Cape Cleare is a headland located at the southwest end of Montague Island, at the entrance to Montague Strait, leading to Prince William Sound, approximately 60 miles (97 km) southeast of Seward, Alaska. The cape was named by Captain Nathaniel Portlock in 1787. In 1791, Captain Alessandro Malaspina referred to it as “Cabo Serena,” reportedly because it was sighted on a beautiful day.

On March 27, 1964, a subduction zone earthquake with a magnitude of 9.2 struck Prince William Sound, Alaska. This remains the most powerful quake recorded in North America. The seismic event occurred as the oceanic Pacific Plate subducted beneath the continental North American Plate. The Aleutian Megathrust, a reverse fault caused by compressional forces, was responsible for the earthquake. Vertical displacement reached up to 38 feet (11.5 meters), impacting an area of 64 million acres (25 million ha). This tectonic activity led to significant geological and environmental changes across the region.

The megathrust fault beneath Prince William Sound marks the boundary between the subducting Yakutat terrane and the overlying accretionary Prince William terrane. West of Montague Island, however, the Yakutat terrane is absent, and the Pacific Plate subducts directly beneath the North American Plate. The area of highest moment release during the earthquake was centered beneath the southwestern end of Montague Island. At Cape Cleare, the seafloor was uplifted approximately 33 feet (10 m). The newly exposed, gently sloping rocky surface at low tide measures about 0.3 miles (0.5 km) in width. Previously, this wave-eroded platform lay below sea level. Read more here and here. Explore more of Cape Cleare and Montague Island here: