Mount Lofty Ranges - Geomorphology

Geomorphology

The ranges are part of the Adelaide Geosyncline. The southern ranges and slopes of Mount Lofty overlooking the Adelaide Plains have been block-faulted to form a half-graben structure. The ranges when viewed from the beach or city have a "stepped" appearance, reflected in an early name for the ranges, "The Tiers".

There are several major normal faults in the Adelaide region, trending northeast to southwest defining these blocks:

• Para Fault. This runs from Gawler in the north, through Elizabeth, before disappearing under younger alluvium in the inner northern suburbs. The scarp which this fault has formed is covered with houses in the northern suburbs (Para Hills) and the township of Gawler is nestled at its base where the South Para River emerges from the range. Closer to the city the scarp becomes less defined and is unidentifiable beyond the low hill upon which North Adelaide rests.
• Eden-Burnside Fault Zone. This fault zone (composed of several different individual faults) lies at the base of the main scarp of the Adelaide Hills, separating the young Quaternary alluvium of the plains from the Proterozoic sedimentary rocks making up the ranges. It begins around One Tree Hill in the northern suburbs and extends as an escarpment of approximately 200 metres (660 ft) high in a slightly curving line for about 30 km (19 mi) before encountering the sea at Marino. This escarpment is known as the "Hills Face Zone" and is subject to special zoning restrictions; house prices are very high, as is demand for land, owing to the magnificent views, but many in the community are concerned with maintaining green hills as a background to the plains. A number of creeks cut deep notches in the scarp; one of these, Glen Osmond Creek, provides the site for the major road east out of Adelaide, now called the South Eastern Freeway; only a handful of other major roads extend up the scarp.
• Kitchener Fault. This long fault, just a little further to the east, extends from north of the Barossa Valley past the Torrens gorge to meet the Eden Fault in the vicinity of Greenhill. It is most apparent as a fault scarp around Williamstown and Kersbrook.
• Clarendon Fault. Running largely parallel to the Eden-Burnside Fault, this forms the escarpment within Belair National Park, which also runs south-east to form the eastern boundary of the southern suburbs, before ending at Old Noarlunga, where the Onkaparinga River emerges from the ranges. An escarpment also extends from the northern end of this fault to form the upper 'tier' of Mount Lofty: Measdays Hill (now carved in half by a massive cutting for the SE Freeway at Crafers West) and Mount Lofty itself are at the top of this scarp.
• Willunga Fault. This fault runs parallel to the Clarendon Fault, further south once more, and is the southernmost of the faults. The escarpment it lies at the base of is similarly dramatic, beginning in the Scott Creek Conservation Park and running southwest: Mount Bold Reservoir forms where the Onkaparinga River has been dammed in the middle of the escarpment. Further south, the townships of Kangarilla and Willunga nestle in gullies of the scarp, and the increasingly dramatic and bare face of "The Range", as it is known (properly Sellicks Hill Range) meets the sea at Sellicks Beach.
• Bremer and Palmer Fault Zones. These faults are at the eastern edge of the Mount Lofty Ranges block, and form even more dramatic escarpments than those in the west due to the general lack of the vegetation in the countryside. The latter fault zone is the eastern edge of the metamorphosed Proterozoic rocks of the Kanmantoo Group; to the east lie the younger sediments of the Murray River. Towns like Palmer, Sedan, and Cambrai, lie at the foot of the scarp.

All the fault zones are still active today, along with the rest of the ranges, and minor earthquakes are relatively common. Larger quakes in the southern ranges are fairly rare: the last to hit a major centre was the March 1, 1954 earthquake in Adelaide itself, measuring 5.5 on the Richter scale.

A significant aspect of the geology of the Adelaide area is a number of Tertiary marine sands deposits, many of which have been extensively quarried. One of these deposits is around the [[List of Adelaide suburbs|outer-northern suburb of Golden Grove; another area is around McLaren Vale.