sea arch

The erosive action of water plays a key role in forming sea arches, just as with their terrestrial cousins, the spectacular rock arches of the Colorado Plateau. In both cases, the minerals in the water act to dissolve the rock, though for sea arches the sculpting process begins with the brute force of waves carving away weaker sections along a coastal promontory or headland. A sea cave formed by such action on one or both sides of a headland, its development aided by weathering, eventually wears through, creating a sea arch. Erosion and gravity then work on the opening until the arch collapses, leaving behind an islanded portion of headland called a sea stack. Sea arches are common along the coast of Hawai‘i Island below active Kilauea Volcano, where lava tubes are sculpted by wave action into sea caves and arches, such as ninety-foot-high Holei Sea Arch.

Pamela Frierson