1. Chapter 15
Soils & Mining

2. SOIL: A RENEWABLE RESOURCE
Soil – formed from mechanical (frost wedging) & chemical weathering (acid rain, oxidation)
Mature soils - arranged in a series of horizontal layers called soil horizons.

3. SOIL: A RENEWABLE RESOURCE
Figure 3-23

4. Layers in Mature Soils O – leaf litter (leaves, twigs, wastes, fungi)
A – topsoil – humus & inorganic minerals – dark, loose, roots of plants
Some have E layer – eluvation (leached mineral layer)
B – subsoil
C – parent bedrock – unweathered
It takes 200 – 1000 years to get 1” of topsoil.

5. Soil Profiles of the Principal Terrestrial Soil Types
Figure 3-24

6. Some Soil Properties Infiltration – water moves through pores in soil
Leaching – dissolved substances move to lower layers of soil
Figure 3-25

7. More Soil Properties
Porosity – measure of the volume of pores & distance between spaces – finer = high water retention, coarser = higher air flow
Permeability – rate at which water & air move through soil
Structure – ways in which particles are clumped together
pH – affects uptake of nutrients by plants (too acidic – add lime/too basic – add S)

8. Wearing Down and Building Up the Earth’s Surface
Weathering - external process that wears the earth’s surface down.
Figure 15-6

9. GEOLOGIC PROCESSES
A very slow chemical cycle recycles three types of rock found in the earth’s crust:
Sedimentary rock – buried sediment under pressure (sandstone, limestone, shale, coal).
Metamorphic rock – pre-existing rock subject to high temps, pressure (slate, marble, quartzite, gneiss, schist, anthracite).
Igneous rock – from cooled magma (granite, pumice, basalt, obsidian, gabbro)

10. Rock Cycle
Figure 15-8

11. Erosion Sheet erosion – water moves in wide flow, peels off sheets
Rill erosion – cuts channels in the soil
Gully erosion – rivulets join – cut wider & deeper until it forms ditches/gullies

12. Soil Degradation
Desertification – productive potential falls by 10% or more – overgrazing, mining, irrigation, compaction
Salinization – irrigation water leaves behind salts
Waterlogging – applying lots of water to move salts down – makes water table move up

13. Soil Conservation
No-till agriculture – cut slits into the soil for seeds – leave last year’s old growth
Terracing – levels across steep slopes
Contour farming – perpendicular to the angle of the slope – prevents gullies

14. Soil Conservation
Strip cropping – plant corn with legumes – alternate rows
Alley cropping – intercropping – crops with trees/shrubs for fruit/fuel
Windbreaks – surround field with trees

15. Soil Restoration
Organic fertilizer - animal manure or green manure (plow clover under)
Compost
Crop Rotation

16. ENVIRONMENTAL EFFECTS OF USING MINERAL RESOURCES
The extraction, processing, and use of mineral resources has a large environmental impact.
Figure 15-9

17. 4 Categories of Mineral Resources
Identified: known location, quantity, and quality or existence known based on direct evidence and measurements.
Undiscovered: potential supplies that are assumed to exist.
Reserves: identified resources that can be extracted profitably.
Other: undiscovered or identified resources not classified as reserves

18. General Classification of Nonrenewable Mineral Resources
Examples are fossil fuels (coal, oil), metallic minerals (copper, iron), and nonmetallic minerals (sand, gravel).
Figure 15-7

19. MINING Surface mining: shallow deposits are removed.
Subsurface mining: deep deposits are removed.
Overburden – soil & rock on top
Spoil – discarded overburden – no topsoil, little plant growth
Tailings – waste separated from ore
Gangue - piles of tailings

20. Open-pit Mining
Machines dig holes and remove ores, sand, gravel, and stone.
Toxic groundwater can accumulate at the bottom.
Figure 15-11

21. Area Strip Mining
Earth movers strip away overburden, and giant shovels removes mineral deposit.
Often leaves highly erodible hills of rubble called spoil banks.
Figure 15-12

22. Contour Strip Mining Used on hilly or mountainous terrain.
Unless the land is restored, a wall of dirt is left in front of a highly erodible bank called a highwall.
Figure 15-13

23. Mountaintop Removal
Machinery removes the tops of mountains to expose coal.
The resulting waste rock and dirt are dumped into the streams and valleys below.
Figure 15-14

24. Dredging
Scrape underwater deposits

25. Heap-Leach Extraction
Spray a pile of ore with cyanide – dissolves gold – removed by electrolysis

26. Subsurface Mining
Room & Pillar – gouge & load – coal supports roof

27. Subsurface Mining
Longwall – steel props support roof – move down the line & the previous roof collapses

28. Mineral Laws
Surface Mining & Control Act of 1977 – Mining companies must restore land to previous conditions
1872 Mining Law – can stake claim on any public lands – buy land for $ $5/acre - take any minerals for free – don’t have to actually mine – take $4 billion in minerals each year
Coal, oil, gas – pay 12.5% royalties for public land use

29. Getting More Minerals from the Ocean
Hydrothermal deposits form when mineral-rich superheated water shoots out of vents in solidified magma on the ocean floor.
Figure 15-17

30. Environmental Effects of Mining/Processing Mineral Resources
Fires (coal mines)
Chokes streams with placer mining
Toxic chemicals (Acid-mine drainage)
Tailings – left after separating ore from gangue
Smelting – separates metal from other elements in the other
Subsidence
Air pollution/land pollution