Ring of Fault
The Smithsonian/NASA Astrophysics Data System
Structure and formation of ring faults in composite volcanoes
Gudmundsson, A.; Nilsen, K.
American Geophysical Union, Spring Meeting 2005, abstract #V23B-01
Most collapse calderas form by vertical displacement (subsidence) along ring faults. One principal problem regarding the formation of collapse calderas is thus to explain the stress conditions that favor the formation of, or slip on existing, ring faults.
The ring faults are shear fractures, more specifically dip-slip faults, so that they cannot form unless the local driving shear stress in the hosting composite volcano satisfies the criteria of shear failure. Many ring faults, however, are perhaps more accurately described as mixed-mode fractures: partly shear and partly extension fractures.
This follows because the ring faults are commonly occupied by ring dikes which, like dikes in general, are extension fractures. Also, ring-fault development at the surface commonly involves tension-fracture formation.
For a ring fault to form, or an existing one to slip, suitable stresses must concentrate at a certain radial distance from the center of the associated magma chamber. Similarly, at the surface, suitable stresses must peak in the circular region that eventually develops the ring fault. Most unrest periods do not generate stress fields suitable for formation of, or slip on, ring faults. By contrast, many unrest periods are favorable to dike injection, some of which reach the surface to feed eruptions.
Thus, even in existing calderas, most unrest periods do not generate the special stress fields needed for ring-fault slip. Here we present new numerical models on ring-fault formation in composite volcanoes. Two common geometries of magma chambers are considered: spherical and sill-like (oblate ellipsoidal). In some models, the chamber itself is located in a single thick layer, whereas in others it is hosted by several layers of different mechanical properties.
In all the models, the crustal segment above the chamber, up to the surface of the volcano, is composed of 30 adjacent layers with stiffnesses (Young's moduli) ranging from 1 GPa to 100 GPa. The thickness of the crustal segment hosting the chamber is 20 km, whereas its width is either 20 km or 40 km.
The loading conditions include (1) crustal segments subject to tensile stress of 5 MPa, (2) crustal segments subject to magmatic pressure of 10 MPa at the bottom (that is, doming of the volcanic field containing the chamber), (3) a combination of tension and doming, and (4) internal excess pressure or underpressure in the chamber. In all models, the top of the chamber is at 3 km depth; the diameter of a sill-like chamber is 8 km (height 2 km), that of a spherical chamber 4 km.
Some of the main results can be summarized as follows. (1) Internal excess-or underpressure in a spherical or sill-like chamber is not very likely to give rise to a ring fault; this loading rather results in dike injections. (2) For doming or tension, a spherical magma chamber is normally unlikely to give rise to a ring fault but favors dike injection. However, a spherical chamber in a very soft (10 GPa) layer, or one with recent dike injections, may generate a ring-fault. (3) A sill-like chamber under tension, doming, or tension and doming may generate a ring fault (and often a ring dike). When the volcanic field is 20 km wide, tension or tension and doming may result in ring-fault formation.
When the volcanic field is 40 km wide, doming alone can also result in ring-fault formation. In conclusion, the numerical results suggest that composite volcanoes with sill-like magma chambers located within volcanic fields subject to tension, doming, or both are most likely to generate stress fields suitable for ring-fault formation.
Keywords: 8020 Mechanics, 8035 Pluton emplacement, 8164 Stresses: crust and lithosphere, 8400 VOLCANOLOGY, 8414 Eruption mechanisms
Ring of Fire
Pacific Ring of Fire
http://en.wikipedia.org/wiki/Pacific_Ring_of_Fire
"The Ring of Fire" redirects here. For other uses of the term, see Ring of Fire (disambiguation).
The Pacific Ring of Fire (or just the Ring of Fire) is an area where large numbers of earthquakes and volcanic eruptions occur in the basin of the Pacific Ocean. In a 40,000 km (25,000 mi) horseshoe shape, it is associated with a nearly continuous series of oceanic trenches, volcanic arcs, and volcanic belts and/or plate movements. The Ring of Fire has 452 volcanoes and is home to over 75% of the world's active and dormant volcanoes.[1] It is sometimes called the circum-Pacific belt or the circum-Pacific seismic belt.
