Weathering, Erosion and Denundation

Weathering

breakdown and alteration of near surface materials of the lithosphere to products which are more equilibrium with newly imposed physical-chemical conditions at earths surface 

2 types of weathering

chemical and physical

chemical weathering

mineral transformations mediated by water

regoliths

the loose, unconsolidated layer of dust, broken rock, and other superficial material that covers the solid bedrock of a planet

why is regolith important

fundamental to the sediment cycle and the development of soil

soil

mixture of rock debris and organic material

what affects chemical weathering 

annual rainfall and temp, rock type(felsic more susceptible), the presence of fissures/fractures and the finer the grain of the rock, the more rapidly it weathers 

what type of rock is more suspetible to chemical weathering

felsic

physical weathering

Altering rocks without chemical transformations incl. fluvial, uplift, glacial abrasian 

erosion

occurs by the wearing away of rock/soil by gravity (mass wasting) through the action of streams, glaciers, waves, wind and groundwater 

types of erosion

 Colluvial(gravity), fluvial (steam/river), aeolian(wind) glacial(ice), alluvial(runningwater) erosion types 

denundation

weathering + erosion which reduces elevation and relief of landsurface  

global mean denudation rate

43 mm/ka

long term measures of denudation

denudation chronology: radiometric dating of minerals, fission-track dating of minerals 

short term measures of denudation 

fluvial denudation: suspended solids & solute loads 

other measurements

Glacial denudation in frigid environments can also be used to measure  

Aeolian denudation in arid environments(grains which are deposited/ structures) 

Radiometric dating

Minerals 'close' (crystallise) at a certain depth and retain products of radioactive decay – recording time 

fission tracking dating

  'tracks' in crystal lattice (created by fission of U-238) recorded when minerals cool beyond an ‘annealing’ T. Numbers of tracks records the time 

denudation calculation 

Depth/recorded time = denudation rate  

fluvial denudation

Estimated from the sediment and solute loads carried by rivers  

denudation calculation

1. Solid & solute mass per year /density* = volume of material per year 

 2. Volume of material per year /drainage basin area  

where do you find high solute loads

in humid catchments: great precipitation greater chemical weathering  

Proportion of solute load increases as mean river channel gradient decreases  

why does large denudation occur in montaneous area 

high relief =. runoff erodes sediments (unconsolidated materials) 

exogenic processes

Processes occurring on the Earth's surface and that generally reduce relief. These processes include weathering and the erosion, transport, and deposition of soil and rocks; the primary geomorphic agents driving exogenic processes.

process drive denudation

endogenic processes

Processes occuring in Earth's interior that create relief by elevating mountains and land masses, and depressing basins and ocean floors. Tectonic, isostatic, and volcanic processes dominate the influence of endogenic processes on land form.

processes responsible for rock generation