Causes and Impacts of Soil Erosion » Water and Wind Erosion

What you'll learn this session

Study time: 30 minutes

The main causes of soil erosion by water and wind
How water erosion processes work (splash, sheet, rill, gully)
How wind erosion processes work (deflation, abrasion, transportation)
Environmental impacts of soil erosion
Social and economic impacts of soil erosion
Case studies of erosion events and their consequences

Introduction to Soil Erosion

Soil erosion is a natural process where the top layer of soil is worn away by physical forces like water and wind. While erosion happens naturally, human activities have greatly sped up this process, causing serious environmental problems worldwide. This guide explores how water and wind cause soil erosion and the impacts this has on our environment and society.

Key Definitions:

Soil erosion: The removal of topsoil by the physical forces of water and wind, or through farming and land-clearing activities.
Topsoil: The upper, outermost layer of soil, usually the top 5-20 cm, which is the most fertile part containing organic matter and nutrients.
Sediment: Particles of soil and rock that have been eroded and transported to a new location.

⊕ Natural Causes of Erosion

Erosion occurs naturally due to:

Rainfall and runoff
Wind movement across exposed soil
Freeze-thaw cycles that break up soil
Gravity pulling soil down slopes
Natural disasters like floods

⊕ Human-Accelerated Erosion

Human activities that speed up erosion include:

Deforestation and vegetation removal
Poor farming practices (overgrazing, over-tilling)
Construction and urbanisation
Mining and quarrying
Altering natural water flows

Water Erosion Processes

Water is the most significant cause of soil erosion worldwide. When rain hits bare soil and flows across the land, it can remove huge amounts of topsoil through several distinct processes.

→ Splash Erosion

This is the first stage of water erosion:

Raindrops hit bare soil with surprising force
Each raindrop works like a tiny bomb, throwing soil particles up to 1 metre away
On flat ground, particles land randomly
On slopes, more soil moves downhill than uphill
A heavy rainstorm can splash away tonnes of soil per hectare

→ Sheet Erosion

When water flows as a thin layer across the soil:

Occurs when rainfall exceeds the soil's absorption rate
Water moves as a sheet, carrying soil particles
Removes soil evenly across an area
Often goes unnoticed until much soil has been lost
Can remove the most fertile topsoil layer

→ Rill Erosion

When sheet flow begins to concentrate:

Small, finger-sized channels form in the soil
Water concentrates and gains more erosive power
Rills are usually 5-30 cm deep
Can be removed by normal tillage
Often the first visible sign of serious erosion

→ Gully Erosion

The most severe form of water erosion:

Deep channels that cannot be removed by normal farming
Usually more than 30 cm deep
Can grow rapidly during heavy rains
Makes land unusable for farming
Can swallow equipment and threaten buildings

Wind Erosion Processes

Wind erosion is particularly problematic in dry areas or during droughts when soil is loose and vegetation cover is minimal. Wind can move enormous amounts of soil over great distances through several processes.

↻ Deflation

The direct lifting of soil particles by wind. Lighter particles like clay and organic matter are removed first, leaving behind coarser, less fertile soil. This can create depressions in the landscape called deflation hollows.

↻ Abrasion

When wind-blown particles hit other soil or objects, they act like sandpaper, breaking more particles loose. This process can damage plants, erode rocks and even damage buildings and infrastructure over time.

↻ Transportation

Wind moves soil in three ways: suspension (fine dust carried high and far), saltation (bouncing particles) and surface creep (larger particles rolling along the ground). During dust storms, millions of tonnes of soil can be transported.

Environmental Impacts of Soil Erosion

Soil erosion causes a range of serious environmental problems that affect ecosystems and biodiversity.

Loss of Soil Fertility

When topsoil erodes, it takes with it:

Organic matter that feeds soil organisms
Essential plant nutrients (nitrogen, phosphorus, potassium)
Beneficial microorganisms that support plant growth
Water-holding capacity, making remaining soil more drought-prone
Soil structure that allows root growth and water infiltration

Water Pollution and Sedimentation

Eroded soil that reaches water bodies causes:

Increased turbidity (cloudiness) that blocks sunlight for aquatic plants
Sedimentation that fills in streams, lakes and reservoirs
Smothering of fish spawning grounds and aquatic habitats
Transport of agricultural chemicals into water systems
Algal blooms from excess nutrients, leading to oxygen depletion

Habitat Destruction

Erosion damages natural habitats by:

Destroying plant communities that wildlife depends on
Silting up wetlands and aquatic ecosystems
Creating unstable landscapes prone to landslides
Reducing biodiversity as specialist species lose habitat
Disrupting food chains and ecosystem services

Social and Economic Impacts

Beyond environmental damage, soil erosion has profound effects on human societies and economies.

£ Economic Costs

Soil erosion leads to:

Reduced crop yields and farm income
Increased need for fertilisers to replace lost nutrients
Damage to infrastructure like roads and bridges
Costs of dredging sediment from waterways
Water treatment expenses to remove sediment
Decreased property values in affected areas

♥ Social Impacts

Communities face challenges including:

Food insecurity when agricultural land degrades
Displacement of people from severely eroded areas
Conflicts over remaining productive land
Health issues from dust and water contamination
Loss of cultural connections to land
Increased poverty in rural communities

Case Study Focus: The Dust Bowl (1930s)

The American Dust Bowl of the 1930s shows the catastrophic potential of wind erosion. After years of intensive farming that removed native grasses, a severe drought hit the Great Plains. Without plant cover, winds whipped up massive dust storms that:

Carried away an estimated 850 million tonnes of topsoil
Created "black blizzards" that turned day into night
Caused respiratory diseases and deaths from "dust pneumonia"
Forced over 500,000 Americans to leave their homes
Destroyed 100 million acres of farmland

This disaster led to major changes in soil conservation practices and showed how quickly erosion can devastate both environments and human communities.

Case Study Focus: Loess Plateau, China

The Loess Plateau in China demonstrates both severe erosion and successful restoration. Covering 640,000 km², this region has some of the most erodible soil on Earth:

Centuries of farming, grazing and deforestation left hillsides bare
The Yellow River earned its name from carrying over 1.6 billion tonnes of sediment annually
Erosion rates reached 5,000-10,000 tonnes per km² per year
Poverty was widespread as land productivity declined

Since the 1990s, massive restoration efforts have included terracing, tree planting and grazing bans. These measures have reduced erosion by 60-80% in treated areas, increased crop yields and lifted millions out of poverty showing that even severe erosion can be reversed with proper management.

Recognising Erosion Warning Signs

Learning to spot the early signs of erosion can help prevent major damage. Watch for:

Exposed plant roots as soil washes away
Small channels forming after rain
Muddy runoff during rainstorms
Dust clouds during dry, windy weather
Sediment collecting at the bottom of slopes
Changes in soil colour as darker topsoil is removed
Stones and rocks becoming more visible at the surface

Understanding how water and wind cause soil erosion is the first step in preventing it. In the next section, we'll explore the methods used to control erosion and protect this vital natural resource.

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