When Magma Meets Water
In this case, water overlying the subducting seafloor would lower the melting temperature of the mantle, generating magma that rises to the. Types and Processes Gallery - Magma meets Water The ensuing eruptions often do not involve any ejection of new magma, but rather the fragmentation and . Mixing molten magma with cool water sounds dangerous. When Magma Meets Water | Breakthrough (YouTube/National Geographic).
Some granite -composition magmas are eutectic or cotectic melts, and they may be produced by low to high degrees of partial melting of the crust, as well as by fractional crystallization.
At high degrees of partial melting of the crust, granitoids such as tonalitegranodiorite and monzonite can be produced, but other mechanisms are typically important in producing them. Evolution of magmas[ edit ] Primary melts[ edit ] When a rock melts, the liquid is a primary melt.
Primary melts have not undergone any differentiation and represent the starting composition of a magma. In nature it is rare to find primary melts.
Magma - Wikipedia
The leucosomes of migmatites are examples of primary melts. Primary melts derived from the mantle are especially important, and are known as primitive melts or primitive magmas.
By finding the primitive magma composition of a magma series it is possible to model the composition of the mantle from which a melt was formed, which is important in understanding evolution of the mantle.
A parental melt is a magma composition from which the observed range of magma chemistries has been derived by the processes of igneous differentiation. It need not be a primitive melt. For instance, a series of basalt flows are assumed to be related to one another. A composition from which they could reasonably be produced by fractional crystallization is termed a parental melt.
Fractional crystallization models would be produced to test the hypothesis that they share a common parental melt. At high degrees of partial melting of the mantle, komatiite and picrite are produced. Migration and solidification of magmas[ edit ] Magma develops within the mantle or crust where the temperature and pressure conditions favor the molten state. After its formation, magma buoyantly rises toward the Earth's surface.
As it migrates through the crust, magma may collect and reside in magma chambers though recent work suggests that magma may be stored in trans-crustal crystal-rich mush zones rather than dominantly liquid magma chambers .
Magma can remain in a chamber until it cools and crystallizes forming igneous rock, it erupts as a volcanoor moves into another magma chamber. There are two known processes by which magma changes: Plutonism[ edit ] When magma cools it begins to form solid mineral phases. Some of these settle at the bottom of the magma chamber forming cumulates that might form mafic layered intrusions. Magma that cools slowly within a magma chamber usually ends up forming bodies of plutonic rocks such as gabbrodiorite and granitedepending upon the composition of the magma.
Alternatively, if the magma is erupted it forms volcanic rocks such as basaltandesite and rhyolite the extrusive equivalents of gabbro, diorite and granite, respectively. Volcanism During a volcanic eruption the magma that leaves the underground is called lava.
Lava cools and solidifies relatively quickly compared to underground bodies of magma. This fast cooling does not allow crystals to grow large, and a part of the melt does not crystallize at all, becoming glass.
Rocks largely composed of volcanic glass include obsidianscoria and pumice. The ensuing eruptions often do not involve any ejection of new magma, but rather the fragmentation and explosive expulsion of pre-existing rock along the path of the volcanic conduit. Phreatic eruptions are gradational into magmatic eruptions, and many eruptions in fact involve the ejection of both old and new volcanic materials and are referred to as phreatomagmatic. Phreatic eruptions are sometimes accompanied by pyroclastic surges, dilute laterally moving clouds of gas, ash, and rock that sweep radially away from the vent.
Ruapehu A small phreatic eruption on February 29,produces a column of ash and steam above Ruapehu's Crater Lake.
A darker central plug is surrounded by a white ring produced by pyroclastic surges traveling across the lake surface. This view is from the NW, with Mitre Peak at the upper left. A series of small phreatic explosions had begun December 5,and lasted until April 15 of the following year. Ruapehu The interaction of magma and water can produce strong phreatic steam-driven explosions, such as seen in this photo of New Zealand's Ruapehu volcano.
Clouds of ash and steam trail from large ejected blocks in the eruption column. Laterally moving pyroclastic-surge clouds form a white basal ring above the surface of a crater lake. Phreatic or phreatomagmatic explosions are common at submarine volcanoes, crater lakes, and other places where hot magma or associated gases encounters surface water or groundwater. Kelut Kelut volcano has been notorious for the repeated ejection of crater-lake water during eruptions, producing devastating lahars.
A series of tunnels and shafts were constructed in the 's to lower the lake level and reduce the hazards of eruptions. The initial tunnels lowered the lake level 50 m, but the eruption deepened the crater by 70 m, leaving 50 million cu m of water.
Following another devastating eruption inlower outlet tunnels were constructed, and prior to the eruption the lake contained only 1 million cu m of water. Photo by John Dvorak, U.
Kusatsu-Shiranesan The turquoise waters of Yu-gama, one of three craters at the summit of Japan's Kusatsu-Shirane volcano, are a popular tourist destination.