Sandman Islands, Gulf of Alaska

The Sandman Islands lie off the south side of the Alaska Peninsula and are mostly composed of columnar basalts creating steep sea cliffs. Igneous rocks, such as columnar basalts, are particularly strong and resistant to erosion. The sea cliffs erode primarily by thermal expansion of freezing ocean spray and rainwater that seeps into cracks and crevices. The broken rock particles tumble into the sea and accumulate as talus at the base of the sea cliff. Ocean waves and currents act only to remove the finer particles from the debris pile. The columns are formed during the cooling of thick lava flows. While a flow can shrink in the vertical dimension without fracturing, it can't easily accommodate shrinking in the horizontal direction unless cracks form; the extensive fracture network that develops results in the formation of columns. The columns are predominantly hexagonal in cross-section, and the size of the columns depends on the rate of cooling. Read more here. Click here to download the CoastView app and explore the Sandman Islands.