You have seen the ways in which volcanoes erupt, and we have already said that volcanoes are not always the simple cones that one usually associates with outpourings of red hot, molten rock.
In fact, eruptions vary a great deal in the type of products that are spewed out, in their intensity, and in the form which the volcanic vent takes.
Types of volcanoes
- Fissure eruption
- Hawaiian volcano
Fissure eruption: First of all there is the type which is known as the fissure eruption. This is simple to describe. Her flood of lava pours out of a crack in the Earth’s crust and flows very freely. When it cools, it hardens into an almost flat sheet. This type of eruption is also known as the Icelandic type, because of the type of lava flows commonly found there.
Hawaiian volcano: In the Hawaiian type of volcano, so called for obvious reasons, lava pours out of a pit-like crater, and gas is quietly released most of the time.
Occasionally, however, there is a sudden spurt of the volcanic gases blowing out a spray of glowing, burning droplets of lava. The well-known Pele’s hair is caused by these droplets being caught in the wind and stretched into threads.
If the lava cannot flow easily (and this occurs when the composition of the magma is richer in silica), the gases have more difficulty in bubbling off. They are only released when the pressure builds up enough to force the gases out.
In This kind of eruption, which is known as the Strombolian type after Stromboli, Sicily, the volcano erupts from time to time carrying lumps of lava or volcanic bombs. Sometimes there are also lava flows.
If the lava is very thick and almost solid, great gas pressure is needed before it is released. When it does erupt it does so with explosive and terrible force, so that hot ash and fragments of lava are thrown high into the air.
This is known as the Vulcanian type, the characteristic cone is developed. There are other types of central volcanic types, that is, where the eruption is from one main centre.
Vulcanology is a very complex study, and for the more adventurous can be an extremely dangerous one, involving climbing to the very top of an active volcano.
Under these conditions, even if the volcano is not actually erupting the ground may be so hot that it burns the shoes of the scientists and the gases may be almost suffocating. Workers have actually looked into open craters into the bubbling, burning lava above.
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