Final Test Flashcards
Water in the Atmosphere, at Earth’s Surface, and Subsurface (notes)
Chapter 7 - Atmospheric Moisture and Precipitation (textbook)
Chapter 15 - Groundwater and Karst Landscapes (textbook)
Basic Physical Properties of Water
Hydrogen Bonding
High Surface Tension
Capillary Action
High Heat Capacity
H2O Molecule
- water is made up of billions of molecules, each consisting of 2 hydrogen atoms combined with one oxygen atom, forming H2O
- oxygen has a partial neg charge, hydrogen has a partial pos charge
Hydrogen Bonding
- water molecules are attracted to each other because of these contrasting pos and neg, known as hydrogen bonding
- these bonds are strongest in ice
- explains water’s physical states
High Surface Tension
- another attribute of water = high surface tension
- results when molecules at the surface of liquid have a strong attachment to each other but not to the molecules of air above them
- particularly strong in water because of hydrogen bonding - water molecules pull harder to create a small surface area, also creating an elastic skin on the surface of the water
Capillary Action
- water has the ability to move upward in thin openings/capillaries against the force of gravity within the soil/plants in a process called capillary action
- water molecules pull other water molecules along through hydrogen bonding
- enables plants to transport nutrients from their roots up into their stems/leaves
High Heat Capacity
- water’s specific heat is 1 calorie/gram or 4190 joules/kg
- compared to copper: 0.092 calories/gram or 386 joules/kg
- water would require much more energy to achieve an increase in heat
- this high specific heat occurs because of the significant kinetic energy required to break the hydrogen bonds between the water molecules
Thermal Properties of Water and Its Physical States
Latent Heat
- latent heat is the energy required to change the state of a substance (form or break hydrogen bonds)
- water absorbs and releases latent heat that is stored in molecular bonds
- capability of water to store and release latent heat is important & contributes significantly to atmospheric circulation and helps regulate climate
- explains how water can exist in 3 states (solid/ice, liquid/water, gas/water vapour) as the movement of water from one phase to another occurs when hydrogen bonds are formed, loosened, broken, or tightened
- loosened/broken: energy is applied to molecules and transformed from sensible heat to latent heat which has a net cooling effect
- formed/tightened: energy is extracted from molecules, energy is converted from latent heat to sensible heat, which has a net warming effect
Specific Heat
- specific heat is the energy required to increase the temperature of a substance
WATER PHASES AND LATENT HEAT TRANSFERS:
Liquid Water turns to Ice
- freezing
- more hydrogen bonds develop and tighten
- begins when the water cools to a temp below 4C because the motion of water molecules begins to slow considerably, allowing hydrogen bonds to strengthen
- when the water cools to 0C, motion slows further, more bonds develop and tighten, and ice forms
- exact temp water crystallizes at depends on air pressure, water has to cool more to freeze at higher air pressure because as density increases, increasing amounts of nitrogen/oxygen molecules go into solution
- during freezing, 80 calories of latent heat energy released for every gram of water as the latent heat of freezing
- ice can float on water because it is less dense
Ice turns to Liquid Water
- melting into liquid water, 80 cal of latent heat is absorbed as the latent heat of melting to change 1 gram of ice to 1 gram of water
- heat energy is applied to and absorbed by ice at 0C, the motion of water increases and some hydrogen bonds begin to break
Liquid Water turns to Water Vapour
- vaporization
- process begins at room temperature when added energy causes hydrogen bonds to further loosen, resulting in the liberation of some water molecules to the vapour phase in the process of evaporation
- added heat is called the latent heat of vaporization and = 600 cal per 1 g of water
- when temp reaches 100C, molecular bonds break and all water molecules move into the atmosphere as vapour
Water Vapour to Liquid Water
- condensation
- 600 cal of energy released as the latent heat of condensation
Ice to Vapour
- sublimation
- occurs if temp. of ice rapidly increases from 0C to 100C
- 680 calories of energy known as the latent heat of sublimation (reflects melting + vaporization)
Vapour to Ice
- deposition
- 680 calories of latent heat released (reflects condensation + freezing)
The Hydrosphere and the Hydrologic Cycle
- total water realm of Earth = the hydrosphere
Hydrosphere
- 97.2% = oceans / salt water
- 2.8% = nonoceanic water
Nonoceanic Water
- 2.15% = ice sheets, glaciers
- 0.63% = groundwater
- 0.02% = available freshwater
Available Freshwater
