What is the direction of ice movement at the Roche Moutonnée location?

Decoding the Direction of Ice Movement at a Roche Moutonnée

Ever seen a rock formation that looks like it was sculpted by a giant hand? Chances are, you’ve stumbled upon a roche moutonnée. These asymmetrical bedrock formations are like nature’s compass, whispering tales of glaciers long gone. What’s truly fascinating is how their shape acts as a roadmap, revealing the direction these icy behemoths once lumbered.

Think of a roche moutonnée as a geological detective, offering clues about ancient ice flows. Ranging in size from a small car to a whole city block, they all share a common story etched into their very form. This story is told through their gently sloping “stoss” side and their steep, jagged “lee” side.

The Directional Signature: Nature’s Arrow

So, how do these rocky formations point the way? It’s all about understanding the stoss and lee sides.

• Stoss Side (Up-Ice Side): Imagine a glacier, a colossal river of ice, grinding its way across the landscape. When it hits a solid rock, the pressure is immense. The ice, armed with embedded rock fragments, acts like sandpaper, smoothing and polishing the upstream side of the obstacle. This creates the stoss side – a gently sloping surface often adorned with glacial striations, those tell-tale scratches and grooves left by the moving ice. Sometimes, you’ll even find glacial polish, where the rock is so smooth it shines!

• Lee Side (Down-Ice Side): Now, things get interesting. As the glacier passes over the rock, the pressure eases off, creating little pockets between the ice and the bedrock. Meltwater seeps into cracks and crevices, and when it refreezes, it’s like a superglue, bonding the rock to the glacier. As the ice continues its relentless journey, it plucks away chunks of rock, leaving behind a steep, irregular, and jagged surface – the lee side. It’s a rough break-up, leaving the lee side looking quite different from the smooth stoss side.

Reading the Clues: Which Way Did the Ice Flow?

Glaciologists, those scientists who study glaciers, use the shape of roches moutonnées to piece together the puzzle of past ice movements. The gently sloping, polished stoss side points to where the ice came from, while the steep, plucked lee side shows where the ice was going. It’s like following breadcrumbs left by a frozen giant!

More Than Just Ice: Other Players in the Game

While abrasion and plucking are the main sculptors, other factors can influence how a roche moutonnée takes shape.

• Bedrock Structure: Think of the rock’s natural weaknesses. Joints and fractures can make it easier for the glacier to pluck away chunks on the lee side.
• Glaciological Regime: The speed and thickness of the ice play a role. Faster, thinner ice tends to encourage plucking. Also, warmer glaciers, with plenty of meltwater at their base, are more likely to create these formations.
• Water Pressure: Fluctuations in water pressure at the base of the glacier can also enhance the quarrying process on the lee side. It’s like the glacier is using water as a tool to break apart the rock.

So, the next time you see a roche moutonnée, remember it’s more than just a rock. It’s a history book written in stone, a testament to the immense power of glaciers, and a clear indicator of the direction they once flowed. By understanding the forces that shaped these formations, we can unlock the secrets of our planet’s icy past. Pretty cool, huh?