Cradle MountainThis fog-shrouded peak is Cradle Mountain on the island of Tasmania. Although the pea

Cradle MountainThis fog-shrouded peak is Cradle Mountain on the island of Tasmania. Although the peak is not the highest on the island at an elevation of 1545 meters above sea level, it is one of the island’s most popular tourist locations in part from the spectacular columnar features that define the mountain’s shape.Tasmania contains one of the world’s largest outcrops of dolerite, a type of igneous rock related to basalt. Dolerite, also called diabase, forms when basaltic lava gets close to Earth’s surface but doesn’t quite erupt. Dolerite is defined by an “intermediate” grain size – it doesn’t stay hot long enough to form large crystals as in a gabbro, but it doesn’t erupt on the surface where it would cool extremely fast to make a fine-grained basalt. The spectacular vertical columns form perpendicular to the cooling direction due to thermal contracting; the rocks shrink as they cool down, causing fractures to form.These basalts were produced during the Jurassic, as the large continent Gondwana broke apart, with Australia rifting away from Africa and the other pieces. Tasmania has a long history of rifting, having both spread away from Gondwana during the Jurassic and from Australia itself more recently, leading to an island with large outcrops of igneous rocks.-JBBImage credit: https://flic.kr/p/7ht28VRead more:http://bit.ly/19hVTIwhttp://bit.ly/1DRxipEhttp://www.parks.tas.gov.au/file.aspx?id=6531 -- source link

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