The 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.
Cascadia subduction zone
Structure of the 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
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
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
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
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