- 0.009% = freshwater lakes
- 0.008% = salt lakes, inland seas
- 0.005% = soil water
- 0.001% = atmosphere
- 0.0001% = rivers, streams
Hydrologic Cycle
- movement of water between the various storage locations
- balanced in the sense that Earth has a finite amount of water, the amount evaporated equals the amount precipitated on a global scale
- variety of local and regional imbalances exist
- sea-level changes due to: eustasy (changes in distribution) or isostasy (subsidence or uplift of continents)
The Global Water Balance
- water flows to the land and ocean surfaces are positive inputs, whereas those leaving are negative
Processes/Mechanism of the Hydrologic Cycle
Movement Toward or Away from Earth’s Surface
- precipitation (of water in all forms)
- evapotranspiration (evaporation - water molecules gain enough energy to become water vapour + transpiration - water transpiring from the pores on plant leaves)
- condensation (opposite of evaporation)
- throughfall (precipitation that makes its way to earth with no interceptions)
- interception (opposite of throughfall, doesn’t make its way directly to earths surface, can evaporate off of the surface it lands on)
- stemflow (when water flows off the surface of interception)
Water at Earth’s Surface and Subsurface
- infiltration (when water breaks the barrier of the surface of the soil)
- percolation (after infiltration, as it moves down through individual soil particles)
- runoff: saturated overland flow (when the soil is slowly fully saturated and water begins to run off), horton overland flow (the intensity of precipitation is greater than the infiltration rate of the soil causing runoff)
- sheet flow (sheets/layers of water flowing over one another after heavy rain, laminar flow)
- channelized flow (turbulent flow)
Soil - Water Balance Concept
- an accounting of water inputs and outputs
- Developed by C.W. Thornthwaite to:
- describe allocation of water
- describe surplus or deficit at a location
- determine timing and quantity of irrigation
- develop climatic classification
Equation:
P - precipitation (moisture supply)
AE - actual evapotranspiration (actual moisture demand)
PE - potential evapotranspiration (moisture demand)
S - surplus (moisture oversupply)
ST - change in soil moisture storage (moisture savings)
D - deficit (moisture shortage)
P = AE + S +/- ST AE = PE - D
Potential Evapotranspiration
- evaporative demand of the atmosphere
- a function of temperature and humidity
- Includes: evaporation from the soil/other surfaces, plus transpiration of water from vegetation
- Measured: evaporimeter, weighing lysimeter, or estimate PE based on mean monthly temperature and day length
Deficit
- PE is satisfied by either: precipitation (monthly) or soil moisture storage (monthly)
- If PE is not met, a deficit (D) occurs
Actual Evapotranspiration
- Difference between PE and D is AE
- example: P= 60mm, PE= 100mm and ST=20… D= 20mm and AE= 80mm
Surplus
- occurs when P is greater than PE and soil moisture storage (ST) is at field capacity
- surplus collects in ponds/puddles, percolates through soil and recharges ground water, or runs off as sheet flow/channelized flow
Issues with this model:
- thornthwaite model assumes that all excess precipitation goes into
soil moisture storage until field capacity is attained, doesn’t consider Horton
overland flow or detained water
Soil Moisture Storage
3 Types of Soil Moisture
- H2O (not available)
- water fully saturated
- infiltrates at surface
- percolates downward in between pore spaces
- draining out the bottom is gravitational water (not available to plant roots) - H2O Available
- capillary and hygroscopic water
- field capacity : occurs when soil is holding the max amount of capillary water - H2O unavailable for plants
- hygroscopic water
- wilting point : occurs when all available capillary water has been used
Soil Porosity and Permeability
- diagram saved
Water Budget Graph
- graphic depiction of water balance
- depicts distribution and use of available water at a given location
- most locations experience seasonal deficits and surpluses
- problem is often timing rather than availability of water
Groundwater & Groundwater Use & Groundwater Pollution
- movement of gravitational water: infiltration and percolation occurring, leading to groundwater
- movement from groundwater systems into streams/other water bodies based on the water level
- ground water moves from higher hydrologic gradient to lower hydrologic gradient
- groundwater recharge happens over millions of years
- cone of depression : change in the location direction of ground water flow where the wells are located
Groundwater Use
- more than 50% of US relies on groundwater
- Volume of available water varies; called specific yield
- Draw down results in a cone of depression, water law
- Groundwater mining occurs when pumping exceeds recharge
