pre midterm 2

What key discovery changed our understanding of the ocean floor in the 19th century?

The mid-Atlantic ridge was discovered in 1853, and the HMS Challenger expedition (1872–1876) mapped its extent using plumb lines. This showed that ocean floors are geologically young, not old as previously assumed, and provided key evidence for plate tectonics.

How do we map the ocean floor? (4 methods)

• Echo sounding measures depth using sound waves.

• Multibeam sonar creates detailed seafloor profiles.

• Satellite altimetry measures sea surface height, which mirrors seafloor topography due to gravity.

• The geoid is an idealized ocean surface shaped by gravitational equipotential.

What are passive vs. active continental margins?

• Passive margins: Continental crust transitions to oceanic crust on the same plate (e.g., Atlantic coast). Features include continental shelf, slope, rise, and turbidity currents.

• Active margins: Plate boundaries where subduction occurs (e.g., west coast of Canada). Features include trenches, accretionary wedges, and volcanism.

Why are glaciers important in geology?

• They cover 10% of Earth’s surface and once covered 95% of Canada.

• They erode, transport, and deposit sediment (rock cycle).

• Glacial ice records past climate (trapped gases, isotopes).

• They influence hydrology by storing water for thousands of years.

What are the main types of glaciers? (5)

• Ice sheets: Continental-scale (Greenland, Antarctica).

• Valley glaciers: Flow through mountain valleys.

• Ice caps: Smaller than ice sheets (<50,000 km²).

• Outlet glaciers & ice streams: Fast-moving channels draining ice sheets.

• Piedmont glaciers: Spread at the base of mountains.

How does glacial ice form and move?

• Forms from snow compaction and recrystallization (similar to metamorphism).

• Moves via:

  • Internal deformation (plastic flow under pressure).

  • Basal slip (sliding over bedrock, aided by meltwater).

  • Soft bed deformation (substrate deforms under ice).

What landforms are created by glacial erosion?

• U-shaped valleys, hanging valleys, fjords.

• Cirques, arêtes, horns.

• Roche moutonnées (asymmetric bedrock hills).

• Striations and glacial erratics (large transported rocks).

What are glacial deposits and landforms?

• Till: Unsorted sediment deposited directly by ice.

• Stratified drift: Sorted by meltwater.

• Moraines: Lateral, medial, terminal, recessional.

• Drumlins, eskers, kames, kettle lakes.

• Outwash plains and valley trains.

What is the distribution and importance of groundwater?

• Makes up <1% of global water but >90% of liquid freshwater.

• Long residence time (~280 years).

• Provides drinking water for >50% of the world, 40% of irrigation, and 25% of industrial use.

Define key groundwater terms (water table, vadose zone, aquifer, aquitard, porosity, permeability)

• Water table: Top of the saturated zone.

• Vadose zone: Above water table, partially saturated.

• Aquifer: Permeable layer holding groundwater (e.g., sandstone).

• Aquitard: Impermeable layer hindering flow (e.g., clay).

• Porosity: Volume of void space.

• Permeability: Ease of fluid flow through rock.

How does groundwater move, and what is Darcy’s Law?

Groundwater flows from high to low hydraulic head.
Darcy’s Law:

V=(Kh)/(ϕL)

• V = velocity

• K = hydraulic conductivity

• h = head difference

• L = distance

• ϕ = porosity

What environmental problems are caused by groundwater extraction? (5)

1. Over-pumping: Depletes aquifers (e.g., Chicago).

2. Subsidence: Ground sinks due to compaction (e.g., Mexico City, San Joaquin Valley).

3. Contamination: From septic tanks, industry, mining.

4. Saltwater intrusion: In coastal aquifers.

5. Reduced recharge: Due to urbanization.

What is the difference between brittle and ductile deformation?

• Brittle: Occurs near surface, low T/P, fast strain rates (forms faults, joints).

• Ductile: Occurs at depth, high T/P, slow strain rates (forms folds).

• Stress types: Compressional (convergent), Tensional (divergent), Shear (transform).

How do we describe the orientation of rock layers?

• Strike: Horizontal line on an inclined plane.

• Dip: Angle of inclination from horizontal.

• Represented on maps with strike (long line) and dip (short line with angle).

What are the main types of folds?

• Anticline: Arch-shaped, oldest rocks in center.

• Syncline: Trough-shaped, youngest rocks in center.

• Monocline: Step-like bend in layers.

• Dome & basin: Circular/elliptical uplift or depression.

Classify faults by movement.

