WEATHERING   1    Weathering  Categories:  

Weathering  Types:   Mechanical   Chemical   Biological  

Description:   Fragmentation  of  soild  rocks  into  smaller  fragments  

Decay  of  soild  rocks  which  crumble  into  smaller  chemically  altered  fragments  

Physical  disintegration  and  chemical  decomposition  of  soild  rocks  

Agent:   Weather  elements  -­‐ Temperature  -­‐ Frost/Ice  -­‐ Salt  Crystals  (ok  not  

really  “weather”  element  D:  )  

-­‐ Pressure  release  

Chemical  reactions  -­‐ Rock  minerals  and  

moisture  -­‐ Rainwater  -­‐ Seawater  -­‐ Organic  Acids  

Organic  Agents  e.g.  plants,  animals  and  man  

Any  change  in  the  rocks?  

Change  in  shape  and  size,  NO  chemical  change  

Chemical  composition  changed  and  structure  changed  

Products:   Coarse  &  angular  particles   Fine  particles  (e.g.  rust,  minerals  dissolved  in  solution)  

Catalyst  for?   Chemical  Weathering  by  increasing  the  rock  surface  i.e.  increase  in  surface  exposure  when  rock  is  broken  up.    

-­‐    

Dependent  on  whether  it  is  biomechanical  or  biochemical  

Climate/  Factors    

Where  it  is  most  

effective:  

Great  diurnal  range  of  temperature  (e.g.  deserts)  And  frost  action  (e.g.  mountainous  regions)  

Hot  and  humid  areas    -­‐ Heat  speeds  up  chemical  

reactions  -­‐ Most  of  the  reactions  

require  water  

Regions  with  continuous  vegetation  cover    High  rates  of  animal  and  human  activity  

Consists  of:     Insolation  weathering  (alternate  insolation  and  radiation,  temperature  changes)  -­‐ Exfoliation  -­‐ Granular  disintegration  -­‐ Block  disintegration  -­‐ Wetting  and  drying  Freeze  Thaw  Action  Salt  Crystal  Growth  Pressure  Release  

Oxidation  Hydrolysis  Solution  Hydration  Carbonation  Spherodial  Weathering  Honeycomb  Weathering    

Biochemical  -­‐ Organic  Reactions  Biomechanical  -­‐ Burrowing  -­‐ Rock  splitting  -­‐ Man’s  activities  

 Mechanical  Weathering:    Insolation  Weathering  (Caused  by  the  repeated  heating  and  cooling  (radiation)  of  rock  over  daily  cycles,  progressively  breaking  apart  the  grains  of  rock  along  joints  as  stress  is  developed)  

Block  Disintegration  

-­‐ The  splitting  of  rocks  along  the  joints  is  known  as  block  disintegration.  -­‐ The  blocks  of  rocks  that  are  detached  are  of  various  shapes,  depending  on  the  

rock  structure.  -­‐ In  daytime,  intense  solar  heating  causes  rocks  to  expand.  -­‐ At  night,  the  temperature  falls  so  rocks  cool  and  contracts.    -­‐ Repeated  expansion  and  contraction  produces  stress  along  joints.  Joints  are  then  

widened  and  deepened  and  finally  break  down  the  rocks  block  by  block.  

Process  

Granular  Disintegration  

Differential  Expansion  -­‐ Different  coloured  mineral  grains  expand  at  different  rates.  -­‐ The  darker  minerals  absorb  more  heat  and  expand  more  than  the  lighter  minerals.    -­‐ This  causes  stresses  between  adjacent  grains  and  the  rock  will  disintegrate  grain  by  

grain.    

2   WEATHERING    

-­‐  Exfoliation   -­‐ Rocks  expand  when  heated  in  the  day  and  contract  when  they  cool  at  night.    

-­‐ However,  the  rocks  are  not  heated  right  through,  and  the  outer  parts  expand  and  contract  more    

-­‐ The  repeated  expansion  of  the  outer  parts  form  cracks  that  are  parallel  to  the  boulder  surface,  while  repeated  contraction  forms  cracks  perpendicular  to  the  boulder  surface.      

-­‐ Eventually,  the  outer  shell  of  the  rocks  peels  and  falls  off  in  slabs.    

