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Intrusive rock is formed when magma penetrates existing rock, crystallizes, and solidifies underground to form intrusions, such as batholiths, dikes, sills, laccoliths, and volcanic necks. [1] [2] [3] Intrusion is one of the two ways igneous rock can form. The other is extrusion, such as a volcanic eruption or similar event.
Volcanic necks are feeder pipes for volcanoes that have been exposed by erosion. Surface exposures are typically cylindrical, but the intrusion often becomes elliptical or even cloverleaf-shaped at depth. Dikes often radiate from a volcanic neck, suggesting that necks tend to form at intersections of dikes where passage of magma is least ...
In geology, a sill is a tabular sheet intrusion that has intruded between older layers of sedimentary rock, beds of volcanic lava or tuff, or along the direction of foliation in metamorphic rock. A sill is a concordant intrusive sheet, meaning that it does not cut across preexisting rock beds.
For example, there is little penetration of magma into the walls of dikes even when the walls consist of highly porous volcanic clinker, and little wall material breaks off into the molten magma. These fissures likely open as a result of bulging of the rock beds above a magma chamber that is being filled with magma from deeper in the crust.
Volcanic group – Collection of related volcanoes or volcanic landforms; Volcanic island – Island of volcanic origin; Volcanic plateau – Plateau produced by volcanic activity; Volcanic plug – Volcanic object created when magma hardens within a vent on an active volcano; Volcano – Rupture in a planet's crust where material escapes
An example of a fingered laccolith is the Shonkin Sag laccolith in Montana, US. [4] The critical radius for the sill to laccolith transition is now thought to be affected the viscosity of the magma (being greater for less viscous magma) as well as the strength of the host rock. A modern formula for the shape of a laccolith is: Idealized ...
An example is the massive Level Mountain shield volcano in northern British Columbia, Canada, which covers an area of 1,800 km 2 (690 sq mi) and a volume of 860 km 3 (210 cu mi). [ 1 ] Perhaps the most extensive of all the subaerial basaltic plateaus existed during the Paleogene [ 2 ] and possibly extended over 1,800,000 km 2 (690,000 sq mi) of ...
Malpaís, in the Southwestern United States, Spain, Mexico, and other Spanish-speaking regions, are rough and barren landscapes that consist of relict and largely uneroded lava fields exhibiting recognizable lava flows, volcanic cones, and other volcanic landforms. This type of volcanic landscape is extremely rough and difficult to traverse.