Download Eons, Eras, Periods and Epochs Dating by radioactive isotopes

‘SIDE’ IMAGE
Planetesimal/nebula hypotheses
(dust-cloud hypotheses)
100,000 ly
‘TOP’ IMAGE
Solar System on outside
of Orion Arm (25000 ly
from centre)
Basis: observations of other systems
1.
2.
3.
4.
5.
6.
Collision or Large star in Milky Way exploded
Nebula (cloud of dust and gas) results
H and He condense into Sun
Other elements form disk of matter around sun
Disk slowly accretes into clumps (planetesimals)
planetesimals → planetoids → planets (including
Earth) and satellites
Eons, Eras, Periods and Epochs
Superposition: youngest rocks superimposed on older rocks
“Relative time”
Dating by radioactive isotopes
Half-life: time for ½ of unstable isotopes to decay
“Absolute time”
Uniformitarianism:
“The same physical processes active in the environment
today have been operating throughout geologic time”
Hutton (1795), Lyell (1830)
Source: University of Calgary
1
Mineral
A natural, inorganic compound with a
specific chemical formula and a
crystalline structure
Examples
silicates (quartz, feldspar, clay minerals),
oxides (eg., hematite)
carbonates (eg., calcite)
A rock is an assemblage of minerals
bound together
• Igneous (solidify and crystallize from
molten magma)
• Sedimentary (settling)
• Metamorphic (altered under pressure)
• from magma
(molten rock
beneath the
surface)
• intrusive or
extrusive (from
lava)
Laccolith
Sill
Dike
Batholith
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Existing rock is digested by
weathering, picked up by erosion,
moved by transportation, and
deposited at river, beach and ocean
sites.
Lithification follows (cementation,
compaction and hardening)
Conglomerate
Sandstone
Siltstone
Shale
Limestone
Coal
Laid down in horizontally-layered beds
Any type of rock is transformed, under
pressure and increased temperature
• Harder and more resistant to
weathering
• Compressional forces: (i) collision of
plates, (ii) rock thrust under crust,
(iii) weight of sediment above
largest clasts
sand cemented together
derived from silt
mud/clay compacted into
rock
calcium carbonate, bones
and shells cemented or
precipitated in ocean waters
ancient plant remains
compacted into rock
Shale
Slate
Granite
Gneiss
Basalt
Schist
Limestone, dolomite
Marble
Sandstone
Quartzite
•Continents are adrift due to convection
currents in the asthenosphere
•Mantle drags around the continents
•225 M BP: Pangaea
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Fossil Record (plant and animal)
Distribution of marsupials vs. placentals
Age of mid-oceanic ridge magnetic stripes
Age and thickness of oceanic crust
Subduction zones
“Ring of fire”
See: http://www.scotese.com/sfsanim.htm (animation)
Divergent Boundaries (constructional)
Convergent Boundaries (destructional)
Transform Fault Boundaries
URL: http://pubs.usgs.gov/publications/text/Vigil.html
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Source: USGS
Earthquakes
Two types of crust “float”
on the upper mantle:
• oceanic crust (heavier, sinks lower)
• continental crust (lighter, floats higher)
Three types
of plate convergence
Oceanic – continental plate convergence
Nazca plate – South America plate
• oceanic – continental
• oceanic – oceanic
• continental - continental
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Oceanic – oceanic plate convergence
New Hebrides Trench near Vanuatu
Continental – continental plate convergence
India/Eurasia plate collision
(forms Himalayan Mountains)
Earthquake Motion
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Historical seismic activity in Canada
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1906
San Francisco
Earthquake
Phillipines, February 2006
Heavy Rainfall + Weak Earthquake?
Photo: Associated Press
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Mercalli
Richter
1964 Alaska earthquake damage
map: modified Mercalli scale
III - IV
V
VI
VII
VIII - X
Liquefaction and slumping
Anchorage, Alaska - 1964
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Earthquake-proof buildings
•Pressure is not always great enough or abrupt
enough to cause faulting (earthquakes).
•Deformation occurs (FOLDING) if pressure does not
exceed the internal strength of the rock or if it becomes
plastic (hot).
•Tensional stress produces thinning crust, folding and
normal faults
•Compressional stress produces thickening crust, folding
and reverse faults
•Shearing stress produces horizontal bending and strikeslip faults
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Is a major earthquake in
California, Alaska or Japan of
any concern thousands of
kilometers away, in Hawaii?
