Describe How Igneous Activity Can Affect The Landscape
Describe how igneous activity can affect the landscape
Igneous intrusions form when cooling, crystallization and loss of gases cause a once fluid magma to solidify. Most rocks that form intrusions originate as either granitic or basaltic magma. Granitic magmas are low density and small quantities, just a few kilometers wide, rise slowly through the earth’s upper crust, pushing existing country rock aside. However, very large granite masses, which can be up to 1,000 times larger, are formed when magma incorporates heated country rock.
An intrusive igneous rock is called a pluton. Major plutons include batholiths and stocks. Minor plutons include dykes, sills and laccoliths. A dyke is a shaft of igneous rocks that cuts across the geological layers, whereas a sill runs parallel to the geological strata. A laccolith forms a larger intrusion that causes rocks above to form domes. The landforms produced by plutons depend on the size of the intrusion and its strength relative to surrounding rocks. If it is more resistant, it forms uplands or elevated areas; if it is weaker, it may form depressions.
Intrusive rocks tend to be coarse grained, since the magma cools slowly and has sufficient time to form large crystals. Extrusive igneous rocks cool rapidly at the earth’s surface, producing fine grained or glassy rocks. Basalt is fine grained because it cools very rapidly, whereas granite is coarse grained because it has cooled slowly.
Batholiths are underground masses of magma often forming dome-like chambers. Granitic magmas are usually viscous, so they tend to produce huge batholiths that have an area of at least 100 km2. The smaller offshoots from one of these lies under the granite moorlands of Devon and Cornwall. In these areas, the magma was pushed into the crust about 300 million years ago. Over millions of years, the rocks in the crust overlying the batholith complex have been worn away, exposing the granites at the surface. Since these granites are hard and
Igneous intrusions form when cooling, crystallization and loss of gases cause a once fluid magma to solidify. Most rocks that form intrusions originate as either granitic or basaltic magma. Granitic magmas are low density and small quantities, just a few kilometers wide, rise slowly through the earth’s upper crust, pushing existing country rock aside. However, very large granite masses, which can be up to 1,000 times larger, are formed when magma incorporates heated country rock.
An intrusive igneous rock is called a pluton. Major plutons include batholiths and stocks. Minor plutons include dykes, sills and laccoliths. A dyke is a shaft of igneous rocks that cuts across the geological layers, whereas a sill runs parallel to the geological strata. A laccolith forms a larger intrusion that causes rocks above to form domes. The landforms produced by plutons depend on the size of the intrusion and its strength relative to surrounding rocks. If it is more resistant, it forms uplands or elevated areas; if it is weaker, it may form depressions.
Intrusive rocks tend to be coarse grained, since the magma cools slowly and has sufficient time to form large crystals. Extrusive igneous rocks cool rapidly at the earth’s surface, producing fine grained or glassy rocks. Basalt is fine grained because it cools very rapidly, whereas granite is coarse grained because it has cooled slowly.
Batholiths are underground masses of magma often forming dome-like chambers. Granitic magmas are usually viscous, so they tend to produce huge batholiths that have an area of at least 100 km2. The smaller offshoots from one of these lies under the granite moorlands of Devon and Cornwall. In these areas, the magma was pushed into the crust about 300 million years ago. Over millions of years, the rocks in the crust overlying the batholith complex have been worn away, exposing the granites at the surface. Since these granites are hard and