Welcome to Glaciated Landscape Development!
In this section, we are going to explore how massive sheets of ice, some kilometers thick, have acted like giant "earth-movers" to sculpt the landscapes we see today. Whether you are looking at the jagged peaks of the Alps or the rolling hills of northern England, you are looking at the work of ice and water over thousands of years. Glaciated landscape development is all about how different processes (erosion, deposition, and meltwater) create specific landforms.
Don't worry if some of the names sound like a foreign language—many of them are! We will break them down into simple steps and use analogies to help them stick.
1. Prerequisite Check: How does ice actually work?
Before we look at the landforms, remember two key ways glaciers erode the land:
- Plucking: Meltwater freezes onto rocks at the base of the glacier. As the glacier moves, it "plucks" chunks of rock out of the ground.
- Abrasion: The rocks trapped in the ice act like sandpaper, grinding down the bedrock.
2. Erosional Landforms: Sculpting the Mountains
These landforms are created when a glacier "carves out" the landscape. Think of these as the "negative space" left behind after the ice has finished its work.
Corries (also called Cirques)
A corrie is an armchair-shaped hollow found on the side of a mountain. It is often the "birthplace" of a glacier.
How they form:
- Snow accumulates in a small hollow on a north-facing slope (in the Northern Hemisphere).
- Over time, the snow turns to ice and begins to move in a rotational slide.
- Plucking steepens the back wall, while abrasion deepens the hollow.
- A rock lip is left at the front where erosion is less intense.
Analogy: Imagine taking a giant ice-cream scoop and carving out a deep hole in the side of a hill.
Arêtes and Pyramidal Peaks
- Arête: A narrow, knife-edged ridge formed when two corries erode back-to-back.
- Pyramidal Peak: A sharp, pointed mountain peak formed when three or more corries erode backwards toward each other (e.g., The Matterhorn).
Glacial Troughs (U-Shaped Valleys)
Glaciers are "lazy"—they follow existing V-shaped river valleys but widen and deepen them into a U-shape. They have steep sides and flat floors.
- Truncated Spurs: These are rounded-off hillsides. A river would wiggle around them, but a glacier is too powerful and simply "chops" the ends off as it moves past.
- Hanging Valleys: Formed by smaller "tributary" glaciers. Because the smaller glacier didn't erode as deeply as the main glacier, its valley is left "hanging" high above the main floor, often creating waterfalls.
Roches Moutonnées
These are outcrops of resistant rock on the valley floor. One side is smooth (the stoss side) due to abrasion, and the other side is jagged (the lee side) due to plucking.
Quick Review: Erosional landforms are "cut out" of the rock.
Mnemonics: C-A-P (Corries, Arêtes, Peaks).
3. Depositional Landforms: Leaving the "Litter" Behind
When a glacier melts or loses energy, it drops the material it was carrying. This material is called Till (unsorted rocks, sand, and clay).
Moraines
Moraines are lines of "litter" (debris) left by the glacier. There are four main types:
- Lateral Moraine: Debris at the sides of the glacier.
- Medial Moraine: Formed when two glaciers join and their lateral moraines meet in the middle.
- Terminal Moraine: A ridge of debris at the snout (end) of the glacier, marking its furthest reach.
- Recessional Moraine: Ridges marking stages where the glacier paused during its retreat.
Drumlins
These are oval-shaped hills made of till, often described as looking like a "basket of eggs." They have a steep "stoss" end facing the direction the ice came from and a tapered "lee" end.
Common Mistake: Don't confuse Drumlins with Roches Moutonnées!
Tip: Drumlins are deposited (made of loose rubble), while Roches Moutonnées are eroded (made of solid bedrock).
Erratics
These are large boulders that have been transported by ice and dropped in an area with a completely different rock type. They look like "strangers" in the landscape.
Key Takeaway: Depositional landforms are built up from unsorted material called till.
4. Fluvioglacial Landforms: The Role of Meltwater
Fluvioglacial landforms are created by water coming from the melting glacier. Unlike glacial till, fluvioglacial deposits are sorted (the water carries smaller pebbles further) and stratified (in layers).
Eskers
A long, winding ridge of sand and gravel.
How it forms: Imagine a tunnel underneath the ice. A river flows through this tunnel, depositing sediment on its bed. When the ice melts, the "bed" of the river is left behind as a ridge.
Kames
Mounds of sand and gravel found on the valley floor. They form when sediment collects in a crevasse (a crack in the ice) or a hole, and then drops to the ground when the ice melts.
Outwash Plains (Sandur)
A flat area in front of a glacier where meltwater streams have spread out and deposited "sorted" sediment. Think of it like a giant, sandy front yard for the glacier.
Did you know? Meltwater channels can flow uphill! Because the water is under immense pressure inside the ice, it can be forced over obstacles that a normal river couldn't cross.
5. Periglacial Landforms: Life on the Edge
Periglacial means "around the glacier." These landscapes are not covered by ice, but they are freezing cold and dominated by permafrost (ground that is frozen for at least two years).
Pingos
These are ice-cored hills. They form when ground water freezes into a massive ice lens, pushing the earth above it into a dome. If the ice melts, the dome collapses, leaving a thaw lake.
Patterned Ground
Over time, the repeated freezing and thawing of the soil (frost heave) pushes stones to the surface and moves them into geometric shapes like circles or polygons.
Solifluction Lobes
In summer, the top layer of soil (the active layer) thaws, but the ground below stays frozen. The soggy top layer becomes a "muddy soup" and slides slowly downhill due to gravity, forming tongue-shaped lobes.
Common Mistake: Students often forget that periglacial features require permafrost. Without the permanently frozen ground underneath, the water would just drain away, and features like solifluction wouldn't happen!
Summary Checklist for Your Revision
To master this chapter, make sure you can describe and explain the origin of:
- Erosional features: Corries, arêtes, pyramidal peaks, U-shaped valleys, hanging valleys, truncated spurs, and roches moutonnées.
- Depositional features: Drumlins, erratics, moraines, and till plains.
- Fluvioglacial features: Eskers, kames, outwash plains, and meltwater channels.
- Periglacial features: Pingos, patterned ground, and solifluction lobes.
Top Exam Tip: When writing about any landform, always use the "Process-Landform" link. For example: "A corrie is an erosional landform created by plucking and abrasion during rotational slip." This shows the examiner you understand how the landscape developed!