanic activity was recorded last January 22, 2018, when it started to spew lava and ash after several months of silence. One of its deadliest eruptions occurred on February 1, 1814, when about 1 200 people from the nearby town of Cagsawa lost their lives.
- 4. 1. An ACTIVE VOLCANO is one that has erupted at least once since the last Ice Age, or in the last 10 000 years, and is expected to erupt again in the future. According to former Philippine Institute of Volcanology and Seismology (PHIVOLCS) director Renato Solidum, the 1814 eruption is the most destructive in terms of the number of casualties and the distance reached by the volcanic hazards. Lava stream and ash fall caused by the eruption had extended over to the Cagsawa church which stood at a ten-kilometer distance away from the volcano.
- 5. 1. An ACTIVE VOLCANO is one that has erupted at least once since the last Ice Age, or in the last 10 000 years, and is expected to erupt again in the future. Another hot spot for active volcanoes is Hawaii in the U.S.A. A hot spot is an area in Earths mantle where magma is generated and causes volcanic activity. Volcanic activity in Hawaii has, in act, helped shape its islands. The Big Island of Hawaii contains five active volcanoes: Mauna Kea, Hualalai, Mauna Loa, Loihi, and Kilauea. Mount Kilauea is one of the most active among the five volcanoes in the Hawaiian islands. The name Kilauea literally means spewing in Hawaiian language, referring to the frequent outpouring of lava.
- 6. 2. A dormant volcano is a volcano that has the capacity to erupt but has not erupted in the last 10 000 years. Mount Pinatubo, prior to its cataclysmic VEI 5 eruption in 1991, had no historical record of eruption. Its unforeseen explosion caused the destruction of thousands of homes and the demise of about 800 casualties.
- 7. 3. An EXTINCT VOLCANO is an inactive volcano that has not erupted over the last 10,000 years and is not expected to erupt in the future. Mount Malinao and Mount Masaraga, both located in Albay, are two extinct stratovolcanoes that have no recorded historical eruptions in the last 10 000 years. With Mt. Mayon, these volcanic mountains make up the Magayan Trio. A volcano becomes extinct when it is disconnected from its supply of magma. The tectonic plates underneath the volcanic region continue to move, separating the magma chamber and the vent from the hotspot in Earths mantle. As a result, the chamber dries up and remains empty. After a long time of inactivity, the volcano goes extinct. Although, extinct volcanoes are not expected to erupt again, geographic and seismic records show that this is not always true. For example, Mount Vesuvius in Italy erupted suddenly in 79 A.D. destroying the towns of Herculaneum and Pompeii. On the other hand, the Soufri竪re Hills volcano on the island of Montserrat in the Caribbean resumed activity only in 1995.
- 8. Types of Volcanoes according to Shape and Explosiveness The plate tectonics theory suggests that the surface of the planet is not one big piece of land. According to World Atlas, the planets surface is broken into micro minor and major tectonic plates which move in relation to one another. The plates float on the layer in Earths mantle called the asthenosphere. When that hot and viscous layer melts because of tectonic activity, it produces magma. As mentioned earlier, the Pacific Ring of Fire is the most seismically active region on the planet. About 90% of earthquakes occur in the Pacific Ring of Fire. According to the United States Geological Survey (USGS), an average of 12 000 earthquakes has happened annually in this region over the past ten years. It has more exploding volcanoes than any other region on Earth.
- 9. Types of Volcanoes according to Shape and Explosiveness Aside from their activity, volcanoes are also classified, based on their shape and the explosiveness of their eruption. 1. Shield Cone Volcanoes 2. Cinder Cone Volcano 3. Composite Volcano/Stratovolcano
- 10. 1. Shield Cone Volcanoes are low mountains with broad sloping sides, formed by flowing lava. The lava flows in all directions from the central vent, creating a seemingly flattered cone with a domical summit similar to that of a hill. Magma escapes either from the central vent or from the fractures on the flanks of the cone. The accumulation of erupted lava spread across great distances, forming a thin, dipping sheet on the surface. Shield cone volcanoes are some of the largest volcanoes in the world. They have a diameter that occupies hundreds of kilometers and a height that reaches up to 10,000 feet or about 3 000 meters. The largest shield cone volcano in the world is Mauna Lao in Hawaii, standing 13 677 feet or about 4 168 meters above sea level. Most shield cone volcanoes, as well as stratovolcanoes, have summit calderas. Summit calderas are volcanic craters that are formed by an explosive eruption or a collapsed peak surface because of an empty magma chamber. Shield cone volcano calderas result from periodic eruptions that create rock terraces at the crater rather than a big bowl-shaped depression.
- 11. 2. Cinder Cone Volcano. The simplest type of volcanoes are the cinder cone volcanoes. These are steep conical hills of volcanic debris formed by particles and blobs of erupted lava. When a cinder cone volcano explodes, a gas-filled lava blows up into the air and breaks into small fragments that gather at the vent, forming a circular oval cone. A cinder cone stands at about 1 200 feet or 366 meters above its surroundings. It usually has a low-impact eruption. Many cinder cones are found in North America. In the Philippines, there is the Smith Volcano on the western part of the Babuyan Island.
- 12. 3. Composite Volcano/Stratovolcano. Composite volcanoes, also called stratovolcanoes, are made of alternating layers of volcanic debris, lava flows, and cinders that run down steep, symmetrical flanks. A stratovolcano rises up to 8 000 feet or 2 438 meters above the surroundings. It is usually formed by the accumulation of erupted volcanic materials in its slope. The crater of a composite volcano is connected to a central vent filled with magma. The magma flows through the crater wall or in the fissures on the flanks of its cone, and the solidified lava forms dikes which are like ribs that strengthen the cones frame.
- 13. 3. Composite Volcano/Stratovolcano. Composite volcanoes, also called stratovolcanoes, are made of alternating layers of volcanic debris, lava flows, and cinders that run down steep, symmetrical flanks. The dormancy of composite volcanoes is the beginning of its destruction. When magma hardens, it plugs the conduit system and strips away the fissures on the flanks, making it prone to erosion. An example of a dormant composite volcano is Mt. Mazama in Oregon, United States. Because of tremendous explosions thousands of years ago, Mt. Mazama lost its top section. Large amounts of volcanic ash and dust rolled down the slopes, draining the lava beneath and weakening the upper part. The peak collapsed and formed a large depression that eventually filled with water and became a beautiful crater lake. A few examples of the worlds most beautiful composite volcanoes are Mt. Fuji in Japan, Mt. Cotopaxi in Ecuador, Mt. St. Helens in the U.S.A. and Mt. Mayon in the Philippines.
- 24. CATACLYSMIC - an event that causes a lot of destruction, or a sudden, violent change. The Volcanic Explosivity Index ( VEI) is a relative measure of the explosiveness of volcanic eruptions. It was devised by Chris Newhall of the United States Geological Survey and Stephen Self at the University of Hawaii in 1982.
- 27. A stratovolcano is a tall volcano shaped like a cone, formed by various layers of materials such as volcanic ash, hardened lava, pumice, and tephra.
- 28. Tectonic plates are pieces of Earth's crust and uppermost mantle, together referred to as the lithosphere. - the Earth's lithosphere to comprise a number of large tectonic plates which have been slowly moving since about 3.4 billion years ago.