Eruption of Mount St. Helens on July 22, 1980.
About 90% of the world's earthquakes and 81% of the world's largest earthquakes occur along the Ring of Fire. The next most seismic region (5–6% of earthquakes and 17% of the world's largest earthquakes) is the Alpide belt, which extends from Java to Sumatra through the Himalayas, the Mediterranean, and out into the Atlantic. The Mid-Atlantic Ridge is the third most prominent earthquake belt.[2][3]
The Ring of Fire is a direct result of plate tectonics and the movement and collisions of lithospheric plates.[4] The eastern section of the ring is the result of the Nazca Plate and the Cocos Plate being subducted beneath the westward moving South American Plate. The Cocos Plate is being subducted beneath the Caribbean Plate, in Central America. A portion of the Pacific Plate along with the small Juan de Fuca Plate are being subducted beneath the North American Plate. Along the northern portion the northwestward moving Pacific plate is being subducted beneath the Aleutian Islands arc. Further west the Pacific plate is being subducted along the Kamchatka Peninsula arcs on south past Japan. The southern portion is more complex with a number of smaller tectonic plates in collision with the Pacific plate from the Mariana Islands, the Philippines, Bougainville, Tonga, and New Zealand; this portion excludes Australia, since it lies in the center of its tectonic plate. Indonesia lies between the Ring of Fire along the northeastern islands adjacent to and including New Guinea and the Alpide belt along the south and west from Sumatra, Java, Bali, Flores, and Timor. The famous and very active San Andreas Fault zone of California is a transform fault which offsets a portion of the East Pacific Rise under southwestern United States and Mexico. The motion of the fault generates numerous small earthquakes, at multiple times a day, most of which are too small to be felt.[5][6] The active Queen Charlotte Fault on the west coast of the Queen Charlotte Islands, British Columbia, Canada, has generated three large earthquakes during the 20th century: a magnitude 7 event in 1929, a magnitude 8.1 occurred in 1949 (Canada's largest recorded earthquake) and a magnitude 7.4 in 1970.[7]Contents [hide]
1 Andes
1.1 Chile
1.2 Bolivia
2 Central America
3 North American Cordillera
3.1 Mexico
3.2 United States
3.3 Canada
4 Russia
5 Japan
6 Philippines
7 Indonesia
8 New Zealand
9 Antarctica
10 Land areas in the Ring
11 See also
12 References
13 Further reading
14 External links
[edit]
Andes
For more details on this topic, see Andean Volcanic Belt.
[edit]
Chile
Main article: Volcanism in Chile
Earthquake activity in Chile is related to subduction of the Nazca Plate to the east. Chile notably holds the record for the largest earthquake ever recorded, the 1960 Valdivia earthquake. Villarrica, one of Chile's most active volcanoes, rises above Villarrica Lake and the town of Villarrica. It is the westernmost of three large stratovolcanoes that trend perpendicular to the Andean chain. A 6-km wide caldera formed during the late Pleistocene, >0.9 million years ago.
Llaima's 2008 eruption
A 2-km-wide postglacial caldera is located at the base of the presently active, dominantly basaltic-to-andesitic cone at the NW margin of the Pleistocene caldera. About 25 scoria cones dot Villarica's flanks. Plinian eruptions and pyroclastic flows have been produced during the Holocene from this dominantly basaltic volcano, but historical eruptions have consisted largely of mild-to-moderate explosive activity with occasional lava effusion. Lahars from the glacier-covered volcano have damaged towns on its flanks.
