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Key Enquiry Question 3 - River Landscapes and Processes
Multiple Choice Quiz 4 River processes and landscapes
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What does the gradient refer to?
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1 point
the slope
the bed and banks of a river
a waterfall
material carried by a river
What features are typical of a river's upper course?
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1 point
meanders and floodplains, where rivers begin to get wider and deeper
includes river estuaries, mudflats and salt marshes
v-shaped valleys, interlocking spurs, small rapids, waterfalls and small streams - which are tributaries
What does the channel refer to in a river?
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1 point
the bed and the banks of the river
a hollow at the foot of a waterfall
a steep valley left behind from the action of a waterfall
when rain dislodges tiny soil particles each time it rains
What is the term for material carried by a river?
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1 point
Rock outcrops
The load
What is traction?
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1 point
How tiny particles of sediment are carried along in the river's current.
How dissolved chemicals are carried along in the river's flow, invisible to the eye.
How smaller stones or pebbles are picked up and then dropped again in a skipping motion within a river's flow.
How large stones are dragged along in the river's flow.
What is saltation?
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1 point
How tiny particles of sediment are carried along in the river's current.
How dissolved chemicals are carried along in the river's flow, invisible to the eye.
How smaller stones or pebbles are picked up and then dropped again in a skipping motion within a river's flow.
How large stones are dragged along in the river's flow.
What is suspension?
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1 point
How tiny particles of sediment are carried along in the river's current.
How dissolved chemicals are carried along in the river's flow, invisible to the eye.
How smaller stones or pebbles are picked up and then dropped again in a skipping motion within a river's flow.
How large stones are dragged along in the river's flow.
What is solution (the transportation version)?
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1 point
How tiny particles of sediment are carried along in the river's current.
How dissolved chemicals are carried along in the river's flow, invisible to the eye.
How smaller stones or pebbles are picked up and then dropped again in a skipping motion within a river's flow.
How large stones are dragged along in the river's flow.
What is abrasion?
1 point
Where sand and pebbles are dragged along the river bed, or knock into it by saltation, wearing away the river bed.
Where rocks and stones wear each other away as they knock together.
Where fast-flowing water is forced into cracks, breaking up the bank over time.
Where alkaline rocks, such as limestone are dissolved by acidic rainwater.
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What is hydraulic action?
1 point
Where sand and pebbles are dragged along the river bed, or knock into it by saltation, wearing away the river bed.
Where rocks and stones wear each other away as they knock together.
Where fast-flowing water is forced into cracks, breaking up the bank over time.
Where alkaline rocks, such as limestone are dissolved by acidic rainwater.
Clear selection
What is solution (the erosion version)?
1 point
Where sand and pebbles are dragged along the river bed, or knock into it by saltation, wearing away the river bed.
Where rocks and stones wear each other away as they knock together.
Where fast-flowing water is forced into cracks, breaking up the bank over time.
Where alkaline rocks, such as limestone are dissolved by acidic rainwater.
Clear selection
What is attrition?
1 point
Where sand and pebbles are dragged along the river bed, or knock into it by saltation, wearing away the river bed.
Where rocks and stones wear each other away as they knock together.
Where fast-flowing water is forced into cracks, breaking up the bank over time.
Where alkaline rocks, such as limestone are dissolved by acidic rainwater.
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How does a waterfall form?
1 point
Waterfalls occur when a river crosses a bed of more resistant rock.
Erosion of the less resistant rock underneath continues - undercutting the hard rock above it. The river's energy creates a hollow at the foot of the waterfall, known as a plunge pool.
The less resistant rock beneath is eroded more rapidly by abrasion and hydraulic action. This creates a ledge, which overhangs and collapses.
The waterfall takes up a new position, leaving a steep valley or gorge.
All of the above
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What is the correct definition for physical weathering?
1 point
Small cracks allow plant roots to penetrate in search of water and nutrients. As they grow, root cells force the cracks apart, widening them and breaking the rock into pieces.
Any chemical change or decay of solid rock. Rainwater mixes with atmospheric gases, eg CO2, to form weak acids which dissolve alkaline rocks such as limestone.
