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Cascadia Subduction Zone | Pacific Northwest Seismic Network

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The Cascadia Subduction Zone (CSZ) "megathrust" fault is a 1,000 km long dipping fault that stretches from Northern Vancouver Island to Cape Mendocino California. It separates the Juan de Fuca and North America plates. New Juan de Fuca plate is created offshore along the Juan de Fuca ridge.

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How do earthquakes generate tsunamis? - International Tsunami Information Center

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The Pacific Northwest is due for a Major Earthquake

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Aniakchak National Monument and Preserve is on the Alaska Peninsula. The eruption of Aniakchak Volcano about 3,500 years ago rivals the eruption and collapse of Mt. Mazama that formed Crater Lake. The original composite volcano was about 7,000 feet (2,000 meters) high, but lost about 2,500 feet (750 meters) of its height. The 6-mile (10-kilometer) wide caldera is about 2,000 feet (600 meters) deep. Like Mt. Mazama, Aniakchak spewed lava across its caldera floor for centuries after its collapse. The volcano is still active, having erupted in 1931. But unlike Mt. Mazama, Aniakchak no longer holds a large lake because the caldera wall is breached.

Katmai National Park and Preserve lies where the world's largest volcanic event of the 20th Century occurred. In 1912 the Katmai region erupted an estimated 7 cubic miles (30 cubic kilometers) of ash and pyroclastic material, roughly 50 times the amount that came out of Washington's Mt. St. Helens in 1980. The collapse caldera from the Katmai eruption is about 3 miles (5 kilometers) across and 2,000 feet (600 meters) deep. The caldera has partially filled with water - an approximately half-scale version of the better-known Crater Lake in Oregon. Katmai volcano did collapse, but unlike Mt. Mazama 7,700 years before, the material expelled from its magma chamber did not spew forth out of the top of the volcano. Rather, it flowed underground to a vent 6 miles (10 kilometers) away! The vent was the source for most of the ash and pyroclastic flows expelled during the 1912 eruptions, and has since filled with a lava dome known as Novarupta.

At 20,625 square miles (53,396 square kilometers), Wrangell - St. Elias National Park and Preserve is the largest U. S. national park - six times the size of Yellowstone. The park is a complex amalgamation of blocks of continental and oceanic crust that have slammed into North America. Poking through the mass of some of the highest mountains in North America are very young volcanoes formed by the ongoing Pacific Plate subduction. Among them are Mt. Wrangell, a 14,163 foot (4,317 meter) volcano that last erupted during the early part of the 20th Century.

Lake Clark National Park and Preserve contains an active composite volcano with a profile and recent history reminiscent of Mt. St. Helens. In 1989 and 1990, Mt. Redoubt, on the eastern side of the park, had four explosive eruptions that resulted in large volumes of ash and mudflows. And, as at Mt. St. Helens, a lava dome later grew within the breached crater near the mountain's summit.

Volcano Monitoring in National Parks

The eruption of Mt. Redoubt, an active volcano in Lake Clark National Park, illustrates how a volcano can pose an unexpected hazard in our modern age - and why monitoring volcanic activity is so important (see photo below). On Dec. 15, 1989 a jet with 244 passengers and crew was en route from Amsterdam to Anchorage. Without warning the plane flew right through the eruption cloud at 25,000 feet (7,500 meters) altitude. Silica-rich ash melted and coated the hot engine turbines with glass, causing all four of them to shut down. After a terrifying free-fall that lasted 8 minutes, the pilots finally managed to restart the engines at only 6,000 feet (2,000 meters). Fortunately, no one was injured. But the incident highlighted the importance of monitoring volcanic activity and making the information immediately available to the airline industry and other segments of the public.

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Convergent Plate Boundaries-Subduction Zones - Geology (U.S. National Park Service)

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Aniakchak National Monument and Preserve is on the Alaska Peninsula. The eruption of Aniakchak Volcano about 3,500 years ago rivals the eruption and collapse of Mt. Mazama that formed Crater Lake. The original composite volcano was about 7,000 feet (2,000 meters) high, but lost about 2,500 feet (750 meters) of its height.