Introduction to Geology

This Introductory course to Geology shows the physical processes and human activities that shape our planet. From earthquakes and volcanoes to the creation of sea-floor crusts and shifting river courses, Introduction to Geology offers stunning visuals that explain plate tectonics and other geologic concepts and principles. This course, along with professionally produced videos, follows geologists in the field as they explore the primal forces of the Earth, additional readings from historical text, interviews with leading scholars, and visits to significant locales bring Introduction to Geology to life. Each lecture in this course will introduce learners to the various and dynamic interacting systems of the Earth and show how they relate to the development of life and help us unlock the secrets of our environments.

Birth of a Theory

Key Terms

Continental Drift -A theory that suggested that continents which had been connected at one time drifted away from one another into their present positions. The weakness of this theory was that it did not propose a physically reasonable mechanism by which the continents were suggested to move.

Crust -The outermost layer of the earth. These solid rocks can be either oceanic crust (mostly basalt and gabbro) or continental crust (various rock types roughly granitic in composition) and vary in thickness from 5 to 75 kilometers.

Guyots - Flat topped submarine peaks with tops that are now between 1,000 and 1,500 meters below sea level. Guyots were once volcanic islands and they are topped by coral and evidence of wave erosion which indicate that they were once found at sea level. The oceanic crust subsides as it moves away from the mid-ocean ridge and the extinct volcanic structure settles below sea level.

Magnetic Stripes -Alternating bands of strong and weak magnetic fields on the sea floor. The magnetic stripes record the episodes of changing magnetic orientation during spreading of the sea floor. 

Mantle -The layer of the Earth that lies immediately beneath the crust. It is solid material. The uppermost mantle is rigid and moves with the crust in plate tectonics. The lower portions of the mantle are plastic and can flow very, very slowly allowing the plates to move on top of the moving mantle.

Paleomagnetism - The ancient magnetic fields of the Earth. We can infer the orientation of ancient magnetic fields because some types of rocks record this information at the time of their formation.

Pangaea -The supercontinent that broke up about 200 million years ago to form the various continents that we see today.

Plate Boundary - The edge of a tectonic plate. Most volcanism, earthquakes, and mountain building occurs along the boundaries of the tectonic plates.

Plate Tectonics -The theory that the surface of the earth is divided into about a dozen major plates that are slowly moving relative to one another. The plates are about 100 kilometers in thickness and can contain continents, ocean basins, or both. The motion causes the plates to shift position and change in size with time.

Plate -A large, moving slab of rock a the earth's surface. Plates are comprised of the uppermost portions of the mantle, oceanic crust, and continental crust.

Tectonics -The study of the origin and development of the broad structural features of Earth. The term originates from the Greek work tecton, meaning ''to build."

The Birth of a Theory

Traces the origins of the concepts of continental drift and sea floor spreading, and discusses their contributions to plate tectonics theory.

Atwater, Tanya Ph.D. University of California, Santa Barbara

Bogue, Scott Ph.D. Occidental College

Douglas, Robert Ph.D. University of Southern California

Ernst, Gary Ph.D. Stanford University

Sadd, James Ph.D. Occidental College

Download the transcript for this video below:

Tanya Atwater, Luminaries Seafloor Spreading 

Tanya Atwater, Luminaries Seafloor Spreading 

Geologic Time

Key Terms

Absolute Time -The age of a geologic event measured in time units such as years.

Fossils - Any traces of life preserved in rocks. Fossils may include recrystallized fragments of plants or animals, or they may be traces such as footprints.

Half Life - The time it takes for the amount of a radioactive isotope to be reduced by one half because of radioactive decay.

Isotopes -Atoms of the same chemical element that differ from one another because they have dif- ferent numbers of neutrons, and therefore different masses.

Mass Spectrometer - The instrument that geochemists use to measure the abundance of different isotopes and therefore to make absolute age determinations.

Principle of Cross-Cutting Relationships - This principle states that disruption by an igneous intrusion,erosion,or faulting must have occurred after the rocks were already there to disrupt.

Principle of Original Horizontality - This principle states that all sedimentary units that are deposited in water (ocean, lakes) are originally flat-lying, thus, any deviation from horizontal must have occurred after deposition.

