• Finish Weathering
• Processes and products
• Variations in soils
• Soil practice
• Hazards related to weathering
• Erosion rates
• Mass Wasting Highlights

A MATRIX OF PROCESSES

WEATHERING FACTORS

• Relief
• Climate
• Rock Type
• Time

RELIEF
(Elevation Gradients)

• Steeper slopes erode faster with less time for weathering in place
• Mechanical effects dominate in steep slopes
• Chemical effects more important on lower slopes
• Steeper slopes tend to be in mountains where it is typically much cooler

CLIMATE

• Temperature
• Rainfall (amount and distribution through year)
• Frost
• Humidity
• Vegetation cover (type and abundance)

Rock Type

• Basalt tends to weather faster than granite
• Granite tends to weather faster than quartzite
• Limestone tends to weather faster than basalt, granite, or quartzite
• Sedimentary evaporites (salt rock) tends to weather fastest of all.

TIME

• The longer rocks and soil matter are exposed to the atmosphere the greater the amount of weathering and soil development.

The degree of soil development in, for example, glaciated terrain can be used to determine the relative ages of soils and therefore the timing of geologic events.

AGENTS OF WEATHERING

• Water (and its change of state)
• Gravity
• Air (oxygen and carbon dioxide)
• Unweathered Parent Rock
• Igneous
• Metamorphic
• Sedimentary
• Plant and Animal life
• Bacteria, fungi
• Soil organisms
• Tree and grass roots
• Burrowing and rooting organisms
• Worms
• Gophers
• Large Mammals

PRODUCTS OF WEATHERING

• Clay Minerals
• Oxides (principally of iron)
• Dissolved substances (Ca, Na, K...)
• Unweathered parent material freed from the rock (grains)
• Organic matter
• e.g. SOILS and debris for erosion

SOILS

• Products of weathering
• Support plant and animal life
• Plants utilize mineral nutrients for growth
• Phosphate
• Potassium, Calcium etc.
• Silica

Soils differences develop due to:

• Age of soil
• Climate of region
• Type and weatherability of the underlying parent rock
• Steepness of slope
• Human intervention

Soil Vegetation Derives Critical Elements from:

• Air
• Carbon
• Nitrogen in organic poor soils
• Organic and Inorganic soil
• Nitrogen and Phosphorus

SOIL PROFILES (Top to Bottom)

O - Organic matter (ìhumusî)

A - Topsoil (mix of organic matter and mineral matter

B - Translocated mineral matter, weathering products (iron, aluminum oxides, calcite)

C - Partially weathered ìbedrockî (fractured, frost heaved, disaggregated)

BEDROCK (fresh, unweathered material)

Some Major Soil Types

• Pedocals (ìarid soilsî)
• Caliche
• Pedalfers (ìtemperate soilsî)
• Podsols
• Chernozems
• Laterites (ìtropic soilsî)
• Bauxite (aluminum ore)

MANAGEMENT OF SOILS

• Soils important to humans to produce livestock and fruits/vegetables
• Plowing has had immediate returns, but long-term losses
• Soil salinization is critical in the arid regions of the earth (Western U.S....)
• Deforestation may be one of the worst world disasters weíve yet to face.
• ALL are POPULATION dependent!

TROPIC SOILS

TROPIC LATERITES AND CLEAR-CUTTING

• Deeply weathered soils
• Thick zones of iron and aluminum oxides (Bauxites)
• Devoid of Mineral Nutrients
• Nutrients regenerated from soil organic matter (SOM)
• Clear-cutting or Slash and Burn Agriculture
• Removes forest canopy
• Sunlight on soil organic matter
• Oxidizes to carbon dioxide (respiration)
• Subject to erosion under intense rainfall
• Mineral nutrients lacking in thick oxide rich soil
• Fresh rock containing needed nutrients will need centuries to millennia_ to become exposed at surface for potential plant growth.

OTHER SOIL RELATED ENVIRONMENTAL CONCERNS AND HAZARDS

• Deforestation
• Clear Cutting
• Forest fires
• Climate change (linked to deforestation)
• Acidification
• Acid Mine Drainage
• Burning of high sulfur coal and auto exhausts
• Salinization

• Swelling Soils
• Clays
• Salts
• Radon
• Quick Clays

• MAJOR POINTS
• Broad range of features
• Varying rates and Scales
• Basic Causes
• Alleviation

A Range of Processes

• Ice/Water Content
• Rapid to Slow

BASIC CAUSES OF MASS WASTING

• Increased loading
• Weakened Material
• Triggering Mechanism
• Geologically Unfavorable Setting

LOADING

• Water
• Construction
• ANGLE OF REPOSE

WEAKENING OF ROCK AND SOIL

• Weathering
• Loading by water
• Swelling (clays)
• Reduced Friction
• Oversteepening of slope

CONSTRUCTION

Accelerated erosion (glacier, river)

TRIGGERS

• Natural
• Earthquake
• Precipitation
• Fire
• Human Caused
• High Lake Levels (Great Lakes)
• Construction
• Enhanced fire intensity by overmanagement of forests and elimination of natural fire

ALLEVIATION

• Zoning
• Construction techniques

Portugese Bend, CA

• A Developer's Dream
• Your home of the future?

Personal Actions?

• Be aware of potential hazards
• Engage professional assistance
• Check out local codes
• Look for a home when the sun isn't shining

• HYDROLOGIC CYCLE, RIVERS, FLOODS, AND FLOOD FREQUENCY
• RIVERS OF THE ARID WEST: The Colorado River Flood Experiment, Spring 1996

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