and results in (in addition to cone of depression): subsidence due to decreased
pore water pressure, and encroachment of sea water in coastal areas
Groundwater Pollution
- Groundwater pollution categorized according to
the origin of the source
- Non-point source pollution originates over a large
area e.g. herbicide or pesticide application
- Point source pollution originates at a specific site
e.g. hazardous waste dump, contaminant spill, or injection well
Aquifers and Aquiludes
Aquifer
- rock or sedimentary unit of sufficient porosity & permeability is able to store and transport significant
amounts of water
- located above the main water table
- confined aquifer: aquiclude above and below it, puts the aquifer under pressure
Aquiclude - rock or sedimentary unit insufficient porosity and/or permeability does not contain or transport significant amounts of water
- located below the main water table
Water Use
Consumptive
- are uses whee the water is not returned to the water system, at least not in the near future
- typically a reduction in quantity, and also a reduction in the quality when returned to the system
- examples: municipal water uses (in home uses), food processing, irrigation
Non-consumptive
- when the water is removed only temporarily
- does not impact the quantity, but can significantly impact the quality
- withdrawal water and use in industrial processes
- examples: industrial applications, cleaning/processing/washing
Instream Uses
- water is not taken out of the system
- ex. canoeing, fishing, waterskiing
- quantity is not changing
- could be significant impacts on the quality, examples like using a boat in the water
Water Resources Vulnerability Index (1995)
- very few countries that are not facing any vulnerability regarding their water resources
- vulnerability is in regard to the cleanliness and the availability for uses
Karst Landforms and Landscapes
Caves and Caverns
- Karst = type of landform or landscape that develops in an area where the bedrock rock is limestone or Dolomite or soluble sedimentary rock
- Karst topography
includes caves,
sinkholes, and
other soluble rock
features - Limestone
dissolves easily
through the
chemical
weathering
process of
carbonation - limestone soluble in water
Cave and Cavern Evolution
- Stage One: Begins when water table is high and carbonation
concentrates in limestone just
below
- Stage Two: Stream cuts a valley into the rock, lowering the water table, and groundwater cuts
channels and caverns into the rock
- Stage Three: The stream
continues to downcut and water table lowers further, revealing caves and caverns
Unique landforms associated with karst landscapes:
- large caves in highly developed areas
- features within caves exist
Geography of the Lithosphere
- To this point, we have focused on systems operating within the atmosphere and hydrosphere
- Now we turn our attention to the lithosphere and
systems operating at or beneath Earth’s surface:
exogenic systems
– at earths surface
endogenic systems - below earths surface
Geography of the Lithosphere
- To this point, we have focused on systems operating within the atmosphere and hydrosphere
- Now we turn our attention to the lithosphere and
systems operating at or beneath Earth’s surface:
exogenic systems
– at earths surface
endogenic systems
- below earths surface
Earth’s internal energy
Two sources of energy drive
endogenic systems:
1. residual
2. radioactive
- radioactive decay of unstable isotopes
- locally within the earths interior, concentrations of unstable isotopes that decay and release heat energy
- ex. in yellow stone area, concentration of heat energy in earths interior, hotspot, caused by unstable isotopes
3. friction heat energy
- only a MINOR source
- caused by one lithospheric plate moving past another
- enough friction to create a minor amount of heat energy
History of Earth History
Creationist interpretations:
- Neptunism
- water
- theory that all rocks are of sedimentary origin and precipitated at the bottom of ocean basins and shaped by running water, related to biblical flooding
- Catastrophism
- catastrophic events
- the idea that earth geography and geology are primary the result of catastrophic events (Biblical flooding)
- shaping and reshaping landforms and landscapes
- most earth surface features had been formed by catastrophic events over short periods of time
Scientific Interpretations of Earths History ::
Plutonism - Earth's interior is molten, all rocks of volcanic origin, James Hutton (1795), Theory of the Earth
Uniformitarianism (gradualism)
- “the present is the key to the past” CATCHPHRASE, the key to understanding the past, is to look at processes/mechanisms today, nothing has changed by natural laws and principles, explains 99% of todays geography
- same processes operating to shape the Earth today
have been operating throughout geologic time, James Hutton (1795), Theory of the Earth; Charles
Lyell (1830), Principles of Geology
