Chapter 15 Soils & Mining

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.

SOIL: A RENEWABLE RESOURCE Figure 3-23

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.

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

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

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)

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

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)

Rock Cycle Figure 15-8

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

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

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

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

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

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

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

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

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

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

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

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

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

Dredging Scrape underwater deposits

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

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

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

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 $2.50 - $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

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

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