Chapter 8- Rivers Flashcards
What is the source?
Where the river begins
What is the course?
The path of the river from source to mouth
What are tributaries?
Small rivers that join a larger river
What is the watershed?
A line dividing the waters of a river basin from the waters of another river basin
What is a delta?
Land that forms at the mouth of a river due to deposition
What is the mouth?
Where the river enters the sea or lake
What is the basin?
The area drained by the river from source to mouth
What is a confluence?
The pace where a tributary joins the main river
What is an estuary?
The tidal mouth of a river
Transition between river and sea, affected by the tide
What are distributaries?
Smaller rivers that break food from the main river
What is the material transported by a river called?
Load
What are the 4 methods of river erosion?
Hydraulic action
Abrasion
Attrition
Solution
What is hydraulic action?
The force of moving water eroding the bed and the banks
What is abrasion?
The load hitting of the bed and the banks wearing them away
What is attrition?
The load hitting off itself, wearing itself down
What is solution?
Rock minerals dissolve in a river and are carried away
What are the four methods of river transport?
Solution
Suspension
Saltation
Traction
What is suspension?
Light material e.g. Silt is transported in the water
What is saltation?
Small stones are bounced along river bed
What is traction?
Large rocks ate rolled along riverbed
What is deposition?
When a river slows down, it loses energy so it deposits some of its load
What are the 3 stages of a river?
Youthful
Mature
Old-age
What are th characteristics of the youthful stage?
Steep slope
Fast moving
V-shaped valley: steep sides, narrow floor
What are the characteristics of the mature stage?
Slower moving
Wider
Gentle slope
Mature valley: gentle sides, wide floor
What are the characteristics of the old age stage?
Slow
Meandering
Almost flat slope
Plain: little/no valley
What stage is river erosion most active?
Youthful
What is vertical erosion?
Wearing away of river bed
Name 2 landforms of the youthful stage of a river
V-shaped valley
Waterfalls
How are v-shaped valleys formed?
River wears down valley floor
Weathering wears back slopes of valley
Gravity causes regolith on valley sides to move downslope
What are interlocking spurs?
When sides of a belly jut into each other
-created when youthful river avoids hard rocks
When do waterfalls occur?
When a river falls from a height
How are waterfalls formed?
A band of hard rock lies next to a band of softer rock
River erodes soft rock faster, creating waterfall
Plunge pool develops at base- caused by hydraulic action and abrasion
River undercuts harder rock creating overhang
Rock over head collapses
Waterfall retreats up stream
Name an example of a waterfall
Powerscourt Waterfall, Co. Wicklow
Name 2 landforms of the mature stage
Floodplain
Meander
What is a floodplain?
A flat area along the river corse that is flooded by the river
As the river floods it lays down alluvium on the valley floor
What is alluvium?
Mixture of clay, silt, sand, gravel and other material
What are meanders?
Bends in the river in the mature and old age stages
How are meanders formed?
*when river wears away on its outer bend and deposits on its inner bend
1. Water flows faster on outer bend- erodes bank by undercutting causing it to collapse
2. Water flows slower on inner bend- deposits load here
This continues and meander becomes more prominent
Name three landforms of the old-age stage
Ox-bow lakes
Levees
Deltas
What is an ox-bow lake?
A curved shape of water formed when a meander in a river is cut off leaving the river to straighten its course
How are ox-bow lakes formed?
- River forms a meander
- River erodes land on outer bends
- River deposits on inner bends
- During a flood, river breaks through to straighten course
- Meander is cut off from river ti form ox-bow lake
Eventually lake will dry out, leaving the shape in the landscape
What is a levee?
A raised bank of earth running along the sides of a river
