Flashcards
Geomorph Midterm lecture 6-10
Cards in this deck (38)
- 1Faults-fracture, usually not clean so we call it a fault zone
-fault trace is where a fault intersects the ground - 2fault types
- 3Fault types (2)
- 4Faults contd-horst: area beside a NORMAL fault that gets lifted up
-graben: beside a NORMAL fault that gets lowered - 5Nappe-sheet like body of rock that has moved >2km on a near horizontal thrust fault
-decollement = thrust fault forming the nappe
-klippe = erosional remnant of a nappe - 6Strike-Slip faults-ex san andreas fault california
- 7Active Faults-known to have slipped at least once in the past 10000 years
-ex) chi chi thrust fault taiwan - 8Geomorphic features of faults
- 9Inactive Faults
- 10Gravitational Slope Deformation-some fault like features are created by erosion, not tectonic activity
-known as sackung
-common in deglaciated terrain, where stress relief on valley walls followed retreat of glaciers - 11Valley Rebound-deep river erosion causes fault like non-tectonic features
- 12Volcanism & Magmatism-Extrusive activity = volcanism ex) garibaldi
-intrusive activity = magmatism ex) north shore mountains
-volcanic centres in BC: Cascade arc, Anahim, Wells Gray/clearwater - 13Instrusive Forms (plutons)-Batholiths: very large intrusions, often roof pendants (masses of country rock)
-stocks: similar to batholiths but smaller & more localized <100km2, discordant (contact is not parallel to bedding/foliation of country rock)
-Laccoliths (sills): similar in size to stocks, concordant (contact is parallel to bedding/foliation of country rock)
-Ring Dykes: radial/concentric from a central source of activity at a depth - 14Examples of Intrusive Forms
- 15Contact Metamorphism
- 16Volcanic Materials1. Lava (basaltic) a. Pahoehoe: 1100-1200C (very hot), low viscosity, smooth, hawaii
b. Aa: 1000-1100C, higher viscosity, rough texture, strong cooling surface
2. Pyroclasts/tephra: a. Ash: <2mm, can cover huge areas, useful as a marker layer
b. Lapilli: 2-64mm, "little stones"
c. Bombs: >64mm, includes pumice, and scoria/cinder (like pumice but sinks) - 17Volcanic Transport1. Lava Flow
ex) Lava lake, hawaii, subsided surface, tree casts
-rapid flows possible with hot, low viscosity Pahoehoe
- 18Volcanic Transport (2)2. Airfall
ex) cinder cone, hawaii
- 19Volcanic Transport (3)3. Pyroclastic Flow
- collapse of dense, eruptive column
-downhill flow of superheated tephra
- temps >400C, speeds >100km/h
-Ignimbrites - welded pyroclastic flow deposits
-guadalajara mexico, example of using ignimbrite building stones - 20Volcanic Landforms - terminologyIgneous activity: formation and movement of molten rock
Plutonic/intrusive igneous rocks are formed under the surface
volcanic/extrusive igneous rocks are formed on surface
molten rock above surface = magma, under surface = lava - 21Magma-forms under high temps and low pressure conditions
-melts usually develop in upper mantle or lower crust and are mafic
- as it rises and cools, rising magma turns more felsic
-remelting of walls of magma chamber can add felsic rocks - 22Mafic vs felsic
- 23Tectonic Setting-Composition/viscosity of magma that makes it to surface depends on:
- composition of original melt
-composition/thickness of rocks that magma migrates thru
-rate of cooling and differentiation
-entrained fluids and gases
-magma @ extensional and hot spots = mafic, lower viscosity
-magma @ compressional = wider range of composition, more felsic, higher viscosity - 24Volcanic Eruptions-involve exhalative (gas), effusive (lava), and explosive (pyroclasts)
-exposiveness is a function of viscosity and gas content of magma
-higher viscosity (more felsic) tends to trap more gas and be more explosive - 25Volcanic Eruption Types1. Icelandic Eruptions: lava from a fissure, Ex) Laki Event in Iceland (1700s), 12km3, 565km2, energy released = a million atomic bombs
-more fluid, less explosive
2. Hawaiian Eruoptions: Similar to icelandic but lava is issued from a central vent
3. Strombolian Eruptions: small, phreatic, producing lava and tephra
4. Vulcanian/Vesuvian Eruptions: alternating pyroclastic explosions and lava outflow
5. Plinian Eruptions: vertical ash columns up to 80km high ex) pompeii, mt st helens
6. Pelean Eruptions: dominated by pyroclastic explosions, rock avalanches
7. Krakatoan: Cataclysmic, total destruction - ex) crater lake, oregon - 26Volcanic Landforms-Flood Basalts: ex) columbia river flood basalts
- from extensive series of fissures
- washington, oregon, idaho
-flows only 10m thick but cover tens of km long
