Honeycomb Weathering in Ku-ring-gai Chase National Park

May 28, 2007

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Provided and copyright by: Phillip Lachman
Summary authors & editors: Phillip Lachman

The photo above was taken at Ku-ring-gai Chase National Park near Sydney, Australia, and shows an excellent example of honeycomb weathering. Between 190 and 225 million years ago, what is now the Sydney region was a large freshwater lake. This lake was slowly filled up by deposits of sand, mud, silt and pebbles, washed in by large streams. Over the millions of years that followed, these sediments were gradually overlaid by others and compressed into rock.

Two to 12 million years ago, the Hornsby plateau was uplifted to between 150 and 250 metres above sea level. As rivers flowed across this plateau, they gradually cut deep V-shaped valleys into it, leaving narrow sandstone ridges behind. The exposed Hawkesbury sandstone was then subject to weathering, one form of which is honeycomb weathering. This results when moisture draws soluble salts out of the rock, carrying them to the surface. Here, salt crystals fret the sand grains away. This type of weathering is most often found in rock overhangs and in caves. Photo taken on January 3, 2007.

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