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The Geology. To understand the Whitsunday landscape, we must go back 110 million years. At that time, volcanoes were active in what was to become Australia, and slow but steady movements of the earth’s crust were breaking up the super-continent Gondwana (which originally included present-day Australia, as well as South America, Africa, New Guinea, New Zealand, India and more).
The Whitsundays lay in a geologically active zone, where volcanic activity continued for 37 million years. Explosive eruptions threw rock and ash into the air to rain down on the surrounding land. Layers of volcanic debris built up and gradually formed a solid bedrock. Today, this bedrock, composed of ash and rock fragments ”welded” together, can still be seen (e.g. on Whitsunday and Hook islands). This hardened rock appears as a smooth greenish grey to brown, and is worn away by saltwater wave action.
Later, less violent volcanic activity injected lava flows into gaps in the bedrock, creating upright bands of darker rock, known to geologists as “dykes”. Examples of these can be seen on Hook Island.
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