Bunjil's cave is located within the Black Range Scenic reserve near Stawell and this is the only rock art painting of Bunjil known.
Bunjil is a significant figure in Aboriginal culture, a legendary hero who provides for all and remains the protector of the natural world, his people and their beliefs.
A return track of about 200m leads to the rock art. It is located in a small shelter at the base of a boulder. A steel mesh fence protects the painting.
The boulder and surrounding rocks are whats known as Granite. You will see plenty of this in the surrounding areas. Large granite blocks are formed when magma (liquid rock) crystallises and hardens deep in the earth's crust. There is slow cooling, and thick layers of sandstone on top of the granite exert extreme downward pressure on the granite. From there, tectonic forces cause folding of the Earth's crust in the area, which lifts the granite. As the granite gets closer to the surface, pressure is diminished and it can expand. It is now also exposed to temperature differences, and the daily cycles of repeated expansion and contraction cause thermal stress, creating cracks which go deep into the granite and may even split it.
Large formations are separated into smaller blocks. As the granite becomes exposed, water containing weak plant acids seeps into the cracks. It eats away at the minerals, turning the surface granite into gravels and clay. Thin layers of loose material start coming off in a process called exfoliation. The chemical processes have more effect on areas with edges and work on the outer few centimetres near these edges and the surface. While these processes work their way inwards, the penetration remains incomplete in the centre of the rock. It is this spheroidal weathering which leads to the rounded shapes.
The erosion of the sandstone exposes the top layer of the granite formation, showing the boulders. Water and wind erosion now takes away the surrounding gravel and soil, and contributes to further rounding. While erosion continues above the surface, ongoing weathering continues below the surface. Over time this continuous process sometimes exposes rounded boulders stacked on top of each other
In order to log this earth cache you must answer 2 questions and email me your answers.
1. Bunjils cave is within a large granite boulder. What has caused the unique shapes of Bunjils cave and other surrounding boulders? Is there evidence in the area of this process still occuring?
2. What did examination of the rock art pigmets tell us they were painted with?
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