Coastal headlands - a natural history - Part II

5 Dec 2011 2:28 PM
Coastal headlands - a natural history - Part II

PART 2 the Currumbin Rocks and Headland 

 

Ian Black of Geo-Nature Walks and Tours continues his fascinating series on the Gold Coast headlands. 

 

Like the other ridges running into the coastline along the Gold Coast, the top of Currumbin Ridge was once the bottom of an ancient river valley that was filled in by the early flows of basalt from the Tweed Volcano around 20 - 23 million years ago (MYA).

 

In 1983, geologists Herbert and Stevens located river gravel in between the NF beds (see Part 1 for more info) and the basalt soils that line the top of the ridge near Crest Drive and Pall Mall Avenue indicating the bottom of an old river valley.

 

Once again when the rainwater couldn’t flow down the old valley, it started to erode the hills either side of the flow and after 23 million years most of the original hills have disappeared leaving the old valley floor sitting on top of the ridge. There are still some large basalt boulders sitting on the ridge above Woodgie Street (photo1).

 

 

Currumbin, Elephant and Flat Rock are good examples of wave-cut platforms. These platforms were developed by wave erosion undermining the cliffs and have now been isolated but not yet completely worn away (photo 2). They are made up of closely bedded argillite and fine-grained greywacke and are steeply inclined.

 

 

Photo 3 shows the Alley as it was before the rock wall was constructed from the shore to stop erosion of the Currumbin beachfront and in an attempt to stabilise the creek entrance. While it was effective in stopping erosion at Currumbin, it stopped the flow of sand on to southern Palm Beach and it took decades for the sand to build up again.

 

 

It was common for the creek entrance to sand over in the past with the creek forced to head north before entering the ocean further along Palm Beach. At one point there was an island in the estuary on which Granny Birch operated a small dairy farm but it was completely washed away in the mid-1930s (photo 4).

  

All black and white images are kindly supplied by the local Studies library.

 

Interested in learning more about the area?  Contact Ian Black of Geo-Nature Walks and Tours for a copy of the latest full colour edition ‘Rocks and Landscapes of the Gold Coast and Hinterland’ by Warwick Willmott of the Geological Society of Australia, Queensland Division. Available for $15 plus postage.

 

Or better still, join one of Geo-Nature’s guided walks for a fascinating and informative introduction to the Gold Coast and surrounds.

 

Contact us today!