 

 

Wetting  and  Drying  

-­‐ Alternate  wetting  and  drying  causes  rocks  to  break  up  -­‐ Physical  weathering  process  where  rocks  are  mechanically  disintegrated  by  the  

accumulation  of  successive  layers  of  water  molecules  in  between  the  mineral  grains  of  a  rock.  Sometimes  called  slaking.  

-­‐ Increasing  thickness  of  the  water  pulls  the  rock  grains  apart  with  great  tensional  stress.  

Factors   ALL  TYPES   Climate  (Extremity  of  weather)  Relief  -­‐ Landslides  and  slumping  happens  frequently  on  steep  slopes,  hence  exposing  

underlying  rock  -­‐ Enables  insolation  weathering  to  work  on  the  exposed  underlying  rocks  

Block  Disintegration  

Well-­‐jointed  rocks  

Granular  Disintegration  

Differential  expansion  needs  rocks  that  are  made  up  of  different  minerals  that  expand  at  different  rates.  Dark  rocks  (e.g.  granite)  weather  faster  physically  as  they  heat  up  faster  and  experience  a  greater  stress  upon  expansion  as  compared  to  light-­‐coloured  rocks.  Rocks  also  need  to  be  coarse-­‐grained.    

Exfoliation   -­‐    

Rock  Type  

Wetting  and  Drying  

-­‐  

Block  Disintegration  Granular  Disintegration  Exfoliation  

Places  with  a  large  diurnal  range  of  temperature,  such  as  deserts.    -­‐ In  the  desert,  day  temperatures  can  rise  to  35oC  or  higher  because  of  the  lack  of  

cloud  cover  to  reduce  incoming  solar  radiation/insolation.    -­‐ Night  temperatures  can  go  down  to  10oC  or  lower  because  of  the  lack  of  cloud  

cover  to  prevent  outgoing  terrestrial  heat  from  escaping  back  to  space.    

Location  

Wetting  and  Drying  

Near  Water  or  have  water  through  precipitation.    Temperatures  should  be  high  enough  for  a  good  rate  of  evaporation  

Products   Block  Disintegration  

Broken  down  into  regular  blocks  

WEATHERING   3    

    Granular  

Disintegration  Coarse-­‐grained  rocks  with  homogenous  structure  break  up  into  gravel  or  sand  

    Exfoliation   Exfoliation  domes  with  angular  debris  at  base  

    Wetting  and  

Drying  Rocks  that  are  flaking  off,  or  forms  TAFONI  (see  salt  crystal  growth  below)  

Salt  Crystal  Growth  (also  known  as  haloclasty)    Process   -­‐ Saline  water  seeps  into  cracks/  joints/  pore  spaces/  cavities  of  rocks  

-­‐ Water  evaporates,  recrystallizing  dissolved  salt  inside  the  rocks  -­‐ Salt  crystals  grow  as  more  evaporation  occurs  -­‐ When  the  rocks  are  heated  up,  the  crystals  will  expand,  putting  pressure  on  the  rock  -­‐ The  rock  would  slowly  disintegrate  into  fragments  due  to  the  stresses  caused  by  the  salt  crystal  

growth  and  the  widening  of  joints.  

4   WEATHERING    

 Factors   Heat:    

-­‐ Affects  the  rate  of  cooling  and  heating  of  the  salt  crystals  -­‐>  affects  the  size  of  the  crystals  Amount  of  solution:    -­‐ Affects  the  rate  of  evaporation  and  hence  the  rate  of  which  salt  crystals  form    Salinty  of  solution:    -­‐ A  less  diluted  solution  will  have  fewer  salt  crystals  compared  to  a  more  concentrated  solution    Type  of  salts:    -­‐ The  salts  which  have  proved  most  effective  in  disintegrating  rocks  are  sodium  sulfate,  magnesium  

sulfate,  and  calcium  chloride.    -­‐ Some  of  these  salts  can  expand  up  to  three  times  or  even  more.    

Rock  Type   If  calcium  carbonate  in  present  in  the  rock  e.g.  chalk/limestone,  it  is  able  to  bind  together  other  sediments  from  salt  crystal  growth  to  form  beachrock  and  in  warmer  areas  dunerock.    

