2ClassificationIgneous rocks are classified into two areas depending on where thy formed.IntrusionsUnderground igneous rock masses.ExtrusionsAbove ground igneous rock masses.
3Extrusive FeaturesInclude volcanoes, flood basalts, lava flows, etc.
4Intrusive Features Form when magma cools and hardens underground. These structures may later be exposed at the surface through erosion.Include:Batholiths, dikes, sills, and volcanic necks.
5Intrusive Features Batholiths Largest intrusive structures. Cover over 100 square kilometers.May be many hundreds of kilometers in width and length and several kilometers thick.Tend to form the cores of major mountain ranges.
7Intrusive Features Stock Similar to a batholith, but… Covers less then 100 square kilometers.
8Intrusive Features Laccolith Forms when magma flows between rock layers and spreads upward, pushing the overlying rock layers into an arc.The floor of a laccolith is parallel to the rock layer beneath it.
9Intrusive Features Dike Forms when magma that has been forced into a crack that cuts across rock layers hardens.
10Intrusive Features Sill Forms when magma that has been forced into a crack running parallel to rock layers hardens.
11Volcanic NeckForms when the magma inside a volcano cools and hardens and the overlaying softer layers are eroded.
12CalderasForm when the top of a volcano collapses into an emptied magma chamber.Example – Crater Lake – Formed after the eruption of Mount Mazama around 7,000 years ago.