Yellowstone Lava Dike
July 17, 2003
The above photo shows an old lava dike above a stream in Yellowstone National Park. If magma rises toward the surface and flows into vertical fissures, later cooling and hardening, dikes are formed. The lower part of the above formation could be a sill connected to the dike. A sill is formed by intrusion of molten rock along bedding planes. Recent erosion has exposed the dike and sill features.