The Volcanic Island Arcs of the Pacific - Term Paper Example

?The Volcanic Island Arcs of the Pacific ISLAND ARCS Rapaport, M mentions that the Pacific has tectonic plates all along the boundary situated in theWest. These plates move under another and sink into the mantle of the Earth. As a result subduction zones establish in broad curves and island chains develop along these zones. These chains are known as island arcs. Islands are formed due to these volcanic activities but at the same time there might be several other reasons. Flexing plates, sometimes, up warp the floor of the sea, lifting it out and form islands. Moreover, if subducting plate has plentiful sediments then these sediments may be slipped off to overriding plates. These scrapped sediment potion builds up into wedge which is called melange. Sometimes this wedge may put up so much that it converts into a ridge. This ridge further dominates the fore arc. Fore arch is the region present in between the trench axis and island arc. When tectonic forces apply to these fore arcs, they get uplift and the ridges are also uplifted and forms islands. Examples of such types of islands include Yap, Guam and Eua. RYUKYU ISLANDS Ryukyu Islands are situated in the Southwest direction of Japan. This island is also known as Nansei Island. It involves an extended chain of islands that cover the area of western Pacific. In the eastern limit, East China Sea is present whereas southwest is surrounded by the islands of Kyushu. So, Ryukyu Islands refer to all those islands that are present in the southwest of Japan. This island is famous for its volcanic activities as it has several active or extinct volcanoes. Some famous volcanoes of this island are enclosed here, Akusekijima: Akusekijima is an island that is famous for its volcanic activities. This island is found in Tokara Islands that are situated in the north of Ryukyu Islands located in Japan. Most of the part of Akusekijimi is enclosed by cliffs that are steep and rigid. Access to this island is quite limited. A sea transport known as “Ferry Toshima” runs twice in a week. With the help of this ferry, geologists travel towards this volcanic island. The elevation of volcano is up to 586m and 1923 feet high. Geographically this volcano is located about 29°27?N 129°36?E? / ?29.45°N 129.60°E? / 29.45; 129.60? (Akusekijima) near Pacific. Iriomotejimi: In the north of Iriomotejimi Island, submarine volcano is present. This volcano is located 25 km north north east (NNE) at the tip of Iriomotejimi island. The estimated depth of the area where this island is located is about 200 to 300 meters. A major eruption took place at this volcanic island in 1924. The after effects of this eruption were terrible. The pumice rafts produced with this eruption had total volume about 1 cu km. This was carried away by water currents along the whole coast of Japan as far as Hokkaido situated in the north. The largest block formed by melted concrete also known as pumice blocks exceeded up to 1x2 meters in size. The volume of eruption proved to be the largest among all the historical eruption. The largest volume made this outbreak volcanic explosion as the largest in Japan’s history. Kikai Caldera Kikai Caldera is a massive volcano up to 12 miles in diameter. This volcano is located in Osumi islands in Japan. This volcano is the remain of ancient volcanic eruptions took place thousands years ago. Akahova eruption is directly connected to Kikai Caldera. This eruption is considered one among the largest volcanic eruptions took place during Holocene ten thousand years ago. The consequences of this volcanic eruption prolonged and about six thousand years ago, pyroclastic flows from that outbreak and the magma reached to the southern coast of Kyushu. This flow extended over an extensive area up to 62 miles away. The ash could be felt at distant areas. This eruption further produced round about 150 cubic kilometers of tephra. The Volcanic Explosivity Index was 7 due to this massive explosion. So, the ongoing conditions made this one of the most destructive and explosive in last 10, 000 years. As far as the present activity of this volcano is related, still it is an active volcano. Minor explosives and eruptions occur time to time. The most recent eruption of this volcano occurred in 2004. Kuchinoerabu-jima This is also an important volcano located in Ryukyu Islands in Japan. This volcano erupted in 1933 and made massive destruction. A village was completely destroyed as a result. This village was present in the northeast of Shindake. Several villagers were badly injured due to the shocks and jolts felt at the time of volcanic eruption. The elevation of this volcano is about 2156 feet and the last eruption took place in 2009. Otake It is another volcanic island in Japan near Tokara Islands. Otake is the largest mountain on a comparatively small island. Just because of this reason, it is also referred as Nakanoshima. This mountain is also referred as an andesitic volcano. This generally means that the mountain has a strong volcanic rock of intermediary composition. The textures of the rocks are aphanitic to porphyritic. In the early months of 1914, this volcano erupted with a minor outbreak. The mud erupted as a result of this explosion. In 1949, the crater turned out heavy ash clouds. The rocks of this mountain are non-alkali. On the