Lake Thetis - Living Fossils
Lake Thetis is a shallow lake that is estimated to have become isolated from the sea about 4800 years ago. It is a salt lake and is approximately 1.5 times saltier than seawater. It is fed by groundwater and rainfall and the only loss of water is through evaporation.
What makes this lake special is that it is home to stromatolites or “living fossils”, and has been identified as a “Threatened Ecological Community”. Strategies have been put in place to minimise the human impact on the area, including a walk trail 1.2km long around the lake with boardwalks in places to allow close up viewing of the stromatolites.
The conditions needed for the formation of stromatolites are quite complex - one requirement involves the presence of different kinds of bacteria in different layers of the lake. The microbes that build these stromatolites are a species called cyanobacteria. This is a very common microbe found all over the world and is also known as blue-green algae. It is only when given these right complex conditions that stromatolites or similar structures have been able to form over thousands of years.
Some cyanobacteria excrete calcium carbonate to form tiny layers as they grow. The end result at Lake Thetis appear as circular rocky formations between 50 and 100 cm in diameter. The examples here are some of the best of their kind in the world and therefore this lake attracts many local and international tourists along with geologists and academics.
To log this cache you will need to
A. Visit the information signs at the given co-ordinates and answer the following questions:-
- How long have the Lake Thetis stromatolites been growing?
- What is the structural difference between the stromatolites and the thrombolites?
- Once widespread, stromatolites are now only found in isolated places. The conditions need to be suitable, as well as what other factor?
- According to Aboriginal legend what are the stromatolites?
B. Post a photograph of your visit to the area but please don’t include the signs.
Please email your answers for the questions to us so we can give you the OK to claim a find, then you can log it and upload your photo.