PACIFIC RING OF FIRE

The 'Pacific Ring of Fire' is an area of frequent earthquakes and volcanic eruptions encircling the basin of the Pacific Ocean. In a 40,000 km horseshoe shape, it is associated with a nearly continuous series of oceanic trenches, volcanic arcs, and volcanic belts and/or plate movements. It is sometimes called the 'circum-Pacific belt' or the 'circum-Pacific seismic belt'.
Ninety percent 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. ^[1][2].
The Ring of Fire is a direct result and consequence of plate tectonics and the movement and collisions of crustal plates ^[3]. 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. 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–Kurile Islands 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. 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. ^[4][5]
The December 2004 earthquake just off the coast of Sumatra was actually a part of the Alpide belt.

Contents

Cascadia subduction zone

Canada

Stikine Volcanic Belt

Garibaldi Volcanic Belt

Chilcotin Plateau Basalts

Anahim Volcanic Belt

Indonesia

Philippines

Kamchatka Peninsula

Antarctica

Victoria Land and Ross Island

Marie Byrd Land

See also

References

Cascadia subduction zone

The Cascadia subduction zone is a 680 mi (1,094 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.
The zone separates the Juan de Fuca, Explorer, Gorda and the North American Plates. Here, the oceanic crust of the Pacific Ocean is pushed toward and beneath the continent at a rate of 40 mm/yr.

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 up 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) downdip from the deformation front. Further downdip, there is a transition from fully locked to aseismic sliding.
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 subduction of the Juan de Fuca, Explorer, and Gorda plates have created a volcanic arc called 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.

Canada

Mount Edziza, a massive shield volcano seen from the Stewart-Cassiar Highway

Mount Cayley as seen from its southeast slopes

Mount Garibaldi as seen from Squamish

Although little-known to the general public, British Columbia and the Yukon Territory is home to a vast region of volcanoes and volcanic activity in the Pacific Ring of Fire.^[6] 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.^[7] There are hot springs at some volcanoes while 10 volcanoes in British Columbia appear related to seismic activity since 1975, including: Mount Silverthrone, Mount Meager, Wells Gray-Clearwater Volcanic Field, Mount Garibaldi, Mount Cayley, Castle Rock, Lava Fork Valley, Mount Edziza, Hoodoo Mountain and Crow Lagoon.^[8] The volcanoes are grouped into five volcanic belts with different tectonic settings.

Stikine Volcanic Belt

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, much larger than the minor stratovolcanoes found in the Canadian portion of the Cascade Volcanic Arc. 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. 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 River Cones and Lava Fork Valley produced some of Canada's youngest lava flows, that are about 150 years old.
Canada's worst known geophyical disaster came from the Tseax River Cones in 1775 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.

Garibaldi Volcanic Belt

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.^[9] 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. 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, sending an ash column approximately 20 km high into the stratosphere.^[10]

Chilcotin Plateau Basalts

The Chilcotin Plateau Basalts are 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).^[11] It is thought to have formed as a result of back-arc extension behind the Cascadia subduction zone. Volcanoes in this belt include Mount Noel, the Clisbako Caldera Complex, Lightning Peak, Black Dome Mountain and many lava flows.

Anahim Volcanic Belt

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.^[12] The volcanoes generally get younger as you go 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. The hotspot is considered similar to the one feeding the Hawaiian Islands The belt is defined by three large shield volcanoes (Rainbow, Ilgachuz and the Itcha Ranges) and 37 Quaternary basalt centers.

Indonesia

Mount Merapi

The volcanoes in Indonesia are among the most active of the Pacific Ring of Fire. They are formed due to subduction zones between the Eurasian Plate and the Indo-Australian Plate. 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 most active volcanoes are Kelut and Merapi on Java island which have been responsible for thousands of deaths in the region. Since AD 1000, Kelut 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.

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.

Kamchatka Peninsula

The Kamchatka Peninsula in the Russian Far East, is one of the most various and active volcanic areas in the world,^[13] 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.
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, 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.

Antarctica

Mount Erebus, 1972

The southernmost end of the Pacific Ring of Fire is the continent Antarctica,^[14] 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. The most well known volcano in Antarctica is Mount Erebus, which is also the world's southernmost active volcano.

Victoria Land and Ross Island

The volcanoes of the Victoria Land area are the most well-known in Antarctica, 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. 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.

Marie Byrd Land

Marie Byrd Land contains the largest volcanic region in Antarctica, covering a length of almost 600 miles (960 km) along the Pacific coast. 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. Protruding up through the ice are a large number of major shield volcanoes, including Mount Sidley, which is the highest volcano in Antarctica. 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. 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.

See also

★ Andesite line

★ Geology of the Pacific Northwest

References

1. U.S. Geological Survey Earthquakes FAQ.
2. U.S. Geological Survey Earthquakes Visual Glossary.
3. [http://pubs.usgs.gov/publications/text/slabs.html Moving slabs [This Dynamic Earth, USGS]].
4. Latest Earthquakes in the USA - Past 7 days, USGS.
5. Schulz, Sandra S., and Robert E. Wallace, "The San Andreas Fault", USGS.
6. Skiing the Pacific Ring of Fire and Beyond: Alaska and Northwest Canada Retrieved on 2007-07-31
7. CAT.INIST: Canadian volcanoes Retrieved on 2007-07-31
8. Volcanoes of Canada Retrieved on 2007-06-24
9. Calalogue of Canadian volcanoes - Garibaldi Volcanic Belt Retrieved on 2007-07-31
10. Catalogue of Canadian volcanoes: Mount Meager Retrieved on 2007-07-31
11. Catalogue of Canadian volcanoes - Chilcotin Plateau basalts Retrieved on 2007-07-31
12. Catalogue of Canadian volcanoes - Anahim Volcanic Belt Retrieved on 2007-07-31
13. Skiing the Pacific Ring of Fire and Beyond: Kamchatka & Kuril Islands Retrieved on 2007-08-01
14. Skiing the Pacific Ring of Fire and Beyong: Antarctica Retrieved 2007-07-31


★ Historic Earthquakes & Earthquake Statistics at the United States Geological Survey

★ DESCRIPTION: "Ring of Fire", Plate Tectonics, Sea-Floor Spreading, Subduction Zones, "Hot Spots" at the USGS Cascades Volcano Observatory, Vancouver, Washington Web site.

★ Map of the Ring of Fire

★ The Ring of Fire at work

★ Physical World Map 2004-04-01 CIA World Factbook; Robinson Projection; standard parallels 38°N and 38°S