Unit 24
Rocks and the surface.
How the surface is built and worn away: the rock cycle, rivers that carve and build, and volcanoes.
Before this unit
The unit, lesson by lesson
Lessons
3 lessons · 18 practice questions · about an hour
The rock cycle
Follow one rock round the cycle: magma that cools into granite, sand pressed and cemented into sandstone, and burial that heats it by 25 °C a kilometre, until it is transformed and finally melts.
Erosion and weathering
Rain and rivers wear down a whole upland over two million years. Tell weathering from erosion, work out how much faster land wears in a monsoon, compare granite with sandstone, and follow the worn rock to the sea.
Volcanoes
Magma rises, the pressure drops and the gas comes out as bubbles. Work out at what depth they appear, and see how silica and gas decide whether the lava flows, piles into a dome, throws up fountains or explodes into ash.