Hint:
(seismic wave)
In Fall 2004, no one answered
this question, but many could in
Spring 2005.
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The power of a tsunami
Source: CTV, Jan 2005
Volcanoes
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Effusive eruptions
(gentle flows, lots of lava)
• cinder cones
• shield volcanoes
• plateau basalts
Explosive eruptions
(viscous lava, trapped gases)
• composite volcanoes
• calderas
Cinder cone
Big Cinder Butte,
Craters of the Moon, Idaho
- forms small hills, less than 450 m high
- black scoria rock with air bubbles
Shield volcano
Mauna Loa, Hawaii
•
Low viscosity magma
Gases readily escape
From this magma
Effusive eruptions
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Kilauea, Hawaii
Seamounts
Hot spot
Plateau basalts
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CONTINENTAL
RIFT VALLEY
Photo of Rift Valley
In East Africa
Composite volcano
Shield/Composite Comparison
Mount St. Helens: the day before
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Live Photo of Mt. St. Helens!
Flooding (from steam-melted ice and snow)
http://www.fs.fed.us/gpnf/volcanocams/msh/
Caldera
Four years later
Crater Lake, Oregon
6600 years ago
windblown ash
landed in Calgary
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Volcanic hazards and effects
•
•
•
•
•
•
•
hot ash (pyroclastics)
steam and gas explosions
lava flows
poisonous gases (carbon dioxide, sulfuric acid)
landslides
tree blowdowns
lahars (steam-melted ice and snow cause flooding
and large mudflows)
• increase in atmospheric dust (decreased global
temperatures)
Volcanic benefits
• new fertile soils
- Hawaii, Philippines
• geothermal energy
- Iceland, Italy, New Zealand
• new real estate
- Iceland, Japan, Hawaii
Diamond-bearing kimberlite pipe
Dynamic Equilibrium Model
Uplift creates potential energy of position
(disequilibrium)
Sun provides heat energy
Hydrologic cycle provides kinetic energy
Atmosphere and crustal reactions provide
chemical energy
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Landforms are constantly being adjusted
toward equilibrium
1. Equilibrium Stability
2. Destabilizing Event (‘geomorphic threshold’ met)
(eg. lava flow, tectonics, heavy rainfall, forest fire,
deforestation, climate change)
3. Period of Readjustment
4. New Condition of Equilibrium Stability
•Material is loosened by weathering, eroded and
transported
•Agents of erosion must overcome friction before
downslope movement occurs
•Slopes are often convexo-concave
•Convex at the top (waxing slope and free face)
•Concave at the bottom (debris slope and waning slope
lead to pediment in the depositional zone)
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Weathering processes disintegrate rock into
mineral particles or dissolve them into water
Two forms:
1.
2.
Smaller fractures throughout
(large)
Limestone bedrock, Kansas, USA
Photo: J.S. Aber, 1977
1. Rock Composition and Structure
Jointing increases surface area exposed to weathering
Some rocks more soluble (eg. limestone) than
others (eg. granite)
5.
Hydrology (Soil water and Groundwater)
Water promotes chemical weathering within the parent
material
6.
Geographic Slope Orientation
Affects exposure to sun, wind and precipitation
Important worldwide, but especially at higher latitudes
7.
Vegetation
Acids from organic decay add to chemical
weathering; shields rock and soil; roots hold soil
together on steep slopes but split jointed bedrock
8.
Time
2. Wetness and Precipitation
Promotes chemical and physical weathering
3. Temperature
Promotes chemical weathering
4. Freeze-thaw cycles
Volume increase of H2O upon freezing mechanically
splits rock, especially in humid continental, subarctic,
polar and alpine environments
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Glacier National Park,
USA – formed due to
freeze-thaw
weathering)
Rock is broken and disintegrated without chemical alteration
Surface area susceptible to chemical weathering increases
Freeze-thaw weathering
•H2O increases in volume by 9% upon freezing
•Repeated freezing and thawing breaks rocks apart
•Humid continental, subarctic, polar and alpine environments
Frost wedging pushes portions of rock apart.
The loosened, angular rock falls from cliffs in steep areas
and accumulates downslope, forming talus slopes
Dry weather: moisture drawn upward to rock surfaces
Dissolved minerals crystallize.
Crystals spread mineral grains apart (especially sandstone)
Opened spaces are then open to water and/or wind erosion.
