Hydrosphere

Question 1

River erosional processes

Answer 1

1. Hydraulic action is when the force of the water compresses air and pressure on the river bank and causes materials to be dislodged.
2. Abrasion is when the force of the water throws bedload against the banks wearing them down.
3. Solution is when soluble rocks react with acids or salts in the water.
4. Attrition occurs when rocks in suspension hit off each other eroding further.

Question 2

Formation of a V-shaped valley

Answer 2

1. Rivers flow quickly down the mountainside and erode the landscape vertically, creating steep valley sides that are shaped like a letter V.
2. The valley sides are then attacked by weathering processes, such as freeze-thaw and biological weathering.
3. The weakened valley sides eventually collapse or move down slope due to processes such as slumping or soil creep.
4. The force of the water and the grinding rocks and stones cut down into the river bed to carve out a V-shaped valley between interlocking spurs.
5. Interlocking spurs are areas of more resistant rock left behind because the river erodes softer rock quicker.
6. Hydraulic action, corrasion and corrosion further erodes the valley sides and the characteristic V shape is created over time.
7. Eventually, the valley becomes deeper and wider.

Question 3

Formation of a waterfall

Answer 3

1. Hydraulic action, abrasion, solution.
2. Differential erosion takes place over bands of more and less resistant rock.
3. Some types of rocks (eg. shale) wear away more easily than others (eg. sandstone).
4. The river wears away the weak rock and travels across the surface of stronger rocks. These more resistant rocks become the capstones to waterfalls.
5. Undercutting causes an overhang of the hard rock.
6. Over time the hard rock is unsupported and collapses due to gravity into the plunge pool.
7. Attrition.
8. Over time, the waterfall retreats upstream.

Question 4

Formation of a meander

Answer 4

1. Hydraulic action, abrasion.
2. Riffles and pools lead to changes in speed and depths in the river channel.
3. Pools are areas of deeper water whereas riffles are shallower with greater turbulence.
4. The river flows fastest on the outside bend increasing the erosive power.
5. River flows slowest on the inside bend.
6. Helicoidal flow moves materials across the river channel. This leads to river cliffs and beaches developing.
7. Meanders migrate downstream as erosion continues.

Question 5

Formation of an oxbow lake

Answer 5

1. Meander.
2. The neck of the meander becomes narrower.
3. During flood there is more energy and the water may cut through the neck.
4. Deposition seals off the old meander.
5. Over time the abandoned channel may dry up.

Question 6

What is a drainage basin?

Answer 6

• A drainage basin is the area from which one river and its tributaries receives water from above and below the ground.
• A drainage basin is an example of an open system because it is open to inputs from outside, such as precipitation, and is responsible for outputs out of the system, such as output of water into the sea and evaporation of water into the atmosphere.

Question 7

Drainage basin input

Answer 7

Precipitation through rain and snow.

Question 8

Drainage basin storage

Answer 8

1. Water vapour in the atmosphere can condense into water moisture. This will form clouds which when big enough produce precipitation.
2. Rainwater can be intercepted by vegetation slowing down the movement of water.
3. On the surface in different volumes from puddles to lakes.
4. In the rocks as groundwater storage.

Question 9

Drainage basin transfer

Answer 9

1. Advection moves clouds/water vapour inland.
2. Over the surface as overland flow/sheet wash.
3. Flow into the soil by infiltration.
4. Water can move downhill through the soil in throughflow.
5. Water may then percolate into the rocks below the soil.
6. It can then flow through the rocks as groundwater flow.

Question 10

Drainage bain output

Answer 10

1. Water vapour can be evaporated due to heat from the sun.
2. Transpiration occurs when water vapour is lost to the atmosphere from vegetation.
3. Surface runoff into the sea.

Question 11

Factors affecting storm hydrographs

Answer 11

1. Large drainage basins catch more precipitation so have a higher peak discharge compared to smaller basins.
2. Smaller basins generally have shorter lag times because precipitation does not have as far to travel.
3. Drainage basins with steep sides tend to have shorter lag times than shallower basins. This is because water flows more quickly on the steep slopes down to the river.
4. Basins that have many streams (high drainage density) drain more quickly so have a shorter lag time.
5. If the drainage basin is already saturated, then surface runoff increases due to the reduction in infiltration. Rainwater enters the river quicker, reducing lag times, as surface runoff is faster than baseflow or through flow.
6. If the rock type within the river basin is impermeable surface runoff will be higher, throughflow and infiltration will also be reduced meaning a reduction in lag time and an increase in peak discharge. Areas that have been urbanised result in an increase in the use of impermeable building materials.
7. Heavy storms with high precipitation result in more water entering the drainage basin which results in a higher discharge.