Water and Ice Erosion Processes and Impacts

Posted on May 1, 2024 in Geology

Water and Ice Erosion

Grand Canyon Time Lapse

Erosion and Sedimentation

  • Erosion: the weathering and/or transport of solid materials (sediment, soil, rock and other particles)
  • Weathering: breaking down rock into smaller rock or mineral fragments through mechanical or chemical processes (happens in one place)
  • Sedimentation: tendency for particles to settle out of suspension and come to rest

Weathering Zone

  • Rock is always cycling, weathering and eroding
  • Erosion takes place in the weathering zone extending downwards from the earth’s surface to the depth at which air, water and microscopic organisms can reach (1 to hundreds of metres)
The product of weathering is called regolith
  • Can be large or small but all are formed by weathering
  • Once small enough, regolith becomes soil

Water Erosion Concerns

  • Agriculture (detailed in week 4 lab)
    • 1 – 2 billion dollars of nutrient replacement required annually in Canada
  • Construction
    • Disturbed earth particularly vulnerable
    • Erosion and Sediment Control Planning
  • River Erosion and Deposition
    • Mass wasting
    • Habitat loss from sedimentation
  • Coastal Erosion (discussed in detail later in the semester)

Overland Flow to Gullying

  • Once soil is fully saturated OR infiltration capacity exceeded, surface saturates and water flows under the pull of gravity>> downslope
  • Step 1: water pools in depressions (detention storage)
  • Step 2: overtops the microtopographic depressions.
  • Step 3: Gains kinetic energy as it flows downslope – picks up particles
  • Step 4: Increased energy builds and creates defined flow paths
  • Step 5: Paths clear the way for more water = more speed = loss of topsoil = more erosion

The process builds on itself becoming rills>then gullies

4 Step Process of Erosion

  1. SPLASH: displacement of solids through the impact of raindrops.>>the detachment and airborne movement of small soil particles.
    http://www.youtube.com/watch?v=J3ROU-D2yVM
  2. SHEET: detachment of solids through splash and the down-slope movement of the particles by water moving overland
    rate of falling rain is faster than infiltration or soil becomes saturated, runoff takes place>>Surface pores get filled with sand/clay (further decreases infiltration capacity)
  3. RILL: formation of defined channels through the displacement of particles down a hillslope
    Can be smoothed by ordinary farm tillage>>Usually only a few cm deep to 30 cm
  4. GULLY: occurs when water flows in narrow channels; 1 to 2 feet (0.61 m) to as much as 75 to 100 feet (30 m)
    Sufficiently deep that it would not be routinely destroyed by tillage operations

River Erosion Processes

Sediment Transport in Rivers

+ Solution

Energy and River Erosion

UPPER
potential energy
• turbulent flow
•bed load
• vertical erosion

MIDDLE
kinetic energy
• smooth channels
•suspended load
• lateral erosion

LOWER
Base Level

Where is Energy the Greatest?

Erosion and Deposition

  • Erosion increases slope angle (β)
     Western Canada Clays
    Recall for dry, cohesionless soil
     Mass wasting potential

Bank Erosion, Down Cutting and Mass Wasting

Little Smokey River, AB

River Erosion in Bangladesh

Factors Affecting Erosion and Erosion Rates

Rates of Water Erosion

Climatic Factors
Rainfall Intensity and Runoff

Rainfall breaks down aggregates and disperses material. Greater intensity means larger particles can be moved.
Runoff can occur whenever there is excess water on a slope that cannot be absorbed into the soil. The amount of runoff can be increased if infiltration is reduced due to soil compaction, crusting or freezing.

Rates of Water Erosion

Geologic Factors
Soil Erodibility
  • estimate of the ability of soils to resist erosion
  • Most vulnerable soils:
    • low infiltration capacities
    • low organic matter content (affects soil structure)
    • Lack of crust (important in desert environments)
    • Young soils (deposited since last glaciation – loose)
    • Typically silty and fine sand soils most susceptible to erosion

Rates of Water Erosion

Geologic Factors
Length and Slope

The steeper the slope, the greater the amount of soil loss from erosion by water:
-greater accumulation of water
-more speed (greater kinetic energy)

Macropores –
Infiltration
Evapotranspiration
Interception
Root stabilization
(particularly on slopes)
Throughfall

Rates of Water Erosion

Biological Factors
  • Animals affect soil structure and erodibility
  • Certain earthworms can enhance organic matter, soil structure and infiltration capacity and reduce erosion

Natural Erosion vs. Anthropogenic Erosion

  • Natural transport of particles:
    • Stream bed
    • Stream bank scouring
    • Rain events
  • Anthropogenic influence:
    • Removal of vegetation
    • Agricultural practices
    • Stream channel straightening
    • Culverts
    • Hardened surfaces
    • Climate change
    • Water flows/waves
    • Dam operation

Anthropogenic Erosion

Ice Erosion

The Power of Ice

  • Ice Erosion: movement of particles with glacial movement; or fracture of rocks through ice formation in pores and cracks.
  • Water is unusual as it expands as it freezes (about 9%) where most liquids decrease in volume

The Power of Ice

In Glaciers: 3 part role
  1. Act as a plow – scrapes up weathered rocks and soil and plucks out boulders from bedrock
  2. Acts as a file – the load of sediment rasps away and polishes rock
  3. As a sled – caries away the sediment it has picked up from plowing and filing
  4. meltwater also capable of transporting large quantities of material

The Power of Ice

Active glacier processes:
  • Plucking: melt water from a glacier freezes around lumps of cracked and broken rock. When the ice moves downhill, rock is plucked from the back wall.
  • Abrasion is when rock frozen to the base and the back of the glacier scrapes the bed rock.

The Power of Ice

Other processes: Freezing and thawing:
  • Frost wedging: fluctuating temperatures allow for a freeze-thaw cycle in a rock joint which acts as a lever prying the rock apart

Glaciated Landscapes

Glacial Meltwater

  • Meltwater beneath a glacier is pressurized from confining ice – greater erosive power

Impacts of water erosion

  • Obvious impacts include:
    • Onsite: eg bank collapse, loss of soil quality
    • Offsite: eg dam siltation downstream, contaminated drink water
  • Other examples?