Outback Geography: The Physical Geography of Australia: Volcanism and Faulting

The Australian Alps stretch across the southeastern border of Australia creating high plateau like mountains. The Australian Alps were formed by the splitting apart or divergent plates of a supercontinent called Gondwana (India, Australia, Antarctica, and Zealandia) 160 million years ago. Extension faults (where the earth crust of the earth pulls apart) formed between Australia and Zealandia as magma from the asthenosphere (partially molten second layer of earth) uplifted the earths crust (lithosphere or top layer) and formed new rock. The faults caused a rift valley (low and usually water filled land) to form between the continents and the Tasman sea (body of water between Australia and Zealandia) expanded in between the two continents drifting them apart. The western scarp (face of the newly faulted land mass) of the split continents left behind what was the start of the Australian Alps. Over time erosion (weathering) played the role of carving out the rest of the Australian Alps.

Photo Credit:
http://www.australianalps.environment.gov.au/nature/geology.html

Australian Alps
Photo Credit:
http://www.undurraarabians.com.au/home/images/stories/location/mthotham.jpg

Australia contains many extinct volcanoes and only two remaining active volcanoes on Australian territory (Big Ben and Mawson Peak). Australia's Western Victorian Volcanic Plains are one of the most volcano dense on the continent and third largest in the world. Around 400 volcanoes exist in this region, mainly cinder cones (extrusive volcanic landforms) that have produced large basaltic (low viscosity) lava flows. Viscosity measures the thickness of a liquid and basaltic lava having low viscosity, is very thick and slow moving. Mt Noorat is a cinder cone that exploded pyroclastics (tephra) out with a basaltic lava flow, leaving a (Maar eruption) crater that dives down lower than the surrounding plain of the volcano. Tephra comes in many forms including ash, small grainy deposits, and large rocks or bombs. A Maar eruption occurs when groundwater collides with lava or magma. The volcano is estimated to be formed between 10,000 and 15,000 years ago with a crater 159 meters deep. The Western Victorian Volcanic Plains contain many types of extinct volcanoes that have erupted forming this vast expanse of basaltic rock and sediment.