Examine the larger boulder at the listed coordinates and prepare your observations to the following earthscience tasks. Please provide your answers to the cache owner in a timely manner, i.e. less than a fortnight.
-Describe the shape and size of the boulder. Why do you think it is this shape?
-Look for a granite erratic. What is different about the shape of this boulder?
-Provide a photo of your visit to Hallet Cove beach.
Hallett Cove is one of Australia’s most outstanding geological and archaeological sites, recording an Australian ice age some 280 million years ago and providing a treasure chest of more than 1,700 Aboriginal artefacts. Magnificently developed glacial pavements along the northern cliff tops are recognised as the best record of Permian glaciation in Australia and being of worldwide significance.
A glacial erratic as a piece of rock that differs in size and type of rock native to the area in which it rests; the name "erratic" is based on the errant location of these boulders. These rocks were carried to their current locations by glacial ice, often over many kilometers. The many of the rocks that can be seen on Hallet Cove beach are erratics moved there by glaciers. The variety of rocks on display have come from many sources. Glacial erratics were derived from nearby outcrops as well as much further afield. Evidence of erratics and other geological features confirm the general direction and sense of glacier ice movement toward the north-northwest.
Erratics of granite were carried from the Victor Harbor area 60kms south east. Erratics of quartzite are local rock carried onto the beach. Erratics of Sturt Tillite and Marinoan Angepena Formation siltstone eroded out of late Paleozoic tillite of the Cape Jervis Formation can be found at the north end of Hallett Cove beach. Two large erratics of fine-grained, cross-bedded sandstone have been carried from Seacliff. Erratic of porphyry from Mount Monster can be found on the beach.