Minerals absorb water and expand
Stresses rock – grains forced apart
•Overburden removed through weathering
•Pressure released - heave for millions of years
•Layers of rock peel off in curved slabs
“pressure-release jointing”
•Exfoliation (sheeting) leaves massive, arch and
dome-shaped features on exposed landscapes
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Exfoliation
Dome
Half Dome,
Yosemite
National
Park, USA
Chemical weathering is the decomposition of rock minerals
Minerals can:
1. Combine with oxygen or carbon dioxide in the air
2. Dissolve or combine with water
Forms of Chemical Weathering:
1. Hydrolysis
Minerals chemically combine with water in a reaction
to the mild acids in precipitation water
Disintegration etches, erodes and softens rock
2.
Oxidation
Oxygen oxidizes metallic elements to form oxides
(eg. iron oxide, Fe2O3)
More susceptible to further chemical weathering
3.
Carbonation and Solution
Water can dissolve 57 natural elements and many of
their compounds – “universal solvent”
•
•
•
•
Carbonic acid (H2CO3) in precipitation
Reacts with rock minerals containing Ca,Mg, K and Na
Minerals dissolved into H2O (eg. CaCO3)
Washed away in rainwater
Florida Sinkhole
Cause of karst topography and landscapes such as
sinkholes, tower karst and stalagtites/stalagmites.
Stalactite and
Stalagmite complex
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• Bedrock
• Regolith
• Sediments
• Rate of organic and
mineral soil production
2. Rate of weathering
and erosion
3. Rate of organic soil
decomposition
4. Time
Type of Mineral
Particle
Size Range
Sand
2.0 - 0.06 mm
Silt
0.06 - 0.002 mm
Clay
less than 0.002 mm
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Maximum water content before gravity
drainage begins
Water content below which water is held
so tightly to the soil that plants cannot
take it up
Any unit movement of a body of material propelled and
controlled by gravity. Slopes and gravitational stresses
are always involved
Physical and chemical weathering weaken rock near the
surface, making it susceptible to mass movement
Angle of repose:
Slope achieved at equilibrium as grains flow downslope
Driving force:
Gravitational forces. The greater the slope angle, the
greater the likelihood of mass movement.
Resisting force:
Cohesiveness and internal friction
Types of Mass Movements
4. Flows (formed due to increased moisture content)
1. Rockfall
- rock falls through air and hits a surface
- pile of irregular, broken rocks results
5. Creep (persistent, gradual mass movement)
-very slow movement of individual soil particles due to
freezing and thawing, wetting and drying, temperature
changes and animal disturbance
2. Landslides (translational or rotational)
- sudden movement of cohesive mass of bedrock/regolith
3. Debris avalanche
Faster than landslide since water or ice fluidize
the debris
- rock, debris and soil
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Effects of Lahar
(form of earthflow)
http://atlas.gc.ca/site/english/maps/freshwater/distribution/drainage
Drainage basin/catchment/watershed:
•Defined by the ridges – every stream has a basin
•A drainage basin collects water, which is delivered to
a larger basin, creating larger streams
Continental Divide:
•The line separating subcontinental-scale watersheds
Water and sediment usually terminate in oceans
Internal drainage
Basins in which water does not terminate in an ocean
(evaporation or subsurface drainage)
Drainage Basins
Red: selected
drainage
basins for first
order streams
(collection of
red areas should
fill the yellow
area but some
streams not
represented)
Yellow:
larger drainage
basins for river
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•determined by dividing the total length of all
streams by the area of the basin
•higher density in humid areas
Arrangement of channels is determined by:
•Slope
•Rock resistance to weathering
•Climate
•Underlying bedrock
•Subsurface hydrology
4. Radial Drainage
Streams flow from central peak or dome
5. Annular Drainage
Occurs in dome structures with
concentric patterns of rock strata
6. Parallel drainage
Steep slopes - similar to dendritic,
but steep slopes cause branches to
appear almost parallel to one another
7. Deranged Drainage
In areas with disrupted surface patterns
there is often no clear drainage geometry
(common in glaciated areas)
1.
Dendritic
Tree-like pattern
Efficient –branch length minimized
2.
Rectangular
A faulted and jointed landscape directs streams
along right angle turns
3.
Trellis
Forms where resistance of bedrock varies
or along a folded landscape
Folds create parallel large streams, capturing
runoff from smaller streams and joining into
larger rivers at right angles
Flow velocity: A measure of how fast a stream
moves downstream (v in m/s). It depends on the
discharge, slope, size and shape of the channel.
