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Northern view from Weereewa Lookout over Lake George showing dry bed in foreground

Lake George Range on right (view from roadside rest area)
At Weereewa Lookout note the upturned rocks resulting from the fault line which runs parallel to Lake George
Southern view from Weereewa Lookout over Lake George showing dry bed foreground

Lake George

Latitude -35.080584, Longitude 149.374924

Located in the Capital Country Region of NSW, nearest large town Canberra

Source: Cartwright, Sarah; Gary Jones (2002). "By George, It Really Is a Lake!" pages 9 - 10 Watershed, Issue No. 27 - August 2002. Co-operative Research Centre for Freshwater Ecology

http://en.wikipedia.org/wiki/Lake_George_(New_South_Wales)

Link to Detailed Map

History

Lake George is called Weereewa in the local Indigenous language of the area. The name Weereewa means "bad water" and it was bestowed upon Lake George because, even when full, the lake is one of the saltiest bodies of water in inland NSW, almost as saline as seawater. The lake is steeped in mystery due to its seemingly unexplained large rises and falls in water height and urban myths have been attributed to these events; it is very shallow and can turn dangerous when winds whip up swells. In 1956 a mishap at the lake was responsible for the deaths of five young cadets from the Royal Military College, Duntroon, who were tragically drowned in a yachting accident when strong winds and penetrating cold wreaked havoc on a sailing excursion.

Geology

Lake George is thought to be one of the world's oldest lakes; it is shallow and has a history of dramatically fluctuating water levels, despite having no outlet. Originally, there was no lake in the area at all, and water drained straight from the Great Dividing Range west into the Yass River. That was before a massive geological uplift that occurred some five million years ago. Around the Mid Miocene period, there was a major crustal movement along a strong fault line and this formed the Lake George Range - a natural dam blocking the creeks. This type of lake is known as an endorheic basin; a closed drainage basin that retains water and allows no outflow to other bodies of water such as rivers or oceans. Any rain or moisture that falls within its small catchment does not flow out naturally and so can only leave the drainage system by evaporation and seepage.

In point of fact, the water levels in Lake George depend simply on the balance between the evaporation rate on the lake surface and the rainfall and water flowing into the lake.

There is, however, a theory that saline water makes its way underground from Lake George to the Yass River which would explain the high salt levels in the Yass River, but this remains unproven.

At 25 kilometres long and 10km wide, Lake George is long, largely flat and extremely shallow, with a very small catchment. Resultant evaporation rates as well as a tendency for strong winds to blow the water back on itself explain the mysterious filling and drying episodes on both short term (hours) and long term (years) time scales that have been observed. The lake's depth when full can range from 1.5 to 4.5m, however, in many areas it is only around 0.8 to 1.0m deep. Its deepest point has been measured as 7.5m. When full, the lake holds about 500,000,000 cubic metres of water. Between the late 1980s and mid 1990s, the lake lapped the Federal Highway on its western edge, whereas at other times, it has remained completely dry. It has a catchment area of about 932km2 and Lake George occupies some 16% of the area of the catchment basin.

The thickness of sediment beneath the lake exceeds 250m, according to a Bureau of Mineral Resources Canberra drilling program conducted in the 1982/83 summer. The oldest sediments, which lie some distance above the bedrock, were dated at 3 to 5 million years using spore and pollen analysis and magnetic reversal stratigraphy. The top 8.6m of sediment, covering the last 350,000 years, - are the longest continuous record of fire and vegetation geological history in Australia. The base of the drilling core, which is 72m long, is estimated to be between 4.2 and 7 million years old. It is thought to extend down to about 134m. This would put the origin of Lake George at about 20 Ma. (Ma stands for megaannum, which is a unit of time equal to one million years.)

The sediments show alternating layers that identify eight different times when the lake was full and eight when it was dry, indicating eight glacial and eight interglacial periods in the past 750,000 years.

The groundwater below the catchment is mainly low salinity, but under the actual lake bed, it is of a much higher salinity, and is confined by a layer of clay. As the lake dries by evaporation, the salt it carries is concentrated into the remaining water. There are complicated interactions between the lake water and the pressurised high saline aquifer beneath the lake bed. The result is that salt has been stored in the aquifer at 10-12m below the sediment surface, at a level of hydrostatic balance. This has been occurring continuously for the last 1-2 million years.

Getting There

Lake George is located on the Southern Tablelands between Goulburn and Canberra and lies adjacent to the Federal Highway. You can view the lake and surrounding landscape from one of the rest stops that dot the edge of the highway. There are picnic tables and toilets and plenty of parking at these sites. There is also a winery nearby if you want to try the local wines. At the southern end of the lake, turn off the highway to Weereewa Lookout which gives sweeping views of Lake George. At the lookout, you can also observe the fractured rocks of the Lake George Fault.


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