What makes mafic magma

Shasta could explode and collapse like Mt. Mazama in Oregon. Volcanic gases can form poisonous and invisible clouds in the atmosphere that could contribute to environmental problems such as acid rain and ozone destruction. Particles of dust and ash may stay in the atmosphere for years, disrupting weather patterns and blocking sunlight. Mafic magma creates gentler effusive eruptions. Although the pressure builds enough for the magma to erupt, it does not erupt with the same explosive force as felsic magma.

People can usually be evacuated before an effusive eruption, so they are much less deadly. Magma pushes toward the surface through fissures and reaches the surface through volcanic vents. Download this video of a lava stream within the vent of a Hawaiian volcano using a thermal camera.

Low-viscosity lava flows down mountainsides. Differences in composition and where the lavas erupt result in lava types like a ropy form pahoehoe and a chunky form called aa. Although effusive eruptions rarely kill anyone, they can be destructive. Even when people know that a lava flow is approaching, there is not much anyone can do to stop it from destroying a building, road, or infrastructure.

Skip to main content. Tectonic Forces. Partial melting of country rock and country-rock xenoliths increases the overall felsic character of the magma; first, because the country rocks tends to be more felsic than the magma, and second, because the more felsic components of the country rock melt preferentially. Settling of ferromagnesian crystals from the upper part of the magma, and possible remelting of those crystals in the lower part can both contribute to the vertical zonation from relatively mafic at the bottom to more felsic at the top.

From the perspective of volcanism there are some important differences between felsic and mafic magmas. Second, felsic magmas tend to have higher levels of volatiles; that is, components that behave as gases during volcanic eruptions. The most abundant volatile in magma is water H 2 O , followed typically by carbon dioxide CO 2 , and then by sulphur dioxide SO 2.

The general relationship between the SiO 2 content of magma and the amount of volatiles is shown in Figure 4. Differences in viscosity and volatile level have significant implications for the nature of volcanic eruptions. When magma is deep beneath the surface and under high pressure from the surrounding rocks, the gases remain dissolved. Hawaii's volcanoes, on the other hand, contain especially low-silica magmas made of basalt , which means they have much less explosive oomph.

Instead, they ooze and spatter, creating shield volcanoes —gently sloped formations that have become the islands' signature geologic silhouette. All rights reserved. Share Tweet Email.

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Typically, they contain a summit caldera , or large central crater, caused by repeated advances and retreats of the magma source. Effusive eruptions commonly occur at hot spots , like Hawai'i and Iceland, and at areas of sea-floor spreading. At the latter locations, mafic magma originates in the upper mantle and rises into the breach caused by diverging lithospheric plates. The resulting underwater eruptions produce long linear, basaltic mountain ranges and large areas covered with lava called flood basalts.

Flood basalts also occur on continents. Mafic lava spills out of cracks in the lithosphere caused by tectonic forces and coats large areas with layer upon layer of hardened basalt.

If you ask someone to describe a volcanic eruption, they are not likely to talk about shield volcanoes and flood basalts. They will probably describe great explosions and towering ash clouds.

The volcanoes that produce this kind of eruption are powered by felsic magma. Felsic magma forms at lower temperatures and has a different chemical composition than mafic magma see table above for comparison. The lower temperature of formation reflects a shallower origin near the base of the lithosphere. At plate collision boundaries with subduction, partial melting takes place at the upper surface of the subducting plate, as shown in the diagram.