Phacolith
Topic: Interior of the Earth: Earthquakes, Volcanoes and the Layered Earth · NCERT: Class 11, Ch 3 "Interior of the Earth"
Meaning
A phacolith is a wavy, lens-shaped mass of igneous rock that formed inside folded rocks. When rocks are folded, they form anticlines (upfolds) and synclines (downfolds). Magma moves into the weak zone at the top of an anticline or the base of a syncline. There it takes the curved shape of the fold. A pipe-like channel connects the phacolith to a magma chamber below. It is an intrusive landform, seen at the surface only after erosion.
Example
Corndon Hill in Shropshire, England, is often given as a phacolith. Its igneous rock sits in the crest of a fold.
Don't confuse with
- Laccolith: a dome with a flat base that pushes the rock layers up. A phacolith is not the cause of the fold. It simply fills the curve of a fold that already exists.