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‘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 2 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 3 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 4 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 5 Oceanic – oceanic plate convergence New Hebrides Trench near Vanuatu Continental – continental plate convergence India/Eurasia plate collision (forms Himalayan Mountains) Earthquake Motion 6 Historical seismic activity in Canada 7 1906 San Francisco Earthquake Phillipines, February 2006 Heavy Rainfall + Weak Earthquake? Photo: Associated Press 8 Mercalli Richter 1964 Alaska earthquake damage map: modified Mercalli scale III - IV V VI VII VIII - X Liquefaction and slumping Anchorage, Alaska - 1964 9 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 10 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. 11 The power of a tsunami Source: CTV, Jan 2005 Volcanoes 12 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 13 Kilauea, Hawaii Seamounts Hot spot Plateau basalts 14 CONTINENTAL RIFT VALLEY Photo of Rift Valley In East Africa Composite volcano Shield/Composite Comparison Mount St. Helens: the day before 15 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 16 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 17 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) 18 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 19 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 20 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 21 • 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 22 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 23 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 24 •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. 25 Entrained Particle Exposed section Buried Portion 26 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. 27 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) 28 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 29 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 6 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 30