fluvial landforms

FLUVIAL LANDFORMS

Fluvial Landforms

Erosional landformsDepositional landformsTypes of channelThe long profile

Fluvial Landforms

Two major groups of landforms:

Erosional landformsDepositional landforms

EROSIONALLANDFORMS

DEPOSITIONALLANDFORMS

COMBINED EFFECTS OF EROSION & DEPOSITION

- V-shaped valley Floodplains Pools & riffles

- Interlocking spurs

Levees Meanders & Ox-bow lakes

- Waterfalls Braiding River terraces

- Rapids Delta

- Gorges Alluvial fan

- Potholes

Upper zone: large, angular boulders often block river channels

Produces a large wetted perimeter high friction which uses up much river’s energy

After friction overcome little energy is available for eroding and transporting material

Erosional Landforms: V-shaped valley

Erosional Landforms: V-shaped valley

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.

Steepness of valley sides depend of factors such as:

(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 spurs

It forms because the river is forced to follow a winding course around the protrusions of the surrounding highland, resulting in spurs interlock.

Interlocking spur.

Waterfalls

Is a sudden step in a river’s long profile

Causes the rejuvenation of a river

Angel Falls

Tallest waterfalls in the world

Height: 979 m (3,212 ft)

How?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.

Reasons for change in gradient along the river:

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

Niagara Falls

Victoria Falls

RapidsAre 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 in the Upper Tees Valley

Rapids are mini-waterfalls

Protruding bands of more resistant strata create steps over which rapids fall - the river bed is ungraded

Shallow, slow flowing river due to large amount of friction.

GORGEA deep narrow valley with

almost vertical

wall.

PotholesWhat?

Cylindrical holes drilled into the rock by turbulent high velocity flow.

PotholesHow?

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