volcanoes

We are now back to volcanoes (: and although todays lessons was not thrilling it was definately a vast improvement upon that of Belfast. We have also been set an essay, nothing like ensuring we don't relax-- it hadnt even been 24 hours after the exam! oh well such as life.

Today was a lesson running through what we were doing before christmas:

There are 2 key types of magma Basaltic and Rhyolitic this is judged upon how much silica (SiO2) is found within the magma, see the table below.

Summary Table
Magma Type	Solidified Rock	Chemical Composition	Temperature	Viscosity	Gas Content
Basaltic	Basalt	45-55 SiO2 %, high in Fe, Mg, Ca, low in K, Na	1000 - 1200 oC	Low	Low

Rhyolitic

Rhyolite

65-75 SiO2 %, low in Fe, Mg, Ca, high in K, Na.

650 - 800 oC

High

High

 

• Hawaiian - These are eruptions of low viscosity basaltic magma. Hawaiian Eruptions are considered non-explosive eruptions.  Very little pyroclastic material is produced.

Strombolian - These eruptions are characterized by distinct blasts of basaltic to andesitic magma from the vent. Strombolian eruptions are considered mildly explosive. Vulcanian - These eruptions are characterized by sustained explosions of solidified or highly viscous andesite or rhyolite magma from a the vent.  Eruption columns can reach several km above the vent, and often collapse to produce pyroclastic flows.  Widespread tephra falls are common.  Vulcanian eruptions are considered very explosive. Pelean - These eruptions result from the collapse of an andesitic or rhyolitic  lava dome. Pelean eruptions are considered violently explosive. Plinian - These eruptions result from a sustained ejection of andesitic to rhyolitic magma into eruption columns that may extend up to 45 km above the vent.  Eruption columns produce wide-spread fall deposits with thickness decreasing away from the vent, and may exhibit eruption column collapse to produce pyroclastic flows.  Plinian ash clouds can circle the Earth in a matter of days. Plinian eruptions are considered violently explosive.

i feel there is a good chance i may add to it soon!