Lecture 3 Soils and Mass Wasting

8/12/2019 Lecture 3 Soils and Mass Wasting

1/34

Impact of Weathering

Changes the colour of rocks/minerals (discoloration)

Breaks rocks into smaller sizes (increases surface areaof rocks)

Mobilization of mineral ores into commercialquantities for exploitation

Soil formation


2/34


3/34

Typical soil composition

(weathered )

Typical Soil Composition

Soil Composition


4/34

Soil Profile/Horizon

Horizon - layers of soil,approximately parallel tothe soil surface, differing in

physical, chemical,and biological properties from

adjacent layersabove or below it

Profile - A vertical sectionof soil through all itshorizons, extending into

parent material


5/34

Possible soil type showing iron oxide enriched B horizon

Soil Profile/Horizon


6/34

Five factors control the type of soil formed and its

formation rate:

SOIL = f (cl, o, r, p, t) Hans Jenny (American soilscientist, 1941) cl = climateo = organismsr = topography

p = parent materialt = time

Factors of Soil Formation


7/34

1. Climate Determines nature/type and intensity/degree of weathering Temperature and precipitation affect rates of all processes Influences natural vegetation (i.e. trees or grasslands)



8/34


9/34

2. Living Organisms

Plant and animal activity (especially microscopic)

organic matter accumulation, biochemical weathering, profile

mixing, nutrient cycling and aggregate stability

Human activities:

Removing trees + cultivating; burning

Irrigating a soil in an arid area, adding fertilizer and lime

Engineered soils in golf greens



10/34

Relief/Topography

nature of the terrain

-Soil loss by erosion (soil depth)

-Less rainfall enters soil

-Less vegetation cover

- Flat land drains slower - waterlog



11/34

Relief/Topography


12/34


4. Parent MaterialComposition and properties of rock being weathered


13/34

Factors of Soil Formation 5. Time

Length of time materials subjected to weathering

Compare adjacent glaciated and unglaciated areas

Influence of parent material more apparent in soils of glaciated regions (relatively young soils

Soils on alluvial/ lacustrine material (young)


14/34


15/34

Mature soil - agriculturally productive

In humid-temperate climate it may take a 100 to tens of thousandsof years to form a mature soil

Factors of Soil Formation5. Time


16/34

Goal of the Topic

define mass wasting

state the types of mass wasting account for factors affecting mass wasting

Mass Movement/Mass Wasting


17/34


18/34

The down slope movement of rock and regolith nearthe Earth's surface mainly due to the force of gravity.

Rates of movements sometimes may be catastrophicallyviolent like the landslide that plunges down a mountainto its base or slow and imperceptible like the creep.

Mass Movement/Mass Wasting


19/34

Factors that Influence the Rate of Mass Movement

1. Climate Factors - Moisture in the form of rainfall in the

tropics or snow melt in the temperate regions increases theweight of the debris. The moisture also acts as a lubricant

2. Nature of bed rock (Lithology) Poorly consolidated,

lubricated and bulky debris are more prone to massmovement down a slope as compared to well compactedsediments which are well bonded by surface tension.

3. Vegetation Sparsely vegetated slopes stimulate masswasting of loose sediments or rock debris than heavilyvegetated topographies. The later thus minimizes soilmovements down slopes. binds rock debris/serves as a

protective cover


20/34

Factors that Influence the Rate of Mass Movement

4. Tectonic Activities (earthquakes) Crustal disturbancessuch as earthquakes, tremors and volcanic eruptions triggerand could accelerate mass movements such as landslides,rock fall

5. Biotic Factors Activities of man and animals such asquarrying, surface mining, road construction, farming,animal grazing etc initiate the movement of loose materials

or the break-away of sediments of scarp slopes.

6. Gravity


21/34

Classification/Types of Mass Wasting

Nature of the movement

1. FLOWSDebris FlowsEarth Flows Mud flows

2. FALLSRock FallsRock topples

3. HEAVES/ CREEP Soil creep Rock creep Talus creep

4. SLIDESSlump

Spread


22/34

Examples of flows: Snout of debris flow deposit


23/34

Spatially continuous movement in which the distribution ofvelocities is that of a viscous fluid.

Flows

Geomorphology of debris flows Intermediate between water flow and sediment flow. Rapid movements of granular solids, water and air.

Vary in flow characteristics depending rheology of flowmaterials (clay content, water content, sediment size).

Occur in a variety of climatic and physiographic zones: i)

mountainous terrain; ii) steep slopes in unconsolidatedmaterials or weak bedrock; iii) deserts and even on steepslopes in the valleys cut through the Prairies.

Have velocities from 1 -10 m/s.


24/34

Debris flows typically

have a point source Originate when poorly consolidated rock or soil masses are mobilized by

the addition of water by:Periods of extendedrainfall Localized areas of

intense rainfallPonding on surfaceupstream of flowSnowmelt or rain on

snow

Debris flows


25/34

Earthflow

Typically high viscosity flows formed from weathered volcanicrock

Large slow moving flows

Several km in length and composed of several million m3 ofmaterial. Form in weathered volcanic rock that form clay materials

Often have a defined slide plane and shear surfaces

Movement and rotation of blocks mean there is mixing Many flows occur over several thousands of years

Have velocities up to 1 m/s.

Earthflow


26/34

Confluence of Muskwaand Chisca rivers,northern British Columbia.

Toe of Drynoch Earthflow alongThompson River


27/34

FallsFalls begin with the detachmentof rock from a steep slope alonga surface on which little or noshear displacement takes

place. The material then fallsor rolls through the air.

Topple is a forward rotation, out

of the slope, of a mass of soil orrock about a point or axis belowthe center of gravity of thedisplaced mass.


28/34

Periodic expansion and contraction of a soil or sediment massthat is usually linked to clay swelling and dewatering or freezing

and thawing.

Heave leads to downslope creep of hillslope materials as thestrength of the materials is decreased.

Heaves/Creep


29/34

Heaves/Creep


30/34

Slide - downslope movement of

soil or a rock mass occurringdominantly along a surface ofrupture or relatively thin zonesof intense shear

Slides A) Pure slide

B) Rotational slide slump involves movementalong a curved surface, withthe upper part movingdownward and the lower partoutwards


31/34

Examples of slides: shallow-seated landslide, BrionesRegional Park, CA


32/34

Examples of slides: shallow-seated rotational landslide, MarinHeadlands, CA

Examples of slides: deep seated landslide Keetmanshoop


33/34

Examples of slides: deep-seated landslide, Keetmanshoop,Southern Namibia


34/34

Examples of slides: Deep-seatedrotational landslide

La Conchita slump.March 4, 1995 Santa Barbara,California.

Examples of slides: Deep-seated

Examples of slides: Deep-seatedrotational landslide, Churchill

Ri L b d

Lecture 3 Soils and Mass Wasting

Documents

Transcript of Lecture 3 Soils and Mass Wasting