In 2008, Chile experienced two volcanic eruptions, the first one from Llaima Volcano (January 1) and Chaitén Volcano (May 1). More recently, an 8.8-magnitude earthquake struck central Chile on February 27, 2010 (2010 Chile earthquake).[8]
[edit]
Bolivia
The country of Bolivia hosts numerous active and extinct volcanoes across its territory. The active volcanoes are located in western Bolivia making up the Cordillera Occidental, the western limit of the Altiplano plateau. Many of the active volcanoes are international mountains shared with Chile. All Cenozoic volcanoes of Bolivia are part of the Central Volcanic Zone (CVZ) of the Andean Volcanic Belt that results due to processes involved in the subduction of Nazca Plate under the South American Plate. The Central Volcanic Zone is a major upper Cenozoic volcanic province.[9] Apart from Andean volcanoes the geology of Bolivia host the remants of ancient volcanoes around the Precambrian Guaporé Shield in the eastern part of the country.
[edit]
Central America This section requires expansion.
[edit]
North American Cordillera
[edit]
Mexico
The Trans-Mexican Volcanic Belt
Volcanoes of Mexico are related to subduction of the Cocos and Rivera plates to the east, which has produced large explosive eruptions. Most active volcanoes in Mexico occur in the Trans-Mexican Volcanic Belt, which extends 900 kilometres (559 mi) from west to east across central-southern Mexico. A few other active volcanoes in northern Mexico are related to extensional tectonics of the Basin and Range Province, which split the Baja California peninsula from the mainland.[10] Popocatépetl lies in the eastern half of the Trans-Mexican Volcanic Belt, which is the second highest peak in Mexico after the Pico de Orizaba. It is one of most active volcanoes in Mexico, having had more than 20 major eruptions since the arrival of the Spanish in 1519. The 1982 eruption of El Chichón killed about 2,000 people who lived near the volcano. It created a 1 kilometre (1 mi) wide caldera that filled with an acidic crater lake. Prior to 2000, this relatively unknown volcano was heavily forested and of no greater height than adjacent non-volcanic peaks.[10]
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United States
Area of the Cascadia subduction zone, including the Cascade Volcanic Arc (red triangles)
In the western United States lies the Cascade Volcanic Arc. It includes nearly 20 major volcanoes, among a total of over 4,000 separate volcanic vents including numerous stratovolcanoes, shield volcanoes, lava domes, and cinder cones, along with a few isolated examples of rarer volcanic forms such as tuyas. Volcanism in the arc began about 37 million years ago, however, most of the present-day Cascade volcanoes are less than 2,000,000 years old, and the highest peaks are less than 100,000 years old. It formed by subduction of the Gorda and Juan de Fuca plates at the Cascadia subduction zone. This is a 680 mi (1,090 km) long fault, running 50 mi (80 km) off the west-coast of the Pacific Northwest from northern California to Vancouver Island, British Columbia. The plates move at a relative rate of over 0.4 inches (10 mm) per year at a somewhat oblique angle to the subduction zone.
Because of the very large fault area, the Cascadia subduction zone can produce very large earthquakes, magnitude 9.0 or greater, if rupture occurred over its whole area. When the "locked" zone stores energy for an earthquake, the "transition" zone, although somewhat plastic, can rupture. Thermal and deformation studies indicate that the locked zone is fully locked for 60 kilometers (about 40 miles) down-dip from the deformation front. Further down-dip, there is a transition from fully locked to aseismic sliding.
Cascade Range volcano eruptions in the last 4000 years
Unlike most subduction zones worldwide, there is no oceanic trench present along the continental margin in Cascadia. Instead, terranes and the accretionary wedge have been uplifted to form a series of coast ranges and exotic mountains. A high rate of sedimentation from the outflow of the three major rivers (Fraser River, Columbia River, and Klamath River) which cross the Cascade Range contributes to further obscuring the presence of a trench. However, in common with most other subduction zones, the outer margin is slowly being compressed, similar to a giant spring. When the stored energy is suddenly released by slippage across the fault at irregular intervals, the Cascadia subduction zone can create very large earthquakes such as the magnitude 9 Cascadia earthquake of 1700. Geological evidence indicates that great earthquakes may have occurred at least seven times in the last 3,500 years, suggesting a return time of 400 to 600 years. There is also evidence of accompanying tsunamis with every earthquake, as the prime reason they know of these earthquakes is through "scars" the tsunami left on the coast, and through Japanese records (tsunami waves can travel across the Pacific).
