Magmais less dense than the surrounding rock and also rises up to the surface through cracks and also crevices under the Earth\"s surfacecausing an eruption the lava.


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

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Magmawith low silica contents is very fluid and also easily erupts onto the surface ar through cracks and crevices at the surface. Gradually the great of lava develop up a volcano cone.Low silicavolcanoes are defined by \"quiet\" eruptions. Lava is able to quickly flow the end of the ground. This eruptions prchathamtownfc.netce many lava, but very little, if any, ash. Gas readily escapes from the lava.Over time short silicaeruptionsbuild a big broad cone.



A typical low silica eruptionprchathamtownfc.netces large amounts the lava.

Tectonic setup for low Silica Eruptions incorporate Spreading Centers such together the Mid-Atlantic Ridge or african Rift Zone and also Aseismic Ridges or hot Spots such together the Hawaiian Islands.

Flood Basalts

If, however, the lava is really low in silica, the lava is not thick enough to construct a cone in ~ all and it will circulation out over the Earth\"s surface lot like a flood. The byprchathamtownfc.netcts of this flow are generally referred to as flood basalts.

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

Volcanic Eruptions: High Silica

Lava with high silica content is thick and also viscous and does not readily flow. Lava rises up towards the surface yet is also thick to squeeze through the cracks and fissures in the Earth.

As lava continues to climb upward, pressure proceeds to build. Gas included in the lava is not released due to the fact that it is \"trapped\" in the viscous fluid. Push will continue to develop under the volcano until it exceeds the stamin of the overlying surface material. At this point the lava will explode outward lot as champagne from a bottle when the cork is released.

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