Principle of Superposition - This principle states that within a sequence of undisturbed sedimentary rocks, the age of the rocks increases downwards.

Radioactivity -The spontaneous nuclear disintegration of unstable chemical elements.

Radiocarbon Dating - or Carbon 14 dating - Using the natural radioactivity of Carbon 14 and its spontaneous decay to date relatively recent carbon bearing materials.

Relative Time - The sequence in which geologic events took place relative to each other. Events are listed as first, second, ...last, not given time units.

Geologic Time

Helps students gain a sense of the vast amount of time over which geologic processes have been at work.

Reed, Walter E. Ph.D. University of California, Los Angeles

Sadd, James Ph.D. Occidental College

Download the transcript for this video below:

Earth's Limited Resources

Key Terms

Fossil Fuels –All solid and liquid hydrocarbon fuels that form from the breakdown of organic mat­

ter. Coal, oil, and natural gas are all fossil fuels.

Geologic Structures -The arrangement of rocks and rock units, especially the folds and faults.

Geothermal Energy -Energy that is produced from naturally occurring steam and hot water. The water is usually groundwater that is heated by cooling magma or hot rocks that lie deep under­ ground.

Horizontal Drilling -A drilling technique that is used to recover oil from nearly depleted oil fields. Horizontal wells are capable of recovering residual oil that is trapped in the pores of the reservoir rock.

Hydrocarbons - The group of chemical compounds that are comprised of carbon and hydrogen atoms. Hydrocarbons may be solid, liquid, or gaseous.

Hydroelectric Power or Hydropower - Energy produced by harnessing the energy contained in moving water.

Migration - The movement of oil from the source rock to a reseivoir rock.

Natural Gas -A mixture of naturally occurring hydrocarbons that are in the gaseous form.

Nonrenewable Resources -Resources that form so slowly over geologic time that they cannot be replenished at the same rate as they are being used. Oil, gas, and coal are nonrenewable resources.

Oil - A mixture of naturally occurring hydrocarbons in the liquid form.

Permeability - The degree to which fluids can flow through a rock through interconnected pore spaces.

Pore Spaces -Void spaces between grains in a rock.

Porosity - The percentage of a rock that is taken up by pore spaces.

Remote Sensing - Geologic investigation using aerial or satellite photography, radar, or other remote methods.

Renewable Resources -Those resources that are capable of replenishment on human time scales.

Solar, wind, and hydropower are examples of renewable resources.

Reservoir Rock - A permeable and porous geologic formation that can store and transmit hydro­ carbons. 

Source Rock -The rock that contains sufficient organic matter for hydrocarbons to form

Earth's Limited Resources

Earths Limited Resources discusses various resources that are used to provide energy for our human population.

Everett, John Ph.D. Earth Satellite Corporation

Harner, John Ph.D. Earth Satellite Corporation

Marino, Anthony Arco - Oil & Gas Company

Sadd, James Ph.D. Occidental College

Scott, Stephen Arco-Oil and Gas Company

Teeters, Fred Red Hill Geothermal, Inc.

Download the transcript for this video below:

Earth's Interior

Key Terms

Core -The innermost layer of the Earth which is composed largely of iron metal. Propagation of seismic waves indicates that the outer-core is a liquid layer and the inner core is solid.

Crust -The outermost layer of the Earth. The crust is a very thin layer (proportionately thinner than the skin of an apple) that varies in both thickness and composition. Continental crust is composed of metamorphic, igneous, and sedimentary rocks. Most oceanic crust is basalt, a dark, fine-grained igneous rock.

Geophysics -The branch of geology that uses the physical laws of nature to reveal the internal structure of Earth. Geophysicists study seismic waves, magnetic, gravity, and temperature characteristics of the Earth.

Heat Flow -The flow of heat out of the Earth's Interior.

Mantle - The middle of the Earth's three major layers. The mantle is the thickest layer and contains most of the mass of the Earth. The mantle is solid and composed of very dense rocks which contains the minerals olivine and pyroxene.

Magnetic Field -The invisible region of magnetic force that surrounds the Earth.