When physical force breaks rock into pieces. In winter, cracks in the limestone rock fill with rain. This freezes, expanding in volume by 10% and widening cracks so that more water gets in (AKA freeze-thaw).
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What affects the shape of river valleys?
1 point
The rate of weathering. If scree piles up, weathering is taking place rapidly.
The rate of mass movement.
How quickly the river can remove the material brought by mass movement.
All of the above
Clear selection
What is the river's discharge?
1 point
The speed of a river, measured in meters per second. It's obtained by timing how long it takes a floating object (a dog biscuit works well!) to cover a distance (e.g. 5 meters).
The fastest current in a river.
A continuous corkscrew motion of water as it flows along a river channel.
The volume of water flowing in a river, measured in cubic metres per second. It is measured by multiplying area (width times average depth across the channel) by velocity.
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What happens in a river's middle course?
1 point
The gradient becomes steeper and the river's discharge slows as less water flows through the river's channel. The river channel is jagged and at angles, which causes the river's velocity to slow.
The gradient becomes gentler but the river's discharge has increased as more streams and tributaries are added to it. The river channel is also smoother and as a result velocity increases.
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How do meanders change a river's valley?
1 point
The river bends in its middle course; each sharp bend is called a meander - this is created from the helicoidal flow of the water within the river's channel.
The helicoidal flow sends the river's energy laterally (eg to the sides). The fastest flow (thalweg) is forced to the outer bend, where it undercuts the bank, creating a river cliff which eventually collapses.
Gradually the river undercuts more and more, so that the channel moves to a new position. Helicoidal flow shifts sediment across the channel to the inner bank where the sediment is deposited by the slower moving water, to form a point bar - over time this will get bigger and eventually form a flood plain.
Continued erosion can create a narrow neck between two meanders. Eventually the neck will be breached, cutting off the meander to create an ox-bow lake.
All of the above
Clear selection
What is an estuary?
1 point
Where the river meets the sea.
A broad, wide area of mud.
A low-lying area at the mouth of a river where a river deposits so much sediment it extends beyond the coastline.
Salt-tolerant vegetation growing on mud flats in bays. These plants trap sediments which gradually raise the height of the marsh. Eventually it becomes part of the coast land.
Natural levees that form beside a river's bank where it first floods.
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What are the features of a river's lower course?
1 point
The river valley's sides are steep and the bottom is narrow; as the river cuts vertically into the surrounding rock, it produces steep sides and winds around areas of more resistant rock.
Because the river has picked up velocity, erosion now occurs laterally (ie side to side, not downwards), creating meanders, point bars and flood plains.
The river is now tidal, affected by incoming and outgoing sea tides; it is now wide and deep, flowing over an almost flat gradient.
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What changes as a river flows from its upper to lower course?
1 point
River discharge increases, channel width increases, channel depth increases and velocity increases.
Sediment load volume increases, however sediment particle sizes decrease, as does channel bed roughness.
Along the long profile, the river goes from being steep in upland areas to gentle in lowland areas.
The river's cross profile changes shape, from v-shaped in the upper course to almost flat by the lower course.
All of the above
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What are the benefits and problems of sea walls?
1 point
They break up incoming waves, restrict beach access and look ugly, and can be destroyed by big storms.
They reflect waves back out to sea, can prevent easy access to the beach and suffer from wave scour - this is where plunging waves erode the beach and attack the wall's foundations.
Clear selection
What makes salt marshes valuable?
1 point
For wildlife they assist migrating birds as shelter during stormy weather, and the mud is rich in shellfish and worms as a food source.
The help to protect farms or towns from flooding.
They contain a great deal of alluvium, which is good for farming.
Clear selection
When does most erosion take place in the upper course?
1 point
During periods of dry weather when most load is blown by wind across the valley.
During periods of wet weather when most load is carried in the river.
Clear selection
Which statement is true about the river's flow in the upper course?
0 points
Streams in the upper course look like they are flowing rapidly, but in fact they flow slowly because so much of the river's energy is lost through friction with the stream bed.
Streams in the upper course look like they are flowing slowly, but in fact they flow quickly because so much of the river's energy is assisted by the smooth channel reducing friction with the stream bed.
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