Location  Climate  

Arid  Climate  -­‐ Strong  heating  causes  strong  evaporation  and  therefore  salt  crystallisation.    Near  the  sea,  near  beaches  -­‐ Wind  carries  salt  spray  onto  rocks,  where  it  is  absorbed  into  small  pores  and  cracks  within  the  rocks.    -­‐ There  the  water  evaporates  and  the  salt  crystallises,  creating  pressure  and  often  breaking  down  the  

rock.    At  places  where  rock  is  decomposing  -­‐ Salt  crystals  of  solutions  formed  by  decomposition  of  rock    

Products  

 Left,  Azerbaiian,  Salt  weathering  of  sandstone.  Right,  Yehliu  Taiwan,  the  surface  pattern  on  this  pedestal  rock  is  honeycomb  weathering,  caused  by  salt  crystallization.      HONEYCOMB  WEATHERING:  -­‐ Caused  by  salt  crystal  growth  on  sea  walls  

WEATHERING   5    

-­‐ Heterogenous  rocks  which  contain  soluble  materials  are  subjected  to  differential  weathering  when  pitted  by  sprays  of  sea  water.  

-­‐ Pits  or  cavities  on  the  cliff  faces  are  exposed  when  the  weathered  materials  are  removed.  -­‐ A  type  of  tafoni  (below  right),  a  weathering  pattern  assumed  to  be  formed  by  salt  weathering  

o Tafoni:  a  class  of  cavernous  rock  weathering  structures,  which  likely  develop  in  large  part  by  chemical  and  physical  salt  weathering  processes.  

o Small  cave-­‐like  features  found  in  granular  rock  such  as  sandstone,  with  rounded  entrances  and  smooth  concave  walls.    

o Occur  in  groups  that  can  riddle  a  hillside,  cliff,  or  other  rock  formation.  They  can  found  in  all  climate  types,  but  are  most  abundant  in  intertidal  areas  and  semi  arid  and  arid  deserts.    

o Currently  favored  explanations  controlling  their  formation  include  salt  weathering,  differential  cementation,  structural  variation  in  permeability,  and  the  length  of  the  drying  period  between  wettings.  

 Freeze  Thaw  Action/  Frost  Shattering    Process   -­‐ Water  seeps  into  joints  and  cracks  in  rocks  or  boulders,  and  gets  trapped  in  them.    

-­‐ When  the  temperature  falls  below  freezing  point,  the  water  freezes  and  increases  in  volume  by  as  much  as  9%.  

-­‐ The  expanding  ice  exerts  pressure  on  the  sides  of  the  joints  and  cracks.    -­‐ When  the  temperature  rises  to  above  freezing  point,  the  ice  melts  and  contracts,  and  the  pressure  

is  reduced.  -­‐ Repeated  freeze  and  thaw  action  over  long  periods  of  time  further  increase  the  size  of  the  joints  

and  cracks,  and  eventually  break  the  boulder  into  smaller  fragments.  

 Rock  Type   Well-­‐jointed  

-­‐ For  water  to  seep  in  Bare,  exposed  rocks  are  more  vulnerable  

Location   Climatic  conditions  

6   WEATHERING    Climate   -­‐ Have  temperatures  that  always  fluctuate  above  and  below  the  freezing  point  to  facilitate  repeated  

freezing  and  thawing  actions  (mountainous  regions:  Alps,  Snowdonia)  -­‐ Rainfall  to  provide  water  to  seep  into  the  cracks    

Products   Talus  slope:  Accumulation  of  freshly  broken  rock  materials  that  have  fallen  from  the  cliffs  Scree:  Freshly  broken  rock  materials  that  are  ANGULAR  and  have  fallen  from  the  cliffs,  are  DEBRIS,  deposited  at  the  base  of  the  cliff  due  to  gravity  Regolith:  Weathered  Remains,  may  or  may  not  be  angular  

 Felsenmeer/Boulder  field:  In  a  felsenmeer  (also  known  as  a  block/boulder  field),  freeze  thaw  weathering  has  broken  up  the  top  layer  of  the  rock,  covering  the  underlying  rock  formation  with  jagged,  angular  bolders.  Felsenmeers  are  formed  in  situ,  meaning  that  they  are  not  transported  during  or  after  their  creation,  and  form  on  extensive  gentle  slopes.  Tors:  Rock  outcrop  formed  by  weathering,  usually  found  on  or  near  the  summit  of  a  hill.    

