lesson 12: australias stability

Question 1

why is aus stable

Answer 1

There are no active volcanoes in Australia, as Australia does not lie near the edge of a plate (we are located on the Indo-Pacific plate). Australia does have a small number of earthquakes, however, since the continent is a long way from a subduction zone, volcanoes do not form. There used to be a hots-spot underneath the crust of Eastern Australia, but the plates have moved, meaning that this hotspot is no more.

Question 2

general/rando volcano knowledge

Answer 2

Earthquakes and volcanoes mainly occur at tectonic plate boundaries as earthquakes are caused by the sudden release of energy as the tectonic plates grind past each other, and volcanoes are often found near plate boundaries where molten rock (magma) can travel upward between plates. Divergent plate boundaries cause volcanic activity and shallow earthquakes. Convergent plate boundaries result in earthquakes and a line of volcanoes on the overriding plate. Transform boundaries cause earthquakes as plates slide horizontally past each other.

Question 3

great dividing range

Answer 3

• The formation of the Great Dividing Range was very unusual.
• Mountain ranges are normally formed at collision zones, but there is no evidence of collision in Australia’s longest mountain range.
• It was formed in two stages. The initial stage of mountain building occurred hundreds of millions of years ago when Australia was still part of Gondwana and is thought to have been accompanied by ‘mantle upwelling’, where the crust is thinned due to hot mantle rising from below. However, some scientists suggest that a continued mantle upwelling (a super swell) during the separation of Gondwana radically changed the Great Dividing Range.
• The movement of Australia away from Antarctica could cause a thinning of the crust which would swell up if a large area of mantle rose underneath it.
• The separation was not perfectly perpendicular and tensional forces would have existed creating slip faults.
• Any subsequent movement along these faults could cause uplift of mountains.
• There are a number of young volcanoes along Australia’s eastern margin, such as the Glasshouse Mountains in Queensland and progressively younger volcanoes throughout Victoria.
• These are not related to subduction. This extensive volcanism cannot be completely explained by hotspot volcanism and may be related to a thinned crust and a mantle upwelling beneath.