Post on 30-Dec-2015
description
Weathering must happen before erosion can take place!
Which comes first
Erosion or weathering?
WEATHERINGWEATHERING
Definition: The physical and chemical Definition: The physical and chemical processes that break down rock on processes that break down rock on earth’s surface.earth’s surface.
2 Types of Weathering2 Types of Weathering
PHYSICAL/ MECHANICAL WEATHERINGPHYSICAL/ MECHANICAL WEATHERING – – rocks are broken rocks are broken apart increasing the surface area.apart increasing the surface area.
ROCKROCK BEFORE WEATHERING = BEFORE WEATHERING =
ROCK AFTER WEATHERING (just ROCK AFTER WEATHERING (just smaller)smaller)
CHEMICAL WEATHERINGCHEMICAL WEATHERING – – Chemical reactions CHANGE Chemical reactions CHANGE minerals. minerals.
ROCK BEFORE WEATHERING ROCK BEFORE WEATHERING ≠ ROCK ≠ ROCK AFTER WEATHERINGAFTER WEATHERING
PHYSICAL WEATHERINGPHYSICAL WEATHERING
INCREASES SURFACE AREA
MORE CHEMICAL WEATHERING CAN OCCUR
There are four main sources of power There are four main sources of power for mechanical weathering.for mechanical weathering.
Gravity, Water, Wind, & WavesGravity, Water, Wind, & Waves
Of these, water appears to be the Of these, water appears to be the leader in changing the surface.leader in changing the surface.
PHYSICAL WEATHERINGPHYSICAL WEATHERING MOST IMPORTANT IN OUR CLIMATEMOST IMPORTANT IN OUR CLIMATE
FROST ACTION – FROST WEDGINGFROST ACTION – FROST WEDGING
ALTERNATE FREEZE AND THAW
Water expands when frozen
ROCKS ARE CRACKED BY WATER FREEZING
EXAMPLES: POT HOLES AND FROST HEAVES
Spheroidal WeatheringSpheroidal Weathering
Fluids enter rock along joints or
fractures and the edges become
rounded.
PHYSICAL WEATHERING – PHYSICAL WEATHERING – ROOT ACTIONROOT ACTION
PLANT ROOTS UPLIFT AND FRACTURE PLANT ROOTS UPLIFT AND FRACTURE ROCKROCK
Root PenetrationRoot Penetration
Powerful plant Powerful plant roots grow into roots grow into rock cracks and rock cracks and cause fractures.cause fractures.
PHYSICAL WEATHERING - PHYSICAL WEATHERING - ABRASIONABRASION
ROCK PARTICLES GRIND AGAINST ONE ROCK PARTICLES GRIND AGAINST ONE ANOTHER ANOTHER
WATER WIND
AbrasionAbrasion
Both wind and Both wind and water can water can
cause abrasioncause abrasion as rock as rock
fragments fragments bounce off bounce off each other.each other.
AbrasionAbrasion
This “moon This “moon looking” picture looking” picture of an Antarctic of an Antarctic
rock, shows rock, shows weathering weathering
from the wind from the wind blown sands.blown sands.
PHYSICAL WEATHERING PHYSICAL WEATHERING EXFOLIATION – PEELING AWAY EXFOLIATION – PEELING AWAY
OF ROCKOF ROCK Unloading – due to reduced pressure at Unloading – due to reduced pressure at
earth’s surface rocks will expand but they earth’s surface rocks will expand but they will crack because they are brittlewill crack because they are brittle
Fluctuating Temperatures will cause rocks Fluctuating Temperatures will cause rocks to contract and expand causing cracks to contract and expand causing cracks Examples: deserts and mountainsExamples: deserts and mountains
PHYSICAL WEATHERING - PHYSICAL WEATHERING - EXFOLIATIONEXFOLIATION
Unloading and ExfoliationUnloading and Exfoliation of Igneous Rocks of Igneous Rocks
Dome ExfoliationDome Exfoliation
Exfoliation domes form as the slabs of rock slip or slide off the bedrock. E.g. Yosemite
Glacial WeatheringGlacial Weathering
Glaciers and avalanches can Glaciers and avalanches can cause weathering as ice and cause weathering as ice and
rock interact.rock interact.
Other Agents of WeatheringOther Agents of Weathering
Things likeThings like flash flash floods, mud floods, mud
slides, slides, landslides, and landslides, and other forms of other forms of mass wasting mass wasting
can cause can cause weathering. weathering.
Chemical
Weathering
EXAMPLES OF CHEMICAL EXAMPLES OF CHEMICAL WEATHERINGWEATHERING
OXIDATION OCCURSOXIDATION OCCURS when free oxygen when free oxygen combines chemically with metallic combines chemically with metallic elements (usually iron) elements (usually iron)
AKA AKA RUSTRUST
Chemical WeatheringChemical Weathering Oxygen dissolved Oxygen dissolved
in water will oxidize in water will oxidize some materials like some materials like
nails and rocks!nails and rocks!