Magnetic Reversal -A change in the polarity of the Earth's magnetic field. Ifthe magnetic pole had been near the geographic north pole, during a magnetic reversal it will switch and point towards the geographic south pole.

Ophiolite -A tectonically emplaced sequence of rocks that originally formed on the seafloor. They usually contain marine sediments, pillow basalts, and the upper layers of the mantle.

Reflection -When it reaches a boundary of materials of different composition and density, a wave (in this context, a seismic wave) bounces off the boundary and travels back to the surface. Geophysicists study the time it takes for the waves to travel down to the boundary and return to the surface to calculate the depth to the boundary.

Refraction -As it travels across a boundary of materials of different composition and density, a wave (in this context, a seismic wave) bends at the boundary. This is the basic principle of correcting vision defects by bending the light rays as they pass through eyeglasses.

Seismic Wave -Vibrations that propagate away from a sudden release of energy in the Earth. These are most commonly caused by earthquakes although they can be generated artificially and from nuclear bomb blasts as well. The vibrations appear as wiggly lines on a seismograph.

P Waves - Primary seismic waves that travel fastest and are therefore the first to arrive at a recording station after an earthquake. They travel as a series of compressions and expansions. P waves can travel through solids, liquids, and gases.

S Waves -Secondary seismic waves that travel slowly and arrive at a recording station after the faster P wave. S waves are shear waves that travel by moving at right angles to the direction of wave propagation.  They travel only through solids.

Shadow Zone -A region on the Earth's surface where seismic waves are not recorded following an earthquake. An  S wave shadow zone does not record S waves, and a  P  wave shadow zone is the region where P waves are not recorded.

Xenolith -A fragment of rock that is tom loose and carried to the surface by an erupting volcano. It is usually very different in composition and appearance from the surrounding volcanic lava.

Earth's Interior

Illustrates how seismic waves occur, and explains the measurement of gravity, heat flow, and earth magnetism, to provide information about Earths interior.

Everett, John Ph.D. Earth Satellite Corporation

Harner, John Ph.D. Earth Satellite Corporation

Marino, Anthony Arco - Oil & Gas Company

Sadd, James Ph.D. Occidental College

Scott, Stephen Arco-Oil and Gas Company

Teeters, Fred Red Hill Geothermal, Inc.

Download the transcript for this video below:

The Seafloor

Key Terms

Abyssal Plain -The deep ocean floor that lies beyond the margin of the continental shelf. Abyssal plains are extremely deep (approximately 4,000 meters), extremely dark, and blanketed with layers of very fine sediment which leave them flat and featureless.

Basalt -Fine-grained igneous rock with a low (about 50%) silica content. Pyroxene and plagioclase are common mineral phases. Basalt is the rock type erupted by volcanoes at the mid­ ocean ridges and underlies all of the ocean basins.

Beach- An accumulation of sediment (usually sand sized, but sometimes pebbles or boulders) that forms where the ocean laps up onto the continent.

Continental Rise -A thick accumulation of sediment that has been washed off the continents, across the Continental Shelf, and down the Continental Slope. At the base of the Continental Slope, the seafloor becomes extremely flat and most of the sediments are deposited.

Continental Shelf - The underwater extension of continental material. This gently sloping, submerged platform can extend many kilometers out to sea. Most of the continental shelves were exposed when sea level was lower during the last Ice Age.

Continental Slope -Beyond the edge of the continental shelf, the seafloor steeply drops off over a relatively short distance. 

Echo Sounding -A method of determining the depth of the seafloor. After sound waves are emitted from a source (usually on a ship), they travel to the seafloor, reflect off the bottom, and travel back to the ship to be recorded. The time it takes for the sound waves to return to the ship indicates the depth to the seafloor.

Hydrothermal Vents -These emissions of hot water form along spreading boundaries and near active volcanoes. The water can be up to 350° C (the high pressure of deep ocean keeps the water from boiling even at these extreme temperatures). Unusual biological communities have been discovered along many hydrothermal vent sites.

Plankton - Microscopic plants and animals that Jive in the ocean. After the animals die, their shells begin to sink to the seafloor. Those shells that do not dissolve in the ocean water accumulate on the seafloor as extremely fine-grained sediments called "ooze".

