The Power of Water – Erosion at Stirling Falls
Tasks:
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Observe the base of the waterfall. What signs of erosion can you see in the plunge pool area?
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Look at the cliffs surrounding Stirling Falls. How does erosion affect the shape and texture of the rock walls?
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What is different about the erosion at Stirling Falls compared to other waterfalls you have seen?
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The Erosive Force of Stirling Falls
Stirling Falls, one of the most iconic waterfalls in Milford Sound, plunges 155 meters (508 feet) straight down into the fjord. Over thousands of years, the relentless force of falling water has shaped the landscape, eroding the rock at the base of the falls and contributing to the dramatic scenery of Milford Sound.
The Erosive Force of Stirling Falls Stirling Falls, one of the most iconic waterfalls in Milford Sound, plunges 155 meters (508 feet) straight down into the fjord. Over thousands of years, the relentless force of falling water has shaped the landscape, eroding the rock at the base of the falls and contributing to the dramatic scenery of Milford Sound.
Geological Context: Stirling Falls flows over layers of different rock types, including:
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Harder Rock (e.g., Granite, Schist): These rocks are dense, with interlocking crystals that make them resistant to erosion. They form the upper layers of the waterfall, creating overhangs as the softer rock below erodes away.
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Softer Rock (e.g., Sandstone, Shale): Found below the harder layers, these rocks are more prone to erosion due to their composition and structure. They are more susceptible to chemical weathering and abrasion, which leads to undercutting.
How Waterfall Erosion Works: Waterfalls are dynamic features that constantly change due to erosion. Stirling Falls demonstrates several key erosional processes:
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Plunge Pool Erosion: The powerful impact of falling water scours the softer rock at the base, deepening the plunge pool over time.
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Undercutting: Softer rock erodes more quickly than the hard rock above, leading to overhangs that eventually collapse.
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Abrasion: Sediment and rock fragments carried by the water grind against the rock surfaces, contributing to erosion.
Differential Erosion Explained:
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Harder rocks, such as granite and schist, erode slowly due to their dense, crystalline structure.
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Softer rocks, like sandstone and shale, erode more rapidly because they are more porous and chemically reactive, allowing water to penetrate and weaken them.
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This difference in erosion rates creates overhangs and steep cliffs, as seen at Stirling Falls.
https://de.wikipedia.org/wiki/Stirling_Falls
https://de.wikipedia.org/wiki/Erosion_(Geologie)
https://www.bbc.co.uk/bitesize/guides/z6jx382/revision/2
picture: https://flexbooks.ck12.org/cbook/ck-12-middle-school-earth-science-flexbook-2.0/section/14.1/primary/lesson/erosion-by-streams-ms-es/
https://en.wikipedia.org/wiki/Waterfall
https://www.britannica.com/science/waterfall-geology