Volcanoes
What is a Volcano?
A volcano is a point in the Earth's crust where magma emerges either quietly or explosively.
Where does the magma come from?
The magmaMagma
Super heated rock which is so hot that it is liquified. is molten rock which has come from the mantle. Molten rock can be 1200-1600 degrees celcius and is constantly moving. Pressure, heat and thus expansion combine to create conditions for the magma to rise to the surface as lava in a volcanic eruption.
Eruptions
Volcanic eruptions vary in activity and type. Typical volcanic eruptions are violent, explosive events also known as Strombolian or vulcanian eruptions. Peleean eruptions also known as pyroclastic flows are fast, destructive and deadly. Hot gas, ash and rocks are propelled down the slopes of volcanoes with little chance of escape.
But not all eruptions are violent. Eruptions on Mauna Lao, (Hawaii) are quieter in comparison. The lava is less viscous and is responsible for the massive shield volcano which is 16km in height but most of it is submerged beneath the Pacific ocean.
Volcanoes
When did the volcanoes in South West Victoria occur?
To illustrate when the volcanic activites in SW Victoria occured a list has been compiled with the addition of other interesting events in history.
3 Mill. years - Cape Bridgewater volcano formation
2 Mill. years - Quaternary period began
2 Mill. years - Mount Richmond formation
1 Mill. years - Hopkins Falls formation
1 Mill. years - Homo Erectus pioneer trek to Asia and Europe
30,000 years - Neanderthal Man extinct
28,000 years - Mount Eccles volcano formation
26,000 years - African rock art - Namibia (created)
23,000 years - Tower Hill volcano formation
20,000 years - Hundreds of footprints made Willandra, Sydney
15,000 years - Dogs first found to be living in communities
8,000 years - Potato first harvested
6,200 years - Cattle domesticated
6,000 years - Mount Napier volcano formation
<6,000 years - Lava Blisters, Byaduk Cave formations
2,500 years - Pyramids of Egypt
2,200 years - Stonehenge
Volcanoes
What types of volcanoes are there?
Composite Volcanoes are steep sided and are formed by successive eruptions of ash and lava as in Mount Napier and Mount Rouse volcanoes.
Shield Volcanoes have shallow cones with lava containing low sillicate levels thus making the lava more runny. Shields volanoes can be vast in size like the Mauna Lao volcano in Hawaii.
Fissure Volcanoes also have shallow areas with lava containing low sillicate levels thus making the lava more runny. Cracks may form along the way with emerging lava. Mount Eccles is an example of a fissue volcano.
Ash cinder Volcanoes are steep sided and are formed by successive eruptions of ash and cinder. Similar to Composite volcanoes.
Caldera Volcanoes are those that show distinct subsidence of its cone either because of the cones shear weight or else the base of the volcano weakens. Tower Hill and Cape Bridgewater have evidence of subsidence.
Maar Volcanoes are formed when hot magma some into contact with ground water to create explosive eruptions of tuffTuff
Consolidated rock material consiting of ash and rock fragments. which falls to the ground to form a ring around the rim of the volcano. Usually the eruptions begin below ground level so water fills the crater afterwards. Maar volcanoes also tend to be wider than they are deep. Tower Hill volcano is an example of a maar volcano.
Volcanoes
Where are volcanoes found?
The are more than 1500 active volcanoes around the world at any one time. Most of these are located on the edges of the world's tectonic plates. However there are instances where volcanoes form as the result of hot spots located in the middle of the tectonic plates.
Subduction
Subduction is where the tectonic plates slide under one another. Usually the oceanic side of a tectonic plateTectonic Plates.
Large sections of the Earth's crust that move slowly. subducts under continental plates because oceanic floor is a heavier basalt layer. The basalt layer is forced down to the mantle where it melts. The extra molten material created at these points help to form new volcanoes. The Pacific plate has around 90% of the world's volcanoes located around it. It is also known as the Ring of Fire.
Hot Spots
Volcanoes in South West Victoria are believed to have formed due to hot spotsVolcanic Hot Spots.
Areas in Earth's crust where the crust is thinner usually at the center of tectonic plates. At these points narrow conduits of magma rise to the surface. in the Earth's crust. Another well known hot spot are the volcanoes that make up the Hawaii Volcano Chain.
Hot Spot Animation
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