AP Syllabus focus:
‘Surface mining removes overburden to reach ore; strip mining removes vegetation and can make land more susceptible to erosion.’
Surface mining is widely used because it is efficient and relatively inexpensive, but disturbing land surfaces can rapidly change drainage, soils, and habitat structure.
This satellite image shows an active surface mine landscape with large excavated pits, haul roads, and adjacent disturbed/reclaimed areas. The sharp contrasts in color and texture illustrate how removing overburden and moving spoil reshapes topography and surface hydrology at a watershed scale. Source
Understanding strip mining helps explain why erosion and sediment pollution often follow extraction.
What “Surface Mining” Means
Surface mining extracts ore close to Earth’s surface by removing the material above it, rather than digging deep underground.
Overburden: the soil, rock, and vegetation that lie above a mineral deposit and must be removed to access the ore.
Removing overburden exposes loose material and bare ground, setting up conditions for runoff and erosion when rain or wind acts on the site.
Core Steps (General)
Site preparation: access roads, clearing vegetation, staging equipment
Overburden removal: scraped, blasted, and hauled away
Ore extraction: digging and loading ore for processing
Waste placement: piling displaced material in dumps or backfill areas
Site stabilisation: grading slopes and re-vegetating where required
Strip Mining (A Major Type of Surface Mining)
Strip mining removes vegetation and soil in long strips to reach near-surface deposits (commonly coal or oil sands).
This cross-sectional diagram shows how strip mining advances laterally from an initial box cut into successive strip cuts. It highlights the highwall/low wall geometry and the placement of spoil (overburden) into previously mined areas, helping explain how large volumes of loose material are created and rehandled during extraction. Source
As one strip is mined out, operations often move laterally to the next strip.
Strip mining: a surface mining method that removes vegetation, topsoil, and layers of rock in strips to expose shallow ore seams.
Because large areas are cleared at once, strip mining can leave wide expanses of exposed ground with reduced root structure and weaker soil cohesion.
Why Strip Mining Increases Erosion Risk
The syllabus emphasis is that strip mining removes vegetation and can make land more susceptible to erosion. Mechanisms include:
Loss of plant cover: fewer leaves and stems to intercept rainfall, and fewer roots to hold soil
Compaction from heavy machinery: reduced infiltration, more surface runoff
Steep, artificial slopes: faster-moving water increases soil detachment
Spoil piles: loosely packed material erodes easily and can slump
Erosion-Related Environmental Impacts
Sedimentation in nearby streams as eroded particles wash off-site
Increased turbidity: less light penetration for aquatic plants and algae
Smothering of benthic habitats: sediment can cover spawning gravels and invertebrate habitat
Channel instability: sediment deposition can alter stream shape and flow paths
Overburden Handling and Land Disturbance
Surface mining’s defining feature—removing overburden to reach ore—creates two major land-management challenges:
Where to place displaced material (temporary dumps vs. backfilling)
How to stabilise disturbed soil and rock to prevent ongoing erosion
Spoil: the broken rock and soil removed during mining and piled or used as backfill; it often erodes more easily than undisturbed ground.
Spoil characteristics (particle size, slope angle, and drainage) strongly influence how much sediment leaves the site during storms.
Reducing Erosion During and After Strip Mining
Erosion control is a practical priority because soil loss can be rapid immediately after vegetation removal.
Limit the disturbed area at one time (phase clearing and extraction)
Separate and store topsoil for later use to support re-vegetation
Install sediment controls: silt fences, sediment basins, and diversion channels
This installation diagram shows how a silt fence is trenched in and keyed into the soil to intercept sheet flow and trap sediment before it reaches streams. It emphasizes that proper anchoring and placement are essential; otherwise, runoff can undercut or bypass the barrier. Source
Regrade slopes: reduce slope steepness and create stable contours
Restore vegetation cover quickly using grasses, shrubs, or native species mixes
What Students Should Be Ready to Explain
How surface mining differs from underground mining in land disturbance (surface removal vs. deep shafts)
The role of overburden removal in exposing erodible material
Why strip mining specifically raises erosion risk through vegetation removal and soil disruption
How erosion from mined land can affect nearby waterways through sedimentation and turbidity
FAQ
Contour strip mining follows hill contours, often concentrating runoff along bench-like cuts.
Area strip mining on flatter land can create broad, exposed fields where sheet erosion dominates.
High-intensity rainfall, fine-textured soils, steep slopes, sparse surrounding vegetation, and short distance to streams all increase risk.
Poorly compacted or poorly graded spoil piles also erode quickly.
If topsoil is stockpiled too long it can lose structure and beneficial microbes.
Mixing topsoil with subsoil or spoil, or compacting it with machinery, can reduce aeration and water-holding capacity.
A highwall is the exposed vertical or steep face left after a strip is excavated.
Instability (rockfalls or slumping) can add sediment, threaten worker safety, and complicate reclamation grading.
Using diversion ditches to keep clean water off disturbed areas and designing stable channels (gentle slopes, lined or armoured where needed) reduces concentrated flow.
Spreading flow with contouring can limit gully initiation.
Practice Questions
State two ways strip mining can increase soil erosion. (2 marks)
Any two valid mechanisms (1 mark each), e.g. removal of vegetation/root structure; soil compaction reducing infiltration; creation of steep exposed slopes; loose spoil piles.
Describe how removing overburden in surface mining can lead to increased sediment in nearby streams, and outline two measures that reduce this impact. (5 marks)
Overburden removal exposes bare soil/rock (1).
Rainfall/runoff increases due to reduced interception/infiltration (1).
Eroded particles are transported into streams (1).
Sediment increases turbidity or deposits on streambeds (1).
Two distinct mitigation measures outlined (max 2 marks): e.g. silt fences/sediment basins; regrading and rapid re-vegetation; diversion channels; storing/replacing topsoil.
