Sherlock Holmes and the Mystery of the Disappearing Lake
Lake George is a geological curiosity of the Southern Tablelands region of New South Wales, Australia. What's curious about it is that, over a cycle of several years, the lake oscillates between being a 150km2 inland body of water, and a 150km2 inland grass paddock.
The Lake George basin is located 40km northeast of Canberra, and some 670m above sea level. It measures about 40km long, and 11km at the widest point. In a region typified by mountains and valleys, the basin itself is a peculiar sight; a dead flat expanse of land nestled between two abrupt elevations. On the eastern side of the basin, you have part of the Great Dividing Range, and on the western side, right up against the edge of the lake, is the 150m high escarpment known as the Lake George Range. And since the Federal Highway between Sydney and Canberra runs right between the escarpment and the lake, there's plenty of time to take it all in while you're driving along. Since the basin is emphatically lower than the surrounding geography, water runs into it, but has no way of getting out.
Oi, Bruce! Where'd all the bloody water go?
Lake George is only a lake half of the time. Despite the large surface area, it is always very shallow. The maximum recorded depth is a mere 7.3m, normally ranging between 1.5m and 4.5m. Every so often, the lake dries out completely, and because of the low depth and flat base, when it does dry out it appears to simply and suddenly vanish. The result is a lake which sometimes features boats and water skiers, and at other times features utes and grazing sheep.
There have been all manner of bizarre theories as to why the lake behaves this way -- volcanic craters, vast underground rivers, mysterious linkages to lakes on the other side of the world, that kind of hogwash. As it turns out, the height of the lake is simply a consequence of the ever-shifting relationship between precipitation and evaporation, as well as the capacity for the salty soil underneath the lake to absorb a huge amount of water.
Lake George was originally known as Weereewaa by the Aboriginals in the area. It was renamed by Governor Lachlan Macquarie in 1820, who noted that "after dinner we drank a bumper toast to the future settlers of the shores of Lake George - which name I have given this grand and magnificent sheet of water in honour of his present majesty", which just goes to show that sometimes, the British who invaded this continent really did talk a load of self-righteous imperialistic crap.
Historically, it's thought that the western escarpment did not exist, and the basin was a flood plain which drained off normally towards the west. However, the escarpment was gradually raised by the underlying fault line, and the drainage route was cut off. Now the fault seems to be inactive, and the escarpment has eroded back considerably.
The basin is a site for ongoing archaeological research, presenting clues about prehistoric climatic and geological changes, as well as the movements and habits of the flora and fauna (anthropods included) of ages past.