Seafloor Spreading- The tectonic process where two tectonic plates spread apart (also known as rifting). Oceanic crust is much more dense and thin than continental crust and spreading almost always occurs within the oceans. Spreading is accompanied by basaltic volcanism forming a volcanic ridge called a mid-ocean ridge.

Seamounts -An underwater mountain, usually volcanic in origin, that extends above the sur­ rounding seafloor far away from a spreading center.

Sediment -Loose particles that make up most of the deposits on the seafloor. In the ocean basins sediments can originate from weathering on the continents, settling of dead marine organ­ isms, or from the water itself.

Subduction -The tectonic process where two tectonic plates come together (converge) and one descends underneath the other (subducts) and returns to the Earth's interior. In the oceans, a deep trench and volcanoes form adjacent to the subduction zone.

Submarine Canyon -V shaped valleys which cut through the continental shelf and slope. They have been found in various shapes and sizes with some greater than the Grand Canyon in depth and form.

The Seafloor

Studies major sea-floor features, including the mid-oceanic ridge, oceanic trenches, and fracture zones.

Atwater, Tanya Ph.D. University of California, Santa Barbara

Gardner, James V. Ph.D. United States Geological Survey

Hazlett, Richard Ph.D. Pomona College

Sadd, James Ph.D. Occidental College

Download the transcript for this video below:

Mountain Building and Continents

Key Terms

Accretion -The plastering on of new material onto the margins of a continent. Accreted material can be seafloor sediments, volcanic structures, small continental fragments, or large continental masses.

Craton - A portion of the continent that has attained tectonic stability and has not undergone significant uplift in the geologically recent past. The cratons are the cores around which continents have grown.

Lithosphere -The rigid layer that makes up the outermost layer of the Earth. It is approximately 100 kilometers thick and is composed of both crust and the upper mantle. It is the lithosphere that is broken into tectonic plates that ride on the lower portion of the mantle during plate tectonics.

Mountain Belt or Chain - An elongate unit, thousands of kilometers long, consisting of numerous mountain ranges. A single mountain belt, the Cordillera, runs along the western edge of the Americas from the tip of South America to northwestern Alaska.

Seamount - A submarine mountain of volcanic origin that rises above the seafloor but does not rise above the sea surface.

Tectonics -The study of the origin and development of the broad structural features of Earth. The term originates from the Greek word tecton, meaning "to build".

Terrane - Geologically unique regions that are surrounded by faults and have characteristics unlike those of adjacent regions. Some terranes may cover thousands of kilometers, while others are much smaller. Exotic Terranes or Suspect Terranes are those terranes for which there is fossil or paleomagnetic evidence that they originated a great distance from where they are currently found.

Mountain Building and Continents

Shows how the major mountain belts and continents have evolved over time.

Anderson, Lawford J. Ph.D. University of Southern California

Sadd, James Ph.D. Occidental College

Download the transcript for this video below:

Lecture 19: Differences Between Oceans and Continents (Part 1) Luminaries

Tanya Atwater, Differences Between Oceans and Continents (Part 2) Luminaries

Earthquakes 

Living Through An Earthquake 

Key Terms

Earthquake-A shaking or rolling motion of the ground caused by seismic waves traveling within the Earth and on the surface. Stress accumulates as blocks of rock slowly move. When the rocks suddenly break, there is a release of energy in the form of vibrations.

Epicenter- This point on the surface of the land is usually where earthquake waves first reach the surface. The epicenter is usually not the exact point of origin of the earthquake, because most earthquakes originate deep underground (this point is the focus).

Fault -A fracture in a rock body where movement takes place. Earthquakes occur as the energy that has built up in rocks along a fault is suddenly released and the rocks move. 

Focus -The point where the first release of energy takes place during an earthquake. The land surface directly above the focus is called the epicenter.

Intensity-A measure of an earthquake's effects on people and buildings. How much shaking you feel is a function of the earthquake's magnitude, the distance to the epicenter, and the ground materials between you and the epicenter. The Mercalli scale is used to measure earthquake intensity.

