Geology and Nonrenewable Minerals Chapter 12. What are the earth’s major geological processes and hazards? Section 12-1.

Geology and Nonrenewable Minerals

Chapter 12

What are the earth’s major geological processes and hazards?

Section 12-1

The earth is a dynamic planet

• Geology is the science devoted to the study of dynamic processes occurring on the earth’s surface and in its interior.

• Three major concentric zones.– The core is the earth’s innermost zone—extremely hot,

with a solid inner part encircled by a liquid core of molten or semisolid material.

– Surrounding the core is a thick zone called the mantle—solid rock, but under its rigid outermost part is the asthenosphere, a zone of hot, partly melted rock that flows.

The earth is a dynamic planet

– The outermost and thinnest zone of the earth is the crust.

• Continental crust, which underlies the continents.• Oceanic crust, which underlies the ocean basins and

makes up 71% of the earth’s crust.

– The combination of the crust and the rigid outermost part of the mantle (above the asthenosphere) is called the lithosphere.

Major features of the earth’s crust and upper mantle

Fig. 12-2, p. 277

Volcanoes

Folded mountain beltAbyssal

floorOceanic

ridgeAbyssal floor Trench

CratonAbyssal hills Abyssal plain

Oceanic crust (lithosphere) Continental

shelfContinental slope

Continental rise

The earth beneath your feet is moving

• Convection cells or currents move large volumes of rock and heat in loops within the mantle like gigantic conveyer belts.

• Flows of energy and heated material in these convection cells caused the lithosphere to break up into a dozen or so huge rigid plates, called tectonic plates.

• Continents have split apart and joined as tectonic plates drifted atop the earth’s asthenosphere.


• The forces produced at these plate boundaries can cause earthquakes, erupting volcanoes and mountains to form.

• Oceanic plates move apart from one another allowing magma, to flow up between them.

• Much of the geologic activity at earth’s surface takes place at the boundaries between tectonic plates as they move in the resulting cracks.– Oceanic ridges may have peaks higher and canyons

deeper than those found on the earth’s continents.


– When two oceanic plates collide, a trench ordinarily forms at the boundary between the two plates.

– When an oceanic plate collides with a continental plate, the continental plate usually rides up over the denser oceanic plate and pushes it down into the mantle in a process called subduction.

– The area where this collision and subduction takes place is called a subduction zone.

– Tectonic plates can also slide and grind past one another along a fracture (fault) in the lithosphere—a type of boundary called a transform fault.

The earth’s crust is made up of a mosaic of huge rigid plates

Fig. 12-3, p. 277

Spreading center

Ocean trench

Subductionzone

Oceanic crust

Oceanic crust

ContinentalcrustContinentalcrust

Continental crust

Material cools as it reaches

the outer mantle

Cold dense material falls back through

mantle

Hot material rising

through the

mantle

Mantle convection

cell

Two plates move towards each other. One is subducted back into the mantle on a falling convection current.

Mantle

Hot outer core

Inner core

The earth’s major tectonic plates

Fig. 12-4, p. 278

EURASIAN PLATEEURASIAN PLATENORTH AMERICAN PLATE

NORTH AMERICAN PLATE

JUAN DE FUCA PLATEJUAN DE FUCA PLATE

CARIBBEAN PLATE

CARIBBEAN PLATE

AFRICAN PLATE

AFRICAN PLATE INDIA

PLATEINDIA PLATE PACIFIC

PLATEPACIFIC PLATECOCOS

PLATECOCOSPLATE

SOUTH AMERICAN PLATE

SOUTH AMERICAN PLATE

ARABIAN PLATE

ARABIAN PLATE

PHILIPPINE PLATE

PHILIPPINE PLATE

CHINA SUBPLATE

CHINA SUBPLATE

ANATOLIAN PLATE

ANATOLIAN PLATE

PACIFIC PLATEPACIFIC PLATE

NAZCA PLATENAZCA PLATE AUSTRALIAN

PLATEAUSTRALIAN

PLATE

SCOTIA PLATE

SCOTIA PLATE ANTARCTIC

PLATEANTARCTIC

PLATE

Divergent plate boundaries

Convergent plate boundaries

Transform faults

The San Andreas Fault

Volcanoes release molten rock from the earth’s interior

• An active volcano occurs where magma reaches the earth’s surface through a central vent or a long crack, called a fissure.

• Many volcanoes form along the boundaries of the earth’s tectonic plates when one plate slides under or moves away from another plate.

• Magma that reaches earth’s surface is called lava.• Volcanic activity can release large chunks of lava

rock, glowing hot ash, liquid lava, and gases into the environment.