• Dip-slip: Movement parallel to dip.

  • Normal: Hanging wall moves down (tension).

  • Reverse: Hanging wall moves up (compression).

  • Thrust: Low-angle reverse fault.

• Strike-slip: Horizontal movement (right- or left-lateral).

• Oblique-slip: Combination of dip- and strike-slip.

What is the hydrologic cycle?

• Water moves between reservoirs: oceans, ice, groundwater, lakes, rivers, atmosphere.

• Processes: evaporation, precipitation, infiltration, runoff, transpiration.

• Only a small fraction of freshwater is readily accessible.

Describe stream erosion, transport, and deposition.

• Erosion: Hydraulic action, abrasion, solution.

• Transport:

  • Dissolved load (ions).

  • Suspended load (silt/clay).

  • Bed load (saltation, rolling).

• Deposition: Creates floodplains, point bars, natural levees, deltas, alluvial fans.

What are the types of stream channels?

• Meandering: Single, sinuous channel; point bars and cut banks.

• Braided: Multiple, intertwining channels; high sediment load.

• Anastomosing: Multiple, stable channels with vegetated islands.

What controls flooding, and how can it be managed?

• Causes: Heavy rain, snowmelt, ice jams, dam failure.

• Flood frequency: Recurrence intervals (e.g., “100-year flood”).

• Management: Levees, dams, channelization, floodways, urban planning, “sponge cities.”

What evidence did Wegener use for continental drift?

1. Continental fit (especially at continental shelves).

2. Fossil distribution across continents.

3. Matching mountain belts (e.g., Appalachians with Caledonides).

4. Paleoclimatic evidence (glacial deposits in now-tropical regions).

What is seafloor spreading, and how was it proven?

• Proposed by Harry Hess: New crust forms at mid-ocean ridges, old crust sinks at trenches.

• Key evidence:

  • Magnetic stripes (Vine-Matthews-Morley hypothesis).

  • Age of seafloor increases away from ridges.

  • Earthquake distribution along ridges and trenches

Describe the three types of plate boundaries.

• Divergent: Plates move apart (mid-ocean ridges, continental rifts).

• Convergent: Plates collide (subduction zones, continental collision).

• Transform: Plates slide past each other (e.g., San Andreas Fault).

What drives plate tectonics?

• Mantle convection (primary driver).

• Ridge push: Gravitational sliding from elevated ridges.

• Slab pull: Subducting lithosphere pulls the plate.

• Measured via GPS, paleomagnetism, hot spot tracks.

What causes earthquakes, and how are they located?

• Caused by sudden slip along faults (elastic rebound).

• Hypocenter: Where rupture starts.

• Epicenter: Point on surface above hypocenter.

• Located using P- and S-wave arrival times from multiple seismographs.

Compare P-waves, S-waves, and surface waves.

• P-waves: Fastest, compressional, travel through solids/liquids.

• S-waves: Slower, shear, only through solids.

• Surface waves: Slowest, cause most damage (Love & Rayleigh waves).

How are earthquake magnitude and intensity measured?

• Magnitude: Energy released (Richter scale, moment magnitude MwMw​).

  • Each unit increase = ~30× more energy.

• Intensity: Damage felt (Modified Mercalli scale I–XII).

• Factors: magnitude, distance, depth, geology, building quality.

What are the effects and hazards of earthquakes?

• Direct: Ground shaking, building collapse.

• Indirect:

  • Liquefaction (saturated soil loses strength).

  • Landslides.

  • Tsunamis (from undersea quakes).

  • Fires (broken gas lines)

How do we study Earth’s interior with seismic waves?

• P- and S-wave shadow zones reveal core structure.

• Moho discontinuity: Crust-mantle boundary.

• Low-velocity zones indicate partial melt (asthenosphere).

• Seismic tomography images 3D structure.

What are key geological features in Alberta?

• Foothills Erratics Train: Glacial boulders transported from Jasper.

• North Saskatchewan River Valley: Terraces from post-glacial erosion.

• Athabasca–Peace River Delta: One of world’s largest freshwater deltas.

• Glacial Lake Edmonton: Former proglacial lake.

• Oil/gas traps: Structural (anticlines, faults) and stratigraphic.

What are major earthquake risks in Canada?

• Cascadia Subduction Zone: West coast; last major quake in 1700, recurrence ~450 years.

• Eastern Canada: Intraplate seismicity (e.g., Charlevoix).

• Induced seismicity: From fluid injection (fracking, wastewater).