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Because the magma is viscous, the bubbles remain trapped in the magma. [2] As the magma nears the surface, the bubbles and thus the magma increase in volume. The pressure of the magma builds until the blockage is blasted out in an explosive eruption through the weakest point in the cone, usually the crater.
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.
Pyroclasts include juvenile pyroclasts derived from chilled magma, mixed with accidental pyroclasts, which are fragments of country rock.Pyroclasts of different sizes are classified (from smallest to largest) as volcanic ash, lapilli, or volcanic blocks (or, if they exhibit evidence of having been hot and molten during emplacement, volcanic bombs).
Magmatism is the emplacement of magma within and at the surface of the outer layers of a terrestrial planet, which solidifies as igneous rocks. It does so through magmatic activity or igneous activity, the production, intrusion and extrusion of magma or lava. Volcanism is the surface expression of magmatism.
Vertical migration of magma is driven by gravity. Stoping occurs when blocks of wall rock material are transferred downward through a pluton. [1] [2] Stoping is an important emplacement mechanism in a variety of tectonic settings and has been widely used to explain discordant pluton contacts. [2]
A laccolith is a type of igneous intrusion, formed when magma forces its way upwards through the Earth's crust but cools and solidifies before reaching the surface. . Laccoliths are distinguished from other igneous intrusions by their dome-shaped upper surface and l
Magma that cools slowly within a magma chamber usually ends up forming bodies of plutonic rocks such as gabbro, diorite and granite, depending upon the composition of the magma. Alternatively, if the magma is erupted it forms volcanic rocks such as basalt , andesite and rhyolite (the extrusive equivalents of gabbro, diorite and granite ...
The molten rock, or magma, in such a chamber is less dense than the surrounding country rock, which produces buoyant forces on the magma that tend to drive it upwards. [1] If the magma finds a path to the surface, then the result will be a volcanic eruption; consequently, many volcanoes are situated over magma chambers. [2]