Darling Scarp
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The Darling Scarp (known earlier as Darling Range) is a low escarpment running North-South to the East of the Swan Coastal Plain and Perth, Western Australia.
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[edit] History
The original inscriptions from maps of the 1830's show "General Darlings Range"; later it became Darling Range, and only in the late twentieth century did it become known as the Darling Scarp. In the late twentieth century it was still being named the Darling Range, despite common understanding of it being an escarpment. Also there was (and still is) a tendency to identify the locations on or behind the scarp as being in or on 'Perth Hills' or 'The Hills'.
Early traverses were by explorers of the 1830's and the most commonly known is that of Ensign Dale, who appears to have gone from the Guildford location, to the south side of Greenmount Hill and up through the Helena Valley.
[edit] Geology
The Darling escarpment is an ancient fault-line, which separates the younger sedimentary rocks of the Perth Basin from the ancient cratonic interior of the continent.
[edit] Darling Fault
The Darling Fault separates the Phanerozoic aged sediments to its west from the Yilgarn Craton to the east. It is concealed by sediments, but is located by geophysical data. The Darling Fault is over 1,000km long and has a downthrow of up to 15 kilometres, with the west side down.
It lies to the west of the current scarp, and a good reference point of its location would be the point that the Great Eastern Highway passes over the current Eastern Railway line in Bellevue.
The Archaean granites and gneisses of the Yilgarn Craton form the high ground of the Perth Hills and can be observed in several road cuts in the Mundaring Weir area.
The sediments of the Perth Basin are Tertiary and Quaternary in age immediately below Perth and include coquina, travertine and sandy limestones with abundant shelly material. Perth is sited on a set of sand dunes formed during the Pliocene-Pleistocene during the last Ice Age.
Offshore, the sand dune system and surficial deposits transition into a system of partly eroded limestones and sandy limestones. These form a series of drowned cuestas which today form submerged reefs.
[edit] Climate effects
Often the Bureau of Metereology identify different weather for 'the hills' in comparison to that of the Swan Coastal Plain
Also, in traditionally hot summers, strong easterly winds travelling across the scarp have presented serious issues for planes using the Perth Airport due to the alignment of the runways. A documented accident in 1999 involving wind shear from the scarp is at the Perth Airport article.
[edit] Landuse conflict
The Darling escarpment has had over the last hundred years been exploited for stone quarries, Forestry and Bauxite Mining. Extensive timber railways and timber mills and the supporting communities existed along the escarpment due to the high quality jarrah forests.
[edit] Water supply
In the early twentieth century, most of the main rivers flowing off the escarpment had mainly been utilised for dams for water supply.
The scarp also defines the easternmost limit of the various aquifers present in the Perth Basin sediments, most notably the Southwest Yarraadee Aquifer. The scarp forms adivide between the hypersaline groundwaters typical of the Yilgarn Craton basement from the fresh groundwaters of the Perth Basin. Some dams along the scarp are contaminated by seepage of saline water from the granite into the base of the dam's water column and must be periodically flushed to preserve water quality.
[edit] Rock quarries
Also in the early to mid-twentieth century numbers of rock quarries existed on the edge of the escarpment - visible and affecting both the aesthetics and the environment of the escarpment.
In the area where the Helena River emerges from its valley to the sandplain, there are still four quarries evident, despite being unused for fifty years or more.
- Bluestone (1850's name), later known as Greenmount Quarry (1850's to 1920's), at Greenmount Hill west side of Greenmount National Park.
- Mountain Quarry (now usually signed as Boya Quarry), south of Greenmount Hill, which ceased operation in 1963.
- Fremantle Harbour Works Quarry (sometimes, C. Y. O'Connor's Mole Reconstruction Quarry, and later known as the Public Works Quarry), now Hudman Road Amphitheatre at edge of Darlington - Boya localities border, operated from the 1900's to the 1930's.
- Statham Quarry at Gooseberry Hill at northern edge of the Kalamunda Zig Zag formation.
There have also been visible quarries on the scarp in the Gosnells and Herne Hill areas.
Legislative restrictions upon such developments were initiated in the late twentieth century to prevent further visible scars on the western face of the scarp.
[edit] Railways
- The Eastern Railway first traversed the Darling Scarp in the 1880's along its first route through Greenmount (where three of the above quarries later were able to utilise the railway).
- By the 1890's the second route passed through Swan View Tunnel and John Forrest National Park.
- In the 1960's the third route utilised easier grades through the Avon Valley
- The Kalamunda Zig Zag or Upper Darling Range Railway ran up the southern steep side of the Helena Valley entrance until 1949.
[edit] Bauxite mining
In the late twentieth century, the proving of bauxite deposits correlating to the extensive Jarrah Forests saw wide ranging protests against the proposals to mine the forests.
The lengthy process of protest forced the government and miners to check their original proposals, and wide ranging processes to guard segments of the Jarrah Forests from mining ensued.
[edit] Dieback and fire
Also in the late twentieth century, dieback effecting Jarrah timber in particular infected large tracts of the forest. Currently only the restriction of vehicle access has proved effective in slowing the spread of this disease. This gained greater acceptance and publicity through the decision to allow Rally Australia to operate along services roads provided that the vehicles had a thorough wash including the under carriage at the end of each stage.
In late 2004, the largest bushfire in the Northern Jarrah Forest for at least 100 years has created significant issues for the forest as well. As a result of this fire intensity the Government increase the volume of controlled burns along the entire escarpment to reduce the build up of flammable materials.
[edit] Current activity
The escarpment is currently the site of a number of approved mines of bauxite (or Aluminium ore), which are mined by the company Alcoa along with others. The bauxite mines (and rehabilitated areas after mining) have erased all the evidence of the networks of the timber railways.
[edit] Suburbs on the Scarp
The localities or suburbs on the 'edge' of the scarp are those that sit at the western edge of the scarp, and in most cases command excellent views of the Swan Coastal Plain:
The suburbs near Midland andd Kalamunda are often referred to as Perh Hills
Near Midland, Western Australia:
Near Kalamunda, Western Australia:
Near Armadale, Western Australia:
[edit] The future
The potential for further landuse conflict exists in the presence of unrelinquished mining leases over large tracts of the escarpment; plans by Governmental operations in Forest reserves; water authority sensitivity towards access to its water catchment areas; bushfire control measures; and demands for further intensification of urbanization on the escarpment.
[edit] Darling Range Regional Park
A network of reserves of crown lands on the escarpment have been connected into a regional park to maintain and conserve parts of the escarpment.
In most cases the reserves or parks had individual names prior to being incorporated into the larger park, for example the Serpentine National Park, John Forrest National Park and the Greenmount National Park, or were simply known as State Forests (eg State Forest No.42).
[edit] Bibliography
- Engineering Geology of the Precambrian Rocks of the Darling Scarp
- Watson, Lindsay The Railway History Of Midland Junction : Commemorating The Centenary Of Midland Junction, 1895-1995 Swan View, W.A : L & S Drafting in association with the Shire of Swan and the Western Australian Light Railway Preservation Association, [1995]
