VHP Photo Glossary: Dike
Dikes are tabular or sheet-like bodies of magma that cut through and across the layering of adjacent rocks. They form when magma rises into an existing fracture, or creates a new crack by forcing its way through existing rock, and then solidifies. Hundreds of dikes can invade the cone and inner core of a volcano, sometimes preferentially along zones of structural weakness.
This dike was exposed when a new pit crater formed in about 1880 A.D. in the northeast corner of the summit caldera of Mauna Loa Volcano. The dike is about 1.5 m wide.