Canyon – a deep river valley with very steep, often steep slopes and narrow bottom – one of the most photogenic landscapes. Introduce you to two dozen of the most spectacular canyons from different parts of the world. Canyons are much more common in arid areas than in wet areas because physical weathering has a greater effect in arid zones. The wind and water from the river combine to erode and cut away less resistant materials such as shales. The freezing and expansion of water also serves to help form canyons. Water seeps into cracks between the rocks and freezes, pushing the rocks apart and eventually causing large chunks to break off the canyon walls, in a process known as frost wedging. Canyon walls are often formed of resistant sandstones or granite. Submarine canyons form underwater, generally at the mouths of rivers.