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Geomorphology Final Exam Study Guide
Geologic Structures
STRUCTURAL GEOLOGY – concerned with shapes, arrangement, interrelationships of bedrock
units & endogenic (within) forces that cause them.
Tectonic Forces
Stress & Strain
+ Compressed Stress – shortening strain
+ Tensional Stress – stretching or extensional strain
+ Shear Stress – shear strain
Behavior of Rocks
+ Elastic – rock returns to original shape after increased / decreased stress.
- Elastic Limit – point when rock reaches too much stress
(Brittle / Plastic Fracture)
+ Plastic – hot under pressure
+ Brittle – rock reaches too much stress quickly and cracks.
FACTORS: dependant on rock lithology, amount of time, and pressure.
Strike – intersection of a horizontal unit against an
Inclined plane. (THAT LINE)
Dip- angle horizontal to the rock layer that’s inclined
(ALWAYS MAX. ANGLE)
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Horizontal Strata
Cliff & Bench Topography
-Cap of resistant rock type over softer rock
(SS, Chert, Dolomite, Quartzite, Sills, Lava Flows, ect.)
-More pronounced in arid regions (Not Very Humid)
Types;
Mesa – wide top (Badlands common on side slopes)
Butte – narrow top
Esplanade – bench of resistant rock (Grand Canyon)
Tilted Strata
Differential Resistance to erosion
-Scarp Face (more rugged, actively eroding)
-Dip Slope
Homoclinal Shifting – adjustment due to basal sapping, stream erosion over time.
(Landscapes change place over time)
Homoclinal Ridges - uniform dip, flat irons, uniform rise, long, One angle.
When cut by streams there is a ‘V’ shape angle to the dip.
WIND GAP – no water flowing through the dip.
WATER GAP – wat flowing through the dip.
Forms;
Cuesta – asymmetric, distinct dip/slip slopes(Dip Slope & Scarp Slope different)
Hogback – symmetric (Dip Slope & Scarp Slope about equal)
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Monoclinal Ridges – uplift, tectonically folded “one”slope.
Dip in one direction with local steepening.
Dome – uplift at a single point.
(All rocks dip away from that point)
STRUCTURAL DOME – oldest material in middle.
Basin – subsidence at a single point.
(All rocks dip towards that point)
STRUCTURAL BASIN – youngest material in middle.
Folds
Anticline – folds away from each other
UP FOLD–oldest rock in center (exposed)
Syncline – folds towards each other
DOWN FOLD-youngest rock in center
(downward movement spares from erosion)
Plunging Fold – folds that are not horizontal anymore, ‘U’ shaped ridge.
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Folds are formed from COMPRESSIONAL SHORTENING
DUCTILE (Plastic Deformation)
Open Folds Isoclinal (hairpin) Folds
Overturned Folds Recumbent Folds
Plunging Folds (noses)
Unconformities
Angular – sedimentary beds of differing dip on either side of the unconformity.
Disconformity – sedimentary beds of the same orientation on either side of the
unconformity.
Nonconformity – sedimentary beds overlying unconformity developed on
crystalline rocks. (Igneous / metamorphic)
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Joints & Faults
STRESS
- Tensional (pull apart) -rifting, flexure
-orientation ‘perpendicular’ to stress
- Shear
-orientation 30o-45o from the max / min stress axes
TOPOGRAPHIC EXPRESSION
- Physical properties of the rock and accelerated weathering and erosion
rates.
Fins – when joints become dominate,
cap rocks preserve the below sediments.
Faults Dip-Slip
Normal Faults
Reverse (thrust) Faults – up and over the top.
Strike-Slip
Left or Right lateral (San Andreas Fault)
Oblique-Slip (scissors)
Components of both the Dip-Slip & Strike Slip.
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• Fault scarp
– steep linear bluff – Relief formed solely by movement • Fault-line scarp – Relief caused by differential erosion along fault • Composite scarp – Combination of the 2 above • Mountain landforms
– Horst – Graben • Forms basin & range
Within the Basin and Range Province, the Earth’s crust has been stretched up to 100% of its original width. The entire region has been subjected to extension that Thinned and cracked the crust as it was pulled apart.
Volcanism Lava – magma at the earth’s surface, silica content controls “explosiveness”. Pyroclasts – fragments of rock due to the explosiveness of
The volcano classified to size & shape.
Lava Flow
Extrusive Rocks – (Plugs & Domes)
Volcanoes
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Extrusive Rocks & Gases
-Scientific study of Volcanism
-Gases
-Primarily H20
-CO2, SO2, H2S, HCI
-Gases & Pyroclasts
-Ashfall
-Pyroclastic Flow
Magma
Physical properties dependent on;
-Temperature (700o – 1300o C or above)
-Composition - felsic (silicic) to mafic
-Gas Content – several % by weight (H2O, CO2, SO2, ect.)
Eruptive Violence
-Gas in lava
-Viscosity (temperature & Silica content)
Silica Lavas – most viscous
Mafic Lavas – least viscous
Classification of Volcanoes
Based on;
-Activity (Active, Dormant, Extinct)
-Morphology (Shield, Composite, Cinder Cone)
-Eruptive Style (Hawaiian, Icelandic, Strombolian, Plinian, Pelean, Krakatoan)
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Eruptive Style
Hawaiian
- Quite, large volumes of basaltic magma
- Eruptions from central vents & cones
Icelandic
-Quite, large volumes of basaltic magma
-Eruptions from fissures (Columbian Plateau, Keweenaw)
Strombolian
-Mild to moderate explosive activity
-Basaltic lava
Plinian
-Explosive
-Ash & expanding gasses thrown ‘upward’
(As high as 60,000 ft., gasses begin expanding deep in the vent)
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Pelean
-Explosive
-Ash & expanding gases thrown ‘outward’
“Nuees Ardentes” – glowing clouds
Pyroclastic Flows
Krakatoan
-Most explosive of all!
-Forms ‘Calderas’ – huge craters
-Infrequent (in human life history)
-Can erupt 4 miles of material, have 3.5 mile diameter Calderas, Be heard
thousands of Kilometers away, and start Tsunamis!
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