Aleutian Ridge

The Aleutian Ridge lacks any pre-Eocene rock record, and was formed since then. The ongoing tectonic interaction between the Pacific and North American plates defines the Aleutian Arc's structure and activity. These plates converge at a rate of approximately 85–90 mm (3.3–3.5 in) per year, with nearly perpendicular subduction along the Alaska Peninsula, becoming increasingly oblique toward the western Aleutian Ridge due to the arc's curvature. In the central Aleutians, the subduction angle is about 30° from perpendicular, while in the western ridge, plate motion becomes nearly parallel to the arc.^[1][3]

The Aleutian Ridge is composed of three main rock layers, beginning with a lower series that forms its igneous basement. This foundation consists primarily of extrusive and intrusive volcanic rocks and coarse volcanic debris, dating back to the early to middle Eocene (55–50 million years ago). Rapid volcanic activity formed the ridge’s core, peaking around 45–40 million years ago, but slowed by the early Oligocene (around 37 million years ago). As volcanic growth diminished, the middle series began forming—made up of volcaniclastic and silty sediments. These materials buried the submerged flanks of the ridge and continued to accumulate until about 5–6 million years ago, near the end of the Miocene, when the Aleutian Terrace basin started to structurally evolve.^[4][5] Most of the active volcanoes are located on the northern boundaries of the Aleutian Islands.^[2]