Geomorphology

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The study of landforms and the processes that create them.

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Geomorphology

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The study of the relationships between landforms and the current processes acting upon them.

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Process or Functional Geomorphology

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The relationship between landforms and human activity.

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Applied Geomorphology

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What do modern geomorphologists study?

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Form, Process, and History

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The nature and rate of geomorphic processes that change throughout time.

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Historical Geomorphology

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The theory expounded by William Morris Davis: Uplift takes place quickly. Geomorphic processes, without further complications from tectonic forces, gradually wear down the raw topography.

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Geographical Cycle

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According to William M. Davis, topography is reduced, little by little, to an extensive, flat region close to base level, called a _____ with occasional hills known as _____.

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Peneplain, Monadnocks

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The reduction process creates a time sequence of landforms that progresses through the stages of...

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Youth, Maturity, Old Age

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A variation of Davis's theory offered by _____ _____ that says that uplift and planation occur at the same time, instead of alternately. The continuous and gradual interaction of tectonic processes and denudation leads to a different model of landscape evolution, in which the evolution of individual slopes is thought to determine the evolution of the entire landscape.

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Walter Penk

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According to Walter Penk, three slope types evolve with different combinations of uplift and denudation...

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(1) Convex slopes - evolve when the uplift rate exceeds the denudation rate.
(2) Straight slopes - when uplift and denudation rates match eachother.
(3) Concave slopes - when the denudation rate exceed the uplift rate.

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Early historical geomorphologists who used geologically young sediments to determine pleistocene events. Their work on the glacial effects on the Bavarian Alps and their forelands provided the first insights into the effects of the Pleistocene ice ages on relief.

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Eduard Bruckner and Albrecht Penck

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The classic river-terrace sequence developed by Eduard Bruckner and Albrecht Penck that gave rise to Quarternary geomorphology:

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Donau, Gunz, Mindel, Riss, Wurm

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What are some of the values brought forth by process geomorphology?

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(1) The buildup of a data base of process rates for various parts of the globe.
(2) The develpoment of models to predict short term and long term changes in landforms.
(3) The development of ideas about stability and instanbility in geomorphic systems.

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The two main thrusts of research in process geomorphology and global environmental change investigate:

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(1) Energy and mass fluxes
(2) The resonse of landforms to hydrology, climate, tectonics, and land use.

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All geomorphic systems can be thought of as resulting from a basic antagonism between _____ processes griven by geological forces and _____ processes driven by climatic foces. In short, tectonic processes create land and climatically influenced weather and erosion destroy it.

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(1) endogenic (tectonic and volcanic)
(2) exogenic (geomorphic)

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Three kinds of geomorphic systems may be identified:

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(1) Form or morphologic systems
(2) Process or cascading systems
(3) Form - Process or Process - Response systems

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Occurs when a system is in balance over a certain time period and no change in state occurs.

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Static Equilibrium

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Occurs when a system has a tendency to revert to a previous state after a small disturbance.

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Stable Equilibrium (Recovery)

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Occurs when a small disturbance forces a system towards a new equilibrium state where it stabilization occurs.

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Unstable Equilibrium

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Occurs when a system crosses an internal or external system threshold, so driving it to a new state.

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Metastable Equilibrium

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Separates different states of a system. It marks some kind of transition in the behavior, operation, or state of a system. Ex) When water reaches a certain temperature, it changes state; when hillslopes reach a certain angle, mass movement occurs.

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Threshold

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When a system constantly fluctuates around about a mean equilibrium state.

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Steady State Equilibrium.

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The tendency of a system towards a state of maximum entropy, as in the reduction of a mountain mass to a peneplain during a prolonged period with no uplift.

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Thermodynamic Equilibrium

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Balanced fluctuations about a mean state that changes in direction (a trending mean).

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Dynamic Equilibrium

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Combines dynamic and metastable tendencies, with balanced fluctuations about a trending mean flipping to new trending mean values when thresholds are crossed.

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Dynamic Metastable Equilibrium

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How may geomorphic processes be related to climate change?

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Young mountains weather and erode quickly. Weathering processes remove carbon from the atmosphere by converting it to soluble carbonates. The carbonates are carried to the oceans, where they are deposited and buried. It is possible that the growth of the Himalayas scrubbed enough carbon out of the atmosphere to cause global climate cooling that culminated the Quarternary ice ages.

