geography weathering, mass movement, rivers

denudation: general lowering of the earths surface due to processes over the long term  

• processes: EROSION, WEATHERING, MASS MOVEMENT 

erosion: breakdown and transport of rocks 

• agents: RUNNING WATER, WAVES, ICE, WIND 

weathering: breakdown of rocks IN SITU 

• processes: PHYSICAL, CHEMICAL, BIOLOGICAL MEANS 

mass movement: process soil, sand, regolith (broken parts of rock- no humus) and rock move downslope as mass, under gravity 

depends on :

• climate (rainfall/temp.) -expeansion + contraction 
• amount of vegetation - detritivores inc. acidity of soil 
• chemical make up of rock - feldspar is weakness in granite 
• rock structure (bedding planes + joints) - cracks allow water/gases to get in 

adv: 

• helps create deep fertile soils 
• create fantastic landforms for tourists (pot holes, cave systems, limestone pavements, stalactites+ stalagmites, swallow holes, dolines, shakeholes) 

dis adv:

• creates unstable slopes 
• damages historical buildings, monuments, statues 

"physical break up of rocks owing to internal + external stresses caused by weathering agents"

FREEZE THAW: 

• breakdown of rocks due to water freezing in cracks- expanding (9.05%)- exerts pressure of 2115 kg/cm2 downwards 
• most effective in jointed rocks (granite) + alternating cycles cause rock to split + break 

PRESSURE RELEASE:

• igneous rocks(granite) formed under pressure- weathering + erosion overlying rocks- underlying rocks pressure released + expand - fractures appear + vulnerable to weathering agents 
• creates dialation joints + cracks parallel to surface + sheeting of rock layers 

EXFOLIATION/INSOLATION:

• large temp change- heating + cooling (expand + contract)- stresses in rock layers- outer layers heat + coo quicker than inner- outer layers peel off 

"processes which lead to decomposition/breakdown of solid rocks by chemical reactions"

CARBONATION:

• significant in areas dominated by limestone + chalk - creates limestone pavements + caves
• rain+ CO2 - weak carbonic acid - insoluble CaCO - soluble CaCO2 + runs away in (aq) 

OXIDATION 

• oxygen dissoves in water -reacts with rock minerals- (especially iron) forms oxides+hydroxides
• weakens + disintergrates rocks + discolours 

HYDROLYSIS

• water+ rocks minerals = insoluble precip. 
• e.g. feldspar (granite) ---> kaolinite (china clay) 

"group of procesess produced by actions of plants+animals"

ROOT ACTION

• plant roots widen rock cracks, increasing their disintegration rates.

EXCAVATION

• animals may excavate (dig) into soil or rock.

ACIDIFICATION

• carbonation - plant canopies (especially coniferous ones) + organic matter inc the acidity of water 
• equals more chemical weatherig processes such as carbonation. (ie. Pine forest)

RAHNS INDEX 

• 1-8 legibility scale on gravestonesto calculate rate- text depth, N or S facing, width of stone 

• both flows characterized by materials no larger than sand particles 

MUDFLOWS: 

• FASTER + fluid end of spectrum - constitency can vary 
• just below the speed + wetness of a river 

EARTHFLOWS 

• THICKER in consistency 
• involve deeper material movements 

• very seasonal 

LANDSLIDES 

• "movement of any mass of material, rock or regolith along a slip plane (icluding rotational slumps + slides) " 
• high magnitude + low frequency + very life threatening 
• slip plane is weak (concave) 
• inc. rainfall, little veg. + low evap causes rotational slumps in permeable rocks (sanstone) leaving crescent shape scar 
• C.S: aberfan 21/10/66 - 
• heavy rain, sandstone + coal, steep, spoil heap no.7 built above spring removing clay 
• 147 dead, 116 pantglas junior school 

ROCKSLIDES 

• effect individual masses of rock - dry and FASTER 
• large scale movements influence large parts of slope 
• bedding + jointing influences rock detachment + slide planes 

• downslope movement caused by expansion + contraction 

SOIL CREEP 

• steep grasses slopes- turf only binded to top layer soil- lower layer moves 
• if moist inc. weight + inc. friction - particles move past each other 
• controlled by -particle size -particle shape -MAV 

SOLIFLUCTION (soil creep plus)

• takes place in permafrost regions (permanently frozen) 
• heave up to 40 cm 
• moist ground undergoing volumetric expansion when frozen 

• movement off steepest bare rock slopes (40 degrees +) 
• fragments fall + bounce 

responsible:

• thermal or freezing expansion 
• water pressure in pores or joints 
• pressure release jointing 
• chemical activity 

• very seasonal due to chlimate related factors above 
• maximum in spring/ atumn when most water present 
• can be triggered by natural disasters 
• FASTEST MASS MOVEMENT 

"area drained by one river and its tributaries. water + sediment are moved downslope by river from highland to sea or lake"

INPUTS:

• only precipitation in form of : rain, snow, hail,sleet...
• snow - delayed response (winter inc. input dec. evap. + interception)
• INTENSITY - in short space of time river system + basin struggle to cope 
• ROBERT E HORTON - overland flow occurs when input > infiltration  
• DURATION - precip. long time = soil saturated + water table at surface + high surface run off

STORES (in sequence)

• INTERCEPTION (vegetation - evergeren VS deciduous   broad leaf VS small leaf    natural VS manmade + other surfaces above groun catch precip.)
• SURFACE STORAGE (puddle to large lake, happens more in impermeable ground) 
• SOIL WATER STORAGE (essential for plant growth) 
• GROUNDWATER STORAGE (permeable rocks- large stores of groundwater called aquifers - top surface called water table) 

FLOWS 

• THROUGHFALL - rain misses plant or not intercepts 
• STEMFLOW - rain drops collect and trickle down plant trunk or stem 
• LEAFDRIP- drips fall off end of leaves 

INFILTRATION (e.g coarse sand = rapid infiltration clay based soil = slow infiltration)

• movement of water from above surface into soil 
• depends on: -amount of water in soil   -porosity + structure of soil   -type + extent of vegetation (helps as provides pathway for water to enter soil)

• PERCOLATION - movement of water down through soil into permeable rock down water table 
• OVERLAND FLOW (FASTEST) - type of surface run off in heavy rainfall across impermeable/saturated surfaces - very fast causing rising limb on hydrograph 
• THROUGH FLOW - above water table- movement of soil downslope below surface down towards river at the valley floor. if appears at surface on a valley side a spring will form 
• GROUND FLOW/BASEFLOW - under water table- water moves downslope+contributes water to river in valley floor-water table meets surface at valley side a spring forms

RIVER RUN-OFF 

• river channels are stores + flows - water stored in river as it flows 
• water can be stored in lake for years or water carried to sea + output from drainage basin 

EVAPORATION 

• liquid water evaporates into vapour + leaves drainage basin to atmosphere 

TRANSPIRATION 

• water enters plant roots from soil (store) - travels up stem- leaves leaf via stomata 
• occurs as part of the process of photo. + greater during growing season (summer in UK)

• evap. + trans. both transfer water to atmosphere + combined as EVAPOTRANSPIRATION 

• WATERSHED - boundary between 2 drainage basins 
• SOURCE - river originates 
• MOUTH - enters sea/lake or leaves drainage basin 
• DISTRIBUTARY - river splits to smaller streams 
• TRIBUTARY - smaller streams join river 
• CONFLUENCE - point where tributary + river meet 
• EPHEMERAL CHANNEL - grass bent over (rarely occupied only in major floods)
• BLUE LINE SYSTEM - rivers shows on a map 

STORES :

• interception - houses and settlements 
• soil moisture 
• groundwater 

FLOWS

• drip 
• infiltration 
• percolation 
• throughflow - extremely quick due to STORM DRAIN 
• baseflow - very little due to STORM DRAIN 

% of water reaching river much higher + faster = FLASHY RESPONSE 

very little evap 

• august 2004 

input

• a months rain (200mm) in one hour 
• remains of hurricane Alex 
• peak discharge 140m3/s between 5:00 and 6:00

basin 

• steep valley + thin soils accel. rainfall + concentrated on village 
• actecedent conditions- saturated land + impermeable shale (clay) meant no infiltration 
• circular basin + little vegetation funneled water in (small bridge area) 

effects 

• 'brown willy effect' highest point (420m) vapour rises + cools forming clouds + precip. 
• roads blocked (no emergency exit) people trapped + homeless
• 6 weeks of the tourist season lost - witchcraft museum 

BRIDGE WIDENED 

• railings above it to allow water to flow over 
• larger volume can flow under 

LANDSCAPING 

• tributaries + vegetation + embankment lowers flood risk 

DREDGING 

• allows extra capacity 

STORM DRAIN (CULVERTS) 

• as soon as water hits basin it travels through + out 

RENOVATED BUILDINGS 

• raised up + grooves allow boards to be placed in as flood defence system 

BRADSHAW:

• "river system is an organised/ordered transport system for water + debris. in general rivers are at or close to equilibrium."