- uniformitarianism/ gradualism - the earth is shaped over thousands/millions of years by the processes
- different processes operating today include continental scale glaciation in mid latitudes
- this theory works very well, with only few limited exceptions
how old is the earth
- the universe : 13.8 billion years
- the milky-way way : 13.6 billions years ago
- our sun - 4.5 billion years ago
- earth - 4.6 billion years ago
Geologic Time
- Most endogenic and exogenic systems operate very slowly
- Intervals of time are determined by:
to determine relative ages of rocks :
- principle of faunal succession: assemblage of fossil plants and animals follow or succeed each other in time predictably
- principle of superposition: each rock layer is older than the one above it
absolute ages (absolute dating technique):
- radioactive dating techniques
- modern techniques that allow us to measure the ratio of radioactive elements and their byproducts; what they decompose into
Geologic Time Scale Divides Earth's history into: Eons Eras Periods Epochs Analogous to: Years Months Weeks Days
Geologic Time Scale Divides Earth's history into: - divisions of earths history -Eons - Eras - Periods - Epochs - Ages
Analogous to:
- Years
- Months
- Weeks
- Days
Holistic View of Geologic Time and the Rock Cycle: The Grand Canyon Earth’s Internal Structure Core
- the grand canyon
- took a long long time to form as it is huge
- layers of rocks that used to exist are no longer there, eroded away by Colorado river
- layers of rock are over 550 million years
Earth’s Internal Structure
- indirect evidence of the earth’s interior available through seismic tomography
- uses shock waves that passes through the interior after an earthquake to provide us with a picture of the layers
Core & Layers of Earth
Core : Inner Core - solid iron and nickel - 3200-5200C - 6370km deep - 5150km deep (1220km) - pressure is so high that even though the temp is above that of the melting point, they remain solid
Outer Core
- liquid iron
- 5150km - 2250km (2250km)
Mantle : Lower Mantle - 2250km deep to 670km - denser, typically solid of iron, magnesium, silicon, lighter material than the core - temp increases with increasing depth - 1300C
Upper Mantle
- 670km deep to 250km
- less dense, typically viscous nickel
- temp increases with increasing depth
Asthenosphere
- 250km deep to 70 km
- drives plate tectonics
- made of molten rock, behaves as a plastic
- temp varies place to place, according to concentrations of radioactive isotopes
- convection currents
Lithosphere
- 70 km deep to 40km
- rigid
- convection currents in asthenosphere pulls the plates apart or makes them collide together
Oceanic crust
- basalt, dense
Continental Crust
- granite, less dense
Magnetic Reversals and Polar Wandering
- earths magnetic field is created as a result of the circulation of the molten outer core around the solid inner core
- orientation & polarity of N and S poles changes over time
- location constantly wandering = polar wandering
- polarity N vs S flip flops, over last 4 million years there’s been 9 magnetic reversals
- important in plate tectonics
Isostatic Adjustment of Earth’s Crust
- Crust is buoyant
- Rising and falling crust
- Oceanic vs. Continental crust
The Geologic Cycle
Hydrologic cycle - exogenic set of processes at or on earths surface - erosion, transport, & deposition of crustal material - driven by solar energy and gravity
Rock cycle
- creation of new rock
- some of these processes are intrusive = endogenic, occurring within earths interior, ex. rock cooling in a magma chamber
- processes are also extrusive = exogenic, ex. lava spewing above the earths surface
- driven by internal heat energy
Tectonic cycle
- result of movement of oceanic and continental crust
- creation, deformation
and recycling of crust
- upwelling, sea-floor spreading, subduction, crust formation
- driven by internal heat energy
Rocks and Minerals
- Crust is composed of rock made of minerals
- Mineral – element or
combination of elements,
forms an inorganic
compound - Rock – assemblage of
minerals bound together - All rocks classified as either:
1. igneous
2. metamorphic
3. sedimentary - A genetic classification
Igneous - Solidify/crystallize from molten rock - Formed by either: - intrusive - from magma • endogenic, coarse grained • extrusive - from lava • exogenic, fine grained
Metamorphic - Transformation of existing rocks by: - heat and/or pressure - change in chemical and/or physical properties - Occur as a result of: - tectonic forces - regional metamorphism - contact metamorphism
Sedimentary
Rock formed from:
-clastic materials, made from bits and pieces of previously existing rock material
-chemical precipitates, made from precipitates of previously existing rock material that were dissolved in water, ex. limestone
- organic deposits, material originated from organic material
- Deposited in layers
