Illawarra Escarpment

Latitude -34.367173, Longitude 150.875845

Located in the Illawarra Region of NSW, nearest town Wollongong

Source:http://ro.uow.edu.au/wollgeo/2 R.W.Young

Source:www.environment.nsw.gov.au

Link to Detailed Map

The Illawarra Escarpment stretches for around 120 km from the sea cliffs of the Royal National Park in the north to the junction of the Shoalhaven and Kangaroo Rivers in the south. Along its length the Illawarra Escarpment rises from 300 metres in the north, to 700m in the southern area around Albion Park.

Geological History

The rocks from which the escarpment was carved were originally deposited in an ancient subsidence known as the Sydney Basin. At the close of the Triassic period (about 180-200 million years ago) layers of sedimentary and volcanic rocks in the area began to rise above sea level. Earth movements on the southern side of the Sydney Basin resulted in broad warping in an upwards direction towards the south and southeast, so that beds like the Hawkesbury Sandstone, which still lie near sea level in the centre of the basin, can be traced to elevations of almost 600m in the vicinity of Kiama and Nowra.

The extremely straight wall like sections of escarpment near Wollongong give the impression of large scale faulting but this is not the case, as bedrock in the coastal plain can be traced under the escarpment with no faulting. The escarpment we see today is the product of erosion: the well developed jointing in the sandstones and the gravitational movement of debris down slope over an extremely long period of time.

It is interesting to consider the flow patterns of the many streams on the Illawarra plateau. Most of the larger streams follow the fall of the Hawkesbury Sandstone and drain to the inland Nepean River system. These larger streams have a greater impact on the profile of the landscape because of their ability to erode a substantial volume of material resulting in the sizeable river valleys immediately to the west of the escarpment. On the eastern side of the plateau (with the exception of the Macquarie and Minnamurra Rivulets) no river systems have been able to breach the escarpment. This has left the steep vertical cliffs topped by Hawkesbury Sandstone leading to slow erosion along the joint planes.

Extant Geology

The escarpment cliffs and plateau are comprised of massive beds of durable quartz sandstone. Beneath the cliffs, weaker claystone tends to erode more rapidly and undermine the sandstone causing the cliffs to periodically collapse.

The vegetative slopes below the escarpment that sweep down from the cliffs to the coastal plain are made of shales, claystones and coal seams. Large sandstone boulders at the base of the slopes are evidence of cliff collapse. The slopes are also prone to landslip. Material that has slid or fallen from the cliffs and upper slopes forms thick layers on the lower slopes and foothills.

In many places, erosion-resistant layers of strata protrude from the slopes and form flat benches. The shales and claystones provide the high nutrient levels required to support the lush rainforests that grow below the escarpment.

The lower escarpment slopes are also rich in coal. For over a century, the region's coal provided the main foundation for its economy. Many sites and relics from the area's past mining history exist within the State Recreation Area.

Budderoo National Park is part of the Illawarra Escarpment. The highest sections of the park (on the plateau) reach 740m above sea level. They give way to huge sandstone cliffs, 50-100m high, which tower over the rainforests in the lower areas of the park.

In places, streams have cut deep into the cliff lines, forming spectacular waterfalls - including Gerringong Falls and the famous Carrington Falls. Over time, water falling over the Carrington Falls, have cut the deep westward facing valley.

The Minnamurra slot canyon is another product of this weathering. It is a large natural amphitheatre that has been carved out of the Illawarra Escarpment by the Minnamurra River over millions of years.

Another significant site, the famous slot gorge of the lower Minnamurra Falls, is the result of erosion of a volcanic dyke. The slot gorge is approximately 50m long, 50m high and 10m wide. You can see it from the top at the end of the Falls Walk.

Getting There

The view from Illawarra Escarpment can be seen from Sublime Point Lookout on the eastern side of the Southern Freeway, just before the Bulli turnoff. There are also excellent views from the top of the escarpment at Mt Keira Lookout accessed via Mt Keira Road. The escarpment can be viewed from its base along Lawrence Hargrave Drive from Austinmer to Otford. The slot canyon is at Minnamurra Rainforest in the Budderoo National Park west of Jamberoo (entry fees apply to Minnamurra Rainforest).