Fluvial geomorphology of erosional environments

Fluvial geomorphology of erosional environments

1. V-shaped valleys with interlocking spurs

   • typical of upland mountain streams as high flow velocities that follow intense precipitation cause intense vertical erosion with this high potential energy thus, producing V-shaped valleys.
     • Upland mountain streams - intense rainfall, vertical erosion = V-shaped valleys.
   • Steepness may vary with climate, vegetation and geology
     • Climate - precipitation affects river discharge and mass movements on valley sides.
     • Vegetation - Roots bind soil together stabilising slope.
     • Geology - Impermeable rocks produce steeper valleys E.g. streams in carboniferous limestone cut canyon like valleys
   • Interlocking spurs = stream forced to wind a sinuous course around the protrusions of the surrounding highland, spurs appear to interlock blocking the view of the valley.
   • Headward erosion/spring sapping - at source where it appears to migrate upslope into its watershed. Undercutting, rock, soil and veg.

2. Waterfalls

   • Form when flowing rivers cross into less resistant rock E.g. Great Whin Sill UK
   • Form when rivers flow over the edge of a plateau E.g. South America and Africa
   • No friction at the brink of the fall so velocity increases.
   • Descending water erodes the underlying rock, forming a deep plunge pool.
     • Overtime, harder rock may become unstable and undercut retreating the waterfall upstream leaving a steep-sided gorge E.g. until stabilised Rainbow Gorge at Niagara Falls was retreating by 1m per year.

3. Rapids

   • Form where gradient of river increases without a break in the slope (otherwise it would become a waterfall)
   • Forms where the river flows over dipping bands of more resistant rock.
   • Rapids increase turbulence and thus, erosive power of the river.