Internal pressure in a volcano can cause lava, ash, and gases to be ejected

Fig. 12-6b, p. 279

Extinct volcanoes

Eruption cloud

Ash Acid rainAsh flow

Lava flow

Mud flow

LandslideCentral ventCentral vent

Magma conduitMagma conduit

Magma reservoirMagma reservoir

Earthquakes are geological rock-and-roll events

• Forces inside the earth’s mantle and near its surface push, deform, and stress rocks.

• The stress can cause the rocks to suddenly shift or break and produce a transform fault, or fracture in the earth’s crust.

• When a fault forms or when there is abrupt movement on an existing fault, energy that has accumulated over time is released in the form of vibrations, called seismic waves, causing an earthquake.

An earthquake has certain major features and effects

Fig. 12-7, p. 280

Liquefaction of recent sediments causes buildings to sink

Two adjoining plates move laterally along the fault line

Earth movements cause flooding in low-lying areas

Landslides may occur on hilly ground

Shock waves

FocusEpicenter


• The severity of an earthquake is measured by the magnitude of its seismic waves.

• The magnitude is a measure of shaking caused by the earthquake, as indicated by the size of the seismic waves when they reach a seismograph.

• Scientists use the Richter scale, on which each unit has amplitude 10 times greater than the next smaller unit.


– Insignificant (less than 4.0 on the Richter scale).

– Minor (4.0–4.9).

– Damaging (5.0–5.9).

– Destructive (6.0–6.9).

– Major (7.0–7.9).

– Great (over 8.0).


• The largest recorded earthquake occurred in Chile on May 22, 1960 and measured 9.5 on the Richter scale.

• The primary effects of earthquakes include shaking and sometimes a permanent vertical or horizontal displacement of the ground. These effects may have serious consequences for people and for buildings, bridges, freeway overpasses, dams, and pipelines.


• One way to reduce the loss of life and property damage is to examine historical records and make geologic measurements to locate active fault zones.– Map high-risk areas and establish building codes that

regulate the placement and design of buildings in such areas.

– People evaluate the risk and factor it into their decisions about where to live.

– Engineers know how to make buildings and structures more earthquake resistant.

Earthquakes on the ocean floor can cause huge waves called tsunamis

• A tsunami is a series of large waves generated when part of the ocean floor suddenly rises or drops.

• Most large tsunamis are caused when certain types of faults in the ocean floor move up or down as a result of a large underwater earthquake, a landslide caused by such an earthquake, or in some cases by a volcanic eruption.

• Tsunamis are often called tidal waves, although they have nothing to do with tides.

How a tsunami forms

Fig. 12-8, p. 281

Earthquake in seafloor swiftly pushes water upwards, and starts a series of waves.

Waves move rapidly in deep ocean reaching speeds of up to 890 kilometers per hour.

As the waves near land they slow to about 45 kilometers per hour but are squeezed upwards and increased in height.

Waves head inland causing damage in their path.

Undersea thrust fault

Upward waveBangladesh

India MyanmarThailand

Sri Lanka MalaysiaEarthquake Sumatra Indonesia

December 26, 2004, tsunami


• They can travel far across the ocean at the speed of a jet plane.

• In deep water the waves are very far apart—sometimes hundreds of kilometers—and their crests are not very high.

• As a tsunami approaches a coast, it slows down, its wave crests squeeze closer together, and their heights grow rapidly.

• Hits a coast as a series of towering walls of water that can level buildings.


• Tsunamis can be detected through a network of ocean buoys or pressure recorders located on the ocean floor to provide some degree of early warning sent through emergency warning centers.– Between 1900 and 2010, tsunamis killed an estimated

280,000 people along the Pacific Ocean.– The largest loss of life (279,900) occurred in December

2004 when a great underwater earthquake in the Indian Ocean with a magnitude of 9.15 caused a tsunami that generated waves as high as a five-story building.

Banda Aceh before and after the tsunami of December 2004

How are the earth’s rocks recycled?

Section 12-2

There are three major types of rocks

• A mineral is an element or inorganic compound that occurs naturally in the earth’s crust as a solid with a regular internal crystalline structure.

• A few minerals consist of a single element such as gold, silver, and diamond (carbon).

• Most of the more than 2,000 identified minerals occur as inorganic compounds formed by various combinations of elements, such as salt (sodium chloride or NaCl) and quartzite (silicon dioxide or SiO2).

There are three major types of rocks

• Rock is a solid combination of one or more minerals found in the earth’s crust.– Some kinds of rock, such as limestone and

quartzite, contain only one mineral while most consist of two or more minerals, such as granite—a mixture of mica, feldspar, and quartz crystals.

– Three broad classes:• Sedimentary rock (e.g. sandstone, limestone).• Igneous rock (e.g. granite).• Metamorphic rock (e.g. slate, marble).

