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 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 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. Yucca Mountain is an example of why dynamic earth processes are included in waste storage.
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 Processes & the Rock Cycle
Communities in deep-sea ocean trenches
PART 2: MINERALS & ROCKS 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. 1.Mineral versus rock 2.Rock types & how they are formed 3.Weathering & sedimentation 4.Rock cycle
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 I.Igneous II.Sedimentary III.Metamorphic Three Types of Rocks
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) Rock Types (continued)
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 water- sculpted 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 (740 million) Aluminum(40 million) Manganese(22.4 million) Copper(8 million) Chromium(8 million) Nickel(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
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. U.S.
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, 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
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.) Types of Geologic Resource Conservation
Recycling of Aluminum - A Big Success Story –Aluminum must be extracted from bauxite by electrolysis. This requires lots of energy! Recycling waste aluminum consumes one- twentieth 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.