The 1980 eruption of Mount St. Helens was the most significant to occur in the contiguous 48 U.S. states in recorded history (VEI = 5, 0.3 cu mi, 1.2 km3 of material erupted), exceeding the destructive power and volume of material released by the 1915 eruption of California's Lassen Peak. The eruption was preceded by a two-month series of earthquakes and steam-venting episodes, caused by an injection of magma at shallow depth below the mountain that created a huge bulge and a fracture system on Mount St. Helens' north slope. An earthquake at 8:32 a.m. on May 18, 1980, caused the entire weakened north face to slide away, suddenly exposing the partly molten, gas- and steam-rich rock in the volcano to lower pressure. The rock responded by exploding into a very hot mix of pulverized lava and older rock that sped toward Spirit Lake so fast that it quickly passed the avalanching north face.
Alaska is known for its seismic and volcanic activity, holding the record for the second largest earthquake in the world the Good Friday Earthquake, and having more than 50 volcanoes which have erupted since about 1760.[11] Volcanoes can be found not only in the mainland but also in the Aleutian Islands.
The most recent activity in the American portion of the Ring of Fire occurred in early 2009 when Mount Redoubt in Alaska became active and finally erupted late in the evening of March 22. The eruption ended in May 2009.
[edit]
Canada
Mount Edziza, a large shield volcano in northwestern British Columbia
See also: Volcanism in Canada
Although little-known to the general public[citation needed], British Columbia and Yukon are home to a vast region of volcanoes and volcanic activity in the Pacific Ring of Fire.[12] Several mountains that many British Columbians look at every day are dormant volcanoes. Most of them have erupted during the Pleistocene and Holocene. Although none of Canada's volcanoes are currently erupting, several volcanoes, volcanic fields and volcanic centers are considered potentially active.[13] There are hot springs at some volcanoes while 10 volcanoes in British Columbia appear related to seismic activity since 1975, including: the Silverthrone Caldera, Mount Meager, Wells Gray-Clearwater volcanic field, Mount Garibaldi, Mount Cayley, Castle Rock, The Volcano, Mount Edziza, Hoodoo Mountain, Crow Lagoon and Nazko Cone.[14] The volcanoes are grouped into five volcanic belts with different tectonic settings.
The Mount Meager volcanic complex as seen from the east near Pemberton, BC. Summits left to right are Capricorn Mountain, Mount Meager, and Plinth Peak
Mount Cayley as seen from its southeast slopes
The Northern Cordilleran Volcanic Province (sometimes known as the Stikine Volcanic Belt) is the most active volcanic region in Canada. It formed due to extensional cracking, faulting and rifting of the North American Plate, as the Pacific Plate grinds and slides past the Queen Charlotte Fault, unlike subduction that produces the volcanoes in Japan, Philippines and Indonesia. The region has Canada's largest volcanoes,[12] much larger than the minor stratovolcanoes found in the Canadian portion of the Cascade Volcanic Arc.[12] Several eruptions are known to have occurred within the last 400 years. Mount Edziza is a huge volcanic complex that erupted several times in the past several thousand of years, which has formed several cinder cones and lava flows. The complex comprises the Mount Edziza Plateau, a large volcanic plateau (65 kilometers long and 20 kilometers wide) made of predominantly basaltic lava flows with four large stratovolcanoes built on top of the plateau. The associated lava domes and satellite cones were constructed over the past 7.5 million years during five magmatic cycles beginning with eruption of alkali basalts and ending with felsic and basaltic eruptions as late as 1,340 years ago. The blocky lava flows still maintain their original forms. Hoodoo Mountain is a tuya in northwestern British Columbia, which has had several periods of subglacial eruptions. The oldest eruptions occurred about 100,000 years ago and the most recent being about 7000 years ago. Hoodoo Mountain is also considered active and could erupt in the future. The nearby Tseax Cone and The Volcano produced some of Canada's youngest lava flows, that are about 150 years old.