Simplified rock cycle

Fig. 12-10, p. 283

Erosion

Transportation

Weathering

Deposition

Igneous rock Granite, pumice, basalt

Sedimentary rock Sandstone,

limestone

Heat, pressure

Cooling

Heat, pressure, stress

Magma (molten rock)

Melting

Metamorphic rock Slate, marble, gneiss, quartzite

Earth’s rocks are recycled very slowly

• The rock cycle is the interaction of physical and/or chemical processes that change rock from one form to another.

• It takes millions of years for this cycle to happen.

WHAT ARE MINERAL RESOURCES AND WHAT ARE THE ENVIRONMENTAL EFFECTS OF USING THEM?

Section 12-3

We use a variety of nonrenewable mineral resources

• A mineral resource is a concentration of naturally occurring material from the earth’s crust that can be extracted and processed into useful products and raw materials at an affordable cost. – Found and extracted more than 100 minerals from the

earth’s crust.– Examples are fossil fuels (such as coal), metallic

minerals (such as aluminum and gold), and nonmetallic minerals (such as sand and limestone).

– Minerals are classified as nonrenewable resources.


• An ore is rock that contains a large enough concentration of a particular mineral—often a metal—to make it profitable for mining and processing.– High-grade ore contains a large concentration of

the desired mineral.– Low-grade ore has a smaller concentration.– Aluminum (Al) is used for packaging and

beverage cans and as a structural material in motor vehicles, aircraft, and buildings.


– Steel, an essential material used in buildings and motor vehicles, is a mixture (alloy) of iron (Fe) and other elements that are added to give it certain properties.

– Copper (Cu), a good conductor of electricity, is used for electrical and communications wiring.

– Gold (Au) is used in electrical equipment, tooth fillings, jewelry, coins, and some medical implants.

Some environmental impacts of mineral use

• Metals can be used to produce many products.• Life cycle of a metal—mining, processing, and using it

—takes enormous amounts of energy and water and can disturb the land, erode soil, produce solid waste, and pollute the air, water, and soil.

• The more accessible and higher-grade ores are usually exploited first.

• As they are depleted, mining lower-grade ores takes more money, energy, water, and other materials, and increases land disruption, mining waste, and pollution.

Each metal resource that we use has a life cycle

Surface mining

Metal ore Separation of ore from gangue

Smelting Melting metal

Conversionto product

Discarding of product

Recycling

Stepped Art

Fig. 12-11, p. 285

There are several ways to remove mineral deposits

• Shallow mineral deposits are removed by surface mining by:– Removing vegetation.– Removing the overburden or soil and rock

overlying a useful mineral deposit.– Placing waste material set aside in piles,

called spoils.

• Open-pit mining.


• Strip mining is useful and economical for extracting mineral deposits that lie in large horizontal beds close to the earth’s surface.– Area strip mining is used where the terrain is

fairly flat; a gigantic earthmover strips away the overburden, and a power shovel removes the mineral deposit.

– Contour strip mining is used mostly to mine coal on hilly or mountainous terrain.


• Mountaintop removal uses explosives, large power shovels, and huge machines called draglines to remove the top of a mountain and expose seams of coal.

• Subsurface mining removes minerals from underground through tunnels and shafts.

Harmful effects of extraction, processing, and use of nonrenewable mineral or energy resources

Types of miningOpen pit, strip, contour strip, and mountaintop removable

Fig. 12-15, p. 287

Undisturbed land

Overburden

PitBench

Spoil banks

Mining has harmful environmental effects

• Scarring and disruption of the land surface. – Mountaintop removal destroys forests, buries

mountain streams, and increases flood hazards. Wastewater and toxic sludge, produced when the coal is processed, are often stored behind dams in these valleys, which can overflow or collapse and release toxic substances such as arsenic and mercury.


– In the United States, more than 500 mountaintops have been removed to extract coal and the resulting spoils have buried more than 1,100 kilometers (700 miles) of stream.

– Surface mining in tropical forests and other tropical areas destroys or degrades vital biodiversity when forests are cleared and rivers are polluted with mining wastes.

– Produces toxic waste material such as lead dust, which can cause lead poisoning and irreversible brain damage in children.


• Subsurface mining disturbs less land than surface mining disturbs, and it usually produces less waste material. – Creates hazards such as cave-ins, explosions,

and fires. – Miners often get diseases such as black lung,

caused by prolonged inhalation of coal dust in subsurface mines.

– Causes subsidence—the collapse of land above some underground mines.


• Mining operations produce large amounts of solid waste and cause major water and air pollution. – Acid mine drainage occurs when rainwater that seeps

through a mine or a spoils pile carries sulfuric acid to nearby streams and groundwater.

– Mining has polluted about 40% of western watersheds in the United States, and it accounts for 50% of all the country’s emissions of toxic chemicals into the atmosphere.

– Much of this degradation comes from leaking storage ponds built to hold a toxic sludge that is produced from the mining and processing of metal ores.

