Photo: Steve Hillebrand, U.S. Fish and Wildlife Service

The largest state in the United states by area but the least densely populated, Alaska has Akun Island having basalt and number of caves.

Columnar jointing is a geological structure where sets of intersecting closely spaced fractures, referred to as joints, result in the formation of a regular array of polygonal prisms, or columns. Columnar jointing can occur in cooling lava flows and ashflow tuffs (ignimbrites), as well as in some shallow intrusions.

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.

Photo: Steve Hillebrand

Photo: Steve Hillebrand