GEOG 312: Geography of Landforms Study guide for Exam 2 Fall 1998

Note: Be prepared to produce labeled diagrams of landforms and processes on the test.

Weathering

An Exogenic processes

Chemical Weathering

Solution

Hydration

Hydrolysis

Carbonation

Oxidation

Products of Chemical Weathering

Mechanical weathering

Unloading/Dilatation/Exfoliation

Thermal expansion/contraction

Freeze/thaw

Crystal growth in voids

Hydration shattering/expansion weathering

Root Growth

Weathering and its Effects on Landforms

Structure -- fissility, massive rx, granular rx, case hardening, tafoni

Process

Time -- rate of weathering

Slopes: Mass Wasting

Slope Stability :

Shear Strength/Shear Stress = Safety Factor

Shear Stress = Wsinq (or understand it graphically)

Shear Strength = C + s' tanf (Coulomb equation)

Cohesion C

effective normal stress s'

The effect of water -- Effective Normal Stress - (s') -- increases if undersaturated (negative pore pressure, or tension), decreases if saturated (positive pore pressure...particles float a bit, thus grip less)

angle of internal friction expressed in degrees (f) or percent (tan f)

same as angle of repose if dry & no cohesion

Simple Model - forces acting on a particle on a slope

Stresses acting on Layers of Soil & Rock -- Deriving Normal Stress

Factors which can alter slope stability -- weathering, joint spacing, dip vs. slope angle, water

Types of Mass Movements

Fall (and talus cone)

Topple

Slide

Translational Slides -- debris slide

Rotational Slides -- soil slip or slump; slump & earthflow

Creep -- soil & rock; speeds, needle ice

Flows -- solifluction, gelifluction, debris flow, earth flow, mud flow, lahar, avalanche

Management considerations

Slopes & the Drainage Basin: Water Erosion

Overland Flow (Hortonian & Saturation) processes -- rainsplash, sheetwash, rill, gully

Effectiveness of Water erosion

laminar vs. turbulent flow conditions

suspension, traction, saltation, solution

relationship to grain size: competence (Hjulstrom diagram)

erosion velocity

settling velocity

capacity

Throughflow/Interflow - subsurface erosion -- & piping

Slope Analysis

convex vs. concave slopes -- and creep vs. slopewash debate

Hypothetical 9-unit slope model

Three-dimensional analysis

Slope Analysis

convex vs. concave slopes—and creep vs. slopewash debate

Hypothetical 9-unit slope model

Three-dimensional analysis

Drainage Basin: relates to slopes, pour point, catchment area, tributaries, discharge, velocity, runoff, drainage divide, network: stream order (Strahler system) and link magnitude, drainage density, badlands,

 

Fluvial Processes & Landforms

Fluvial processes: suspension, traction, saltation, solution, bed load + saltation + suspended load = solid load, dissolved load, capacity, competence; Hjulstrom diagram: erosion velocity, settling velocity, relationship with type of load; frequency & magnitude concept.

Channel Cross-Section: channel response: stream power f(QS) scour & fill, Principle of Continuity: Q = AV; Impact on W, D, & V of change in discharge, relationship to meandering, braided, concrete and bedrock channels.

Longitudinal Profile: meaning of, relationship with sediment load, discharge, base level. Concept of Grade; Base Level: sea level and resistant bedrock; knickpoint; stream terraces; headward erosion, caprocks, sapping, plunge pools.

River Channel Habit: straight (structural control), riffle/pool sequences—how formed; rapids; sinuous, meandering (suspended load, lateral migration of deep channel, cut bank, point bar, thalweg), braided (easily erodible banks, shallow multiple channels, bed load dominant, bars).

Historical development of stream valleys: youth, maturity, old age – characteristics of valley form, flood plain development, causes of rejuvenation,entrenched meanders.

Landforms: point bar, flood plain, oxbow lake, meander scar, natural levee, meander cutoff, stream terraces, entrenched meanders, alluvial fan, delta, lakes