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)
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)
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.
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)
Joints & Faults STRESS - Tensional (pull apart) -rifting, flexure -orientation perpendicular to stress - Shear -orientation 30 o -45 o 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.
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
Extrusive Rocks & Gases -Scientific study of Volcanism -Gases -Primarily H 2 0 -CO 2, SO 2, H 2 S, HCI -Gases & Pyroclasts -Ashfall -Pyroclastic Flow Magma Physical properties dependent on; -Temperature (700 o 1300 o C or above) -Composition - felsic (silicic) to mafic -Gas Content several % by weight (H 2 O, CO 2, SO 2, 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)
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)
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!