Magmais less thick than the surrounding rock and rises up to the surface ar through cracks and crevices under the Earth"s surfacecausing one eruption of lava.

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The silica contents of the magma determines how thick the magma is, how easily it flows and how easily liquified gases in ~ the magmacan escape; therefore the silica content determines the properties of the volcanic eruption and also the shape and size the the resulting volcanic cone.

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Magmawith short silica content is really fluid and easily erupts onto the surface through cracks and also crevices in ~ the surface. With time the layers of lava build up a volcano cone.Low silicavolcanoes are defined by "quiet" eruptions. Lava is may be to easily flow the end of the ground. These eruptions prtennis2007.orgce lots that lava, but an extremely little, if any, ash. Gas readily escapes indigenous the lava.Over time short silicaeruptionsbuild a big broad cone.

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A typical low silica eruptionprtennis2007.orgces big amounts that lava.

Tectonic setup for low Silica Eruptions include Spreading Centers such as the Mid-Atlantic Ridge or afri Rift Zone and Aseismic Ridges or warm Spots such together the Hawaiian Islands.

Flood Basalts

If, however, the lava is an extremely low in silica, the lava is not thick enough to construct a cone in ~ all and it will circulation out end the Earth"s surface much like a flood. The byprtennis2007.orgcts of this flow are commonly referred to together flood basalts.

Between 17 million and 6 million years ago the Columbia river flood basalts covered component of the surface ar of Washington, Idaho and also Oregon come a depth of 9,000 ft.

Volcanic Eruptions: High Silica

Lava v high silica contents is thick and viscous and also does not conveniently flow. Lava rises up towards the surface yet is also thick to squeeze v the cracks and fissures in the Earth.

As lava proceeds to rise upward, pressure proceeds to build. Gas consisted of in the lava is not released due to the fact that it is "trapped" in the viscous fluid. Pressure will proceed to construct under the volcano until it above the toughness of the overlying surface material. At this allude the lava will certainly explode outward much as champagne native a bottle as soon as the cork is released.

See more: What Has The Lowest Density Solid Liquid Or Gas Es, Why Does Gas Have Less Density Than A Liquid

These varieties of eruptions are very destructive and also cause numerous deaths. The tectonic settingthat createsexplosive eruptions is a subduction zone. Recent explosive eruptions include: Mt. St. Helens, Mt. Pinatubo and Monserrat. The 4drawings listed below illustratehow a high silicaeruption occurs.