Canada's worst known geophysical disaster came from the Tseax Cone during the 18th century at the southernmost end of the volcanic belt. The eruption produced a 22.5 km long lava flow, destroying the Nisga'a villages and the death of at least 2000 Nisga'a people by volcanic gases and poisonous smoke. The Nass River valley was inundated by the lava flows and contain abundant tree molds and lava tubes. The event happened at the same time with the arrival of the first European explorers to penetrate the uncharted coastal waters of northern British Columbia. Today, the basaltic lava deposits are a draw to tourists and are part of the Nisga'a Memorial Lava Beds Provincial Park.
The Garibaldi Volcanic Belt in southwestern British Columbia, is the northern extension of the Cascade Volcanic Arc in the United States (which includes Mount Baker and Mount St. Helens) and contains the most explosive young volcanoes in Canada.[15] It formed as a result of subduction of the Juan de Fuca Plate (a remnant of the much larger Farallon Plate) under the North American Plate along the Cascadia subduction zone.[15] The Garibaldi Volcanic Belt includes the Bridge River Cones, Mount Cayley, Mount Fee, Mount Garibaldi, Mount Price, Mount Meager, the Squamish Volcanic Field and much more smaller volcanoes. The eruption styles in the belt range from effusive to explosive, with compositions from basalt to rhyolite. Morphologically, centers include calderas, cinder cones, stratovolcanoes and small isolated lava masses. Due to repeated continental and alpine glaciations, many of the volcanic deposits in the belt reflect complex interactions between magma composition, topography, and changing ice configurations. The most recent major catastrophic eruption in the Garibaldi Volcanic Belt was the 2350 BP eruption of Mount Meager as well as Canada. It was similar the 1980 eruption of Mount St. Helens,[15] sending an ash column approximately 20 km high into the stratosphere.[16]
The Anahim Volcanic Belt centers
The Chilcotin Group is a north-south range of volcanoes in southern British Columbia running parallel to the Garibaldi Volcanic Belt. The majority of the eruptions in this belt happened either 6–10 million years ago (Miocene) or 2–3 million years ago (Pliocene), although there have been some slightly more recent eruptions (in the Pleistocene).[17] It is thought to have formed as a result of back-arc extension behind the Cascadia subduction zone.[17] Volcanoes in this belt include Mount Noel, the Clisbako Caldera Complex, Lightning Peak, Black Dome Mountain and many lava flows.
The Anahim Volcanic Belt is a line of volcanoes stretching from just north of Vancouver Island to near Quesnel, British Columbia, Canada. These volcanoes were formed 8-1 million years ago and the Nazko Cone which last erupted only 7,200 years ago.[18] The volcanoes generally get younger as one moves from the coast to the interior. These volcanoes are thought to have formed as a result of the North American Plate sliding westward over a small hotspot, called the Anahim hotspot.[18] The hotspot is considered similar to the one feeding the Hawaiian Islands.[18] The belt is defined by three large shield volcanoes (Rainbow, Ilgachuz and the Itcha Ranges) and 37 Quaternary basalt centers.
Eruptions of basaltic to rhyolitic volcanoes and hypabyssal rocks of the Alert Bay Volcanic Belt in northern Vancouver Island are probably linked with the subducted margin flanked by the Explorer and Juan de Fuca plates at the Cascadia subduction zone. It appears to have been active during the Pliocene and Pleistocene time. However, no Holocene eruptions are known, and volcanic activity in the belt has likely ceased.
[edit]
Russia
Avachinsky, an active volcano on the Kamchatka Peninsula.