by? exogenic
processes
Lithification (chemical process of sedimentary rock)
- process of converting loose sediments into solid rock material
1. compaction - result of being buried under overlying sedimentary material
2. cementation - cementing with chemical precipitates
3. dehydration
- Study of sequence, spacing, distribution,
and age of sedimentary rocks is called stratigraphy
Plate Tectonics and Continental Drift
- Continental drift is the process that broke up the supercontinent, Pangaea, and formed into the current configuration of plates - As accurate maps showing entire continents became available, it was noted that some continents appeared to “fit together”
- Alfred Wegener (1912) was the
first to present a hypothesis to
explain this : continental drift - He used evidence from:
- fossil record, there are the same fossils in South America and Africa of lizards that cannot swim
- climatic record, certain landforms/ landscapes/ deposits the same in different continents
- geologic record
- But . . . he couldn’t explain how entire continents actually
move?
Sea Floor Spreading
- Then in 1960’s Harry Hess and Robert Dietz
propose theory of sea floor spreading
- Based on existence of
interconnected ridges, called mid-ocean ridges
- result of crust being pulled apart
- caused by convective currents in the
asthenosphere
- extrusion of lava creates new sea floor
- magnetic reversals
- dating the sea floor shows that the floor is being destroyed and recycled
Eventually led to theory of plate tectonics which explains processes such as:
- lithospheric plate movements
- sea-floor spreading
- subduction zones
- orogenic activity
- crustal deformation
- earthquakes
- volcanism
Types of Plate Movements:
Passive Margins
Transform Plate Margins
Plate Divergence
Plate Convergence
Passive Margins - Relatively stable localities - Not geologically active - Where continental crust and bordering oceanic crust are actually on the same tectonic plate and do not move relative to each other
Transform Plate Margins
- Boundaries where plates slide horizontally past each other
- Plane of motion is along a nearly vertical break (or fault) that extends through much
of the lithosphere
- sheering forces
- transform boundaries often occur in conjunction with divergent plate boundaries along sea floor spreading centres
Plate Divergence - Occurs where rising magma plumes spread plates apart, in rifting - tensional forces - low viscosity magma - Midocean ridges are a product of this process by which the extrusion of magma creates ridge-like features on the seafloor - Rifting can also happen within continents, causing a gradual split in the landmass - Continental rifting produces distinct valley landscapes bordered by steep canyon walls - Lowlands can fill with water, forming lakes
Plate Convergence - Where two plates collide directly - compressional forces - high viscosity magma - Occurs in three general settings, depending on the types of crust at the plate boundary - Type of convergence results in distinctive processes that produce specific landforms 1. Oceanic crust to continental crust - Oceanic crust is denser so subducted - Heated and partially recycled 2. Oceanic crust to oceanic crust - Similar densities; one will be subducted - Form a deep trenches - Island arcs 3. Continental crust to continental crust - Similar low densities, so neither plate rides over or sinks below the other - Crust is compressed and folds
Fractures, Faults and Earthquakes
- Occurs when a sudden release of accumulated
tectonic stress results in an instantaneous
movement of the Earth’s crust - Produce shockwaves
through the lithosphere - Stress creates a fracture, or a fault, between adjoining plates
- The Focus is the place in the lithosphere
where the fault breaks - The Epicenter is the point directly above the focus
Locating the Epicenter - Accomplished by triangulation - Distance to epicenter is compared by three separate seismographs - Based on the wave types produced in an earthquake - P waves are compressional and travel faster - S waves are vertical and travel slower - Difference in arrival time of P waves and S waves helps estimate distance to epicenter
Measuring Earthquakes:
Seismographs and the Richter Scale
- A seismograph is the device used to measure
the magnitude of seismic waves, including both P
waves and S waves - The Richter scale is related
to the amplitude of seismic
waves and is a logarithmic
measure, with each whole
number representing 10x the shaking of the next smaller
number - Moment Magnitude scale
calculates earthquake
magnitude based on rock strength, area of broken
rock, and the amount of
movement across the fault
Earthquakes:
Measuring Shaking Intensity
- The Modified Mercalli Intensity Scale measures the intensity of an earthquake based on an area’s local
damage - The ranking is based on
observed effects, taken after the earthquake
occurs.
