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Sydney waters - changing sea levels
Sydney Harbour is a deep water estuary. Its present form was created by changes in sea level which occurred over many thousands of years. These changes in sea level altered Sydney Harbour's coastline dramatically. During periods of low sea level, the coastline had long, unbroken sandy beaches with few headlands and no extensive rock platforms and deep estuaries
Around 18,000 years ago, at the height of the Last Glacial Period, the polar ice caps had enlarged and sea level was at its lowest. At this time, a river ran on the bottom of Sydney Harbour. This river ran out to a sandy coastline which was about 15 km to the east and up to 120 m below the present sea level.
As the ice-caps melted, the level of the sea rose and spread, flooding the river and turning it into an estuary. However, as the sea level was still rising, this estuary was much smaller than it is today.
The sea reached its present level about 6000 years ago and, apart from minor changes, has remained relatively constant since. Today the coastline of Sydney Harbour is characterised by a rocky shoreline broken by small sandy beaches, vast rock platforms and intricately eroded sandstone cliffs.
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