River Landscape Flashcards
What are the 3 weathering processes
Mechanical
Chemical
Biological
Describe how mechanical weathering works
- Water fills a crack or joint in the rock
- Water freezes and the crack is widened
- Repeated freeze-thaw action increases the size of the crack until the block of rock breaks off
- Loose blocks of rock are called scree
Describe how chemical weathering works
Rainwater is slightly acidic. The acid reacts with minerals in the rocks and dissolves them.
Describe how biological weathering works
Roots grow into cracks and split rocks apart
Define sliding
Where rock, weathered or eroded material or Earth moves down a slope. Gravity pulls the weakened material quickly downwards
Define slumping
Where the river erodes the bottom of the valley slope, making it steeper. Material above slides downwards, particularly if it is saturated with rainwater
What is the point where two rivers meet called
Confluence
The _ is an imaginary line that separates on drainage basin from the next
Watershed
What is a flood plan
The land that may get flooded when a river flows
What are tributaries
Smaller rivers join the main one
What is a channel
Where the river flows
What is a mouth of the river
This is were it flows into a lake or the sun, or the ocean
What is drainage basin
The river is fed by the rain that falls in the area inside the red dished line
Define source
The starting point of the river
Define weathering
The breakdown and decay of rock by natural processes
What are the three types of weathering
Physical
Chemical
Mechanical
What is Freeze Thaw Action
This happens when rainwater enters cracks or gaps in the rock and then freeze if the temperature drop below zero degrees. The water expands and turns into ice and experts pressure on the rock, causing it to break into smaller pieces
Define scree
Loose pieces if rock with sharp edges. They are broken off by Freeze Thaw Action, roll down the mountainside
What is biological weathering
Roots if a plant, especially trees, can growing creates in a rock and split them apart
What is mass movement
Movement of rocks and soil downslope due to gravity, helped by weaker rocks, steep slopes and heavy rotation
Define soil creep
Individual particles of soil more slowly down a slope
Define flows
Masses of soil or rock usually mixed with water flow like liquid downhill
What is sliding and slumping
Material moves radially down a slope in one go (landslide). In a slump material often rotates it moves
Define hydraulic action
In a fast-flowing river, water is forced into cracks on time it break them up
Define solution
Water also dissolves soluble minerals from the bed and banks. This helps to break them up
Define discharge
Is the volume of water flowing through the river
Define velocity
The speed at which a river flows
How is an Oxbow Lake formed
○ Erosion makes the neck narrow
○During floods river takes shortest course through the neck
○ There is a new straighter river course
How are Interlocking formed
As the river erodes the landscape in the upper course, it winds and bends to avoid areas of hard rock. This creates interlocking spurs, which look a bit like the interlocking parts of a zip.
When a river runs over alternating layers of hard and soft rock, rapids and waterfalls may form.
How is a V-shaped Valley formed
○ The river cut down and deepens its valley
○ The river widens its valley as it deepens it
○ The river continues to widen its valley
How are waterfall and gorges formed
The soft rock is eroded quicker than the hard rock and this creates a step.
As erosion continues, the hard rock is undercut forming an overhang.
Abrasion and hydraulic action erode to create a plunge pool.
Over time this gets bigger, increasing the size of the overhang until the hard rock is no longer supported and it collapses.
This process continues and the waterfall retreats upstream.
A steep-sided valley is left where the waterfall once was. This is called a gorge.
How is a meander formed
As the river erodes laterally, to the right side then the left side, it forms large bends, and then horseshoe-like loops called meanders.
The formation of meanders is due to both deposition and erosion and meanders gradually migrate downstream.