Transcript No Slide Title

ESC110 Chapter Eleven
Environmental Geology & Earth Resources
Chapter Eleven Readings & Objectives
Required Readings
Cunningham & Cunningham, Chapter Eleven
Environmental Geology and Earth Resources
After finishing this chapter, you should be able to:
• understand some basic geologic principles, including how
plate-tectonic movements affect conditions for life on the
earth;
• explain how the 3 major rock types form and how the rock
cycle works;
• summarize economic mineralogy and strategic minerals;
• discuss the environmental effects of mining and mineral
processing; and,
• recognize the geologic hazards of earthquakes, volcanoes,
floods and erosion.
Chapter Eleven Key Terms
Barrier islands - page 269 of text
Midocean ridges 256
 core 256
 mineral 257
 crust 256
 rock 257
 earthquakes 265
 rock cycle 258
 flood 267
 sedimentary rocks 258
 floodplains 267
 sedimentation 259
 heap-leach extraction 264
 smelting 263
 igneous rocks 258
 landslides 268
 strategic metals and
minerals 261
 magma 256
Tectonic plates 256
 mantle 256
 volcanoes 266
 metamorphic rocks 258
 weathering 259
Chapter Eleven Topics
•
•
•
•
•
•
•
Case Study: Radioactive Waste Disposal
A Dynamic Planet
Minerals and Rocks
Economic Geology and Mineralogy
Environmental Effects of Resource Extraction
Conserving Geologic Resources
Geologic Hazards
Yucca Mountain is an
example of why dynamic
earth processes are
included in waste storage.
• Yucca Mountain is the first
selection by the U.S. for
long-term storage of high
level radioactive waste.
Some of this material will
stay radioactive for
>500,000 years.
PART 1: A DYNAMIC PLANET
•Earth Is a Layered Sphere
–Its core has an interior
composed of dense,
intensely hot metal that
generates a magnetic field
enveloping the earth.
–Its mantle is a hot,
pliable layer surrounding
and less dense than the
core.
–Its crust is a cool,
lightweight, brittle
outermost layer that floats
on top of the mantle.
Tectonic Processes and Shifting Continents
The upper layer of the earth's mantle contains magmatic
convection currents that break the overlaying crust into a
mosaic of tectonic plates.
– These plates slide slowly across earth's surface.
• Ocean basins form where continents crack and pull apart.
• Magma forced up through cracks in oceanic crust form mid-oceanic
ridges.
• Earthquakes are caused by grinding and jerking as plates slide past
each other.
– Mountain ranges are pushed up at the margins of colliding
plates.
• When an oceanic plate collides with a continental landmass, the
continental plate will ride up over the seafloor and the oceanic plate
will subduct down into the mantle.
• Deep ocean trenches mark subduction zones.
Pangea: The Super-continent
•Geologists suggest
that several times in
earth's history most, or
all, of the continents
gathered to form a
single super-continent,
Pangea, surrounded by
a single global ocean.
Tectonic Plates
Tectonic Processes & the Rock Cycle
Communities in
deep-sea ocean
trenches
PART 2: MINERALS & ROCKS
1. Mineral versus rock
2. Rock types & how they are formed
3. Weathering & sedimentation
4. Rock cycle
• A mineral is a naturally occurring, inorganic, solid
element or compound having a definite chemical
composition and a specific internal crystal structure
• A rock is a solid, cohesive, aggregate of one or more
minerals. Each rock has a characteristic mixture of
minerals, grain sizes, and ways in which these grains
are mixed together into a solid mass.
Three Types of Rocks
I. Igneous
II. Sedimentary
III. Metamorphic
• Igneous is the most common rock type in earth's crust.
– It is solidified from magma extruded onto the
surface from volcanic vents.
• Quick cooling of magma produces fine-grained rocks.
– Basalt
• Slow cooling of magma produces coarse-grained rocks.