(Rust)(Rust) Carbon dioxide Carbon dioxide dissolved in water dissolved in water forms a weak acid forms a weak acid
called carbonic called carbonic acid, which helps acid, which helps
dissolve rock dissolve rock material.material.
Chemical Weathering of Statues, Bath, UK
CARBONATIONCARBONATIONWater containing carbonic acid dissolves Water containing carbonic acid dissolves
minerals (all rain water is slightly acidic)minerals (all rain water is slightly acidic)
Most strongly affected are calcite Most strongly affected are calcite minerals:minerals:
limestone and marblelimestone and marble
CARBONATIONCARBONATION
Stalagmites and stalactitesStalagmites and stalactites
CARBONATION – SINK HOLESCARBONATION – SINK HOLES
Karst Topography Karst Topography
forms caves, caverns,forms caves, caverns,
and sinkholesand sinkholes
CAVES AND SINK HOLES
How Granite WeathersHow Granite WeathersChemical weathering – the alteration of the internal structure of minerals by chemical reactions
Potassium Feldspar + carbonic acid + water
Clay mineral + Potassium bicarbonate + Silica
CHEMICAL WEATHERING CHEMICAL WEATHERING HYDRATIONHYDRATION
OCCURS WHEN OCCURS WHEN WaterWater combines with combines with minerals – most often in granite (mica and minerals – most often in granite (mica and feldspars) to form feldspars) to form CLAYCLAY
Chemicalweathering
CLIMATE CONTROLS WEATHERINGCLIMATE CONTROLS WEATHERING
PHYSICAL WEATHERING:PHYSICAL WEATHERING:
COLD AND MOIST COLD AND MOIST
ALTERNATE FREEZE / THAWALTERNATE FREEZE / THAW
CHEMICAL WEATHERING:CHEMICAL WEATHERING:
WARM AND MOISTWARM AND MOISTIN BOTH CASES – WATER IS THE PRIMARY IN BOTH CASES – WATER IS THE PRIMARY INGREDIENT THAT PROMOTES WEATHERINGINGREDIENT THAT PROMOTES WEATHERING
WHAT KIND OF CLIMATE WHAT KIND OF CLIMATE SUPPORTS WEATHERING?SUPPORTS WEATHERING?
COLD →→→→→→→→→→ HOT
HIGH
PPT
↑
↑
↑
↑
↑
↑
↑
LOW
PPT
Differential Weathering due to Differential Weathering due to Climate and CompositionClimate and Composition
• Masses of rock do not weather uniformly due Masses of rock do not weather uniformly due to regional factors and to regional factors and compositioncomposition..
• Results in many unusual and spectacular rock Results in many unusual and spectacular rock formations and landformsformations and landforms
Differential WeatheringDifferential WeatheringRocks weather at different rates because of different
mineral makeup, degree of jointing, and exposure to the elements.
More resistant rock protrudes as ridges and pinnacles.
Bryce National Park, Utah
More resistant More resistant rock on toprock on top
Rates of WeatheringRates of Weathering
Granite versus Marble
Factors influencing weathering:
-Mineral makeup
WHICH LAYER IS MORE WHICH LAYER IS MORE RESISTANT TO WEATHERING?RESISTANT TO WEATHERING?
LEAST RESISTANT?LEAST RESISTANT?
A
BC
D
YOU MIGHT ALSO SEE IT LIKE YOU MIGHT ALSO SEE IT LIKE THIS.THIS.
WHICH DIAGRAM IS AN ARID WHICH DIAGRAM IS AN ARID CLIMATE? HUMID CLIMATE?CLIMATE? HUMID CLIMATE?
A B
Humid – more rounded
Arid – more angular
Weathering ReviewWeathering Review
ChemicalChemical Rocks are broken Rocks are broken
down through down through chemical changes chemical changes
Common in warm, Common in warm, humid climateshumid climates
Example: Limestone Example: Limestone highly affected by highly affected by acidsacids
MechanicalMechanical Rocks are broken Rocks are broken
down through down through physical changesphysical changes
Common in harsher Common in harsher climatesclimates
Example: water Example: water freezing in cracks freezing in cracks expands and breaks expands and breaks rock apartrock apart
WEATHERING SUMMARYWEATHERING SUMMARY
PHYSICAL WEATHERING – PHYSICAL WEATHERING – INCREASES SURFACE AREA - INCREASES SURFACE AREA - COLD/HUMID CLIMATECOLD/HUMID CLIMATE
CHEMICAL WEATHERING – CHEMICAL WEATHERING – WARM/HUMID CLIMATEWARM/HUMID CLIMATE
IN BOTH CASES, WATER IS THE IN BOTH CASES, WATER IS THE PRIMARY INGREDIENT PRIMARY INGREDIENT
THE END PRODUCTS OF THE END PRODUCTS OF WEATHERINGWEATHERING
CALLED CALLED SEDIMENTS OR SOILSEDIMENTS OR SOIL
SOIL: a combination of sediment, rock SOIL: a combination of sediment, rock minerals, and minerals, and humushumus (organic material (organic material from biologic activity)from biologic activity)