Types of Faults
- Earthquakes cause deformation of the rocks within the crust and on the surface
Depend on the force that
creates the deformation
Fault types 1. Normal fault - creates a fault escarpment landform - pulling apart movement - hanging wall drops from foot wall - tensional - associated with any kind of plate boundary where there are tensional forces, not occur at a subduction zone or any convergent zones 2. Reverse fault - pushing together - hanging wall pushed up the foot wall - compressional 3. Strike-slip fault - sheering motion (sliding past each other) - translational - right lateral or left lateral strike-slip fault 4. Overthrust fault - pushing together - compressional - sharp angle fault plane - hanging wall pushed up the foot wall
Volcanoes
- A mountain or a large hill containing a conduit that extends
down into the upper mantle, through which magma, ash, and
gases are periodically ejected - Most volcanoes are inactive and only erupt when the pressure of
the rising magma becomes excessive - May be explosive or effusive
Explosive Volcanoes
- high viscosity (thick) magma
– rich in silica and
aluminium
– producing felsic or granitic rock
- steep sloped composite volcanoes - layers of ash, rock lava - ejection of pyroclastic material
- associated with convergent plate boundaries where there are subduction zones (so not at continental/continental)
Effusive (Fluid) Volcanoes
- low viscosity (watery)
magma
‒ high in iron and magnesium
‒ producing basaltic or mafic rock
-gently sloped shield volcanoes- from a single
vent or fissure
- flood basalts - from elongated fissures
- associated with divergent plate boundaries and tensional forces (continental and oceanic)
Hot Spots
- Concentration of radioactive materials = increased volcanic
and geothermal
activity - As plate moves:
location of volcanic
features migrates, hot spot remains in same location
The Yellowstone Hotspot
- Continental hotspot with explosive eruptions - Location of hotspot has moved over time, reflecting plate movement - Three major cataclysmic eruptions in past 2 million years
- Geothermal features:
= Geysers - Mudpots
- Fumeroles
Geomorphology
- Science that describes landforms and processes
that shape and create them - Landform - an assemblage of landforms
- Landscape - individual features, elements of the landscapes
Denudation - geomorphic processes that cause the reduction & rearrangement of landforms • includes: • erosion • transport • deposition • exogenic processes, caused by: water, wind, waves, moving ice
Geomorphology
- Science that describes landforms and processes
that shape and create them - landscape - an assemblage of landforms
- landform - individual features, elements of the landscapes
Denudation - geomorphic processes that cause the reduction & rearrangement of landforms • includes: • erosion • transport • deposition • exogenic processes, caused by: water, wind, waves, moving ice
Physical Weathering
Physical Weathering In situ mechanical disintegration of rock - no chemical alteration - no mineralogical change - Increases surface area so increases effectiveness of chemical weathering
Most effective when: - lower temperatures because max. freeze thaw cycles - sufficient moisture for frost wedging to occur
4 TYPES:
- Frost Action (water freezing)
- Water expands up to
9% upon freezing
- Force easily exceeds
tensile strength of
granite
- Includes
hydrofracturing - Crystallization (Salts)
- Dehydration results in
formation of crystals
Most common/effective:
- arid climates
- high/fluctuating water
table
- bedding planes - Pressure Release Jointing (Unloading)
- Intrusive igneous rocks form under
conditions of extremely high pressure
- Removal of overburden results in expansion
- Process called pressure release jointing
- Separation of curved slabs called spalling
- Resulting landform exfoliation dome
4.
