Transcript Soil

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