-Columnar Basalts: joints form perpendicular to cooling front ex) along sea to sky
-Cinder Cones: Built up in layers during multiple stages of eruption Ex)mauna kea hawaoii, mt. etna, italy
-Littoral Cones: formed by phreatic eruptions when lava reaches the beach
-Shield Volcanoes: gentle slope, broad, many lava flows
-Subsidence caldera: collapse of ground into emtied magma chamber
-Craters: circular depressions above vents
-Stratovolcanoes: steep slopes built up by alternating layers of lava and pyroclastic deposits
-Explosive Caldera: collapse of ground into an active magma chamber which causes violent ejection
-Lava Dome: Formed by viscous lava, a sign of resurgent and potentially explosive volcanic activity
-Ignimbrite Sheets: extensive layered, pyroclastic flow deposits - 27Volcanic Hazards-tephra = pyroclasts
-unstable ground is a secondary hazard associated with lava flow deposits
-also aggradation, flooding, tsunamis - 28Lava Flow-slow moving - usually enough time to evacuate
-still property damage - 29Unstable Ground-subsidence/collapse of lava deposits into subsurface voids ex) lava tubes
- 30Gas, pyroclasts, tephra-H2S, CO, CO2, SO2, water vapour = results in acid rain
-ash, lapilli, bombs - 31Landslides-rock avalanches
-extremely rapid, massive, flow like motion of fragmented rock
-volcano flank collapses and associated directed blast effects
-layered nature of volcanoes make them unstable
-meager creek landslide (2010) see photos
- 32Lahars-volcanic debris flows
-extremely rapid, surging flow of saturated debris in a steep channel
-hot lahars: during eruptions
-cold lahars: when volcano is dormant
-ice can contribute to lahar hazard
-ex) Nevado de Ruiz, colombia (1985): downstream flow 60km/h, explosive eruption triggers pyroclastic flows over ice covered summit, pumice and meltwater create lahars, city covered, 23,000 people killed
-Landslide volume and area relationship: A=cV^(2/3) where c = 10 for rock avalanches, c=20 for debris flows, lahars: c=100 - 33Other Hazards-Aggredation: increase in elevation of a channel caused by sediment deposition
-Flooding: Landslide dams are channel blockages and dam breaches that cause flooding
-Tsunamis: displacement waves generated by subaerial or submarine mass movements - 34Weathering-First type of exogenic process to learn
-Physical: fragmentation/disaggredation of rock by mechanical processes
-Chemical: decomposition of minerals in rock by rxns - 35Physical Weathering-crack propogation: tensile stress concentrates at end of crack
Types: 1. Exfoliation: stress relief, jointing/sheeting
2. Frost Shattering: ice jacking due to freeze/thaw cycles, water expands 9% when freezing, high pressure in water trapped in cracks - this is positive feedback: frost shattering enlarges joints, more room for water to enter joints, more frost shattering occurs
3. Thermal Fracturing: differential expansion due to extreme heating.
-sun not enough to do this
-forest fires
-v high temp gradient needed
4. Slaking: swelling due to water absorption, common in shale but can occur in any rock with high clay content
5. Salt Crystallization: evaporation of salt water causing growth of salt crystals
-they can expand up to 3x
-exerts high pressure on rock
-crystalloblastic pressure detaches grains
Tafoni (honeycomb patterns): from seepage convergence
-Positive feedback: water attracted to local depression (seepage convergence), more evaporation happens, more salt crystallization occurs - 36Chemical Weathering1. Dissolution: some minerals dissolve in water, ex) silica is soluble in water, calcite is soluble in acid water
- produces karst
2. Hydrolysis: reaction of minerals with water ions, producing clay minerals
3. Carbonation: water with CO2 leaches metal ions from minerals
-Cations recombine to form clays
-volume change and disaggredation
-carbonation sequesters CO2
4. Chelation: organic compounds dissolve cations
-not well understood
5. Oxidation: gain of oxygen, loss of hydrogen, forms rust, sulphuric acid
6. Reduction: loss of oxygen, gain of hydrogen
7. Hydration: water molecules in the crystal lattice , can cause large volume increase and cracking - 37Mineral Stability-light rock=good rock, dark rock=bad rock
- 38Temp/Humidity Effects-Higher temp = increased chem weathering
-rxn rates double for each 10C inc
-slow down carbonation
-higher humidity: inc chem weathering
-more water avail for rxns
-water promotes organic activity
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- Flashcards on Geomorph Midterm lecture 6-10, created by Maddi Everton on 09/10/2018.
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