We love our coasts - especially in this heat! - but don't often think about how they came to be. Here's how #Halifax's #NorthwestArm formed:
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Much of peninsular #Halifax’s bedrock is slate. Sediments deposited as deep-sea muds 500 million years ago were compacted into shale 450 million years ago. When North America and North Africa collided 400 million years ago as a result of tectonic plate movement...
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...the heat and pressure generated by the collision turned the shale into slate. That’s how slate is formed – it’s metamorphosed (transformed) shale.
The #NorthwestArm was formed by glaciers eroding the slate and carving a trough in the bedrock.
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Slate erodes relatively easily because it is layers of sediment. The layers make it easy for water and frost to get in between and break it apart. Mountain building – upward pressure from the continents colliding – also fractured the slate along the Arm.
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After glaciers removed the fractured rock, the trough filled with water after the last ice age as sea levels rose. (Sea levels are lower during ice ages because so much water is frozen in glaciers).
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Alternating layers of mud and sediment – the original sediment from 500 million years ago - can be seen in the picture below at #PointPleasantPark's Black Rock Beach.
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