The Kamchatka Peninsula in the Russian Far East, is one of the most various and active volcanic areas in the world,[19] with an area of 472,300 km². It lies between the Pacific Ocean to the east and the Okhotsk Sea to the west. Immediately offshore along the Pacific coast of the peninsula runs the 10,500 meter deep Kuril-Kamchatka Trench. This is where rapid subduction of the Pacific Plate fuels the intense volcanism. Almost all types of volcanic activity are present, from stratovolcanoes and shield volcanoes to Hawaiian-style fissure eruptions.[19]
There are over 30 active volcanoes and hundreds of dormant and extinct volcanoes in two major volcanic belts. The most recent activity takes place in the eastern belt,[19] starting in the north at the Shiveluch volcanic complex, which lies at the junction of the Aleutian and Kamchatka volcanic arcs. Just to the south is the famous Klyuchi volcanic group, comprising the twin volcanic cones of Kliuchevskoi and Kamen, the huge volcanic complexes of Tolbachik and Ushkovsky, and a number of other large stratovolcanoes. The only active volcano in the central belt is found west of here, the huge remote Ichinsky. Farther south, the eastern belt continues to the southern slope of Kamchatka, topped by loads of stratovolcanoes.
[edit]
Japan
See also: 2011 Japanese nuclear accidents
Ten percent of the world's active volcanoes are found in Japan, which lies in a zone of extreme crustal instability. They are formed by subduction of the Pacific Plate and the Philippine Sea Plate. As many as 1,500 earthquakes are recorded yearly, and magnitudes of four to six on the Richter scale are not uncommon. Minor tremors occur almost daily in one part of the country or another, causing slight shaking of buildings. Major earthquakes occur infrequently; the most famous in the twentieth century were: the Great Kantō earthquake of 1923, in which 130,000 people died; and the Great Hanshin earthquake of 17 January 1995, in which 6,434 people died. On March 11, 2011 a magnitude 9.0 Earthquake hit Japan, the country's biggest ever and the fifth largest on record, according to US Geological Survey data.[20] Undersea earthquakes also expose the Japanese coastline to danger from tsunamis.
Mount Fuji at sunrise from Lake Kawaguchi
Mount Bandai, one of Japan's most noted volcanoes, rises above the north shore of Lake Inawashiro. Mount Bandai is formed of several overlapping stratovolcanoes, the largest of which is O-Bandai forming a complex volcano. O-Bandai volcano was constructed within a horseshoe-shaped caldera that formed about 40,000 years when an earlier volcano collapsed, forming the Okinajima debris avalanche, which traveled to the southwest and was accompanied by a plinian eruption. Four major phreatic eruptions have occurred during the past 5,000 years, two of them in historical time, in 806 and 1888. Seen from the south, Bandai presents a conical profile, but much of the north side of the volcano is missing as a result of the collapse of Ko-Bandai volcano during the 1888 eruption, in which a debris avalanche buried several villages and formed several large lakes.
Nearly a century ago, the north flank of Mount Bandai collapsed during an eruption quite similar to the May 18, 1980 eruption of Mount St. Helens. After a week of seismic activity, a large earthquake on July 15, 1888, was followed by a tremendous noise and a large explosion. Eyewitnesses heard about 15 to 20 additional explosions and observed that the last one was projected almost horizontally to the north.
Mount Fuji is Japan's highest and most noted volcano. The modern postglacial stratovolcano is constructed above a group of overlapping volcanoes, remnants of which form irregularities on Fuji's profile. Growth of the younger Mount Fuji began with a period of voluminous lava flows from 11,000 to 8,000 years ago, accounting for four-fifths of the volume of the younger Mount Fuji. Minor explosive eruptions dominated activity from 8,000 to 4,500 years ago, with another period of major lava flows occurring from 4,500 to 3,000 years ago. Subsequently, intermittent major explosive eruptions occurred, with subordinate lava flows and small pyroclastic flows. Summit eruptions dominated from 3,000 to 2,000 years ago, after which flank vents were active. The extensive basaltic lava flows from the summit and some of the more than 100 flank cones and vents blocked drainages against the Tertiary Misaka Mountains on the north side of the volcano, forming the Fuji Five Lakes. The last eruption of this dominantly basaltic volcano in 1707 ejected andesitic pumice and formed a large new crater on the east flank. Scientists are saying that there may be some minor volcanic activity in the next few years.
