Aleutian subduction zone

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The Aleutian subduction zone is about 4,000 km long and marks where the Pacific Plate dives beneath the North American Plate, from the Alaska Range to the Kamchatka Peninsula. The subduction rate is faster in the west (about 7.5 cm per year) and slows toward the east (about 5 cm per year).

Two main features define the zone: the Aleutian Arc, a long chain of volcanoes, and the Aleutian Trench, a deep, narrow trench where the sinking plate bends under the overlying plate. The Aleutian Arc forms as water released from the sinking slab at around 100 km depth melts the overlying rock to feed volcanic eruptions. The trench’s curved shape reflects changes in the direction of the North American plate over millions of years.

The arc began forming tens of millions of years ago as plates moved, producing a thick, volcanic crust that is different from typical continental crust. Today, about 40 active volcanoes line the arc from mainland Alaska to the far western Aleutians. Much of the Aleutian Islands’ rocks are marine and volcanic, with eastern and western parts showing different magma styles.

Sediment-rich conditions in the trench come from turbidity currents and other deposits, building a wedge of sediment up to 20–30 km wide and about 1 km thick. The maximum trench depth is around 2 km, and sediment accumulation has varied over time, including a major influx from Pleistocene glacial erosion.

The region is known for powerful earthquakes. In the last several decades, five megathrust earthquakes larger than magnitude 8 have occurred along the megathrust: 8.2 in 1938 (Shumagin Islands), 8.6 in 1957 (Andreanof Islands), 9.2 in 1964 (Good Friday), 8.7 in 1965 (Rat Islands), and 8.2 near Perryville in 2021. Scientists also observe tremor and slow-slip earthquakes, with low-frequency earthquakes occurring down-dip where the plates are only partly locked.

The depth of these tremors relates to the age of the subducting plate: older, cooler plate depths tend to be deeper than those in the east, where the plate is younger and warmer. This combination of a long, active volcanic arc, a deep trench, and frequent large earthquakes makes the Aleutian subduction zone a key area for studying how subduction works.