Igneous rocks are a type of rock formed by the crystallization of magma or lava. Many of the landforms within Big Bend National Park are composed of igneous rock or have been influenced by igneous processes. There are three different classifications of igneous rocks, intrusive, extrusive, and pyroclastic.

Rocks that crystallize below the surface of the earth are known as intrusive or plutonic rock. Some examples of intrusive igneous features are dikes, sills, batholiths, and laccoliths. Click here to take a tour of some of the intrusive igneous formations found in Big Bend.

Rocks that crystallize above the surface of the earth are known as extrusive or volcanic rock. When volcanoes erupt and sheets of lava pour out across the surrounding area, the feature that is created is called a lava flow. These flows can be broken into two groups, pahoehoe and aa. Pahoehoe is a term used for a lava flow that has a ropy appearance as pours. Aa is the term for lava flows that move with sharp spiny elements being carried along. Click here to see some examples of extrusive features that can be found in Big Bend.

Rocks that crystallize above the earth during violent volcanic eruptions are pyroclastic rocks. These rocks form as a result of lava and ash being thrown into the air and cooling as it falls to the ground. Some examples of pyroclastic rocks are tuff and volcanic bombs. Click here to see some examples of pyroclastic features found in Big Bend.