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 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.

• 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 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)

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!