Intrusive Forms
The lava that is released during volcanic eruptions on cooling develops into igneous rocks.
Depending on the location of the cooling of the lava, igneous rocks are classified as volcanic rocks (cooling at the surface) and plutonic rocks (cooling in the crust).
The lava that cools within the crustal portions assumes different forms. These forms are called intrusive forms.
Caldera
These are the most explosive of the earth’s volcanoes.
The collapsed depressions are called calderas.
Flood Basalt Provinces
These volcanoes outpour highly fluid lava that nows for long distances.
Flood Basalt Provinces
These volcanoes outpour highly fluid lava that flows for long distances. Batholiths
Batholiths are the cooled portion of magma chambers.
Lacoliths
These are large dome-shaped intrusive bodies with a level base and connected by a pipe-like conduit from below.
It resembles the surface volcanic domes of the composite volcano, only these are located at deeper depths.
Lapolith, Phacolith and Sills
As and when the lava moves upwards, a portion of the same may tend to move in a horizontal direction wherever it finds a weak plane.
It may get rested in different forms. In case it develops into a saucer shape, concave to the sky body, it is called lapolith.
A wavy mass of intrusive rocks, at times, is found at the base of synclines or at the top of anticline in folded igneous country. Such wavy materials have a definite conduit to source beneath in the form of magma chambers (subsequently developed as batholiths). These are called the phacoliths.
The near horizontal bodies of the innusive igneous rocks are called sill or sheet, depending on the thickness of the material. The thinner ones are called sheets while the thick horizontal deposits are called sills.
Dykes
When the lava makes its way through cracks and the fissures developed in the land, it solidifies almost perpendicular to the ground.
It gets cooled in the same position to develop a wall-like structure. Such structures are called dykes.