– Granite
Rock Types (continued)
• Sedimentary rock is derived from deposited materials that
remain in place long enough, or are covered with enough
material for compaction, such that the materials may again
become rock.
– Often formed from crystals that precipitate out of, or
grow from, a solution.
•
•
•
•
Shale
Sandstone
Tuff
Limestone
• Metamorphic rock form when pre-existing rocks are
modified by heat, pressure, and chemical agents.
– Chemical reactions can alter both the composition and
structure of rocks as they are metamorphosed.
• Marble (from limestone)
• Quartzite (from sandstone)
• Slate (from mudstone and shale)
Weathering and Sedimentation
•Mechanical - Physical break-up of rocks into smaller
particles without a change in chemical composition.
•Chemical - Selective removal or alteration of specific
components that leads to weakening and disintegration
of rock.
–Oxidation is combination with oxygen or removal of
electrons from atom, ion or molecule during rx.
–Hydrolysis is splitting of water. Hydrogen of water
combines with anion of mineral and hydroxyl of water
combines with cation of mineral to form acid and
base.
•Sedimentation - Deposition of loosened material
Below is wind-blown
sandstone
Above is watersculpted sandstone
Rock Types & the Rock Cycle
The rock cycle involves creation, destruction, and
metamorphosis. Mechanisms include crushing, folding,
melting and recrystallization by dynamic processes
related to those same ones that shape the earth's crust.
PART 3: ECONOMIC GEOLOGY &
MINERALOGY
• Economic mineralogy is the study of
minerals that are valuable for
manufacturing and trade.
• Public policy in the U.S. has
encouraged mining on public lands as
a way of boosting the economy and
utilizing natural resources.
Most economic minerals are metal ores (ores are
minerals with high concentrations of metals).
• Metals are elements that easily give up an electron
and thus have a positive charge (cations).
– Metals consumed in the greatest quantity by world
industry (metric tons annually) are:
•
•
•
•
•
•
Iron
Aluminum
Manganese
Copper
Chromium
Nickel
(740 million)
(40 million)
(22.4 million)
(8 million)
(8 million)
(0.7 million)
Nonmetal Mineral Resources
• Sand and gravel production for road and building
construction make up the greatest volume and dollar
value of all nonmetal mineral resources. This includes
brick and concrete construction, paving, sandblasting
and glass production.
• Evaporites include halite (rock salt), gypsum, potash
• Sulfur deposits are mined mainly for sulfuric acid
production (industry, car batteries, some medicinal
products).
• Limestone is used to make concrete and building
stone. Pulverized, it is used to neutralize acidic soil.
• Soils
U.S.
• Strategic metals and
minerals are ones that a
country uses but cannot
produce itself
• Wealthy industrial
nations often stockpile
strategic resources,
especially metals.
• Of the 80 industrial
metals and minerals,
between one-third and
one-half are considered
strategic resources.
Global Metal Trade
PART 4: ENVIRONMENTAL EFFECTS OF
RESOURCE EXTRACTION
• Geologic resource extraction involves the physical
processes of mining and the physical or chemical
processes of separating minerals, metals, and other
geologic resources from ores or other materials.
• Ore - a rock in which a valuable or useful metal occurs
at a concentration high enough to make mining it
economically attractive
Mining
• Underground, tunnel mining is very dangerous due to:
• Gas
• Inhaling Particulate Matter
• Tunnel Collapse
•
•
•
•
•
Placer mining
Strip-mining or open-pit mining
Tailings - surface waste deposits
Groundwater contamination
Spoil banks - acid and sediment runoff
Implications of Resource Extraction
• Mining
– Placer Mining - Hydraulically washing out metals deposited
in streambed gravel.
• Destroys streambeds and fills water with suspended solids.
– Strip, Open Pit or Mountain Removal Mining
• Large scars on land surface.
• Tailings
– Toxic runoff
• Surface Mining Control and Reclamation Act (SMCLRA) (1977)
requires better restoration of strip-mined lands, especially if the
mined land is classified as prime farmland.
