How Rivers and Waterfalls Work: Processes & Formation

Rivers: Gravity-Driven Landscape Sculptors

Rivers flow from high to low elevation, driven by gravity. Key processes:

River Processes

• Erosion: Hydraulic action, abrasion, attrition, solution. Cuts channels, creates V-shaped valleys.
• Transport: Traction (rolling), saltation (bouncing), suspension (fine), solution (dissolved). Capacity ∝ velocity⁶.
• Deposition: Velocity drops → sediment settles. Forms floodplains, deltas, alluvial fans, point bars.
• Meandering: Helical flow erodes outer banks, deposits inner banks → sinuous curves. Cutoffs form oxbow lakes.
• Flooding: Overbank flow deposits nutrients; hazard for settlements.

Waterfalls: Vertical Erosion in Action

Waterfalls form where resistant rock overlies softer rock, or at fault lines, glacial hanging valleys, or lava flows.

Formation Sequence

1. Undercutting: Water erodes soft layer → overhang forms.
2. Collapse: Overhang breaks → waterfall retreats upstream.
3. Plunge pool: Impact excavates deep pool at base.
4. Gorge formation: Retreat carves steep-walled canyon.

Famous Examples

• Niagara: Retreating ~1 ft/yr (slowed by engineering).
• Victoria Falls: Basalt fractures control shape.
• Iguazú: Multiple falls on basalt steps.

Rivers and waterfalls are dynamic—constantly reshaping Earth's surface.