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
8/12/2019 Lecture 3 Soils and Mass Wasting
2/34
8/12/2019 Lecture 3 Soils and Mass Wasting
3/34
Typical soil composition
(weathered )
Typical Soil Composition
Soil Composition
8/12/2019 Lecture 3 Soils and Mass Wasting
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
8/12/2019 Lecture 3 Soils and Mass Wasting
5/34
Possible soil type showing iron oxide enriched B horizon
Soil Profile/Horizon
8/12/2019 Lecture 3 Soils and Mass Wasting
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
8/12/2019 Lecture 3 Soils and Mass Wasting
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)
Factors of Soil Formation
8/12/2019 Lecture 3 Soils and Mass Wasting
8/34
8/12/2019 Lecture 3 Soils and Mass Wasting
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
Factors of Soil Formation
8/12/2019 Lecture 3 Soils and Mass Wasting
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
Factors of Soil Formation
8/12/2019 Lecture 3 Soils and Mass Wasting
11/34
Relief/Topography
8/12/2019 Lecture 3 Soils and Mass Wasting
12/34
Factors of Soil Formation
4. Parent MaterialComposition and properties of rock being weathered
8/12/2019 Lecture 3 Soils and Mass Wasting
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)
8/12/2019 Lecture 3 Soils and Mass Wasting
14/34
8/12/2019 Lecture 3 Soils and Mass Wasting
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
8/12/2019 Lecture 3 Soils and Mass Wasting
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
8/12/2019 Lecture 3 Soils and Mass Wasting
17/34
8/12/2019 Lecture 3 Soils and Mass Wasting
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
8/12/2019 Lecture 3 Soils and 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
8/12/2019 Lecture 3 Soils and Mass Wasting
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
8/12/2019 Lecture 3 Soils and Mass Wasting
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
8/12/2019 Lecture 3 Soils and Mass Wasting
22/34
Examples of flows: Snout of debris flow deposit
8/12/2019 Lecture 3 Soils and Mass Wasting
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.
8/12/2019 Lecture 3 Soils and Mass Wasting
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
8/12/2019 Lecture 3 Soils and Mass Wasting
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
8/12/2019 Lecture 3 Soils and Mass Wasting
26/34
Confluence of Muskwaand Chisca rivers,northern British Columbia.
Toe of Drynoch Earthflow alongThompson River
8/12/2019 Lecture 3 Soils and Mass Wasting
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.
8/12/2019 Lecture 3 Soils and Mass Wasting
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
8/12/2019 Lecture 3 Soils and Mass Wasting
29/34
Heaves/Creep
8/12/2019 Lecture 3 Soils and Mass Wasting
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
8/12/2019 Lecture 3 Soils and Mass Wasting
31/34
Examples of slides: shallow-seated landslide, BrionesRegional Park, CA
8/12/2019 Lecture 3 Soils and Mass Wasting
32/34
Examples of slides: shallow-seated rotational landslide, MarinHeadlands, CA
Examples of slides: deep seated landslide Keetmanshoop
8/12/2019 Lecture 3 Soils and Mass Wasting
33/34
Examples of slides: deep-seated landslide, Keetmanshoop,Southern Namibia
8/12/2019 Lecture 3 Soils and Mass Wasting
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
Top Related