The Cronulla sand dunes are located on the Kurnell Peninsula in the local government area of Sutherland Shire, Sydney, New South Wales. The Cronulla sand dunes are a protected area that became listed on the NSW State Heritage Register.

The Cronulla Sand Dunes

Geological history

The sand dune system, also referred to as the Kurnell sand dune, is an oddity in the coastal area of NSW as there are generally cliffs from the land into the sea.

The sand dune system is estimated to be about 15,000 years old. It was formed when the sea reached its present level and began to stabilise, between 9,000 and 6,000 BCE. The Georges, Cooks and Towra Rivers flowed to the south-east beneath the present sand dune system near Wanda and joined the ocean at Bate Bay. This resulted in the isolation of Kurnell which became an island from the mainland. The rivers eventually became blocked with accumulating sand and sediment as the sea level rose. As the rivers gradually silted up they were forced into changing their course and were led out to sea via La Perouse rather than continue to maintain an opening in an ever-growing sand barrier near Wanda. This resulted in a tombolo being formed and joined Kurnell with the Cronulla mainland. The deepest part of the ancient river channel now lies 100 meters below the surface at the southern end of the peninsula, near Wanda Beach.

European settlement

The Kurnell Peninsula, also the site of the Cronulla Sand Dune System was the first landing place for Captain James Cook in Australia. On 29 April 1770, HM Bark Endeavour landed in Botany Bay and Cook stepped ashore. Shortly after, James Cook looked down from the sand hills at what is now known as Cronulla Beach. The sand dunes were completely covered in vegetation, so Cook made no mention of any sand dunes during his visit to the Kurnell peninsula.

Around 1870, Thomas Holt who was the first owner of the area planned to use the dunes for farming sheep. To promote grass growth he destroyed as many of the oldest trees but all that regrew was dense impenetrable thorny scrub. By 1868 the forests of blackbutt and ironbark were cut down for houses and bridge construction whilst the remaining vegetation was cleared for grazing.

The land on his estate was not suited for intensive grazing, so after most of the trees were felled the herds of cattle removed the stabilizing grass cover and exposed the sand dunes underneath. Large expanses of sand had been exposed along the coastline. The dune system that covers an area of 1,000 acres (4.0 km2), measuring 40 meters above and 90 meters below sea level, became unstable and began to move north at a rate of 8 meters a year. Land clearing and cattle grazing resulted in a degraded landscape, but created the distinctive Cronulla sand dunes of today.

Between 1920 and 1930 the sand hills were considered to be a deserted and desecrated landscape, and their economic value was considered minimal. However, by the 1920s Cronulla had become notable for its beaches with over five kilometres of sand stretched along the coastline. The bare sand dunes became synonymous with Cronulla.

Sand mining and regeneration

In the 1930s the Holt family began sand mining operations to supply the expanding Sydney building market and continued until 1990 with an estimate of over 70 million tonnes of sand being removed. The sand has been valued for many decades by the Sydney building industry, mainly because of its high crushed shell content and lack of organic matter. The site has now been reduced to a few remnant dunes and deep water-filled pits which are now being filled with demolition waste from Sydney's building sites. Removal of the sand has significantly weakened the peninsula's capacity to resist storms. Ocean waves pounding against the reduced Kurnell dune system have threatened to break through into Botany Bay, especially during the storms of May and June 1974 and August, 1998.

Regeneration projects in the 1980s and 1990s have covered most of the dunes in the Wanda Dunes area and the areas are now green again. However, the sand mining area of the Holt estate is a huge lake waiting to be filled with recycled building materials.

Questions about the area

To log this cache, investigate the following:

1. About 17,000 years ago, the rivers shifted towards a new exit between Kurnell and La Perouse. This didn't happen overnight, it happened during the time that the then-exit became silted up and the capacity was not big enough to get rid of the water of the rivers. During that time the Kurnell area was fully surrounded by water. It transformed from a peninsula into an ______.
2. Erosion by wind and rain of the sand of the dunes to shift northwards, about currently about eight meters per year. What can be done to reduce this erosion and keep the dunes stable?
3. At the published coordinates, there is an observation platform. Looking towards the pond, on the right hand side there is bare sand while on the left hand side there is vegetation on the sand. Compare the state of the sand in the two areas and describe the differences. Think about humidity level of the sand under the surface, temperature differences of the sand on the surface and how good the sand sticks together under the surface.

Sources and further information

• https://en.wikipedia.org/wiki/Cronulla_sand_dunes
• http://www.ssec.org.au/our_environment/our_bioregion/kurnell/history/origins/index.htm
• http://www.ssec.org.au/our_environment/our_bioregion/kurnell/environment/dunes.htm
• https://www.theguardian.com/australia-news/gallery/2015/dec/27/cronulla-sand-dunes-the-15000-year-old-landscape-that-greed-destroyed-in-pictures