NEWCASTLE: Matthew Flinders & the Coastal Landforms of SE Australia

' ... at noon the Coal Island [Nobby Head] in the mouth of Port Hunter bore NW by N; the wind then shifted more to the southward ... ' *- Matthew Flinders in Terra Australis* [6 Sep 1803]**
Nobby's (rock type: mainly chert) Near the mouth of the Hunter River, Newcastle, is an interesting landform feature, Nobby's. It appears to be a prominent headland, connected to land to the south by a causeway, sand spit and beach (i.e. a tombolo). Nobby's summit is the site of maritime and weather monitoring stations. Near the base is a 20th Century wartime observation post. The layers of rock are horizontal, of sedimentary origin. Softer rocks have been weathered away more rapidly, leaving resistant strata poking outwards (this effect is called differential weathering). Of interest are the rocks themselves; their properties are varied enough to give the cliff face its appearance. The main rock type is chert, found in beds alternating with softer shale and tuffaceous sandstone. A coal seam occurs near the base. The chert is a fine-grained composite of tuff and volcanic glass. It is relatively resistant to weathering. The origin of this sediment is volcanic, but as the chert beds are intermixed with other sedimentary rock layers, it is likely that the materials were deposited and settled in water, thus sharing properties with other sedimentary rocks.	'Port Hunter ... Coal Island ... Coal Head ... Tide rises 6 feet ...Hunter River ...' - from Flinders' chart Photo 1: Nobby's, from Newcastle Breakwater, NSW
		Nobby's was first described by Captain Cook in 1770 as a 'small clump of an island'. On Flinders' chart, Nobby's appeared as 'Coal Island' (it has also had other names). It was then higher and separated from the mainland. Later, the island was to be significantly altered.
Nobby's has had an interesting geological and recent history. It is formed from rocks many millions of years old (Permian age). The sedimentary materials piled up under water, consolidating, hardening, and being gently uplifted above sea level. Surrounding hard materials were eventually removed by marine and river erosion, producing an island. The island appeared on Flinders' chart (from the work of Barralier) as 'Coal Island'. However, the island has been much altered by people since then. The summit was removed, reducing it to less than half its original height, while giving a flat space for buildings. A rock wall (Macquarie Pier, 1818) was built by convicts on the governor's order, to connect the island to the mainland. This wall has since collected sand from the northerly longshore drift against its seaward side. A wall that connects an island to the mainland, and which itself becomes sand-covered, can be regarded as an artificial tombolo. Much of the sand has been stabilised by hardy dune vegetation. The beach here is popular in hot weather.	Photo 2: The constructed causeway that 'tied' Nobby's (Coal Island) to the mainland The photo views appear hazy; this is due to widespread smoke from bushfires across much of central NSW, December 2001 - January 2002.
The headland shown was called 'Coal Head' on Flinders' chart. Fort Scratchley is located on its summit. Colliers' Point, at the southern end of the breakwater, was the site of the NSW colony's first coal mine (in fact, the first coal mine in the southern hemisphere - 1801). Tunnels were driven into the cliffs shortly after the establishment of settlement at Newcastle. Flinders' chart also shows the network of channels of the Hunter River mouth (with sounding depths), rivers of the hinterland (Hunter's River, Paterson's River, William's River) , as well as cliffs along the coastline to the south.	Photo 3: Fort Scratchly (Coal Head)

The area was discovered by Shortland in 1797, who named the Hunter's River. The first settlement of Newcastle was made in 1801 (after Flinders had first sailed past on his way north to Moreton Bay and Hervey Bay. Flinders rowed past the Newcastle coast in the Hope, a ship's boat saved from the wreck of the Porpoise at Wreck Reef. He was on his way to Sydney to mount a rescue operation for those remaining behind. (Note: These events took place on his way back to England after the great voyage or circumnavigation.)
Along the rugged coastline south of Newcastle, excellent exposures of various sedimentary beds are visible. Layers of coal, light and dark shale and sandstone are easily seen. The cliff is kept steep through ongoing attack and removal of rock debris at the base by wave action. Erosion is most rapid along vertical joint planes (see lower portion of photo). This location is just south of the Bogey Hole, a pool carved into the rock platform (lower right). The coastal walk offers a display of sedimentary erosional scenery of great interest to those wishing to observe landform features.	Photo 4: Along the layered cliff, near the Bogey Hole
The coastline at Newcastle (and for some kilometres south) offers a marvellous range of scenery and features. At Redhead another rock type is found to make up the headland; sedimentary breccia. The steep headland appears resistant to marine erosion and there is little rock platform development. The rock, breccia, is composed of angular gravel surrounded by strongly cemented sand - thus it is similar to a commonly used building material, concrete. From a distance the headland appears similar to the hard sandstone cliffs of Sydney's coast. The breccia here occurs as horizontal and gently inclined layers, with sandstone beds between. The layers represent different depositional events; breccia is deposited in a higher energy environment than sand (more water force is needed to transport gravel than sand). In places (see photo, right) the somewhat softer sandstone layers have been weathered into the headland. This undercutting eventually causes parts of the cliff above to collapse along a joint plane, maintaining a vertical profile as the cliff retreats. [ Note: The rock described above is sedimentary breccia. There is also a rock called volcanic breccia - it is made up of angular volcanic fragments bonded together by ash. There may even be another form of breccia, angular rock formed along a fault plane when rocks grind past each other under pressure.]	Photo 5: Surf and seagulls (above) Redhead Headland and Beach (south of Newcastle) Photo 6: Redhead rocks: breccia and sandstone