Glaciers and how ice shapes the land
Geography · Key Stage 2 · The School
A river of slow-moving ice
A GLACIER is a huge mass of ice that moves very slowly downhill. It forms where snow builds up faster than it melts, year after year. Unlike a river, it can take years to move just a short distance. Yet given enough time, it reshapes an entire valley.
Ice as a giant tool
A glacier carries rocks frozen into its base. Those rocks scrape and grind the ground beneath it. This is a powerful form of erosion. It can carve out a wide, U-shaped valley over thousands of years. The scratches it leaves on bare rock can still be seen today.
What is left behind
When a glacier melts, it drops everything it was carrying. Rocks of every size are dumped in a jumbled pile. That pile is called MORAINE. It marks exactly how far the glacier once reached. Finding moraine far from any modern ice is a real clue to the past.
A valley in Snowdonia has very steep, straight sides. Its floor is wide and flat, shaped like a letter U. A river now flows small and thin along the bottom. That river alone could never have carved such a wide valley. The clues point somewhere else. A huge glacier once filled this valley completely. It scraped the sides as it moved. It carved the wide, flat floor. The river came later, after the ice had melted away. Walkers today can still spot deep scratches left in the bare rock.