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.