Illawarra escarpment


Illawarra escarpment

The Illawarra Escarpment is the fold created cliffs and plateau/ eroded outcrop mountain range west of the Illawarra coastal plain south of Sydney, Australia, enclosing the region known as the Illawarra which stretches from Stanwell Park in the north to Kiama, Gerringong and the Shoalhaven river in the south. The hills of the plateau reach over 800 m, like at Bells Hill west of Knight's Hill and the escarpment reaches a maximum of 768 metres at Mount Murray southwest of Dapto. As a whole it is known as the Illawarra Coast Range or Illawarra Coast Ridge.

The escarpment or scarp was created, it is believed, between 225 to 280 million years ago [ [http://hsc.csu.edu.au/geography/ecosystems/case_studies/mmfweb/mmf_6.html HSC Online ] ] and since eroded by creeks to its present height around 30 million years ago. Most of it is sandstone, with many Hawkesbury Sandstone boulders and ledges visible in addition to the actual cliffs. Its maximum heights are reached in the south, west of Albion Park at Knight's Hill, 709 metres above sea level, and Mount Murray, 768 metres above sea level. This forms the eastern edge of the Southern Highlands plateau, uplifted along with the Blue Mountains around 70 million years ago.

Many of the towns on the coastal plain adjacent to the escarpment were first founded to harvest the cedar trees on the slopes of the escarpment or the coal seams beneath it. With the original logging industry of the area came the need for passes over the escarpment, creating such ones as Rixon's Pass, Bulli Pass, O'Brien's Road and Macquarie Pass. The city of Wollongong is the central city in the Illawarra.

The escarpment contains a wide variety of native flora and fauna and is a haven for many forms of wildlife. It is known for the Illawarra Flame Tree with its bright foliage, as well as rare surviving red cedar trees that haven't been logged. On Saddleback Mountain and at Minnamurra Rainforest and other places there are remnant localities of rainforest bushland, as well as, to the north, dry sclerophyll forests. The southern typical bush meets the northern at Mount Kembla, creating a unique effect. Many bird and animal species thrive here and the escarpment also contains many historic sites such as mine entrances and passes.

There are many walking tracks and lookouts with views of the surrounding countryside to the south, or suburbs to the north and coastal villages to the far north, and bushland and suburbs to the north. There are several well known lookouts, such as Bald Hill, Bulli Pass, Sublime Point and Mount Keira, as well as lesser known tracks with views such as Hoddle's Track west of Saddleback Mountain.Some tracks have gone into disrepair such as the Wodi Wodi track at Stanwell Park, but some such as the Mount Keira Ring Track have been upgraded. Weed infestation is a problem, with many areas invaded by Lantana and other invasive weeds.

Numerable areas are protected as part of the Illawarra Escarpment State Conservation Area or as state forests such as Kembla State Forest southwest of Wollongong. Much is however private property or owned by mining companies like BHP. Well known and popular lookouts such as at Mount Keira and Bald Hill are reserves or parks, the Mount Keira Summit Park is an annexe of the Wollongong Botanic Garden like Puckeys Estate Reserve on the plain.

Geographically it stretches from the white cliffs of the Royal National Park and its northern hilly ridge formations like Bulgo and Otford Hills and Stony Batter, Undola Ridge and Bald Hill, south past the Otford Valley to the west and around an eroded valley containing Stanwell Park, then it goes south, featuring cliffs and running close to the coastal headlands, approximately 300 metres above sea level at Scarborough to the turn at Sublime Point (415 m) near Thirroul, south to Broker's Nose (440 m) promontory, south to Mount Keira, which juts out from the main cliffs, south to a similar eroded sandstone outcrop, Mount Kembla (534 m), then southwest along the Dapto scarp cliffs including Mount Bong Bong to the turn inland at Macquarie Pass, then back east to the promontory at Knight's Hill (709 m), south including Jamberoo Mountain and east to Noorinan Mountain promontory at Barren Grounds Plateau, then along a ridge to its southern tip, Saddleback Mountain. (Although the escarpment actually continues around Noorinan promontory and forms the Cambewarra Range or Escarpment. The Escarpment itself continues around Kangaroo Valley)

It ranges in height from the tops of Bald Hill and Stony Batter around 300 metres above sea level, to 440 metres at Broker's Nose, generally above 350 metres high south of Mount Ousley Road (between Keira and Broker's Nose) it reaches 464 at Mount Keira, 464 at Mount Warra, 469 at Mount Brisbane, 531 at Mount Burelli, 512 at Kembla West, 534 at Mount Kembla, 564 at Wanyambilli Hill on the plateau to the west and 709 at Knight's Hill, just over 663 metres at Noorinan Mountain and about 600 metres at Saddleback Mountain.

It is mostly of hard sandstone, with outcrops like Mount Keira and Mount Kembla rising above 450 metres. There are many tracks to the top of such summits including the southern tip of the escarpment, Saddleback Mountain and Noorinan Mountain promontory. The flora ranges from northern and southern eucalypts and at Mount Kembla fuses, providing an interesting phenomena. The range has much history, including Hoddle's Track which used to go to Bowral from Kiama.

Details of Geology & landscape

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 steep slopes 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 form thick layers on the lower slopes and foothills.

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

To the north the range is mostly a coastal ridge east of Otford, becoming a cliff at Mount Mitchell, and continuing to include an eroded cliff at its top until Bulli Pass where it becomes rounded, forming Woonona Mountain, until Broker's Nose where the cliff reappears, before appearing again on the edge of Mount Keira and Warra, disappearing until west of Dapto where it forms the famous southern escarpment and curves in for Macquarie Pass National Park and Mount Murray (768 m) before turning into Knight's Hill(709 m) and then forming Noorinan promontory, its summit at 663 metres, and Saddleback Mountains.

There are many passes over the escarpment. The first is at Bald Hill, where Lawrence Hargrave Drive descends into Stanwell Park. The next pass is at Bulli, where the road goes down from Bulli Pass Lookout near Sublime Point Lookout, around a tight bend and then down into the town of Thirroul. The third is at Rixon's Pass. Rixon's Pass descends around several tight curves just north of Broker's Nose promontory, now a management trail used by mountain bikers. The fourth is at Mount Ousley Road, now a freeway, the main route used for truck and bus traffic. The fourth is at Mount Keira Road, built by convict labour and still, in a slightly changed form, used today. The fifth is at O'Brien's Road, now partially used by Harry Graham Drive, the Mount Nebo section now a walking and riding track. The fifth is at Cordeaux Road at Mount Kembla, which climbs around Kembla West, 512 m, to reach the catchment area to the west. The sixth is at Macquarie Pass, south of Dapto, protected by a national park. The seventh is at Jamberoo Mountain Road pass, east of the mountain of that name, which climbs through a winding pattern to the summit and along the escarpment to Knight's Hill and beyond west. Saddleback Mountain Road only reaches the summit after a short, steep, turnoff, but was once part of Hoddle's Track, which is now only in existence in a small ridge track from the summit but used to extend west to the Southern Highlands.

References

* [http://hsc.csu.edu.au/geography/ecosystems/case_studies/mmfweb/mmf_6.html]
*R.W. Young (1980-1984)"The Illawarra Escarpment", "Wollongong Studies in Geography No. 2" Department of Geography, University of Wollongong

External links

* [http://www.illawarracoal.com/ "Illawarra Coal"] - An unofficial history of coal mining in the Illawarra

* [http://www.nio.net.au Northern Illawarra Community Web Portal]

* [http://www.seacliffbridge.com Sea Cliff Bridge website]


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