View from Crater Rim Drive toward the southwest along a crack of the southwest rift zone. This is one of many ground cracks that formed as magma has moved underground from the summit reservoir into the rift zone. The crack is 4-6 m deep.
The crack exposes fragmental deposits of the Keanakako`i Ash Member that were erupted explosively, most recently in A.D. 1790. In this area, the unit is 6-8 m thick. Lava erupted during the September 1971 summit eruption covers the top and drapes the sides of the crack, and a short eruptive fissure occurs near the far end of the crack.