Flowing water at the land surface - Fundamentals of the Physical Environment - page 453

Figure 14.18 Global mean annual run-off.
Source: After L'vovich (1973).
Plate 14.11 The Minapin glacier valley descending from
Mount Rakaposhi (7788 m) into the Hunza valley, Karakoram
range, Pakistan. Continuing tectonic uplift and intense
glacial and fluvial erosion distinguish this place, together
with Nepal, as the steepest on Earth.
Photo: Andrew Goudie.
In older, lower mountains and uplands, fluvial channels dominate the narrow floors of
valleys with V-shaped cross-sections and rock slopes barely concealed beneath thin
regolith. Valley floors are usually irregular. Steep sections, marked by waterfalls and
associated plunge pools, rapids, potholed bedrock channels and angular boulders,
separate gravel-lined stretches in profile concavities. Tributaries enter higher-order rivers
across small, steep debris cones or more extensive and less steep alluvial fans , which
mark significant reductions in channel slope and stream competence (Plate 14.12). This
applies on the grand scale along mountain fronts, where they may coalesce into huge