Dikes are tabular or sheet-like bodies of magma that cut through and across
the layering of adjacent rocks and then solidify. They form when magma rises
into a fracture or creates a new crack by forcing its way through rock.
Hundreds of dikes can invade the cone and inner core of a volcano,
often along zones of structural weakness.
Left: An exposed dike, approximately five feet wide, at the
caldera of Mauna Loa Volcano in Hawaii.