– Difficult and expensive.
• Often more than $10,000.00 per hectare.
– 50% of US coal is strip mined.
Processing is the extraction of metal from
ores by heating or with chemical solvents
Damage due to air pollutants from smelting
(roasting ore to release metals)
Heap-leach extraction is when large piles of crushed ore are
sprayed with a alkaline cyanide solution that percolates through
the pile to dissolve gold. The effluent is left behind in ponds.
PART 5: CONSERVING GEOLOGIC
RESOURCES
Types of Geologic
Resource Conservation
• Recycling is common for
aluminum, platinum,
gold, silver, copper, lead
• Steel and iron recycling
is easily done at
minimills (photo to left).
Cars also contain
platinum as a catalytic
converter catalyst.
• Substituting new
materials (polymers,
high-tech alloys, glass
cables, etc.)
• Recycling of Aluminum - A Big Success Story
– Aluminum must be extracted from bauxite by
electrolysis. This requires lots of energy!
• Recycling waste aluminum consumes onetwentieth the energy of extraction from raw ore.
– Nearly two-thirds of all aluminum beverage cans in
US are recycled.
– It makes environmental and economic sense to
recycle aluminum. Everyone agrees!
PART 6: GEOLOGIC HAZARDS
•Earthquakes
•Volcanoes
•Floods
•Landslides
•Erosion
Earthquakes
• Creep is gradual movement.
– When friction prevents creep, stress
builds up until it is eventually
released with a sudden jerk.
• These jerks (earthquakes) frequently
occur along subduction zones.
• Earthquakes are sudden
movements in the earth's crust
that occur along faults where one
rock mass slides past another.
• Soil liquefaction is when shaking
causes soil to lose structure
• Tsunamis are seismic sea swells
that accompany oceanic and
coastal landslides and
earthquakes.
Volcanoes
• Volcanoes and undersea magma vents are the sources of most
of the earth's crust.
– Many of world's fertile soils are weathered volcanic material.
• Human/Environmental dangers include:
– nuees ardentes ("glowing clouds")
– Mudslides
– ash and dust
– sulfur emissions
• Flood - excess water that
overflows stream banks
and covers adjacent land.
• Biggest economic loss is
usually contamination
(carpet, drywall, drapes,
electronics, etc. must be
discarded if touched by
flood water), not buildings
or property carried away.
• Many human activities increase both the severity and frequency
of floods (e.g., channelization, soil compaction, pavement
and rooftops) put more storm runoff into streams quicker.
• Floodplains are flat, fertile farmland that help mitigate flooding.
Flood control structures (locks, dams, levees, etc.) separate
floodplains from rivers and transfer the problems downstream.
• Government care of flood victims encourages building and
resetlement on floodplains.
Erosion is the wearing away of land surfaces by
water, wind, ice, gravitational creep or other
geological agents.
• Landslides (mass wasting or
movement) occur when masses
of material move downslope
(slow or fast).
• Gully formation is the
development of deep trenches
on flat ground.
• Agricultural soil erosion is "an
invisible crisis!"
Erosion
• Landslide is a general term for rapid down-slope
movement of soil or rock.
• Many human activities such as forest clearing and
building homes on steep, unstable slopes increase both
frequency and damage done by landslides.
• Barrier Islands and beach erosion
– These islands are located between the mainland
and open sea.
– Contain many of world's sandy beaches.
• Many people place a high value on the ocean view and
beach access. These are highly prized areas in which to
build structures.
– Development is undertaken with the understanding that modern
technology will provide protection.
Grains starve
beaches and
increase erosion
downstream.
Problems with development on the Barrier
Islands sums up environmental issues
associated with high real estate properties
in treacherous locations of the U.S.
• People place high value on views and recreational
access.
• Construction directly on geological hazardous areas
can: 1) cause irreparable damage to entire
ecosystems; and, 2) worsen storm damage.
• Government policies often encourage people to build
in risky places.
Beach Erosion