Unstable continent – Did you know?
An Active Continent
The earthquake which hit Newcastle in 1989 was the most destructive in recent Australian history, but a relatively minor episode in Australia’s long record of geological transformation.
Australia was originally part of the southern mega-continent Gondwanaland. Over the aeons, this gradually split and drifted apart to form India, Africa, South America, Antarctica – and Australia. At that period, it was linked to Asia by a land bridge joining what are now the islands of Indonesia and the Philippines to South-East Asia. Several times, the entire interior of Australia became flooded, its submarine surface forming the ocean bed. Sand, as well as layers of sea shells and crushed coral, are a regularly occurring geological feature of the present-day interior.
Around two million years ago, the interior rose for the last time above the surface of the ocean. Subject to heavy rainfall, it became covered with rich tropical rainforest and jungle (remnants of which can still be found in the occasional sheltered and watered creeks).
Later, the east of the continent was transformed by violent geological turbulence. As a result of this, the Great Dividing Range was thrust up just inland of the east coast. When the subsequent Ice Ages came, they reached as far north as the Snowy Mountains on what is now the New South Wales-Victoria border. When this ice melted, it flooded the land which linked Tasmania and New Guinea to the Australian mainland, as well as creating a number of inlets and natural harbours along the coast, the most notable of which is Sydney Harbour.
Nowadays, Australia is comparatively free of violent geological activity, though it’s subject to the odd warning tremor – as the earthquake which hit Newcastle shows only too well.