Whitsunday Islands are all that remain of an intense volcanic period around 100 million years ago during the breakup of Gondwana, when the microcontinent of Zealandia, was being torn away from Australia by rifting.

 

The volcanic episode that accompanied the rifting was enormous; geologists estimate that roughly 2.5 million cubic kilometres of silica-rich magma were produced along the 2,500-kilometre long rift.

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This volcanic pile is called the Whitsunday Silicic Large Igneous Province, or SLIP. This is the largest SLIP on the planet, although you’d never guess it by looking at the  Whitsunday Islands today.  

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As stated, the rocky outcrops on Whitsunday Island are remnants of this volcanism. But a quick look at the rock at Tongue Point and the rocks at the south end of Whitehaven Beach shows that weathering of these rocks could not have produced the beach’s stunning white silky quartz sand; any quartz grains those rocks contain are microscopic. Whitehaven’s sand had to come from somewhere else.

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Marine surveys have revealed that an enormous 1.85 billion tons of this sand reside in the Whitsunday area, all deposited there within the last 10,000 years.

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It is believed that longshore drift — a process in which currents moving along the shore operate like a conveyor belt for sand — delivered the quartz sand to a number of beaches around the Whitsundays.  Since waves and tides keep sand ever on the move, the beaches that had accumulated small amounts of quartz sand lost it as time passed. But Whitehaven was so richly endowed that even though it has been losing sand for the last 4,500 years, there is still enough there to keep it covered.

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