At the given coordinates you will be standing on the edge of the South Saskatchewan River looking at some cliffs on the opposite side of the river to the East. These cliffs have some stories to tell.
The South Saskatchewan River has eroded away through almost 100 metres of sediment. The resulting cliffs in front of you have several stories to tell.
First is the Valley itself. North of here, to your left, (downstream), the valley dates to before the last ice age, at least 100,000 years ago. West, or upstream of Police Point, the valley is less than 10,000 years old. How can we tell?
The Plain yellow-brown cliffs are composed of glacial materials, identified by the mammal fossils within the sediments. Most of your favourite Ice Age friends are represented including Ellie and Mannie, the hairy mammoths and Sid, the ground sloth. In fact, similar cliffs just downstream of this location are one of the best fossil sites in Canada. This deep sediment means that the river had a valley at least this deep that was available to be filled in by glacial material.
As the glaciers melted back towards the North East, the new South Saskatchewan River re-established itself in the old channel. Most of the sediment was carried away, but the cliffs along the side of the valley remain to show the glacial sediment.
The cliffs opposite continue to be eroded away. As the river undercuts the cliff, large chunks slide into the river. The material moves along deep, rotational faults. The almost horizontal surfaces are covered with intact remnants of the prairie that lies behind the cliff. These have slid down, as blocks, unlike slumps (slides or collapsed cliff faces) where the surface material is jumbled as it slides over undisturbed bedrock. This type of slumping is evident in cliff to the west on cliff close to Redcliff, AB.
As recently as the 1940s, a gravel road crossed the cliff, connecting the farm to the north (your left) with the Flats neighbourhood to the right. In the 1980s, the end of the road could still be seen at the farm, but the road in front of cliff had been carried away. Since then, 2 major slides have taken place taking a matter of minutes to a few hours.
The pinnacles visible partway down the slope are NOT hoodoos caused by erosion, but were created by the sliding motion. A sliver of soft rock was squeezed upward between two parallel faults, ending up higher than the adjacent blocks. Just imagine what incredible pressure that required!
To learn more about the different types of landslides, visit
http://www.bgs.ac.uk/discoveringGeology/hazards/lndslides/rotationalSliides.html
To claim this Earthcache, please e-mali the CO with the following: Do not post the answers in the logs.
- Name of the Earthcache:
- Approximately how high is the cliff? (feet or metres)
- Based on the vegetation cover, which part of the cliff has slumped (slid or collapsed) most recently?
- What would you expect this to look like in about 100 years?
- Not necessary, but a nice idea, a picture of yourself with the cliff in the background, this can go in the log.
Thanks for visiting.