Pressure  Release    Process   -­‐ Pressure  release  of  rock  can  cause  physical  weathering  due  to  unloading.  The  majority  of  igneous  

rocks  were  created  deep  under  the  Earth's  surface  at  much  higher  pressures  and  temperatures.    -­‐ As  erosion  brings  these  rock  formations  to  the  surface,  they  become  subjected  to  less  and  less  

pressure  as  the  overlying  rocks  are  removed.    -­‐ This  unloading  of  pressure  causes  the  rocks  to  fracture  horizontally  with  an  increasing  number  of  

fractures  as  the  rock  approaches  the  Earth's  surface  due  to  expansion.    -­‐ Spalling,  the  vertical  development  of  fractures,  occurs  because  of  the  bending  stresses  of  unloaded  

sheets  across  a  three  dimensional  plane.  -­‐ Sheeting  then  occurs  due  to  this  unloading  of  pressure.  (Removal  of  rock  layer  by  layer)  

Factors   Need  erosion  to  occur,  in  order  for  uplift  of  rock  layers  to  surface  to  occur  Rock  Type   Igneous  Location  Climate  

-­‐    

Products   Looks  similar  to  exfoliation    Chemical  Weathering:  Oxidation    Process   -­‐ Oxygen  comes  into  contact  with  other  minerals,  then  forming  a  new  compound  which  is  known  as  

the  oxide  of  that  mineral.  (oxygen  can  be  dissolved  in  rainwater)  -­‐ This  new  compound  is  less  resistant,  has  a  weakened  rock  structure.  -­‐ A  mineral  that  is  commonly  oxidized  is  iron,  which  is  found  in  most  rocks.  When  oxidized,  the  iron  

changes  into  reddish-­‐brown  iron  oxide  which  crumbles  readily,  weakening  the  rock  structure.  -­‐ However,  the  iron  oxides  coat  the  whole  rock  giving  it  some  protection  from  further  oxidation.  -­‐ The  problem  that  arises  (which  leads  to  more  erosion)  is  that  the  iron  oxide  is  very  brittle  and  can  

be  broken  off  very  easily,  making  the  rock  again  susceptible  to  oxidization.    -­‐ When  this  process  happens  over  a  long  period  of  time  the  strength  of  the  rock  will  begin  to  erode  

and  it  will  eventually  break  apart.  -­‐ Rusting:  Iron  may  have  been  blue  or  grey  in  color  originally  as  this  is  characteristic  of  rocks  with  a  

lack  of  oxygen.  However,  after  it  has  come  into  contact  with  oxygen,  it  is  oxidized  and  its  rock  structure  is  broken  down,  leading  to  it  being  discolored  into  a  reddish  brown.    

WEATHERING   7    

-­‐ Commonly  oxidized  minerals  are  iron,  aluminium,  manganese,  etc.  Factors   Amount  of  moisture  

-­‐ Water  is  needed  as  it  helps  to  quicken  the  oxidation  process.  Temperature    -­‐ Aids  in  increasing  the  rate  of  oxidation.    -­‐ When  temperature  is  increased,  the  molecules  in  the  rock  will  move  around  faster  and  have  more  

collisions,  creating  greater  opportunities  for  oxidation  to  occur.    Rock  composition  -­‐ Different  compositions  will  subject  the  rock  to  different  types  of  weathering  and  affect  the  rate  and  

extent  of  that  weathering  process.    -­‐ Certain  minerals  particularly  iron  and  manganese  weather  primarily  by  oxidation.  Jointing/Lines  of  weakness  -­‐ When  there  are  many  cracks  and  joints  in  the  rocks,  more  rock  surface  is  exposed  to  weathering  

agents.    -­‐ The  rocks  that  have  cracks  will  be  more  susceptible  to  coming  into  contact  with  oxygen  in  the  water.    -­‐ This  further  weakens  the  bonds  between  rocks  and  causes  the  rock  structure  to  be  broken  down  

more  easily  through  oxidation.    Rock  Type   Must  contain  the  minerals  that  can  be  oxidized  Location  Climate  

-­‐ Hot  and  humid  climate  is  more  conducive  for  oxidation  to  occur.      

