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William P. CunninghamUniversity of Minnesota
Mary Ann CunninghamVassar College
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Chapter 14Chapter 14
Lecture OutlineLecture Outline
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Geology and Earth Resources
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Outline
•Tectonic Processes
•Rocks and Minerals
Rock Cycle
•Economic Geology and Mineralogy
•Environmental Effects of Resource Extraction
Mining
-Reclamation
•Conserving Geological Resources
•Geological Hazards
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Our Earth is a Dynamic Planet
•A Layered Sphere
Core - interior composed of dense, intensely hotmetal, mostly iron. Generates magnetic fieldenveloping the earth.
Mantle - hot, pliable layer surrounding the core.Less dense than core.
Crust - cool, lightweight, brittle outermost layer.Floats on top of mantle.
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Earth’s Cross Section
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Tectonic Processes
•Upper layer of mantle contains convection currentsthat break overlying crust into a mosaic of tectonicplates.
Slide slowly across earth’s surface
-Ocean basins form where continents crackand pull apart.
-Magma (molten rock) forced up through thecracks forms new oceanic crust that piles upunderwater in mid-ocean ridges.
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Tectonic Plates
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Tectonic Processes
•Earthquakes are caused by grinding and jerking asplates slide past each other.
Mountain ranges pushed up at the margins ofcolliding plates.
-When an oceanic plate collides with acontinental landmass, the continental platewill ride up over the seafloor and the oceanicplate will subduct down into the mantle whereit melts.
Deep ocean trenches mark subductionzones.
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Tectonic Plate Movement
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Rocks and Minerals
A mineral is a naturally occurring, inorganic, solidelement or compound with a definite chemicalcomposition and regular internal crystal structure.
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Rock Types
•A rock is a solid, cohesive, aggregate of one ormore minerals.
Each rock has a characteristic mixture ofminerals, grain sizes, and ways in which thegrains are mixed and held together.
•Rock Cycle - cycle of creation, destruction, andmetamorphosis
Three major rock classifications:
-Igneous
-Sedimentary
-Metamorphic
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Rock Cycle
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Igneous Rocks
•Most common type of rock in Earth’s crust.
Solidified from magma extruded onto the surfacefrom volcanic vents
-Quick cooling of magma produces fine-grainedrocks.
Basalt
-Slow cooling of magma produces coarse-grained rocks.
Granite
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Metamorphic Rock
•Preexisting rocks modified by heat, pressure, andchemical agents
Chemical reactions can alter both thecomposition and structure of rocks as they aremetamorphosed.
-Marble (from limestone)
-Quartzite (from sandstone)
-Slate (from mudstone and shale)
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Weathering and Sedimentation
•Mechanical weathering - physical break-up of rocksinto smaller particles without a change in chemicalcomposition
•Chemical weathering - selective removal oralteration of specific components that leads toweakening and disintegration of rock
Oxidation
Hydrolysis
•Sedimentation - deposition of particles of rocktransported by wind, water, ice and gravity untilthey come to rest in a new location
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Sedimentary Rock
•Deposited materials that remain in place longenough, or are covered with enough material forcompaction, may again become rock. Examples:Sandstone, shale
•Also can be formed from crystals that precipitateout of, or grow from, a solution. Example: Halite
•Sedimentary rock can be shaped by erosion.
•Geomorphology is the study of the processesthat shape the earth’s surface and the structuresthey create.
•Humans shape the Earth’s surface more than anyother single geomorphic process except platetectonics.
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Sedimentary Rock
The sedimentary rock of Bryce Canyon National Parkhas been carved by erosion into tall spires.
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Economic Geology
Economic mineralogy is the study of minerals that arevaluable for manufacturing.
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Economic Geology and Mineralogy
Metals
Metals consumed in greatest quantity by worldindustry (metric tons annually):
-Iron (740 million)
-Aluminum (40 million)
-Manganese (22.4 million)
-Copper and Chromium (8 million ea)
-Nickel (0.7 million)
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Non-Metal Mineral Resources
•Gemstones and Precious Metals
Their monetary value bankrolls despots, criminalgangs, terrorism, inhumane labor conditions.