Physical Weathering
Physical Weathering In situ mechanical disintegration of rock - no chemical alteration - no mineralogical change - Increases surface area so increases effectiveness of chemical weathering
Most effective when: - lower temperatures because max. freeze thaw cycles - sufficient moisture for frost wedging to occur
4 TYPES:
- Frost Action (water freezing)
- Water expands up to
9% upon freezing
- Force easily exceeds
tensile strength of
granite
- Includes
hydrofracturing - Crystallization (Salts)
- Dehydration results in
formation of crystals
Most common/effective:
- arid climates
- high/fluctuating water
table
- bedding planes - Pressure Release Jointing (Unloading)
- Intrusive igneous rocks form under
conditions of extremely high pressure
- Removal of overburden results in expansion
- Process called pressure release jointing
- Separation of curved slabs called spalling
- Resulting landform exfoliation dome - Hydration
- Absorption of water
- Cycles of wetting and drying
- Affect primarily
fine grain sedimentary rocks
- Results in expansion and
disintegration of rock
- E.g. wetting and drying of shale (slaking)
Chemical Weathering Processes
- In situ chemical decomposition of rock - Results in either: - chemical alteration and/or - formation of new minerals - Facilitated by physical processes Most effective when: - higher temps - higher precip
3 TYPES:
- Hydrolysis
- Occurs when water reacts with minerals
- Formation of
new weaker minerals
- Granular decomposition;
selective attack - Oxidation
- Oxygen reacts with
metallic minerals
- Commonly occurs in
water, free oxygen
- Rusting of metal is a
familiar example
3. Solution and Carbonation - Water vapour reacts with carbon dioxide resulting in formation of weak carbonic acid - Process know as carbonation - Acidic solution dissolves minerals more readily
Equilibrium
Equilibrium
• Balance between:
• process and form
• through feedback and self regulation
a threshold event can upset equilibrium
Nelson River
- isostatic rebound
- plate is rebounding, going upward
- shoreline in hudson bay retreating
- lifting of lithospheric plates
- continually trying to achieve balance but continually changing
Forces Operating on a Slope
- gravity is both a driving and a resisting force
- angle of internal friction vs angle of repose
- resisting forces - cohesion (water, electrostatic forces, etc)
Angle of Repose
- the angle at which material comes to rest
- when it stops moving
Angle of Internal Friction
- when it begins to move, varies between every object
- not always necessary for a mass wasting event, other factors can also influence that
Mass Wasting
- Downslope movement of material due to the force of gravity
- Occur due to changes in driving and/or resisting forces
- Gravity must overcome
material’s cohesiveness and internal friction - Angle of internal friction vs. angle of repose
What causes change in sheer strength or sheer stress of materials resting on a slope?
- weathering
- accumulation of more loose materials resting on a slope through often physical but sometimes chemical weathering - angle changes
- usually increasing
- variety of reasons: river/running water, man-made activity - add water increasing weight
- increases likelihood to move downslope - add water increasing pore water pressure
- increases outward pressure exertion within the pores on the particles resting on the slope - raindrops
- dislodge material resting on slope
- net increase in material gradually moving downslope
Slope Mechanics and Form
- steepest part at the top = waxing slope/convex surface
- bottom = concave surface/waning slope
Types of Mass Wasting
Four classes: 1. falls (F) 2. slides (S) 3. flows (FL) 4. Creeps (C) Differentiated by: 1. type of movement 2. amount of water involved 3. speed
Falls and Avalanches - Rapid movement of rock, debris, snow - No water necessary - Not in constant contact with surface - Accumulation of debris called a talus slope or cone - Avalanche "rides" on a cushion of air/dust
Slides - Rapid movement of cohesive mass - Not saturated but may be wet - Two types: 1) Translational slides movement is along plane 2) Rotational slides (slumps) movement along concave surface - slides have finite boundaries as compared to flows - slump - bite shaped mark
Flows - Comparatively slow (walking - running pace) - Wet to saturated material - Viscous flow - Earthflows (less water) - Mudflows (more water) - Debris flows - contains boulder, trees, etc
Creep & Solifluction - Slow, persistent movement - Normally unsaturated; but solifluction may be - Result of expansion & contraction of material due to: • 1) freezing - expand • 2) thawing - contract - Expansion perpendicular, contraction vertical
