Shaping Earth's Surface by Water and Wind

Water and Wind Shaping the Earth's Surface

Erosion and Deposition

  • Erosion: Transporting sediment (weathered rock and soil particles) to new locations.
  • Agents of erosion: water (including ice and glaciers), wind.
  • Water is a more powerful agent of erosion than wind.
  • Deposition: Sediment is placed in a new location.
  • Erosion and deposition shape the Earth's surface, creating various features like sand dunes.

Surface Water Erosion

  • Surface water: Water moving across the Earth's surface (e.g., rain, rivers).
  • Runoff: Water flowing over the surface instead of soaking in.
  • Common cause: Rainfall.
  • Variables affecting runoff:
    • Rainfall amount.
    • Vegetation.
    • Soil type.
    • Land shape.
    • Land use.
  • Plants reduce runoff and erosion.
  • Hard soil leads to more runoff; sandy soil absorbs more water.
  • Steep slopes generate more runoff.
  • Paved surfaces increase runoff.

Land Features from Runoff and Erosion

  • Rills: Small grooves in soil created by runoff.
  • Gullies: Larger channels formed as rills grow and connect.
  • Streams: Channels formed when gullies connect, filling with water.
  • Tributaries: Streams connecting to form rivers.

River Erosion

  • Rivers cause faster erosion than runoff.
  • Waterfalls: Develop when rivers erode less resistant rock, creating height differences.
  • Meanders: Bends or curves in a river caused by erosion on outer curves and deposition on inner curves.
  • Oxbow Lakes: U-shaped bodies of water cut off from a river due to the growth of meanders.

River Deposition

  • Alluvial Fan: Wide, sloping, fan-shaped deposits formed by rivers decreasing in velocity.
  • Delta: Deposits created by flows into lakes or oceans.
  • Floodplain: Flat area on either side of a river formed by flooding deposits.

Groundwater Erosion

  • Groundwater: Water found underground, filling spaces around soil particles and fractured rocks.
  • Saturated Zone: Area where water fills the ground.
  • Water Table: Top of the saturated zone.
  • Groundwater causes chemical weathering through acidic water interacting with minerals.
  • Carbonic acid (from rainwater absorbing carbon dioxide) dissolves rock, creating caves and sinkholes.

Cave Features

  • Caves formed by chemical weathering over long periods.
  • Stalactites: Icicle-shaped formations hanging from cave ceilings, formed by dripping groundwater depositing minerals.
  • Stalagmites: Upward-growing mounds of mineral deposits on cave floors, formed by evaporating water deposits.
  • Karst Topography: Includes caves, sinkholes, and underground rivers, characterized by barren rocky ground.
  • Sinkholes: Depressions formed when cave tops collapse, common in karst topography.

Preventing Groundwater Erosion

  • Planting trees/shrubs to bind soil particles.
  • Protecting steep slopes with trenches and vegetation.
  • Avoiding soil compaction.
  • Improving drainage with ditches or drains.

Glaciers

  • Glaciers: Huge, long-lasting masses of ice that move slowly.
  • Form in high latitudes/altitudes from accumulated snowfall.
  • Cause erosion through:
    • Plucking: Picking up larger rocks and sediment.
    • Abrasion: Scraping underlying rock.
  • Till: Sediment deposited by melting glaciers.
  • Moraines: Thick layers of sediment left behind by retreating glaciers.
  • Kettle Lakes: Small ponds formed when ice chunks left in till melt.

Waves

  • Waves: Mainly a product of wind energy.
  • Wave Crest: Highest point of a wave.
  • Shape coasts through erosion by:
    • Impact: Breaking down rocks with force.
    • Abrasion: Wearing down rocks with sediment.
    • Changing Direction: Headlands cause erosion of the shore.
  • Wave-cut Cliffs: Steep rock faces caused by waves crashing against rocky shores.
  • Sea Arches: Arcs created by wave erosion.
  • Sea Stacks: Vertical columns of rock near the coast.

Wave Deposition

  • Beaches: Areas along the coast made of deposited sand and gravel.
  • Spits: Ridges of sand connected to land extending into the water.
  • Barrier Islands: Islands formed over time as waves deposit sediment.
  • Sandbars: Submerged ridges of sand formed by waves offshore.

Preventing Wave Erosion

  • Building homes farther inland.
  • Constructing breakwaters.
  • Addressing global warming by limiting fossil fuel use.

Wind Erosion

  • Wind erodes land by removing soil and sediment (deflation) and wearing away solid objects (abrasion).
  • Deflation: Wind moves loose sediment, lowering the ground surface.
  • Abrasion: Wind wears away solid objects with sediment impact (sandblasting).

Wind Deposition

  • Sand Dunes: Ridges/hills formed when wind deposits sand against obstructions.
  • Loess: Loosely packed, fine soil rich in minerals.

Preventing Wind Erosion

  • Installing windbreaks (walls, trees, shrubs).
  • Alternating strips of row crops and soil-conserving crops.
  • Using mulch to cover exposed soil.