Discharge: The amount of water flowing through
a cross section of a stream (Q in m3/s). Fluctuates
seasonally and diurnally Q=wdv
Capacity: The amount of sediment that can be
carried by a stream (m3/s or kg/s). Capacity
increases with discharge.
Competence: The maximum particle size that can
be carried by the stream (related to flow velocity)
Sedimentary load is the total amount of sediment carried
by a stream. Sedimentary load is carried by bedload,
suspended load and washload.
1. Bedload Coarse particles (eg. sand) which have high
settling velocity. Sediments are transported near the
streambed, kept loose by turbulence and particle interaction.
2. Suspended load: Particles are in the water column,
sorted by weight (larger particles near the bottom).
The higher the discharge, the higher the suspended load.
3. Washload: Fine particles with low settling velocity,
which travel at the same speed as the flow.
Almost independent of discharge.
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Entrained Particle
Exposed section
Buried Portion
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Coastal Processes and Landforms
Erosional and depositional landforms of coastal areas are
the result of the action of ocean waves.
Erosional Landforms
Sea Cliffs
Wave-cut Notches
Caves
Sea stacks
Sea arches
Depositional landforms
Beaches
Barrier Spit
Baymouth Bar
Lagoon
Tombolo
Wavelength
Distance from one wave crest to the next
Wave height
The distance between trough and crest
Wave period
The time taken for two crests to pass a given point (remains
almost constant)
λ=V*P
The wavelength, λ, is the product of its velocity and period.
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Wave Properties
Wave motion
The energy source for both coastal erosion and sediment
transport are the ocean waves generated by the frictional
effect of the winds incident on the ocean surface
(b) Ocean depth < ½ the wavelength
- wave height increases and wavelength decreases
(a) Ocean depth > ½ the wavelength
- waves not affected by ocean floor
(1) Kinetic Energy:
The motion of the water within the wave.
The wave becomes more peaked
“Breakers” form
(2) Potential Energy:
Due to the position of water above the wave trough.
Breaking of waves: conversion
of potential to kinetic energy
Wave energy increases with wind speed and fetch
Work done on the shoreline
Wave Refraction
Straight shoreline
- drag exerted by the ocean floor causes waves to break
parallel with the shoreline.
The direction of travel of a wave varies as it approaches an
indented coast.
Crests approaching the headlands experience the drag of
the ocean floor first, which causes:
1. Increase in wave height
2. Decrease in wavelength
3. Decrease in velocity
Transport of Sediments by Wave Action
Rock particles are eroded from one area and deposited
elsewhere. Wave refraction affects this process.
Beach Drift:
Swash and backwash rarely occur in exactly opposite
directions
Upward movement occurs at some oblique angle
Backward movement occurs at right angles to the beach.
This creates lateral movement of particles (beach drift)
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Longshore Currents:
Rip Currents:
Rip currents form when
waves are pushed over
sandbars.
The weight of excess water
near the shore can ‘rip’ an
opening in the sandbar,
causing water to rush seaward.
Source: NOAA web site
Influence of Perigee, Apogee, Perihelion and
Aphelion on the Earth’s Tides
Spring Tide
Tides enhanced
during full Moon
and new Moon
Sun-Moon-Earth
closely aligned
Neap Tide
Tidal effects of
Moon and Sun
not additive
Stronger for perigee and perihelion
Erosional Coastal Landforms
Along rugged, high-relief, tectonically-active
coastlines
Sea cliffs
A tall, steep rock face,
formed by the undercutting
action of the sea
Wave-cut notches
A rock recess at the foot of a sea cliff where the energy
of waves is concentrated
Sea Caves
Caves form in more erosive sediment when the rock does not
fully collapse in a deeply-notched environment
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Barrier Spit
Wave-cut platform
Horizontal benches in the tidal zone extending from the
sea cliff out into the sea
If the sea level relative to the land changes over time
(becoming lower with respect to the land), multiple wave
cut platforms (terraces) result
1
2
3
4
5
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Material transported by
littoral drift deposited along
ridge, extending outward
from a coast in an area with
weak offshore currents
If the spit grows to completely
block an embayment, it is
called a bay barrier or
baymouth bar
A lagoon is a body of water
behind the barrier
http://www.rgs.edu.sg/events/geotrip/cliff.html
Bay Barrier
A tombolo occurs when sediment deposits connect the
shoreline with an offshore sea stack or island
http://www.geog.ouc.bc.ca/physgeog/contents/11m.html
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