Mountain building processes
The Earth's outer shell is broken into big pieces called plates. They move a few centimetres a year, about as fast as your nails grow.
When two plates push towards each other, the rock between them is squeezed. Soft layers bend into folds. The up-folds are peaks and the down-folds are valleys. Mountains made like this are fold mountains.
- Alps: raised when the African plate pushed towards the Eurasian plate.
- Himalaya: raised when the Indian plate pushed into the Eurasian plate. It is still moving, so the range still rises a little each year.
Other mountains form in other ways: block mountains rise between cracks (faults), and volcanic mountains are built from lava and ash. This lesson follows fold mountains because the Alps are fold mountains.
Landslides and avalanches
A mountain slope is steep, so gravity pulls hard on loose material.
- Landslide: rock, soil and mud slide down. Triggers: long heavy rain, an earthquake, cutting a road into the slope, or cutting down trees whose roots hold the soil.
- Avalanche: a slab or cloud of snow breaks off and rushes down. Triggers: fresh heavy snowfall, a warm day, wind, or a skier's weight.
They are dangerous for roads, railways, villages and walkers. Protection: forest on the slope, walls and nets, snow fences, warning signs, weather and snow watching, and not building in the path.
Glacier retreat and permafrost thaw
A glacier is a slow river of ice. With warmer air, more ice melts in summer than snow adds in winter, so the glacier gets shorter. This is glacier retreat.
Meltwater feeds rivers, farms and power plants. At first rivers carry more water, but when the glacier is small the water supply drops.
Permafrost is ground that stays frozen all year in high places. The ice acts like glue in the cracks of the rock. When it thaws, the rock loosens and can fall. Huts, cable-car posts and paths built on frozen ground can become unsafe.
Tourism and big projects in the Alps
The Alps bring in money through skiing, walking and sightseeing. Big projects include cable cars, ski runs, hotels, roads, and long railway tunnels through the mountain that carry goods across Europe.
Good: jobs, income for mountain villages, less moving away.
Bad: cleared forest and steeper risk of landslides, noise and air pollution, damaged plants and animals, and artificial snow that uses much water and energy.
Many valleys now try sustainable tourism: limit visitors, protect forest, use trains, and plan for a warmer climate. The same questions appear in the Himalaya, such as pilgrim and trekking routes in the Indian hills.
Try it
Put a thick towel on a table. Push both ends towards the middle. Watch folds rise. Now put a few marbles on a fold and tilt it: they roll like a landslide. In the 3D, push the plates to 100%, then raise the warming and see the ice left and the risk number change.
Key formulas and definitions
- Fold mountain = two plates push together + layers bend into folds
- Landslide = rock and soil moving down a slope
- Avalanche = snow moving down a slope
- Glacier retreat = melting is more than new snow, so the ice front moves back
- Permafrost = ground frozen all year; thaw = loses its glue, rock falls
Worked examples
1. Why are the Alps called fold mountains?
Plates pushed together and bent flat rock layers into folds that rose as a mountain range.
2. After four days of heavy rain, a hill road is blocked by mud and stones. Which hazard is this and why did it happen?
A landslide. Rain makes soil heavy and slippery on a steep slope, so it slides down.
3. A glacier front moved back 30 m each year for 20 years. How far did it retreat?
30 m x 20 = 600 m.
Common mistakes
- Mixing up landslide (rock, soil) and avalanche (snow).
- Thinking mountains stopped growing. The Himalaya still rises as the plates keep pushing.
- Saying glacier retreat means the glacier walks backwards. The ice still flows down; the front moves back because melting wins.
- Thinking tourism is only good or only bad. It brings money and also pressure on nature.