[edit]
Philippines
Map showing major volcanoes of the Philippines.
The 1991 eruption of Mount Pinatubo is the world's second largest terrestrial eruption of the 20th century. Successful predictions of the onset of the climactic eruption led to the evacuation of tens of thousands of people from the surrounding areas, saving many lives, but as the surrounding areas were severely damaged by pyroclastic flows, ash deposits, and later, lahars caused by rainwater remobilising earlier volcanic deposits, thousands of houses were destroyed.
Mayon Volcano overlooks a pastoral scene approximately five months before the volcano's violent eruption in September 1984.
Mayon Volcano is the Philippines' most active volcano. The volcano has steep upper slopes that average 35–40 degrees and is capped by a small summit crater. The historical eruptions of this basaltic-andesitic volcano dates back to 1616 and ranges from Strombolian to basaltic Plinian eruptions. Eruptions occur predominately from the central conduit and have also produced lava flows that travel far down the flanks. Pyroclastic flows and mudflows have commonly swept down many of the approximately 40 ravines that radiate from the summit and have often devastated populated lowland areas.
Taal Volcano has had 33 recorded eruptions since 1572. A devastating eruption occurred in 1911, which claimed more than a thousand lives. The deposits of that eruption consisted of a yellowish, fairly decomposed (non-juvenile) tephra with a high sulfur content. The most recent period of activity lasted from 1965 to 1977, and was characterized by the interaction of magma with the lake water, which produced violent phreatic explosions. Although the volcano has been dormant since 1977, it has shown signs of unrest since 1991, with strong seismic activity and ground fracturing events, as well as the formation of small mud geysers on parts of the island.
Canlaon is the most active volcano in central Philippines and has erupted 25 times since 1866. Eruptions are typically phreatic explosions of small-to-moderate size that produce minor ashfalls near the volcano. On August 10, 1996, Kanlaon erupted without warning, killing British student Julian Green and Filipinos Noel Tragico and Neil Perez, who were among 24 mountainclimbers who were trapped near the summit.
[edit]
Indonesia
See also: List of volcanoes in Indonesia and 2010 eruptions of Mount Merapi
Mount Merapi in Central Java.
Major volcanoes in Indonesia
The volcanoes in Indonesia are among the most active of the Pacific Ring of Fire. They are formed due to subduction zones of three main active tectonic plates namely the Eurasian Plate, Pacific Plate and the Indo-Australian Plate.[21] Some of the volcanoes are notable for their eruptions, for instance, Krakatau for its global effects in 1883, Lake Toba for its supervolcanic eruption estimated to have occurred 74,000 BP which was responsible for six years of volcanic winter, and Mount Tambora for the most violent eruption in recorded history in 1815. The eruption of Mount Tambora in 1815 caused wide spread harvest failures in Northern Europe, the Northeastern United States, and eastern Canada in 1816, which was known as the Year Without a Summer.
The most active volcanoes are Kelud and Mount Merapi on Java island which have been responsible for thousands of deaths in the region. Since AD 1000, Kelud has erupted more than 30 times, of which the largest eruption was at scale 5 on the Volcanic Explosivity Index, while Merapi has erupted more than 80 times. The International Association of Volcanology and Chemistry of the Earth's Interior has named Merapi as a Decade Volcano since 1995 because of its high volcanic activity.
[edit]
New Zealand
See also: Earthquakes in New Zealand and Volcanism in New Zealand
Major volcanoes of New Zealand
New Zealand contains the world's strongest concentration of youthful rhyolitic volcanoes, and voluminous sheets blanket much of the North Island. The earliest historically-dated eruption was at Whakaari/White Island in 1826.[22] Much of the region north of New Zealand's North Island is made up of seamounts and small islands, including 16 submarine volcanoes. In the last 1.6 million years, most of New Zealand's volcanism is from the Taupo Volcanic Zone.
