1.2 Physical processes give rise to characteristic river landforms Flashcards
River environments
Define weathering:
Involves elements of weather wearing away something
Define physical weathering:
Breaks down rock into smaller pieces, changes in temperature and rainfall freezing and thawing in rock cracks
Describe freeze thaw action:
Water seeps into cracks of rocks and freezes and expands breaking rock
Describe exfoliation (onion):
Occurs as internal of rock expands from heat and while outside cools quicker contracting and breaking rock
Define chemical weathering:
This causes rock to decay and disintegrate. Largely done by slightly acidic rainfall seeping into porous rock
Describe hydrolysis:
When water dissolves minerals in rock
Describe oxidation:
Reacting with oxygen
Describe acid rain:
Weak acid formed when water and CO2 react wearing rock
Define biological weathering:
Roots of plant growing in cracks in rocks gradually split rock apart
Define mass movement:
Once rocks broken down weathered material moves down under influence of gravity.
Describe slumping:
When bottom of valley slope cut away by river at base, slope unstable and weather material slumps down. Rain acts as lubricant and makes material heavier.
Describe soil creep:
Weathered material moves down slope slowly, collects at bottom and is eroded by river
Define attrition:
large particles such as boulders collide breaking into smaller pieces
Define hydraulic action:
Sheer force of the river dislodges particles
Define abrasion:
Smaller particles rub against river banks and bed
Define solution in terms of erosion:
Acid in rivers dissolve rocks
What is transport in river?
Material known as load moving along the river
Describe traction (transport):
Large boulders rolled along the bed
Describe saltation (transport):
Rocks bounce along the bed
Describe suspension (transport):
Lighter material carried by river flow
Describe solution (transport):
Material dissolved in river
Describe deposition:
When the river lacks energy to carry load heavier particles begin to get deposited, when less water or where current slows, Large boulders deposited at top and small at end resulting in sorting
How does a river change downstream?
Increases:
Discharge, channel width, channel depth, velocity, load
Decreases:
Particle size, Channel bed roughness, Slope
Describe formation of V-Shaped valley:
Formed by erosion, rocks and stones carried. Force of water and grinding causes vertical erosion to carve out valley. Gets deeper and wider over time. Interlocking spurs formed as weaker parts cut.
Describe formation of waterfalls:
Water flows over hard rock which erodes slowly and beneath softer rock eroded faster to form a step. Force of water erodes bottom to form plunge pool. Hard rock gets undercut soft rock erodes so it eventually collapses.
Describe formation of meanders:
Lateral erosion as softer rock eroded faster causing a bend and deposition occurs on slower part of bend making the bend less straight as faster part also cuts fast part of bend quicker.
Describe formation of oxbow lakes:
When neck of meander comes narrow water begins to straighten its course cutting right through the bend and deposition occurs on bank of river and the cut off meander is an oxbow lake
Describe formation of levees:
When river floods coarsest material deposited an edges of river forming natural embankment.
Describe formation of deltas:
Occurs where river carries large amount of sediment which get deposited where river meets sea causing main channel to split into smaller channels/dis-tributaries
Describe formation of flood plain:
As meander moves down slowly valley erodes to create wide valley floor, deposits layers of alluvial on slip off slopes builds up into large flood plain