Products   Patina:  Green  layer  covering  Statue  of  Liberty  Precipitation  of  Iron  produces:  -­‐ Iron  Stains  on  rock  surfaces  -­‐ Iron  dykes  along  joints  -­‐ Iron  Caps:  A  layer  of  iron  “skin”  broken  by  running  water  

Carbonation    Process   -­‐ A  type  of  chemical  weathering  

-­‐ Carbonation  occurs  on  rocks  which  contains  calcium  carbonate  such  as  limestone  and  chalk  -­‐ Atmospheric  carbon  dioxide  dissolves  in  rainwater  and  water  vapour  in  the  surrounding  air  to  form  

weak  carbonic  acid.  -­‐ When  rain  falls  on  these  rocks,  the  carbonic  acid  reacts  with  the  calcium  carbonate  in  the  rocks  to  

form  calcium  bicarbonate  (insoluble  Calcium  Carbonate+  Water  +  Carbon  Dioxide  —>  soluble  Calcium  Bicarbonate)  

-­‐ Breaks  down  the  rock  which  then  can  be  dissolved  by  any  form  of  aqueous  solute  (e.g.  rainwater)  in  the  surroundings  

-­‐ Rocks  are  dissolved  in  rainwater  and  are  washed  away  Factors   Mineral  Composition  of  rocks  (Calcium  carbonate)  

Temperature  -­‐ Decrease  in  temperature    Colder  water    Can  hold  more  carbon  dioxide    Greater  acidity  in  

rainwater    Speeds  up  process  of  carbonation  Water  -­‐ Carbonation  is  maximized  in  wet  environments.      

Rock  Type   Limestone,  rocks  that  contain  calcium  carbonate  Location  Climate  

High  amounts  of  precipitation  

Products   Karst  landscape  shaped  by  dissolution  of  layer(s)  of  soluble  bedrock  Some  features  of  karst  regions  include  sinkholes,  caves,  limestone  pavements  and  springs  Grykes:  Grooves  formed  along  joints  of  limestone  pavements  Clints:  Flat  platforms  in  between  grykes  

8   WEATHERING    

 Swallow  holes  (SINKHOLES!):  Widened  entrances  to  joints  Dolines:  Larger  swallow  holes  

   

Hydration    Process   -­‐ Swelling  (Expansion)  of  rock  minerals  when  they  absorb  water  

-­‐ Swelling  causes  stress  in  rocks,  forcing  grains  apart  -­‐ Repeated  wetting  and  drying  of  minerals  led  to  flaking  of  rocks;  granular  disintegration  -­‐ Reversible  change  as  mineral  composition  remains  unchanged

Factors   -­‐ Water  -­‐ Temperature  -­‐ Mineral  types  

Rock  Type   -­‐  Location  Climate  

High  amounts  of  precipitation/near  water  Also  need  high  amount  of  heat  as  evaporation  is  needed  

Products   -­‐ Anhydrous  calcium  sulphate  absorbs  water  to  form  hydrated  calcium  sulphate  (gypsum)  -­‐ Flaking  of  rocks,  granular  disintegration  -­‐  

Hydrolysis    Process   -­‐ �Chemical  weathering  involving  rainwater  and  some  minerals  in  rocks  (feldspar  +  ferromagnesian)  

-­‐ Acidic  rainwater  (carbonic  acid  in  rainwater)  react  with  feldspar  and  mica  to  form  kaolin  clay  that  crumbles  easily  and  are  washed  away  

-­‐ The  clay  is  soft  and  expands  in  volume;  causing  granular  disintegration  -­‐ Iron  in  mica  oxidised  to  form  reddish-­‐brown  iron  oxide  -­‐ More  effective  at  the  angular  edges  of  the  blocks  of  rocks.  (See  Spheroidal  weathering)  

Factors   -­‐ Temperature  

WEATHERING   9    

-­‐ Moisture/Water  Rock  Type   Must  contain  feldspar  and  mica  (usually  igneous  rock)  

Felsic  rock  such  as  granite  Location  Climate  

Common  in  hot,  wet  regions  

Products   Granitic  tors,  deep  weathering  profile  

 Solution    Process   -­‐ Soluble  minerals  e.g.  salt  and  gypsum  in  rock  are  dissolved  by  standing  water,  causing  the  rock  to  

crumble  Factors   -­‐ Amount  of  water  

-­‐ Type  of  rock  minerals  and  their  solubility  Rock  Type   -­‐ Contains  the  minerals  that  are  water-­‐soluble  