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Processes responsible for bringing ingenous and other rocks, gases, and water to the base of the atmosphere and hydrosphere.

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Volcanoes, folding, faulting, uplift

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Once exposed to the surface, these rocks begin to _____ and _____ by the action of _____.

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decompose, disintegrate, weathering

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Elements responsible for transporting weathered products to the oceans.

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wind, water, gravity

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Burial of loose sediments leads to compaction, cementation, and recrystalization to form...

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Sedimentary rocks

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aggregate mixtures of crystalline forms of minerals.

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rocks

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The cheif minerals in the lithosphere...

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feldspars, quartz, clay minerals, iron minerals, ferromagnesian minerals

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The decay of rocks by biological, chemical, and mechanical agents with little or no transport.

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Weathering

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The conjoint action of weathering and erosion, which processes simultaneously wear away the land surface.

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Denudation

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They laying down of sediments by a chemical, physical, or biological means.

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Deposition

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High concentrations of quartz, in association with high ratios of silica to alumina, in river sediments indicate what type of weathering regime?

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intense tropical weathering

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the particulate load of tropical rivers have high amounts of iron and aluminum relative to soluble elements because...

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the particulate load is derived from soils in which the soluble material has been thoroughly leached.

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John D. Milliman (1980) identified several natural factors that appear to control the suspended sediment load of rivers:

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drainage basin relief, drainage basin area, specific discharge, drainage basin geology, climate, presence of lakes

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The climatic factor influences suspended sediment load through...

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mean annual temperature, total rainfall, seasonality of rainfall

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Heavy seasonal rainfall, as in the monsoon climate of southers asia, produces _____ loads of suspended sediment, while in climates of high, year-round rainfall, such as the Congo basin, _____ loads of suspended sediment are produced.

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high, low

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The lowest minimum and possibly the lowest maximum rates of denudation occur in _____ _____ _____, where creep rates are slow, wash is very slow owing to the dense cover of vegetation, and solution is relatively slow because of the low temperatures.

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humid temperate climates

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Landscapes that appear to denude relatively quickly as a result of climate...

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semi-arid, savannah, and tropical landscapes

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The geomorphic or exogenic agents which act outside or above the toposphere:

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wind, water, ice, waves

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The endogenic agents wich act upon the toposphere from inside the planet:

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volcanoes, tectonic forces

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One of the chief mineral types in the lithosphere (aluminum silicates with potassium, sodium, or calcium)

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feldspars

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One of the chief mineral types in the lithosphere (a form of silicon dioxide)

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quartz

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One of the chief mineral types in the lithosphere (complex aluminum silicates)

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clays

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One of the chief mineral types in the lithosphere (example: limonite or hematite)

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iron minerals

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One of the chief mineral types in the lithosphere (complex iron, magnesium and calcium silicates)

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ferromagnesian minerals

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The eight main elements found in the lithosphere:

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oxygen, silicon, aluminum, iron, calcium, sodium, potassium, magnesium

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The ability of rocks to resist the agents of denudation depend upon such factors as:

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1. Particle size
2. Hardness
3. Porosity
4. Permeability
5. Degree to which particles are cemented
6. Mineralogy

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Determines the surface area exposed to chemical attack. Gravels and sands weather much more slowly than silts and clays

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Particle size

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Three factors of rocks that influence the RATE at which weathering decomposes and disintegrates them: A siliceious sandstone is more resistant to weathering than a calcareous sandstone.

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1. Hardness
2. Mineralogy
3. Degree of cementation

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Determines the rate at which water seeps in to a rock body and dictates the internal surface exposed to weathering.

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Permeability

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The strongest ingenous and metamorphic rocks that tend to form the relief features in landscapes:

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quartzite, dolerite, gabbro and basalt, followed by, marble granite and gneiss.

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The greatest suspended sediment yeilds come from:

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mountainous tropical islands, mountainous areas near coasts, and areas draining loess soils (not all of which are determined directly by climate)

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Some of the factors affecting the chemical composition of riverwater:

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1. the amount and nature of rainfall and evaporation
2. drainage basin geology
3. weathering history
4. average temperature
5. relief
6. biota

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Changes in _____, such as the uplift of mountain belts and plateaux, can influence regional climates.

