Coalstoun Lakes
Small volcanic crater lakes set in rainforest
Access
The park is situated between Ban Ban Springs and Biggenden. Travel to the township of Coalstoun Lakes. The park is 3 kilometres north of this town.
Activities
Coalstoun Lakes is an area of remarkable geological interest. Activities that can be undertaken in the park include walking, birdwatching and the exploration of some unique.geological features. Should you do any walking near the lakes, try to keep away from the lake edges as walking here can cause soil erosion.
Features
Looking at the Coalstoun Lakes it is hard to imagine that just 600000 years ago, a relatively short time in geological history, this area was the scene of volcanic activity. The two craters that are sometimes filled with water were part of a volcanic cone, known as Mount Le Brun. The sides of this cone are mainly composed of the volcanic rock, basalt and the sedimentary rock, agglomerate. This basalt comes in several different forms. There is vesicular basalt which is formed when lava with a lot of gas in it cools quickly. The result is a fine-grained rock, riddled with holes. Other forms of basalt found here are marked and twisted by the movement of lava. Agglomerate is a sedimentary rock, formed with broken pieces of vesicular basalt fragments.
From the radiocarbon dating of lake bottom sediments, it has been found that sediment is being laid down on the bottom of these lakes at a rate of 1 metre every 9000 years. From these readings scientists can calculate just how old these lakes are. Some interesting crystalline spheres have been found throughout the mud of the lakes. These spheres are found up to the size of a tennis ball and contain a non-flammable gas under high pressure. Microscopic plant fossils called diatoms have also been found in this mud.
To really gauge the extent of the volcanic activity which once took place in the area it is necessary to look outside the present national park. There are two other volcanic features in this area, an un-named hill, 5 kilometres south-west of Mount Le Brun, composed of vesicular basalt, and Harvey’s Knob, located approximately 1.5 kilometres north-west of Mount Le Brun. It isn’t a cone but rather a dome-shaped hill of basalt and agglomerate. It is likely that Harvey’s Knob is a volcanic dome, a mass of lava that has solidified around a vent soon after eruption.