southeast part of this mountain, sulphur mining took place. During rainy seasons the craters are filled with water to form crater lakes. Suwanosejima This is another popular volcanic island situated in Tokara Islands which is present in the northern parts of Ryukyu Islands in Japan. This volcano is about 8 km long and it is considered one of the most active volcanoes present in Japan. Toshima is a village near this volcano. This island has perhaps been populated for many thousand years. However, at times, the population depends on the volcanic activity. In fifteenth century, this volcano erupted with a great blast and that was the time when the place being discarded for living creatures. However, in 19th century this island was resettled. Yokoatejima This is another volcanic island situated in Tokara Islands in Japan. Historical studies showed ash plumes from this volcano in time period from 1603 to 1868, the Edo Period. THE KURIL ISLANDS The Kuril Islands formed volcanic arc composed of 45 volcanoes present on 20 islands. The Pacific Plate shifts with great velocity. This speed is about 90 mm per year. The Pacific plate sub ducts under Okhotsk Plate near Kuril trench. Here it goes deeper in northwest direction. This area is seismically very active to a depth of about 680 km. the volcanoes present here are heated up with melted magma. Two important plates that play a role in tectonic and seismic activities involve, 1. Okhotsk Plate: It is a tectonic plate covering Kamchatka Peninsula, Okhotsk Sea and the Eastern part of Japan. This plate is also known as an important part of North American Plate. However, many recent studies show that it is an independent plate. This plate is bounded on north by North American Plate, on east by Pacific Plate at Japan and Kuril Kamchatka Trench, on south by Philippines Plate and on west side by Eurasian Plate. In the southwest direction, this plate is bounded by Amurian Plate. So, the boundary of Okhotsk plate is poorly controlled. This plate is compressed between Eurasia and North America. 2. Amurian Plate: This plate is also important as far as seismic activities are related. This plate covers the Korean Peninsula, Manchuria, Primorsky Krai and Western Japan. It is not very clear whether the plate is independent or a part of Eurasian Plate. However, this plate is bounded on its north as well as west by Eurasian Plate. On the north east direction, Okhotsk Plate is present and on the south, Philippine Plate is present. There is a boundary between Okhotsk Plate and Amurian Plate and this boundary is known as Lake Baikal. ALEUTIAN ISLANDS The Aleutian Islands involve round about 300 volcanic islands. These islands join together to form Aleutian Arc which is situated in the north of Pacific Ocean. These islands occupy area of 17, 666 square kilometers. The region extends 1900 km towards west from Alaska Peninsula towards Kamchatka Peninsula. It makes a line between Bering Sea and Pacific Gulf. When this region crosses the longitude 180°, it becomes the western most region of the United States. When we compare this region with Pacific Ring of Fire then we may see these islands situated in the north of this area. This Aleutian Arc forms a large volcanic arc in United States of Alaska. Here most of the volcanoes have been shaped after subduction along Aleutian Trench. In these islands, active as well as dormant both types of volcanoes are present. The Aleutian Arc expands from Alaska Peninsula to Aleutian Islands. Aleutian Islands have many active as well as dormant volcanoes. Some of them are described below, Mount Akutan This volcano is situated in Aleutian Islands. About 1600 years ago, a major volcanic eruption occurred here during which 2 kilometer wide caldera was formed. Recently some more explosions and eruption have been originated from the parts of caldera. Frequent explosion with occasional lava occur time to time that cover the floor of caldera. In 1992, the most recent volcanic activity had emerged and there are hot springs and volcanic activity at the base of this volcano. Amak Volcano This volcano is present 995 km away from Anchorage in Aleutian Islands. This island can be accessed only through boats. The lava that flows through this volcano has great amount of melted crystals and minerals. Three most famous historical eruptions of this volcano include two that took place in 18th century. The first one took place from 1700 to 1710 and the later happened in 1796. The third eruption goes back to centuries as it is an old volcano present in Aleutian Islands. Amukta Volcano This volcano is situated in Aleutian Arc, the chain of volcanoes. The ridge present in this volcano is extended towards southwest and eastern sides of Aleutian Islands and indicates the presence of old caldera. However, hot springs are not reported in this volcano. As far as the volcanic activities are related, this volcano does not possess frequent eruptions. The most noted activity came forward from 1786- 1791. Again another volcanic activity occurred in 1876. In 1963, another eruption took place forming craters and vents. From this eruption lava and ash were produced. As far as the recent activities of this volcano is concerned, in 1987 a pilot of a commercial flight observed high eruption near Amukta Island. Later on, another pilot observed the same on September 4 of the same year. On September 18, another pilot accounted the same incident. He enclosed the presence of thick ash clouds. In 1996, a ship further reported clouds of smoke and ash. So, this volcano showed itself quite active in past recent years. Bobrof Volcano This is an inactive volcano present in Aleutian Islands, USA. This volcano is very old and no record can be found as far as recent volcanic activity is considered. Buldir Volcano This is also a dormant volcano. So, no recent activity is recorded for this volcano. JAPAN ARC This arc is also known as Honshu arc. While describing the area, David Ritchie, and Alexander E Gates mention that it is also situated in the area of ‘The Pacific Ring of Fire.’ This arc moves from north to south along Honshu Island. The volcanoes present here are also the result of subduction of Pacific Plate beneath North American Plate at Japan Trench. The end at the south converges with South Western Japan Arc. This forms a geological boundary between the eastern and western parts of Honshu Island. The Ou Mountains present here form volcanic part of the arc. Quaternary volcanoes are the volcanic front that extends with the length of range present here. On the other hand, the Iide Mountains and Dewa Mountains are not volcanic ranges. These mountain ranges run in parallel direction along with Ou Mountins. INDONESIA ARC This arc is also dominated by volcanoes that are shaped due to subduction zones. This zone created between Indo Australian Plate and Eurasian Plate. In this chain, some volcanoes are very much notable for their volcanic activity like Krakatau’s eruption in 1883. This outbreak produced global effects. Lake Toba eruption is also a notable incident occurred many years back. This eruption was responsible for a volcanic winter for round about six years. Next to it, Mount Tambora was the volcanic eruption of Indonesia arc. This was considered the most violent outbreak in the history that has been recorded. Volcanoes present in Indonesian arc are also a part of Pacific Ring of Fire. This arc involves about 150 volcanoes that are grouped in six important geographical regions. Four among these regions belong to Sunda Arc Trench. Remaining two categories involve the volcanoes of Halmahera. In Indonesia arc, the most vigorous volcanoes involve Merapi and Kelut that are located near Java Island. These volcanoes and their eruption result in thousand deaths in that region. Since 1000 AD, Kelut has been exploded more than thirty times. On the other hand, Merapi has been exploded more than eighty times. Since 1995, Merapi is also named Decade Volcano because of its activism and high volcanic action. PHILIPPINES ARC Philippine is situated in the western of Pacific Ocean. Taiwan is located in the north of Philippine. Vietnam is in the west across South China Sea. This arc is located near Pacific Ring of Fire and the climate of the area makes the arch prone to typhoons and earthquakes. This area is also rich in natural vegetation in the world. Philippine is comprised of 7,107 islands. Mount Pinatubo is the second largest terrestrial outbreak of 20th century in the world. This eruption caused many people dead and thousands of evacuated from surrounding areas. However, Pyroclastic flow and ash deposits severely damaged the houses and land. Mayo Volcano is the most active volcano present in Philippines. This volcano is capped by small crater. This volcano erupted in 1616. Here the outbreak ranges from Strom to basaltic Plinian eruption. The lava flows far down. However, such eruptions badly affected the environment at one end along with the devastations at lowland areas of the regions. Taal Volcano is another large volcano in Philippines arc. Since 1572, there are 33 recorded explosions and outbreaks from this volcano. In 1911, an eruption occurred here that devastated thousands live. The deposits produced through this eruption were composed of yellowish decomposed tephra having high content of sulphur. Recent activities of this volcano has lasted from 1965- 1977. This occurred when the magma got an interaction with lake water. Since 1977, this volcano has been dormant. However, it has showed some signs of unrest in 1991. Strong seismic activities happened as a result. Moreover, mud geysers were also formed on different parts of the island. Canlaon is another volcano present here and this volcano is considered the most active in Philippines arc, it has been erupted many times since 1866. Some studies show that the eruptions took place 25 times. The explosions, usually, occurred in the form of small to moderate blasts that further produced ash falls near Canloan Volcano. In 1996, this volcano suddenly erupted and killed some British mountain climbers. Japan Tectonic Plates Tectonic plates are the large pieces in which the earth’s crust is broken down. These tectonic plates lie above mantle which contains hot and liquid molten matter. These tectonic plates are composed of continental crusts as well as oceanic crust. As already mentioned, mantle contain the molten matter which circulates deep in the middle layer of earth. This circulation causes the plates to move slowly on earth’s surface. It is a fact that the edges of these tectonic plates are considered the most active places as far as volcanic activity is related. Actually these edges are the places where new rocks are created or destroyed. So, tectonic plates