•Sand and Gravel - greatest volume and dollar value
Brick and concrete construction, paving,sandblasting
Glass production
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Environmental Effects of MineralExtraction
•Disturbance or removal of land surface
•80,000 metric tons of dust
•>100 Toxic air pollutants
•Chemical and sediment runoff
When sulfide ores are exposed to air and water,they produce sulfuric acid.
•Vast quantities of ore must be crushed and washedto obtain small quantities of metal; enormousamounts of freshwater are thereby contaminatedwith acid, arsenic, heavy metal.
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Types of Mineral Extraction
•Placer Mining - hydraulically washing out metalsdeposited in streambed gravel by using watercannons to blast away stream beds
-Destroys streambeds and fills water withsuspended solids.
•Underground mining - tunneling into mineral seamsis very dangerous
Tunnels can collapse.
Natural gas explosions
Water seeping into mine shafts dissolves toxicminerals and contaminates groundwater.
Fires in mines which burn for years
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Types of Mineral Extraction
Open pit or strip mining
• 50% of U.S. coal is stripmined.
•creates huge holes in theearth which fill withcontaminatedgroundwater.
•Surface material is left inlong ridges called spoilbanks, because these donot contain topsoil, thereoften is no vegetation formany years.
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Restoration of Extraction Sites
•Surface Mining Control and Reclamation Act (1977)requires better restoration of strip-mined lands,especially if land classed as prime farmland.
Difficult and expensive
-Complete reclamation often costs more than$10,000 / hectare.
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Mountaintop Removal
•Mining companies have recently begun to removeAppalachian coal via mountaintop removal.
•Ridge tops are removed to access a coal bed. Thematerial from the ridge top is crushed and dumpedinto adjacent river valleys, burying streams in toxicsubstances.
•Environmental lawyers sued over violation of CleanWater Act.
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Mountaintop Removal
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Processing Ores
•Metals are extracted from ores by heating ortreatment with chemical solvents.
Smelting - roasting ore to release metals
-Major source of air pollution
Heap-Leach Extraction - crushed ore piled inlarge heaps and sprayed with a dilute alkalinecyanide solution which percolates through thepile to dissolve the gold
-Effluent left behind in ponds can leak intosurface water or groundwater.
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Conserving Geologic Resources
•Recycling
Aluminum must be extracted from bauxite byelectrolysis which is energy expensive.
-Recycling waste aluminum consumes one-twentieth the energy of extraction from rawore.
Nearly two-thirds of all aluminum beveragecans in U.S. are recycled.
Other metals commonly recycled:
-Platinum, gold, silver, copper, lead, iron, steel
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Substituting New Materials for Old
•We can reduce metal consumption by using newmaterials or new technologies such as-
Metal pipes replaced by plastic pipes
Metal wires replaced by fiber optics
Steel replaced by polymers, aluminum, ceramicsand new alloys
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Geologic Hazards
•Asteroid impact led to extinction of dinosaurs.
•Floods take the greatest number of lives, while
•Wind causes the most property damage.
•Earthquakes - sudden movements of the Earth’scrust that occur along faults where one rock massslides past another
Gradual movement - called creep or seismic slip
-When friction prevents creep, stress builds upuntil eventually released with a sudden jerk.
-Point at which first movement occurs is calledthe epicenter.
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Earthquakes
•Worst death tolls from earthquake occur whenconstruction is poor. Now buildings in earthquakezones are reinforced.
•Most seismically active region in U.S. is west coast.
•Largest earthquake recorded was in New Madrid,Missouri.
•Tsunami can be generated by earthquakes as wesaw in 2011.
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Seismic Map of Earthquake Risk in the US
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Volcanoes
•Volcanoes and undersea magma vents are thesources of most of the Earth’s crust.
Many of world’s fertile soils are weatheredvolcanic material.
500 million people live in danger zones.
Nuees ardentes - deadly clouds of hot gas andash like those that destroyed Pompeii,temperatures exceed 1000oC,they move at 60mph and can kill in minutes.
Mudslides often accompany eruptions.
Volcanic dust and sulfur emissions reducesunlight and temperature around the globe.
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Volcanic eruption
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Landslides
•Landslides are examples of mass wasting, in whichgeologic materials are moved downslope from oneplace to another.
Can be slow and subtle or swift as in rockslidesand avalanches
•Road construction, forest clearing, cultivation, andbuilding on steep, unstable slopes increase thefrequency and damage done by landslides.
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Landslide in Pacific Palisades, California
