Akun Island, Alaska: Columnar Basalt

Akun Island lies within the Aleutian volcanic arc, a classic example of a convergent plate boundary where the Pacific Plate is subducting beneath the North American Plate. This subduction has generated extensive calc-alkaline volcanism, forming the Aleutian Islands — a chain of mostly stratovolcanoes, lava domes, and basaltic flow fields.

Akun Island is located in the Aleutian Islands chain of Alaska. It is known for its impressive columnar basalt formations, which are some of the tallest and most dramatic in the world.

Columnar basalt is a geological formation that consists of closely spaced, vertically oriented basalt columns. These columns form when lava cools and contracts, creating cracks in the rock. The columns are typically hexagonal or pentagonal in shape, and they can range in size from a few centimeters to several meters in diameter.

Akun Island Columnar Basalt - Alaska. Photo by: Steve Hillebrand, U.S. Fish and Wildlife Service

Akun Island in Alaska is home to a spectacular example of columnar basalt. The columns on Akun Island are up to 60 meters (200 feet) tall and 3 meters (10 feet) in diameter. They are formed from lava flows that erupted from volcanoes on the island millions of years ago.

The columns can vary from 3 meters to a few centimeters in diameter, and can be as much as 30 meters tall. They are typically parallel and straight, but can also be curved and vary in diameter.

Natural columnar basalt rock formation on Akun Island, Alaska. Photo by: Steve Hillebrand

Environmental and Geomorphic Factors

• Akun’s columnar basalt is often exposed along sea cliffs and coastal benches, shaped by marine erosion.
• Frost action and periglacial processes may contribute to the disarticulation of columns.
• Wave-cut platforms expose these columns at low tide, offering excellent views for geologic mapping.

Volcanic columnar basalt formation on Akun Island, Alaska. Photo by: Steve Hillebrand

Akun Island lies within the Aleutian volcanic arc, a classic example of a convergent plate boundary where the Pacific Plate is subducting beneath the North American Plate. This subduction has generated extensive calc-alkaline volcanism, forming the Aleutian Islands — a chain of mostly stratovolcanoes, lava domes, and basaltic flow fields.

The columnar basalt on Akun Island formed from relatively low-viscosity basaltic lava flows that cooled slowly enough to contract and fracture, producing columnar jointing.