 Location  Climate  

-­‐ Has  to  be  near  standing  pools  of  water,  maybe  in  caves  where  water  collects,  rock  pools  -­‐  No  particular  climate,  but  must  have  some  access  to  water  though  precipitation  perhaps  

Products   -­‐ Solution  pans  -­‐ Solution  pools  

-­‐  Spheroidal  Weathering    Process   -­‐ Rainwater  percolating  the  joints  of  large  rectangular  blocks  starts  chemical  weathering  

(carbonation,  hydrolysis,  oxidation,  all  the  above)  along  the  joints  and  at  the  angular  edges  of  the  blocks.  o Have  higher  surface  area  to  volume  ratio,  hence  these  areas  weather  faster  

-­‐ The  weathered  materials  break  away  from  the  core  in  concentric  shells,  revealing  a  rounded  

10   WEATHERING    

“corestone”  Factors   Amount  of  moisture  

Temperature  Rock  Type   -­‐    Location  Climate  

Hot  and  humid  e.g.  tropical  

Products   -­‐ Creates  rounded  boulders  and  domed  monoliths  -­‐ Rectangular  blocks  are  reduced  to  rounded  boulders  and  eventually  the  entire  corestone  is  reduced  

to  weathered  materials  -­‐ Can  form  granitic  tors  and  contribute  to  a  deep  weathering  profile  (Refer  to  Hydrolysis  too!)    

-­‐

   Biological  Weathering:  Biochemical:    Biochemical  Process  

Chelation:  -­‐ Chelation  is  a  biological  process  where  organisms  produce  organic  substances  (chelates),  that  

decomposes  minerals  and  rocks  by  the  removal  of  metallic  cations.  Carbonation/Other  Acids:  -­‐ Organic  acids  are  produced  when  leaves  and  other  parts  of  plants  fall  to  the  ground  and  

decompose,  hence  breaking  up  the  rocks.  Organic  acids  can  also  be  produced  from  the  decomposition  of  animal  waste  and  dead  animals.    

-­‐ In  addition,  plants  gives  out  carbon  dioxide  and  when  this  is  combined  with  water,  a  weak  carbonic  acid  is  formed.  This  acid  is  able  to  weaken  rocks  and  cause  them  to  disintegrate.  

-­‐ Organisms  in  the  stagnant  water  gives  out  carbon  dioxide  which  forms  carbonic  acid  and  reacts  with  the  rock.    

-­‐ Plants  such  as  mosses  and  lichens  clinging  to  rock  surface  can  cause  the  weathering  of  rocks  through  a  chemical  process.  They  produce  organic  acids  that  react  with  minerals  in  rocks  and  cause  the  rocks  to  decompose.  

Algae  and  bacteria  can  break  down  the  rocks,  leeching  them  of  their  nutrients  and  causing  them  to  weather.  

Biomechanical  Process  

-­‐ Simple  breaking  of  soil/rock  particles  occurs  when  particles  fracture  because  of  animal  burrowing  or  by  the  pressure  from  growing  roots.    

-­‐ Roots  of  plants  penetrate  rocks  by  growing  into  the  cracks  and  joints,  and  hence  widen  the  cracks  and  joints.  

WEATHERING   11    

-­‐ Many  large  soil  organisms  cause  the  movement  of  soil  particles,  thus  introducing  the  materials  to  different  weathering  processes  found  at  distinct  locations  in  the  soil  profile.  

 Factors   Climate:    

-­‐ Takes  place  faster  in  warm,  moist  climates  with  high  temperature  and  high  rainfall  as  chemical  reactions  take  place  faster  in  the  presence  of  heat  and  moisture.    

-­‐ The  warm  and  moist  climate  also  leads  to  rapid  plant  growth  and  great  rate  of  animal  activities  which  accelerate  biological  weathering.  

