Blue Lake (South Australia)

Infobox_lake
lake_name = Blue Lake
image_lake = Mount_Gambier_Blue_Lake.jpg
caption_lake = The lake in early March with the original pumping station in the foreground.
image_bathymetry =
caption_bathymetry =
location = Mount Gambier, South Australia
coords = coord|37|50|48|S|140|46|41|E|region:AU-SA_type:waterbody|display=inline,title
type = Crater Lake
inflow =
outflow =
catchment = Blue Lake Catchment Area
basin_countries = Australia
length =
width =
area =
depth = 70 m
max-depth =
volume =
residence_time =
shore = None
elevation =
islands = None
cities = NoneThe Blue Lake in Mount Gambier, South Australia is a large monomictic lake located in an extinct volcanic maar associated with the Mount Gambier maar complex. It is one of four crater lakes on Mount Gambier. Of the four lakes, only two remain, as the other two (Leg of Mutton and Brown) have dried up over the past 30 to 40 years.

Conflicting dates have been estimated for its last eruption, of 28,000 years ago [cite web |url=http://www.penshurstvolcano.org.au/volcanoes/Handouts/Volc_Ages_2007.pdf |title=The Ages of Our Volcanoes |accessdate=2008-05-07 |first=Ken |last=Grimes |year=2007] and 4300 years ago. [cite web |url=http://www.seismicity.segs.uwa.edu.au/welcome/seismicity_in_australia/volcanoes_and_earthquakes_in_southeastern_australia |title=Volcanoes & Earthquakes in SE Australia |accessdate=2008-05-07 |publisher=University of Western Australia] If the more recent date is correct, this could be the most recent volcanic eruption on the Australian mainland.

Blue Lake is thought to be of an average depth of 70 m and in places 75 metres deep (250 feet). Although the crater rim measures 20 metres (66 feet), due to the lakes great depth, the bottom of the lake is 30 metres (100 feet) below the level of the main street of the nearby town. Each year a festival is held when the lake turns blue.Fact|date=July 2008 The Blue Lake supplies the town with drinking water, providing approximately 3,600 ML per year from its 36,000 ML store.

Mechanism of colour change

During December to March, the lake turns to a vibrant cobalt blue colour, returning to a colder steel grey colour for April to November. The exact cause of this phenomenon is still a matter of conjecture but it is generally considered likely that it revolves around the warming of the surface layers of the lake during the summer months to around 20 degrees °C, causing calcium carbonate to precipitate out of solution and enabling micro-crystallites of calcium carbonate to form. This results in scatter of the blue wavelength of sunlight. During winter the lake becomes well mixed, and recent research indicates that during this phase of the colour cycle the lake is somewhat murkier due to the redistribution of tannins and calcium carbonate particles throughout the lake. Solar elevation has also been found to influence the perceived colour of the lake. The movement of planktonic life-forms within the lake during the seasons and during the day may also play a part in the visibility changes.

Environmental Issues

During early August, 2008 Residents of Mount Gambier engaged their concern of the amount of dog faeces along the walking path of the Blue Lake.

Little Blue Lake

Ten kilometres or so South of Mount Gambier, take the turnoff by the Bellum pub, is the Little Blue Lake. It is one of a number of small nearby lakes whose waters also used to turn blue annually. However, pollution from agricultural fertilizers has increased the nutrient levels of these lakes to the extent that they now remain a year-round green colour. Swimming is discouraged and warning signs for the presence of blue-green algae have been erected.

Gallery

Notes

References

* Sheard, M.J. (1978) Geological History of the Mount Gambier Volcanic Complex, Southeast South Australia. Transcript from "Royal Society of South Australia" 102(5), Aug. 1978
* Telfer, A. (2000) Identification of processes regulating the colour and colour change in an oligotrophic, hardwater, groundwater-fed lake, Blue Lake, Mount Gambier, South Australia. Lakes and Reservoirs: Research and Management. 5 161-176.
* Turoczy, N.J. (2002) Calcium chemistry of Blue Lake, Mt Gambier, Australia, and relevance to remarkable seasonal colour changes. Archiv fur Hydrobiologia. 156 (1) 1-9.
* Emeny, J., Turner, G., Turoczy, N.J. and Stagnitti, F. (2006) The influence of weather and solar elevation on perceived colour of Blue Lake, Mount Gambier, South Australia. Transactions of the Royal Society of South Australia. 130(1) 101-108.