Removing metals from ores has harmful environmental effects

• Ore mining typically has two components:– Ore mineral, containing the desired metal.– Waste material.

• Removing the waste material from ores produces waste piles called tailings.

• Heating ores to release metals is called smelting.– Without effective pollution control equipment, smelters emit

enormous quantities of air pollutants, including sulfur dioxide and suspended particles.

• Chemicals can be used to remove metals from their ores.

HOW LONG WILL SUPPLIES OF NONRENEWABLE MINERAL RESOURCES LAST?

Section 12-4

Mineral resources are distributed unevenly

• The earth’s crust contains fairly abundant deposits of iron and aluminum.

• Manganese, chromium, cobalt, and platinum are relatively scarce.

• The earth’s geologic processes have not distributed deposits of nonrenewable mineral resources evenly among countries.

Mineral resources are distributed unevenly

• Five nations—the United States, Canada, Russia, South Africa, and Australia—supply most of the nonrenewable mineral resources used by modern societies.

• Experts are concerned about four strategic metal resources—manganese, cobalt, chromium, and platinum—which are essential for the country’s economy and military strength. The United States has little or no reserves of these metals.

Supplies of nonrenewable mineral resources can be economically depleted

• The future supply of nonrenewable minerals depends on two factors:– The actual or potential supply of the mineral. – The rate at which we use it.– Minerals may become economically depleted when it

costs more than it is worth to find, extract, transport, and process the remaining deposits. Options when this occurs are:

• Recycle or reuse existing supplies.• Waste less or use less.• Find a substitute or do without.

Market prices affect supplies of nonrenewable minerals

• Geologic processes determine the quantity and location of a mineral resource.

• Economics determines what part of the known supply is extracted and used.

• An increase in the price of a scarce mineral resource can lead to increased supplies and encourage more efficient use.

• Standard economic theory may not apply because most well-developed countries often use subsidies, taxes, regulations, and import tariffs to control the supply, demand, and price of minerals.

• Most mineral prices are kept artificially low.

Is mining lower-grade ores the answer?

• Extraction of lower grades of ore is possible due to new earth-moving equipment, improved techniques for removing impurities from ores, and other technological advances in mineral extraction and processing.

• Mining low-grade ores is limited by:– Increased cost of mining and processing

larger volumes of ore.

Is mining lower-grade ores the answer?

– Increasing shortages of freshwater—which is needed to mine and process some minerals—especially in arid and semiarid areas.

– Environmental impacts of the increased land disruption, waste material, and pollution produced during mining and processing.

• Can use microorganisms that can break down rock material and extract minerals in a process called in-place, or in situ, mining or biomining.

Can we get more of our minerals from the oceans?

• Some ocean mineral resources are dissolved in seawater.

• Low concentrations take more energy and money than they are worth.

• Hydrothermal ore deposits are rich in minerals such as copper, lead, zinc, silver, gold, and some of the rare earth metals.

• Growing interest in deep-sea mining.

• Manganese nodules cover large areas of ocean floor.

HOW CAN WE USE MINERAL RESOURCES MORE SUSTAINABLY?

Section 12-5

We can find substitutes for some scarce mineral resources

• Human ingenuity will find substitutes.

• Current materials revolution in which silicon and other new materials, particularly ceramics and plastics, are being used as replacements for metals.

• Finding substitutes for scarce minerals through nanotechnology.

We can recycle and reuse valuable metals

• A more sustainable way to use nonrenewable mineral resources (especially valuable or scarce metals such as gold, copper, and aluminum) is to recycle or reuse them.

• Recycling has a much lower environmental impact than mining and processing ores.

• Cleaning up and reusing items instead of melting and reprocessing them has an even lower environmental impact.

We can use mineral resources more sustainably

• Instead of asking how we can increase supplies of nonrenewable minerals, we should be asking, how can we decrease our use and waste of such resources?

• Since 1990, a growing number of companies have adopted pollution and waste prevention programs that have led to cleaner production.

We can use nonrenewable mineral resources more sustainably

Three big ideas

• Dynamic forces that move matter within the earth and on its surface recycle the earth’s rocks, form deposits of mineral resources, and cause volcanic eruptions, earthquakes, and tsunamis.

• The available supply of a mineral resource depends on how much of it is in the earth’s crust, how fast we use it, the mining technology used to obtain it, its market prices, and the harmful environmental effects of removing and using it.

• We can use mineral resources more sustainably by trying to find substitutes for scarce resources, reducing resource waste, and reusing and recycling nonrenewable minerals.

Geology and Nonrenewable Minerals Chapter 12. What are the earth’s major geological processes and hazards? Section 12-1.

Documents

earths crust

oceanic plates

earths continents

earths asthenosphere

earths surface

continental plate

denser oceanic plate

plate boundaries