The oceanic crust of the Pacific Plate subducts underneath surrounding continental plates, causing a circular ring of earthquakes and volcanoes around its border. Subduction is the process by which an oceanic plate is pushed down beneath a continental plate, causing the formation of deep sea trenches and volcanoes. The Sarawak Chamber in Malaysia is the largest cave in the world is 2300 feet (701 meters) long, 1300 feet (400 meters) wide, and more than 230 feet (70 meters) high. The United Kingdom is very organised, with all these neat hedges, but Scotland is very rough, very natural.
Redoubt is a subduction zone volcano, deriving its magma from melt created when the Pacific plate dives beneath the North American plate. Simplified plate tectonics cross-section showing how Redoubt is located above a subduction zone formed where the Pacific and North American plates collide.
The most recent eruption began in December 1989 with a short period of intense seismicity and vent-clearing explosions that continued for more than five months.
Large lahars (volcanic mudflows) occurred in late March and early April, and have inundated the Drift River Valley and its downstream coastal fan. The Alaska Volcano Observatory cautions that there will likely be additional cycles of dome-building and explosions in the coming days to months, but their nature and timing are uncertain.
Jessica Ball is a graduate student in the Department of Geology at the State University of New York at Buffalo.
Redoubt is also capable of producing pyroclastic flows and surges, but aside from ash-related hazards, the next most pressing concern of a Redoubt eruption would be lahars. This subduction zone has created both the Aleutian Trench, about 270 miles to the southeast of the volcano, and the Aleutian volcanic arc, of which Redoubt is a part. On March 22, major plinian explosions began at the volcano, and since then more than 19 separate explosions have been recorded.
The lahars also reached the Cook Inlet, where the Drift River Oil Terminal is located, and overtopped the levees meant to protect the facility. It is in this crater that an elongated lava dome began forming, and was destroyed by the April 4 eruption.
The summit domes may become unstable and produce hot rock avalanches, pyroclastic flows, and ash columns, and melting snow on Redoubt will likely produce more lahars that may threaten downstream areas. The early stages of its growth were characterized by dacitic explosive eruptions, including pyroclastic flows and lava domes. Activity in the last 10,000 years has included a major collapse of the summit which resulted in a debris flow that reached the Cook Inlet, and clay-rich lahars that formed when hot material (most likely ash and gas eruptions) melted parts of the glaciers which cover Redoubt.
The oldest historical eruption occurred in 1902, when explosions were heard hundreds of kilometers away and extensive ashfall blanketed the Cook Inlet area.

Explosive eruptions in the 1960s caused flooding and lahars from melting glaciers, and created ash plumes that reached 6 km in height. Several of Redoubt's eruptions have produced ash falls up to hundreds of miles away, including areas on the Kenai Peninsula and in Anchorage. However Compare Infobase Limited,its directors and employees do not own any responsibility for the correctness or authenticity of the same.
Redoubt is a steep-sided stratovolcano located at the northeast end of the Aleutian volcanic arc. Isotopic data suggests that the volcano's magmas include melted rocks from the North American continental plate as well as the downgoing Pacific Plate and the melting mantle above it. Redoubt has erupted explosively at least five times since Captain James Cook observed the volcano steaming in 1778. Following a period of above-background seismicity beginning on January 25, 2009, Redoubt had a minor gas-and-ash explosion on March 15. A worldwide organization of Volcanic Ash Advisory Centers (VAACs) exists to monitor and issue warnings about ash and gas clouds created by volcanic eruptions. The latest cone-building stage saw Redoubt's chemistry becoming more silicic again, with andesite lava and block-and-ash flows and silicic andesite ash falls. Aerial view, looking north, of Redoubt Volcano during a continuous, low-level eruption of steam and ash on December 18, 1989.
Areas where explosive volcanic eruptions are common, such as the Kamchatka Peninsula in Russia, the islands of Indonesia and the Philippines, and the highlands of Central and South America, are constantly being monitored in order to prevent disastrous interaction between aircraft and volcanic clouds.
This hazard would be especially dangerous if Redoubt were to erupt, since volcanic ash that reaches the jet stream can be carried for hundreds or thousands of miles. The debris flows reached Cook Inlet and temporarily shut down the Drift River Oil Terminal. Lava flows in the crater built several lava domes which were later destroyed by explosions. Photography and thermal images showed that the dome, as of April 17, is about 500 m by 700 m (1640 ft by 1300 ft) in size and at least 50 m (160 ft) thick. Built above the Aleutian subduction zone over the last 890,000 years, Redoubt is now heavily glaciated and boasts an ice-filled summit crater. Redoubt's eruptions pose a direct hazard to aircraft, especially in the high-traffic flight paths that pass over the Aleutian volcanic arc. Renewed activity would pose a major risk to air traffic in the region around the volcano, and ash from an eruption could reach as far as the continental US.
Her concentration is in volcanology, and she is currently researching lava dome collapses and pyroclastic flows.

In 1990, one aircraft that flew through a suspected eruption cloud from an Alaskan volcano experienced a shutdown of all of its engines, and its crew managed to restart them just in time to prevent a deadly crash. The eruption clouds have reached more than 50,000 feet (15 km) above sea level, and have forced airlines to reroute their flight paths away from the volcano. She also writes the Magma Cum Laude blog, and in what spare time she has left, she enjoys rock climbing and playing various stringed instruments. Ash that enters a hot aircraft engine is quickly melted and resolidifies on moving engine parts as glass, which can cause the engine to flame out or shut down entirely.
There have been many explosive eruptions, ash has blanketed the landscape and floods have swept down the Drift River. In 1990, lahars initaited by hot erupted material reached the Cook Inlet in only a few hours, and completely shut down the Drift River Oil Terminal.
In order to better monitor Redoubt's eruptions, scientists at AVO have installed several new seismometers, GPS receivers, and a new webcam, and are carefully monitoring the growth of the lava dome, seismic activity, and gas emissions at the volcano. Examples of hotspots include Hawaii and the Portuguese island of Madeira, but for the most part, volcanoes lie at the edge of tectonic plates.Geological features, including types of volcanoes.
Al Werner and Kristi Wallace of the Alaska Volcano Observatory are using a pontoon boat as a coring platform to recover volcanic ash erupted from Redoubt and other Aleutian Arc volcanoes.
The mushroom-shaped plume rose from avalanches of hot debris (pyroclastic flows) that cascaded down the north flank of the volcano. They use visual, chemical and thermal satellite data as well as direct visual observations to identify dangerous ash clouds, and issue alerts to aviation control administrations around the world. But when the magma reaches the surfaces, another interesting thing happens.A spectacular eruption in Stromboli, Italy.
Later cone-building eruptions, beginning about 340,000 years ago, became less silicic, producing basalt and basaltic andesite lava flows, scoria and ash flows. However, we haven’t been able to find composite volcanoes anywhere else in the solar system, except for one exception, on Mars.
The 1989-90 dome is completely covered and no anomalous holes or steaming were observed on this day.

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