active and ancient volcanic features

Active and ancient volcanic features, including laccolith.

A laccolith is a dome-like intrusion of igneous rock, usually arching the overlying strata and with an approximately flat base. Laccoliths are generally less than 16 km (10 mi) in diameter with thickness of 30–900 m (100–3,000 ft). They are formed of magma; they are smaller than batholiths.


Phacoliths are similar but lens-shaped, with a concave side facing downward and a convex side facing upward. See also dike and sill.