Magnitude -A measure of the total amount of energy released by the earthquake. The Richter scale is the most common scale of earthquake magnitude. Each unit increase in Richter magnitude corresponds to about thirty times more energy being released during the quake. Each unit increase also corresponds to about ten times more shaking occurring.

P Waves - Primary seismic waves that travel fastest and are therefore the first to arrive at a recording station after an earthquake. They travel as a series of compressions and expansions. P waves can travel through solids, liquids, and gases.

S Waves -Secondary seismic waves that travel slowly and arrive at a recording station after the faster P.wave. S waves are shear waves that travel by moving at right angles to the direction of wave propagation.  They travel only through solids.

Seismic Waves -Vibrations that propagate away from a sudden release of energy in the Earth. These are most commonly caused by earthquakes although they can be generated by explosions or from nuclear bomb blasts as well. The vibrations appear as wiggly lines on a seismograph.

Seismograph - The instrument used to detect seismic waves. Seismographs contain a large mass, such as a block of iron, which is resistant to sudden movement. During an earthquake, part of the instrument is free to shake and move, but the pen which is attached to the heavy mass remains still -thus a record of the shaking is produced.

Stress -A force acting on a rock unit that acts to change the size or shape of the rock. As tectonic forces move Earth's crust, stress accumulates in the rocks until it is so great that the rocks bend or break and release the accumulated stress as an earthquake.

Surface waves - Seismic waves that travel along Earth's surface much like ripples in a pond. Although these waves travel relatively slowly; they can cause tremendous ground movement and can be very damaging to structure.

Earthquakes

Explores the nature and consequences of earthquakes, the factors that cause quakes, their location and characteristics.

Hazlett, Richard Ph.D. Pomona College

Roeloffs, Evelyn Ph.D. U.S. Geological Survey 

Sadd, James Ph.D. Occidental College

Download the transcript for this video below:

Living Through an Earthquake

Observes human responses to the destructive forces of earthquakes, and identifies steps humans can take to survive this destructive natural phenomenon.

Bakun, William U.S. Geological Survey

Reasenberg, Paul Ph.D. U.S. Geological Survey

Download the transcript for this video below:

Lecture 23: Plate Tectonics and Earthquake Distribution Luminaries

Minerals

Introduction and Background

Key Terms

Atom -The smallest possible particle of an element which retains all of the chemical properties of that element.

Chemical Bonds -The points where an atom attaches to adjacent atoms.

Physical Properties -The characteristics of a mineral that can be used to help distinguish it.

The following important ones will allow you to identify most unknown minerals:

Cleavage -The tendency of minerals to split along planes where the bonding between the atoms is weak.

Fracture -The way that a mineral breaks where it is not controlled by cleavage.

Hardness -Resistance of a mineral to being scratched.

Luster -The appearance of light reflected from a mineral, or its "shininess"

Color -Although an obvious characteristic, many minerals come in a wide range of colors.

Streak -The color of the powdered mineral.  Streak is usually tested by scratching the mineral on a porcelain plate; if the mineral is harder than porcelain it will not leave a streak.

Crystal form -The geometric shape that the mineral occurs in. Other properties include effervescence, density, phosphorescence, fluorescence, double refraction, and magnetism. 

Silicates- Minerals composed primarily of silica and oxygen. Because silica and oxygen are the two most common elements of the earth's surface, most rock-forming minerals are silicates.

Minerals

Offers a comprehensive look at the origins, classifications and uses of minerals found on Earth.

Sadd, James Ph.D. Occidental College

Download the transcript for this video below:

Sedimentary Rocks

What are Sedimentary Rocks

Key Terms

Bedding - A series of layers that were originally deposited in a horizontal orientation. Each individual layer is called a sedimentary bed.

Bedding Plane -The nearly flat surface that separates two beds.  The bedding plane reflects changes or breaks in the deposition process.

Cementation -The chemical process in which solid material (cement) precipitates in the pore spaces between grains of sediment. This cement helps to solidify the grains of sediment into a hard sedimentary rock.

Crossbedding- A relatively unusual case where bedding is deposited an angle to adjacent (and generally horizontal) bedding planes. Crossbedding usually develops in sand dunes or in delta deposits and is an indication that the sediments were deposited by flowing water or wind.

