Ring of Fire
The Pacific Ocean is the world's largest ocean, covering more than one-third of the total surface area of our planet. It is surrounded by a series of mountain chains, deep ocean trenches, and island arcs, sometimes called a "Ring of Fire." The great size of the Pacific Ocean and the large earthquakes associated with the "Ring of Fire" combine to produce deadly tsunamis. In less than a day, these tsunamis can travel from one side of the Pacific to the other. However, people living near areas where large earthquakes occur may find that the tsunami waves will reach their shores within minutes of the earthquake. For these reasons, the tsunami threat to Japan can be be immediate.
Many subduction-zone volcanoes in the "Ring of Fire" also cause tsunamis. Here volcanism is associated with subduction of the Pacific seafloor. As oceanic plates sink, they carry sediments and oceanic crust containing abundant water to great depths. The presence of water contributes to the high gas content and explosive nature of volcanoes that make up the "Ring of Fire."
Pacific Ring of Fire
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.
The Ring of Fire is a direct consequence of plate tectonics and the movement and collisions of crustal plates.
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 December 2004 earthquake just off the coast of Sumatra was actually a part of the Alpide belt. 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.
Major volcanic areas in the Ring of Fire
- In South America the Nazca plate is colliding with the South American plate. This has created the Andes and volcanoes such as Cotopaxi and Azul.
- In Central America, the tiny Cocos plate is crashing into the North American plate and is therefore responsible for the Mexican volcanoes of Popocatepetl and Paricutun (which rose up from a cornfield in 1943 and became a instant mountains).
- Between Northern California and British Columbia, the Pacific, Juan de Fuca, and Gorda plates have built the Cascades and the infamous Mount Saint Helens, which erupted in 1980.
- Alaska's Aleutian Islands are growing as the Pacific plate hits the North American plate. The deep Aleutian Trench has been created at the subduction zone with a maximum depth of 25,194 feet (7679 meters).
- From Russia's Kamchatka Peninsula to Japan, the subduction of the Pacific plate under the Eurasian plate is responsible for Japanese islands and volcanoes (such as Mt. Fuji).
- The final section of the Ring of Fire exists where the Indo-Australian plate subducts under the Pacific plate and has created volcanoes in the New Guinea and Micronesian areas. Near New Zealand, the Pacific Plate slides under the Indo-Australian plate.
Plate Tectonics
Another reason why Japan is continuously hit by tsunamis is because of plate tectonics. On several occasions, tsunamis various meters high have swept across Japan, washing whole villages into the sea. Such events are not infrequent around the tectonically active Pacific Ocean basin. Most tsunamis are caused by submarine earthquakes. Thus, they are most common in the Pacific Ocean, where earthquakes occur frequently in the subduction zones that form the "Ring of Fire." The central most reason why tsunamis hit Japan, however, is because Japan is precariously situated near the colliding margins of four tectonic plates - the Eurasian, the North American, the Pacific, and the Philippine. The subduction of these plates create high levels of seismic activity, leading to more tsunamis.
This Dynamic Earth is a great website that describes the background of the plate tectonics theory, how it developed, and also information for a deeper understanding of the concept. It includes great information and even cool pictures!! Please try it!!
How do we detect tsunamis?
Japan Meteorological Agency
The Japan Meteorological Agency (JMA) is a unique agency in the government of Japan. It is responsibile for issuing tsunami forecasts by analyzing seismic data from the nationwide observation network on a real-time basis, 24 hours a day and 7 days a week. In order that authorities of the national government and local governents can take emergency response to reduce tsunami disasters properly and immediately, the JMA issues tsunami warning/advisory three minutes after an earthquake occurrence if a tsunami is anticipated to have been generated by it. The JMA is using the empirical relationship between an earthquake location/magnitude and tsunami generation for its tsunami forecast at present. Tsunamis can sometimes propogate far from epicenters. The tsunamis originally caused near the American continent can travel across the Pacific Ocean and hit the Japanese archipelago. JMA issues tsunami forecasts for such long-propogated tsunamis for the purpose of mitigating these disasters, in co-operation with the Pacific Tsunami Warning Center (PTWC) in Hawaii, which exchanges information on tsunamis among pan-Pacific countries.
Go to the Japan Meteorological Agency website
Another description of the JMA at www.goin.nasda.go.jp/GOIN/JMA/
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