6 18 14 CHAPTER 13 WEATHERING SLOPES AND MASS MOVEMENTS WEATHERING Weathering refers to the breakdown of earth s materials Two groups of weathering process Physical breaking things down into smaller pieces mechanical Chemical chemical reactions that weaken the material or that break it down and sometimes into other substances Key things Bedrock parent material exposed Over time it s broken down by weathering and we make a regolith which is smaller material of parent material Over more time it mixes with organic material with plants and bugs and all and we get soil which is bedrock and organics and are exposed to air and water etc Controls on rates and types of weather 1 Rock characteristics physical and chemical So like rock salt will dissolve in water so it ll weather quickly unlike granite that need long periods of exposure A physical characteristic is the jointing in the rocks The more joints the more surface area exposed Hardness solubility jointing 2 Climate temperature and precipitation The more water available the more potential to weather Look at annual rainfall on chart on bottom and temp from cold to hot going up none that are wet and cold Tends to control rates For cold it s all physical For warm both weathering types For hot chemical is dominant With more rain in the colder hotter places increasing in weak to strong weathering 3 Hydrology how water moves through a portion of the environment Pathway involved Like a hill then depression If water lands on slope it was run down and has little exposure of water on slope Down at the bottom the water will form puddles until evaporation Then the depression sunken way below will fill up with water and be exposed for days to weeks So max exposure and maybe most rapid Water table movement topography 4 topography mountains Moist air across ocean from west to east in lat Reaches coastal mountains and goes up mountain and cool Forms clouds and rains On other side of the mountain descending air will warn up and be drier Slope orientation 5 Biological agents animals like shellfish will bore into rocks in coastal zone and be a mechanical weathering agent and break it down Tree roots will fracture stuff with force The detritus from living organisms will do something too So enhance it or play protective role Dense vegetation will catch like 40 of water or something and it won t even reach the ground Roots can act like nets and hold stuff together vegetation Slope orientation with microclimate vegetation with inhiti enhance PHYSICAL WEATHERING PROCESSES One common one and important is frost action freeze thaw Freezing and thawing cycles of water Like beer bottle in freezer overnight will shatter Increase by 10 if frozen Crystallization is important in coastal areas Like fence post The salt spray is deposited on wood When water evaporates it leave salt and they grow and crystalize and break down the material of the wood Also happens in rock too Same result as they grow Root wedging root grows and concrete cracks Also does this to rock Exfoliation pressure release spalling like layers of an onion Expanding bc its released of pressure that was pushing inwards Intrusive igneous rock in ground and tons of pressure then cooled to equilibrium The overlying material eroded and rock lifted It still pushes out bc of equilibrium but there s nothing also pushing on it back so it expands and cracks High pressures deep in earth then exposed and swells CHEMICAL WEATHERING PROCESSES Solution some minerals are exposed to water and their molecules do something and dissolve Oxidation rust Oxygen from water bonding onto metallic materials in rocks like iron or copper Hydrolysis water molecules bonding to materials that makes up a rock Like granite it has quartz and feldspar and the quartz is resistant to water Feldspar is susceptible to water and it bonds to it and turns it into clay and will crumble away Carbonation like solution but that the fluid is not just water It s a weak solution called carbonic acid Rain from atmosphere and makes it It s effective in attacking limestone and marble The statues on Notre Dame are disfigured bc of acid rain We increased this from burning fossil fuels and all Process of carbonation is also important in making karst topography Found in areas where the parent material is limestone of some sort Pinnacle karst and Tower karst or Haystack karst Sinkholes as well Solution ones are from Collapse is from collapse of overlying material into cavern below the ground All karst areas have huge caverns The empty space that is the cavern is from erosion It was hole and then the water table was higher in the past and it was dissolved through carbonation and pulled away under the ground It s like a chamber Dripstones are things that happen after this Like stalactites They are dripstone that is from the overlying water and calcium carbonate makes it hang down and they turn to cemented material A stalagmite is the same thing but from the bottom Soda straws are thin from top Drip curtain is from a crack and runs all from it They all look like icicles Karst valley Disappearing stream caves column SLOPES Slope curved or inclined surface that reps the boundary of a landform Like the side of a hill Slope steepness determines the activities that will happen on it like cultural like building homes and all Vertical slope is 90 degrees So angle is important Second approach besides angle to talk about steepness is tangent Tangent is rise over run in math The rise is how much we go upwards on a slope and run is the horizontal distance that we travel as we go up Third system is gradients or grade Recording tangent basically Tangent times 100 SLOPES AS A SYSTEM Inputs to weathering Faster weathering is the faster the system Outputs get pushed off the slope through mass movements like a landslide and this is transport The equilibrium is the angle of repose which is the steepest angle that a material can maintain As it accumulates the slope gets sleeper and gets the repose angle and more material will cascade down if it goes over Whether it s stable depends on the balance of force acting on it Some forces are trying to move it downhill and some are resisting forces Particle on slope not steep slope Gravity is not trying to pull it down the slope but straight down FG force of gravity The slope is not perpendicular of the gravity force but some of the gravity force will be downhill of the slope FD driving The portion acting as resisting will be pulling