Delta - Sediments that accumulate at the mouth of a river where the velocity of the water de­ creases dramatically.

Deposition -The settling of sedimentary material. Sediments are usually deposited through a water column but can also be deposited after transportation by wind or glacial ice.

Evaporites - Rocks that form by the evaporation of water. The crystals that form are most commonly halite and other salts.

Lithification - The consolidation of sediments into sedimentary rocks. This process usually entails compaction along with cementation, and/or crystallization.

Mud Cracks- Polygonal arrangements of cracks in fine grained sediments. Fossilized mud cracks indicate sediments that were dried by air and they only form in sediments that are periodically exposed to the surface such as tidal flats or streams.

Principle of Uniformity- The principle that indicates that geologic processes of the present are identical to those that have operated throughout geologic history. Often summarized as 'The present is the key to the past''.

Ripple Marks - Small ridges that form on sediment surfaces and are indicators of sediment deposition in shallow moving water or currents.

Sediment - Particles that form by the breakdown of pre-existing rocks or chemical precipitation.

Unconformity -A surface that represents a break in the geologic record and usually indicates a gap in time.

Weathering- The processes that break down rocks when they are exposed to the conditions at the earth's surface. Mechanical Weathering is the physical breakdown of rocks by the actions of water, wind, or ice. Chemical Weathering is the breakdown of rocks into their chemical components.

Sedimentary Rocks

Illustrates the importance of sedimentary rocks in understanding the nature of Earths surface.

Busby-Spera, Cathy Ph.D. University of California, Santa Barbara

Reed, Walter E. Ph.D. University of California, Los Angeles

Sadd,James Ph.D. Occidental College

Trent, Dee Ph.D. Citrus College

Download the transcript for this video below:

Metamorphic Rocks

Key Terms

Directed Stress -Pressures upon a rock which are different in different directions and result in the rock being "squeezed" and developing a foliated texture.

Facies -A group of characteristics that distinguishes a rock unit

Foliation -Planar alignment of minerals or textures found in a metamorphic rock. Most foliated rocks have a platy, or flaky, appearance.

Metamorphic Grade -The degree of, or level of, metamorphism as determined by the temperature and pressure conditions at which the rock was metamorphosed.

Metamorphism -The process of changing a preexisting rock Into a new rock as a result of changes in pressure and temperature. All changes take place in the solid state; although some of the original minerals disappear and new ones form, there is no melting that takes place. The new, metamorphic, rock is characterized by distinct texture and minerals from the original rock.

Protolith - The preexisting rock that existed before metamorphism. Also called the Parent Rock and the Precursor.

Snowball Garnet -A metamorphic garnet (aluminous silicate) that rotated as it grew and incorporated small inclusions in a swirling, snowball, pattern. Snowball garnets are used by geologists to indicate how the direction of pressure changed during metamorphism and mountain growth.

Metamorphic Rocks

Studies the causative factors of metamorphism and identifies the kinds of rocks produced through the metamorphic process.

Anderson, Lawford J. Ph.D. University of Southern California

Morton, Douglas M. Ph.D. United States Geological Survey

Sadd, James Ph.D. Occidental College

Download the transcript for this video below:

Intrusive Igneous Rock

Key Terms

Anorthosite -Coarse grained intrusive igneous rock comprised almost entirely of Calcium rich pla­ gioclase.  Anorthosite is uncommon on Earth, but very common on the moon.

Batholith -A very large igneous intrusion with an irregular shape. Batholiths are often accumula­ tions of numerous plutons and form large mountain ranges.

Dike -A tabular body of intrusive igneous rock which cuts any preexisting layering or fabric in the rocks.

Diorite - Coarse grained intrusive igneous rock with an intermediate silica content. Diorite is the coarse grained equivalent of andesite and contains plagioclase and amphibole.

Gabbro - Coarse grained intrusive igneous rock with a relatively low silica content. Gabbro is the coarse grained equivalent of basalt and contains plagioclase and pyroxene.

Granite -Coarse grained intrusive igneous rock with a relatively high silica content.  Granite is the coarse grained equivalent of rhyolite and contains quartz, potassium feldspar and plagioclase.