Plant  and  Animal  Activity:    -­‐ As  plants  and  animal  activities  aid  biological  weathering,  hence  the  more  the  activities,  the  more  

rapid  the  weathering  process  will  get.    -­‐ The  shade  and  roots  from  trees  can  also  create  an  increase  of  water  in  soil,  which  lends  itself  to  

physical  and  chemical  weathering  processes.    Human  Activities:    -­‐ Such  as  overgrazing,  mining,  burning,  digging,  ploughing,  lumbering  -­‐ When  vegetation  is  removed,  biological  weathering  is  reduced,  also  cause  exposure  of  more  

rock  surface  Rock  Type   -­‐    Location  Climate  

-­‐ Occurs  mainly  along  coastal  areas  and  tropical  rainforests.    -­‐ Coastal  areas  are  habitats  for  algae,  limpets.  -­‐ There  is  more  biotic  activity  and  vegetation  cover  in  tropical  rainforests  as  well  as  a  hot  &  

humid  climate.  Products   No  specific  

e.g.  Angkor  Wat  

     

12   WEATHERING    Factors  Affecting  Rate  of  Weathering  Processes:  C3R3AM:  Factor   Description  Climate   -­‐ One  of  the  VERY  IMPORTANT  factors,  can  even  be  considered  the  most  important  factor  for  

LONG-­‐TERM  CONTROL  OF  WEATHERING  PROCESSES  -­‐ Can  be  understood  as  two  parts:  Temperature  and  amount  of  precipitation  (moisture/humidity)  -­‐ If  asked  to  compare  Temp.  and  Moisture/Precipitation:  -­‐ Temperature  affects  all  the  weathering  processes  

o Low  temp.  favourable  for  carbonation  and  freeze  thaw  o High  temp  favourable  for  insolation,  oxidation,  hydrolysis  etc.    o High  temp  favourable  for  biotic  activity  

-­‐ Precipitation  can  speed  up  rate  of  chemical  reactions  (water  acts  as  a  solvent)  o Except  for  insolation  but  can  argue  that  it  is  the  ABSENCE  of  precipitation  that  allows  

this  form  of  weathering  to  thrive.    Composition  of  Rock  

-­‐ Key  factor  influencing  the  resistance  of  rock  to  weathering  -­‐ Constituent  minerals  and  how  they  are  cemented  determine  the  rock’s  resistance  and  what  

chemical  process  will  affect  it  more  -­‐ Igneous  rocks  are  resistant,  contain  silica  and  feldspar  (more  resistant  minerals)  -­‐ Sedimentary  rocks  less  resistant  due  to  soft  cement  -­‐ Quartzite  (a  metamorphic  rock  type)  is  more  resistant  due  to  the  hard  silica  cement!    

Cover  from  Vegetation  

-­‐ Minor  factor  as  a  whole    -­‐ Vegetation  speeds  up  biological  weathering  -­‐ Protects  underlying  rocks  from  physical  weathering  -­‐ Fungi,  algae,  lichens  help  to  retain  water  in  the  ground  

Rock  Jointing   -­‐ Important  influence  on  ALL  TYPES  OF  WEATHERING  -­‐ Increases  the  surface  areas  exposed  for  attack,  accelerates  block  disintegration  -­‐ Jointing  pattern  determines  the  character  of  the  landforms  produced.  

o Granite  =  rectangular  blocks  when  weathered  leaves  rounded  corestone  o Basalt  =  weathered  into  vertical  polygonal  columns  

-­‐ Allow  for  greater  penetration  of  water  and  acidic  solutions  into  rock,  facilitate  root  penetration  and  animal  burrowing  

Rock  Texture   -­‐ Coarse  grained  rocks  are  more  susceptible  to  granular  disintegration  -­‐ Rocks  with  coarse  grains  also  weather  more  rapidly  as  once  a  weakened  mineral  is  weathered,  

the  entire  rock  is  weakened  and  breaks  up  more  easily.    Relief   -­‐ Landslides  and  slumps  occur  more  frequently  on  steep  slopes,  and  these  expose  the  underlying  

rock  to  weathering  processes  -­‐ On  gentle  slopes,  the  weathered  material  protects  the  underlying  rock  from  weathering  

processes  Activities  of  Man  

-­‐ Activities  can  cause  the  removal  of  vegetation  cover  hence  leading  to  more  exposed  rock  surface  for  weathering  processes  to  take  place,  but  at  the  same  time  can  disrupt  some  biological  weathering  

-­‐ Urbanization  and  industrialization  lead  to  higher  levels  of  carbon  dioxide  (so  carbonation  will  be  enhanced),  and  chemical  weathering  is  more  prevalent  due  to  the  acidic  rainfall  

 Colour  Code:  Orange  =  MAJOR  FACTOR    Blue  =  MINOR  Factor