GEOG 1114 1st Edition Lecture 24 Outline of Last Lecture Vulcanism Volcanic peaks Volcanic Distribution Outline of Current Lecture Weathering Weathering processes Biological Weathering Mass wasting Current Lecture External Processes Weathering The Mechanical disintegration and or chemical decomposition that breaks down rock masses into progressively smaller pieces Most are atmospheric Oxygen carbon dioxide and water most important Temperature changes Water penetration in bedrock openings Biotic agents Burrowing and or plant roots Chemical alteration These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Facilitated by Jointing A fracture in a rock separating it Faulting A break in a rock where the rock moves past each other Pore Spaces The spaces in a rock that are unoccupied by material Processes of Physical or Mechanical Weathering The breakup of rocks by physical processes such as crustal movement and frost shattering Frost Shattering Water expands when it freezes When water enters natural cracks in rock and freezes it breaks apart that rock Chemical Weathering Decomposition of rock material through chemical alteration of minerals Processes involving water and assisted by root activity Chemical reactions cause rock disintegration by swelling and softening Three General Types 1 Oxidation chemical reactions involving oxygen Examples orange rust that forms on iron and the green coating that appears on copper Most soils and decayed rocks are shades of brown due to the oxidation of iron bearing minerals 2 Hydrolysis chemical union of water with another substance to produce a new component that is softer and weaker Igneous rocks in particular Silicate material combined with water causes expansion and contributes to mechanical disintegration 3 Carbonation reaction between carbon dioxide in water and carbonate rocks to produce calcium bicarbonate which is a vary soluble product It is either carried away in run off or it can be deposited in crystalline form if the water is evaporated Biological Weathering Root Activity penetration of growing plant roots into cracks and crevices which opens cracks further and contributes to mechanical weathering Lichens algae and fungi living as a single unit on bare rock soil or bark They draw mineral from the rock by ion exchange which weakens the rock Expansion and contraction of lichens during wet and dry period flake off tiny particles of the rock Burrowing Animal mixes soils and can be a factor in rock disintegration Exfoliation A physical and chemical weathering process in which curved layers of bedrock peel off in sheets Occurs when curved and concentric joints develop in bedrock weakening rock letting water in Often lichen and frost shattering contribute to exfoliation Layer are removed expansion of rocks occurs Common in granites Exfoliation dome Mass Wasting The process whereby weathered material is moved downslope under the direct influence of gravity Factors that influence mass wasting Angle of repose Impact of water on lubrication of rock material Clay water mixture is a very slick and mobile substance Rates are related to slope angle material forming the slope and moisture content of the slope material Rock fall Talus Scree Uniform accumulation of rock fall material talus apron Material tends to collect in the cone shaped heaps Land Slide Instantaneous mass slope collapse with no fluid flow lubrication Initiated from added weight from rainfall or earthquakes Rock avalanches Lost material leaves land scar Damming of valley streams Rotation of sliding material slump Creep Unobtrusive downslope flow of soil and regolith Freeze thaw and wet dry effects on creep Burrowing animals and plant root effects Principle variables are slope angle vegetative cover and moisture supply Slump Slope collapse Concave in nature Mudflow Wasting initiated or enhance by addition of water Water primary force clay can enhance motion as well Earthflows water saturated land moved downhill Mudflows originate in arid basins muddy downslope flow that can accumulate large rock materials Rock Glaciers Not all glaciers are made of ice Some glaciers are made of rock Need a climate cold enough to sustain permafrost Compared to ordinary glaciers rock glaciers are rare and may look like a rocky field shaped like a glacier While regular glaciers flow rock glaciers creep Erosion The removal of weathered material to another location Primary Agents Water Fluvial Processes Wind Aeolian Processes Fluvial Processes Overall flow of water eroding transporting and depositing material Aeolian Processes Erosion transport and deposition of material by wind Both produce a variety of landscapes Streams rivers lakes flood plains deltas and sand dunes