River landscapes Flashcards
What are the stages of freeze-thaw?
Water fills a crack or joint in rock, water freezes and crack is widened. Repeated freeze-thaw action increases size of crack until block of rock breaks off, loose blocks of rock are called scree.
How does acid rain affect rivers?
Rainwater is slightly acidic. Acid reacts with minerals in rocks and dissolves them. E.g. granite contains feldspar, which is converted into soft clay minerals as result of chemical reaction with water
How do plants and animals affect rivers?
Plants grow into cracks and split rocks apart, animals burrow in cracks in rock.
How does sliding work?
Rock weathered or eroded material or earth moves down a slope. Gravity pulls weakened material quickly downward.
How does slumping work?
River erodes bottom of valley slope, making it steeper. Material above slides downwards, particularly if it is saturated with rainwater.
How does hydraulic action work?
Force of water on bed and banks of river removes material.
How does attrition work?
Load that is carried by river bumps together and wears down into smaller, smoother pieces.
How does solution work?
Some rock minerals dissolve in river water.
How does abrasion work?
material carried by river rubs against bed and banks and wears them away.
What is transportation?
Way which river carries eroded material or load.
What is traction?
Large boulders are rolled along river bed.
What is suspension?
Finer sand and silt particles are carried along in flow, giving river a brown appearance.
What is saltation?
Smaller pebbles are bounced along river be, picked up then dropped as river flow changes.
What is solution?
Some minerals e.g. chalk, are dissolved in water and carried along in flow, although they cannot be seen.
What are landforms?
In upper course, river erodes vertically. Gradient is steep and channel is narrow.
What are interlocking spurs?
River at its source is small and has limited energy. It flows naturally from side to side, around ridges in valley sides, called spurs. Spurs become interlocking with those on other side of valley.
What are waterfalls?
Common feature in upper course where is an increase in vertical erosion. Form where is layer of hard, resistant rock overlying softer, less resistant rock.
What are gorges?
Over long time, process of undercutting and collapse is repeated, and waterfall retreats, forming steep-sided gorge.
How do v-shaped valleys form?
Rain falls(solution) onto land, rain is slightly acidic, eroding land. River is flowing quickly due to downward flow of water due to gravity. Solution from rainfall combined with lateral and vertical erosion leads to formation of v-shaped valley. Only happens in upper course-youthful stage. When v-shaped valley interlock, become inter-locking spurs.
How do waterfalls form?
River erodes softer rock underneath harder rock. Creates undercut. Hard rock overhangs soft rock which collapses. Plunge pool develops at bottom of waterfall. Finally, steep forge-like valleys occur causing waterfall to retreat back upstream. Most occur in upper course/youthful stage.
What is a floodplain?
Wide,flat area of land either side of a river and experiences floods when river tops its banks.
How do floodplains form?
In lower course, river is nearing sea and carries huge amount of sediment(alluvium). When river floods, excess water spills over surrounding area. During flooding, velocity of river is reduced, loses energy, and deposits sediment, forming floodplain. Floodplain is shaped by lateral erosion of meanders as they gradually migrate downstream and by deposition of material on inner bends.
How do levées/floodplains form?
In lower course/old stage. Because river caries and drops material. Rate of deposition depends on speed of river and size of sediment/material. When river floods, bursts its banks but eventually river water dries up, leaves layers of sediment and alluvium. Material is first dropped along banks creating levées. Fewer material carried/dropped further away from banks building up land called floodplains.
How do levées form?
Deposition process, which takes place during flooding, continues until eventually embankments, made of larger, heavier sediment, are created beside river. When flooding occurs heaviest material deposited first due to decrease in river’s energy. Material creates natural embankments-levées. Smaller and finer sediment, or alluvium, is deposited further from river because it requires less energy to carry it.
How do meanders form?
In middle course, width depth and velocity of river all increase. River erodes laterally and starts to form large bends. Bend get bigger and wider, eventually develop into horseshoe shape. On outside bend faster flow, eroding bank to create river cliff. Water in inner bend flows slower deposits eroded material to create slip-off-slope.
How do ox-bow lakes form?
Narrow neck of meander is gradually eroded. Water now takes quickest route-times of flood river cuts through meander. Deposition takes place, sealing off old meander. Meander neck has been cut through completely. Ox-bow lake left behind when meander completely cut off.