are considered the most active places where volcanic eruptions take place. The Causes of Tsunamis and Earthquakes in the area of Pacific While writing the causes of earthquakes and tsunamis, Larry Greenemeier enclosed the terrible Tsunami recently took place near eastern coast of Honshu in Japan. This natural destruction claimed hundreds of human lives and the jolts were felt far away on the coast of North America. This coast is present eight thousand kilometers away from Honshu Island. In this case, depth of the oceans played a great role making the incident more devastating. This earthquake had magnitude of 8.9 which was considered the strongest recorded in the history of Japan. The waves produced after the tsunamis were very high and recorded as high as seven meters. Closed shore areas and coastal lines were seriously damaged. Coastal areas were evacuated. Round about the coastal areas of twenty countries were at great risk including United States, Chile and Indonesia. In Japan, tsunamis are most often generated by earthquakes on the crust situated beneath Pacific Ocean and driving down below Japan. The upper most crust about 50- 100 kilo meters in Pacific Ocean is moving to the northwest at very slow speed about few centimeters annually. It is important to understand that the earth crust around Japan is lighter as compared to the crust of Pacific. When these two crusts come together, the crust of ocean goes down as it is heavier than the crust around Japan. At this point, the two plates grind against one another. This give rise to a force and finally it suddenly snaps. As a result of this force, the Pacific Plate suddenly goes down and Asian Plate bounces up. Japan is a part of Asian Plate. The abrupt motion of these two plates moves the overall volume of water. This causes tsunami in the region of Pacific. Tsunami waves travel so fast as compared to the normal waves. Normal waves are most often driven by wind so they pass through at the speed of wind. On the other hand, tsunamis speed depends on the deepness and strength of water. The more the ocean will be deep, more will be the speed of tsunami. After an earthquake, when some stress get released along subduction zones then the other parts of the zone get out of equilibrium. The subduction zone is very large and it is about hundred to thousand kilometers long. This is a place where Pacific Plate goes down underneath the Asian Plate. Only a very small portion of these plates snap together to generate earthquakes and finally tsunamis. But the real issue is that, the snap, push and pull change the state of balance along the overall system. So, there could be a chance of another earthquake. Moreover, after terrible earthquakes, aftershocks are quite a normal phenomenon. However, these shocks are of mild nature and these are not strong enough. Most of the time, light nature jolts are felt as compared to the original earthquake. It is generally believed by geologists that the magnitude of 6 and higher earthquake can give rise to tsunami conditions because this magnitude is strong enough to trigger the waves of ocean. So it can be said that higher magnitudes pave the way for tsunamis. Sometimes, the aftershocks of high magnitude may give rise to tsunami conditions. The Pacific: “A Ring of Fire” Pacific Ring of Fire is the region where half of the world’s volcanoes are located. This region spread over an extensive area. It is like a circle stretching downward towards the eastern part of Pacific, from Alaska in northern direction and passes through the stony and shaky mountains of USA and Canada. This region loops back around western side of Pacific through New Zealand, Japan and Indonesia. Most of the world’s biggest volcanoes are present in this region like Cotopaxi in Ecuador which was erupted last time in 1928, Mount St Helens in USA last time erupted in 1980 and Krakatoa situated in Indonesia which was erupted in 1883. What Causes Volcanoes to Erupt? While talking about volcanic activities, Barbara B. Decker, Robert W. Decker mentions that a volcano always erupts when magma present inside the earth pushes the weak crust. The magma inside the earth tries to escape as a result of which huge force is released. So, this volcanic eruption takes place in the form of huge explosive. This is the basic reason why many explosions and eruptions produce enormous quantities of dust, ash and gases. Sometimes, it also occurs that magma rises under huge pressure. If it occurs then there might occur crack on lithosphere. Finally, when the magma comes out and reaches the surface of the earth then it is called lava. REFERENCES 1. Rapaport, M. The Pacific Islands: Environment & Society. Hong Kong: The Bess Press, 1999. 2. James Stewart Monroe, Reed Wicander, and Richard W. Hazlett. Physical Geology: Exploring the Earth. United States of America: Thomson Brooks, 2007. 3. David Ritchie, and Alexander E Gates. Encyclopedia of Earthquakes and Volcanoes. New York, Info base Publishing, 2007. 4. Barbara B. Decker, Robert W. Decker. “Volcano.” Encyclopedia Britannica: Science & Technology. 14 November 2011. 5. “Plate Tectonics.” What on Earth: Pacific Plate. 14 November 2011. 6. Greenemeier, L. “How does an earthquake Trigger Tsunamis Thousands of Kilometers Away?” Scientific American. 15 November 2011. 7. Geographic Region. “Earth’s Active Volcanoes.” 15 November 2011. Read More