Upper zone: large, angularboulders often block riverchannelsProduces a large wettedperimeter high frictionwhich uses up much river’senergy After friction overcome little energy is available foreroding and transportingmaterial
Steep slope small amt of water can move large boulder with the help of gravity After heavy rain or snowmelt material transported Water flowing between boulders become turbulent dislodging particles increasing transportation Large amt of large particles mean high rates of abrasion / corassion cutting into channel bed A river erode vertically by traction or saltation which resulted in a steep-sided valley called a V-shaped valley.
(i) Climate: Rainfall lubricates and increases the weight of hillsides increases discharge which erodes river bed and removes bedload.(ii) Rock structure: - hard rocks are erosion resistant and produce steep valley - soft rocks give gentler valley(iii) Vegetation: it helps to bind soil together and keep the hill slope more stable. Interception reduce the amt of rainfall that reaches the soil surface.
Interlocking spur.It forms becausethe river is forcedto follow awinding coursearound theprotrusions ofthe surroundinghighland,resulting in spursinterlock.
Is a suddenstep in a river’slong profile Causes therejuvenation ofa river
Tallest waterfalls in the world Height: 979 m (3,212 ft)
Forms when water flows over sudden change in gradient The fall is so fast that the water, by hydraulic action erodes rock at the base The loose material is used as tool to further erode and deepen the base by abrasion to form a plunge pool The undercutting at the base of the waterfall creates a overhanging cliff, which will eventually collapse. A waterfall may appear to retreat upstream (headward erosion), leaving a deep sided gorge.
a band of resistant rock lies over a layer of less resistant rock – Niagara Falls on the USA- Canada border When a fault-line scrap lies across a river – Victoria Falls in Zambia-Zimbabwe, Africa When a river plunges down the edge of a plateau – Livingstone Falls in Zaire, Africa
Are associated with very disturbed turbulent water Usually occur in the upper coarse of the river where the long profile of the river is steep Sometimes river on the area with alternating bonds of resistant and less resistant rock Less resistant rock erodes much faster than the resistant rock by the process of hydraulic action which they create an uneven river bed
Rapids are mini-waterfallsShallow, slow flowingriver due to largeamount of friction. Protruding bands of more resistant strata create steps over which rapids fall - the river bed is ungraded
A deep narrowvalley with almost vertical wall.
What? Cylindricalholes drilled intothe rock byturbulent highvelocity flow.
How? Potholes in the beds of rivers are common feature of rapid abrasion Vertical eddies may be strong enough to rotate a small pebble, which grinds a hole in the rock. Overtime, they may widen and join with other potholes to form larger potholes and the whole river is deepened. It is most active when river levels are high