Dig This! Erosion Investigation Background Information Created by Melissa Breuer Wilmington School District

Related Topics: soil, plants, air/water, agriculture, quality, weather, water cycle, ecology, engineering, forests/ forestry.

Ohio Academic Standards Alignment: Click here to view content standards alignment to Science for Ohio by grade level.

Background Information:

"Erosion and sedimentation are complimentary geological processes."

• Erosion Terminology.
  • Erosion is the wearing away of rock materials and removal from one area of the Earth’s surface. Erosion tends to occur in two forms:
    • Earth processes which move material on the Earth’s surface over long periods of time, such as weathering and gravity
    • Human activity which moves material on the Earth's surface over short periods of time, such as residential and commercial development, farming, etc., that results in the alteration of the landscape and surrounding animal communities
  • Sedimentation is the act or process of depositing sediments which have usually been transported for some time and distance. Sedimentation is caused when something carrying the sediment has to deposit it in an area and the sediment begins to accumulate. Examples include when gravity causes sediments to move down the slope of a mountain or hill and they are deposited at the base of the slope; when sediments carried by wind or water are released because these currents are slowed and lack the force to continue moving them; when glaciers melt and the carried sediments are deposited in one area; or when materials that have dissolved in water are left behind as the water is evaporated.
  • Soil is the thin and loosely packed layer of earth materials composed of decaying organic matter and weathered minerals which provides nutrients, physical support, and adequate amounts of air and water for plant growth.
  • Rills are cuts made in the soil due to the action of flowing water as it picks up sediments in the soil. Over time, rills may grow to become gullies, creekbeds, rivers, the Grand Canyon, etc.
  • Forces which drive erosion include:
    • physical forces (also known as mechanical forces) such as wind, flowing water, flooding, gravity, temperature shifts (expansion and contraction), evaporation due to the sun, and glacial ice melts
    • chemical forces such as acid rain acting upon exposed rock and forest fires which remove plants anchoring the soil
    • biological forces such as beavers who dam rivers and flood land areas and people whose human practices expose soil
    • biochemical forces such as acids deposited by plant roots or fallen leaves or by animal waste such as urine. Both can lower the pH of the soil making it difficult for protective plant growth to occur.
• What are the types of erosion?
  • Subaerial erosion describes erosion that occurs when land is exposed to the atmosphere. Chemical or mechanical processes alter exposed rock (weathering) which is then transported in a variety of ways. The leading causes of subaerial erosion include gravity, running water, ice (often in the form of glaciation), wind, and nearshore ocean waves.
  • Gravity erosion (also known as mass wasting) occurs where slopes and other irregularities in land surface allow gravity to weather away and transport rock debris downward. Crystal movements, also known as diastrophism, commonly cause slope formation, along with valley cutting by streams. This process of downhill creep of rock debris may be accelerated by the effects of running water but generally is so gradual that it is imperceptible.
  • Running water (fluvial) erosion is when the force of moving water dislodges rocks and other solid particles which are carried along by the water. These particles scrape and scour the soil, loosening it and carrying it away. This scouring caused by the bouncing and rolling of solid particles is called saltation.
  • Ice or Glacial erosion occurs when glacial ice freezes to rock particles and the rocks are then pulled loose and become stuck to the glacier. The rocks are then carried along, scraping and eroding the Earth’s surface as the glacier moves.
  • Wind (Eolian) erosion is most destructive in areas where there is little to no ground cover and small rocks, sand, and silt are blown across the land. Deflation is the process by which rocks are picked up and moved by wind.
  • Wave erosion is caused by the recurring crash of waves along coasts and beaches. The impact of the waves and the sediment that is carried in erode the shoreline.
  • Subaqueous erosion is when currents move along the bottom of bodies of standing water and the currents move solid fragments of rock/soil which, in turn, scrape the soil layer and cause soil loss in the area.

Note: Grolier’s 1998 Interactive CD Encyclopedia was used to gather the above information.

• What is the effect of erosion on the environment? Thirteen negative effects are listed below.
  • Sedimentation in rivers
    • pollutes water with soil particles
    • damages water ecosystems through reduced sunlight for aquatic plants and animals
    • increases water treatment costs for human water consumption
    • reduces the depth of rivers, thus creating waterways that can't be navigated by commercial crafts
  • Removal of topsoil from land areas
    • prevents plant growth
    • alters ecosystems, thus reducing the biodiversity of life
    • destroys crops
    • reduces agricultural food production
    • reduces farming income
• Wind erosion
  • increases the amount of particles in the air
  • reduces visibility
  • reduces air quality
  • causes breathing problems (asthma, etc.)

Misconception(s). Misconception: Students tend to think of natural geologic erosion as being as large-scale and fast-paced as the types of erosion which occur due to human activity. Fact: Natural geologic erosion is a very slow, small-scale form of erosion.

Cautions: Wear old clothing when investigating and working outside, wash hands following investigation, teach proper handling and storage of tools, and watch for poison ivy.

Expected Results: Students will propose plans to correct erosion problems on their school grounds that may lead to implementation. Students will learn about the different types of erosion and further develop their observation skills and group teamwork.