UPPER COURSE

• inefficient- high friction (low volume) + high PE 
• water moves in all direction 

MIDDLE/LOWER COURSE 

• slighty HIGHER VELOCITY as tributaries meet + more efficient flow 

• v-shaped valley formed by constant movment of river channel as result of PE (gravity) and KE (downhill)
• + hydraulic action + abrasion channel deepended 
• soil creep + mass movement cause vertical erosion resulting in further deepening 
• takes most effiecint + less energy consuming routes + therefore bends around objects 

E.G. - Ashes hollow - tibutary of the river severn 

• hard rock sediments flowing freely along river bed trapped in small depressions + swirl 
• abrasion, turbulent flow around + over object causes sediments to wedge further + widen eventually a vortex or eddy is formed
• CAVITATION - bubbles collapse where water is broken up + exert pressure on rocks as shockwave loosening material 
• takes place in porous limestone rocks - small cracks/fissures makes sediments cracked 

e.g river clyde 

RAPIDS - high force + low force

• downstream from waterfall where is has once stood 
• happen at knick point of rejuvanating rivers where bed is at 2 diff. levels 
• can also be due to hard rock standing above soft rock 
• large jagged bed load create low efficiency therefore turbulence is name "white water" 

WATERFALLS 

• result of differential erosion - softer rock erodes faster creating step 
• HYDRAULIC ACTION pronounces step 
• water forced over at high speeds creating plung pool - headwardly erodes rock underneath 
• top heavy rock falls then used as tool of abrasion + hydraulic action 

e.g. high force waterfall, river tees NE England 

as you go DOWNSTREAM things that INC. are: 

• discharge - (volume of water passing through cross section per unit of time m3/s)
• load quantity 
• occupied channel width (distance across actual channel measured at waters surface) 
• channel depth (height from water surface to bed) 
• average velocity (speed of water flow measured 40% up) 

things that DEC. are:

• load particle size 
• channel bed roughness 
• slope angle (gradient)

THALWEG 

• place of maximum velocity : 
• just below suface + mid point between two banks (air resistance and friction) 
• ISOVELS = lines of equal velocity 

AVERAGE VELOCITY = 40% up from bed 

• inc. due to "F" dec. + smaller smoother load 
• despite PE decreasing 

A.V shown by HYDRAULIC RADIUS (cross sectional area/wetted perimeter) 

to get largest hydraulic radius = largest C.S.A/smallest W.P

MEAURE A.V = measure passage of object over 10m then times by 0.8 

• use flowmeter record 1 min (counts/min) 

DISCHARGE (m3/sec)(cumecs)(q) = CROSS SECTIONAL AREA(m2)  x  VELOCITY (m/s)

method: 

• stretch measuring tape between 2 banks 
• peg tape so tort 
• measure channel depth + water depth at regular intervals (e.g.25 cm)

rivers perform 3 main functions : 

• EROSION 
• TRANSPORTATION
• DEPOSITION

bedload = particles moves or rolls + always in contact with bed 

how it happens:

• particle rocks on bed + lifts slightly into faster flowing water 
• rolling action rocks off corners + gets pushed forward 

saltation happens by bedload:

• other particles pushed into motion due to impact of intial particle = "BEROULLI EFFECT"

suspension load:

• bedload + saltation load become suspension load as velcoity inc. prevalent in lower course 

• particles smaller then 0.2 mm difficult to pick up (miscroscopic + platelet shape means water moves over) creating no variation in velocity therefore no lift.
• large SA:VOL +ve charges means particles cohesive + stick together 
• CLAY 0.001mm stays in suspension  + floculates at sea (fresh wate meets salt water)
• coarse/ sand materials >0.1 mm are deposited due to weight + size