Mount Ruapehu at the southern end of the Taupo Volcanic Zone, is one of the most active volcanoes.[23] It began erupting at least 250,000 years ago. In recorded history, major eruptions have been about 50 years apart,[23] in 1895, 1945 and 1995–1996. Minor eruptions are frequent, with at least 60 since 1945. Some of the minor eruptions in the 1970s generated small ash falls and lahars (mudflows) that damaged skifields.[24] Between major eruptions, a warm acidic crater lake forms, fed by melting snow. Major eruptions may completely expel the lake water. Where a major eruption has deposited a tephra dam across the lake's outlet, the dam may collapse after the lake has refilled and risen above the level of its normal outlet, the outrush of water causing a large lahar. In 2000, the ERLAWS system was installed on the mountain to detect such a collapse and alert the relevant authorities.
The Auckland volcanic field on the North Island of New Zealand, has produced a diverse array of explosive craters, scoria cones, and lava flows. Currently dormant, the field is likely to erupt again with the next "hundreds to thousands of years", a very short timeframe in geologic terms.[25] The field contains at least 40 volcanoes, most recently active about 600 years ago at Rangitoto, erupting 2.3 cubic kilometers of lava.
The February 2011 Christchurch earthquake was a 6.3-magnitude earthquake that struck the Canterbury region in New Zealand's South Island at 12:51 pm on 22 February 2011 local time (23:51 21 February UTC), causing widespread damage and multiple fatalities. The earthquake was centred 2 kilometres (1.2 mi) west of the town of Lyttelton, and 10 kilometres (6.2 mi) south-east of the centre of Christchurch, New Zealand's second-most populous city.
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Antarctica
Mount Erebus, 1972
The Pacific Ring of Fire is completed in the south by the continent of Antarctica,[26] which includes many large volcanoes. The makeup and structure of the volcanoes in Antarctica change largely from the other places around the ring. In contrast, the Antarctic Plate is almost completely surrounded by extensional zones, with several mid-ocean ridges which encircle it, and there is only a small subduction zone at the tip of the Antarctic Peninsula, reaching eastward to the remote South Sandwich Islands.[26] The most well known volcano in Antarctica is Mount Erebus, which is also the world's southernmost active volcano.[26] In many respects the geology of the Antarctic Peninsula is an extension of the Andes, hence the name sometimes used by geologists: "Antarctandes". At the opposite side of the continent, the volcanoes of Victoria Land may be seen as the 'other end' of the Antarctandes, thus completing the Pacific Ring of Fire and continuing up through the Balleny Islands to New Zealand.
The volcanoes of the Victoria Land area are the most well known in Antarctica,[26] most likely because they are the most accessible. Much of Victoria Land is mountainous, developing the eastern section of the Transantarctic Mountains, and there are several scattered volcanoes including Mount Overlord and Mount Melbourne in the northern part.[26] Farther south are two more well-known volcanoes, Mount Discovery and Mount Morning, which are on the coast across from Mount Erebus and Mount Terror on Ross Island. The volcanism in this area is caused by rifting along a number of rift zones increasing mainly north-south similar to the coast.[26]
Marie Byrd Land contains the largest volcanic region in Antarctica, covering a length of almost 600 miles (970 km) along the Pacific coast.[26] The volcanism is the result of rifting along the vast West Antarctic Rift, which extends from the base of the Antarctic Peninsula to the surrounding area of Ross Island, and the volcanoes are found along the northern edge of the rift.[26] Protruding up through the ice are a large number of major shield volcanoes, including Mount Sidley, which is the highest volcano in Antarctica.[26] Although a number of the volcanoes are relatively young and are potentially active (Mount Berlin, Mount Takahe, Mount Waesche, and Mount Siple), others such as Mount Andrus and Mount Hampton are over 10 million years old, yet maintain uneroded constructional forms.[26] The desert-like surroundings of the Antarctic interior, along with a very thick and stable ice sheet which encloses and protects the bases of the volcanoes, which decreases the speed of erosion by an issue of perhaps a thousand relative to volcanoes in moist temperate or tropical climates.