Hallett Cove Conservation Park: Keith gets a geography lesson in the Adelaide Coast region of South Australia
The 50-hectare Hallett Cove Conservation Park hugs the coastline north from Hallett Cove. It's one of our most outstanding geological sites recording an Australian ice age 280 million years ago.
For geologist and President of the Friends of the Park, Bob Major, this place is one gigantic open-air classroom. Follow the boardwalk and interpretive signs to the Sugarloaf - one of the most bizarre landforms in the park. It looms like a miniature volcano smack bang in the middle of a lunar landscape. And the vivid colours? They're a window to its fascinating formation.
Bob Major: "Starting at the top those brown sediments are gravels deposited about 3-million years ago when the present Mount Lofty Ranges were uplifted. The white stuff was deposited about 280 million years ago when the ice cap which covered Australia was melting. And the same with the red and the grey material here."
The layers of mud laid down millions of years ago are like pages in a fascinating geological history book. And every now and then, there's a ruddy great rock - a very loud punctuation mark in the story.
Bob Major: "The big rocks were carried here on icebergs. From the melting ice which is out the west of us somewhere. The iceberg was carrying this material and carrying the sand and silt and clay as well and as the ice and the iceberg melted it just dropped it onto the sea floor - and that's what these boulders are."
That was a mere 270-280 million years ago! But take the walking track to the top of the cliff overlooking the Cove and the numbers become even more impressive. The view's worth the walk but it's what's at the base of the Black Cliff that's significant - a layer of rocks deposited on the sea floor a staggering 600-million years ago.
Bob Major: "They were sediments deposited in a shallow sea. They were horizontal and then Australia got squeezed from east and west about 500 million years ago. And a great package of rocks were folded and uplifted to form a mountain range that went from here to Western Victoria."
There's a great photo on the interpretive sign that shows the folds - and a sobering thought - it's still being squeezed! On top of the cliff is the geological phenomenon that sparked all the interest.
In 1875 Professor Ralph Tate was walking along Hallett Cove beach picking up shells when he climbed up Black Cliff and he saw a large flat rock which had a smooth and scraped surface. He knew it has been caused by ice - in an ice age! This stunning glacial pavement was formed when Australia was part of the great super-continent of Gondwana over the South Pole.
Bob Major: "What we're looking at is a glaciated surface that's been smoothed and scratched by material which has frozen into the bottom of an icecap in this area. It moved very slowly, over the country, undulating country as it was then 280 million years ago and the rocks are hard enough to take the smoothing and the polishing of the fine rock flour and sand. The lines were the cobbles and boulders, which were locked into this ice - dragging over that smooth and scratched surface. So you had two things going on - smoothing and polishing and scratching. So the surface was being polished and ruined at the same time."
You can see why Bob calls it an open-air classroom. Further along the boardwalk - another lookout and another lesson.
All this world famous geology from 600 million year old rocks right up to now is easily accessible - it's in the southern suburbs. You can get to it either along the Marion Coastal Walking Trail or you can drive right up to Hallett Cove.
The park is 22 kilometres south of Adelaide - for maps and brochures contact the Department of Environment and Heritage
Hallett Cove Conservation Park
22 kms south of AdelaidePublished 19th July 2009
