Here's why:
* Water's Power: Moving water, especially in rivers, has incredible erosive power. It can wear away rock and soil over time, carving out deep channels.
* Downcutting: Rivers often flow downhill, and gravity contributes to their erosive force. This downward erosion, called downcutting, is responsible for creating the deep, vertical walls of canyons and gorges.
* Lateral Erosion: Rivers also erode sideways, widening their channels. This lateral erosion contributes to the overall shape and breadth of canyons and gorges.
Other Factors:
While river erosion is the primary force, other factors can contribute to canyon and gorge formation:
* Tectonic Activity: Earthquakes and other geological events can create faults and fissures, which rivers can then exploit and erode.
* Weathering: Weathering processes like frost wedging (water freezing and expanding in cracks) and chemical weathering can weaken rock, making it more susceptible to erosion.
Key Takeaway: Canyons and gorges are primarily sculpted by the relentless power of rivers over long periods.