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topography can influence climate by locally increasing precipitation, especially on the windward side of a barrier, and through the cooling effect of raising the ground to a higher elevation.

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Over geologic timescales (milions and tens of millions of years), atmosheric carbon levels depend on inputs of carbon through _____ and carbon withdrawals through _____.

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volcanism, the weathering of silicate rocks by carbonation

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The main processes of mechanical weathering:

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1. unloading
2. frost action
3. thermal stress
4. swelling and shrinking due to wetting and drying
5. pressures exerted by salt-crystal growth

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A significant ingredient in mechanical weathering, which is the repeated generation of stress, by for instance heating and cooling, in a rock. The result is that a rock will fracture at a lower stress level than a rock that is not under the influence of this process.

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fatigue

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When erosion removes surface materials and the pressure on underlying rocks is eased. The lower pressure enables mineral grains to move further apart, creating voids, and the rock expands or dilates. This can cause trecherous explosive rockbursts.

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Unloading

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Water occupying the pores or interstices of a soil or rock body expand upon freezing by about 9%. This expansion builds up stress in the fissures and pores, causing the physical disintegration of rocks.

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Frost action

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Mechanical weathering caused by heating and cooling of a rock that creates rock flakes, shells, and huge sheets.

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Thermal stress

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Materials such as mudstone or shale that contain shrink-swell clays such as smectite or vermiculite, expand considerably upon wetting, causing the disintegration of the rock mass. Also, upon drying, the rock mass shrinks and the form cracks.

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Wetting-drying

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In arid regions, crystals may grow in saline solutions on evaporation. Crystalization within the interstices of rock produces stress by exapansion which may cause the disintegration of the rock.

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Salt-crystal growth

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The six main chemical processes associated with chemical weathering:

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1. solution
2. hydration
3. oxidation and
4.reduction
5. carbonation
6. hydrolysis

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The dissociation of molecules into their anions and cations and each ion becomes completely surrounded by water.

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Solution

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The chief forces acting upon geomorphic materials...

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1. gravitational forces
2. fluid forces
3. water pressure forces
4. expansion forces
5. global fluid movements
6. biological forces

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Under saturated soil conditions, water creates and upward, bouyant force equal to its own weight that displaces and relieves some of the downward force created by the sediment.

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water pressure force

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Under unsaturated conditions, charges in the soil tend to hold water within the pores and even draw it up through capilllary rise. This increased the normal force between sediment grains and increases their resistence to movement.

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negative pore pressure or suction force

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The expansive or contractive forces created by changes in temperature or moisture in geomorphic materials. The force tends to act and dislocate materials in all directions, however materials tend to move downward because of gravitational force.

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exapsion forces

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three forces that resist downslope movement:

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1. friction
2. cohesion
3. sheer strength

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A force that acts against gravity to resist movement and depends on the roughness of the plane separating the soil and the underlying material.

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Friction

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the tendency of particles within the soil body to stick together.

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Cohesion

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Whenever the force acting on a soil or rock body is greater than the _____ _____, the material will fail and move downslope.

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sheer strength

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The six basic types of mass movement:

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1. creep
2. flow
3. slide
4. heave
5. fall
6. subsidence

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The very slow, plastiv deformation of rock or soil. Results from the stress applied by the weight of the soil or rock body and usually occurs at depth, below the weathered mantle.

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Rock creep, Continuous creep,

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Invovles shear through the soil, rock, snow, and ice debris. The rate of flow is slow at the base and increases towards the surface. Most movement occurs as turbulent motion.

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Flow

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Type of slide that occurs along planar shear planes and include debris slides, earth slides, earth block slides, rock slides, and rock block slides.

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Translational slides

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Types of slides that occur alonf concave shear planes, normally during conditions of low to moderate water content, and are commonest on thick, uniform materials such as clays. They include rock slumps, debris slumps, and earth slumps.

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Rotational slides

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Material moves downslope during phases of expansion/contraction or because of the influence of burrowing animals. Classifies as soil creep (finer materials) or talus creep (coarser materials)

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Heave

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The downward movement of soil or rock through the air... occurs especially on steep slopes or cliffs.

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Fall

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Type of subsidence where rock or soil plummets into underground cavities, as in kart terrain, lava tubes, or in mining areas.

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Cavity collapse