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📘 How a glacier carves a valley into a U

Stand beside a mountain stream and look across its valley: the slopes meet in a narrow V. Running water cuts near the channel; that is the shape a later glacier may inherit.

4
lessons
~20 min
to learn
Adults
level
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What you’ll learn

  1. Before the ice arrivesContrast a river-cut V-shaped valley with the inherited valley a glacier later occupies.Rivers begin the story by concentrating erosion in a narrow channel; glaciers later fill and work across the whole valley.
  2. The tools beneath the iceExplain how abrasion, plucking, and ice thickness let moving ice widen and deepen a valley.Embedded rocks grind bedrock while freeze-thaw-assisted plucking removes blocks, allowing thick ice to attack floor and walls.
  3. What retreat revealsIdentify hanging valleys, cirques, moraines, lakes, and fjords as results of glacial erosion or deposition.When ice retreats, unequal erosion and deposited debris remain as waterfalls, bowls, ridges, and water-filled troughs.
  4. The landscape as evidenceUse several landforms together to reconstruct a glacier’s former route and behavior.U-shaped profiles, striations, erratics, moraines, and sharp ridges form a connected record of moving ice.

Questions this course answers

What shape does a river commonly cut before glaciation?

Running water concentrates erosion near its channel, producing a narrow V-shaped profile.

What makes debris beneath a glacier act like sandpaper?

Embedded rocks scrape and groove bedrock as the glacier moves.

What is glacial plucking?

Freeze-thaw loosens jointed rock; moving ice then freezes onto the pieces and transports them.

Why can a tributary valley become a hanging valley?

Different ice thicknesses and erosive power leave the tributary floor higher after retreat.

What is a moraine?

Moraines are accumulations of unsorted material carried and deposited by glaciers.

What does an erratic show?

An erratic is a transported boulder that can help reveal a former ice route.

Grounded in trusted sources

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