Igneous Rock - Rock formed from the cooling and solidification of a molten magma.

Extrusive Igneous Rock -Rock formed by the solidification of magma at the Earth's surface. Also called Volcanic Rock.

Intrusive Igneous Rock- Rock formed by the solidification beneath the Earth's surface. Also called Plutonic Rock.

Lava -magma (see below) at Earth's surface.

Magma -Molten rock that usually contains some solid mineral phases and dissolved gases. Called lava once it reaches Earth's surface.

Mantle -The thick layer of rock that occurs between the core and the crust. Pluton -An irregularly shaped intrusive igneous body.

Sill -A tabular body of igneous intrusive rock which lies parallel to any preexisting layering or fabric in the rock.

Intrusive Igneous Rock

Unveils the rock-forming processes of magma that do not reach Earths surface, but instead solidify underground.

Anderson, Lawford J. Ph.D. University of Southern California

Sadd,James Ph.D. Occidental College

Sigurdson, David Ph.D. California State University Dominguez Hills

Download the transcript for this video below:

Volcanism

Key Terms

A Andesite- Fine-grained igneous rock with an intermediate (about 60%) silica content. Amphib­ ole and plagioclase are common mineral phases.

Ash - Tiny particles of glass or rock powder produced by a violent volcanic eruption.

Basalt -Fine-grained igneous rock with a low (about 50%) silica content. Pyroxene and plagio­ clase are conunon mineral phases. Very low viscosity of the lava leads to quiescent eruptions and the lava can travel for great distances.

Dome -Steep-sided, dome shaped masses of volcanic rock formed from highly viscous lava that solidified above a volcanic vent.

Composite Volcano- Steep-sided volcanic edifices which are built of alternating layers of andesitic lava and pyroclastic  ash deposits.

ConvergentPlate Boundary -A plate tectonic boundary where two lithospheric plates are converging, or coming together. Usually a subduction zone develops as one plate descends into the mantle.

Divergent Plate Boundary- A plate tectonic boundary where two lithospheric plates are spreading apart and new crust is being created.  These boundaries  usually occur at mid-ocean  ridges.

Explosive Eruption -An eruption that is associated with enormous pressure resulting from accumulated gases.

Fissure -Cracks through which lava can erupt. These are often a great distance away from the central vent.

Hot Spot-Surface expression of mantle plumes where columns of molten magma rise beneath the sea floor. Hot-spots usually occur away from plate boundaries and form volcanic island chains such as the Hawaiian Islands.

Lava -Magma (see below) at Earth's surface.

Magma - Molten rock that usually contains some solid mineral phases and dissolved gases. Called lava once it reaches Earth's surface.

Pillow Lava - Rocks composed of accumulated ''blobs" or pillow shaped masses which form when basaltic lava is erupted underwater.

Pyroclastic Rocks - (Pyro = fire and elastic = broken) During a violent, gas-rich volcanic eruption, rock and lava can be fractured into fragments of various sizes ranging from dust to boulder sized. After these pyroclastic particles settle back to earth and are compressed into rocks, they become pyroclastic rocks. A pyroclastic flow is a hot cloud of ash and other pyroclastic  material  that races down the mountainside.

Quiet Eruption- An eruption that is composed of lava that is very runny and pours out smoothly.

Rhyolite- A fine-grained igneous rock with a high  (about 70%) silica content. Quartz and potassium feldspar are conunon mineral phases. Extremely high viscosity of the lava leads to very explosive eruptions.

Shield Volcano -A gently sloped volcanic edifice constructed of low viscosity basaltic lava.

Vent-The central portion of a volcano where a volcanic eruption takes place.

Viscosity- Tendency of material to resist flow. VIScosity of the lava depends on the silica content and the temperature. Generally basaltic lava has very low viscosity and can travel for great distances; andesitic and rhyolitic lavas are much more viscous and tend to erupt violently.

Volcanism

Explains how volcanoes are formed, and assesses the importance of volcanic activity to Earths geology and climate.

Sadd, James Ph.D. Occidental College

Tilling, Robert U.S. Geological Survey

Download the transcript for this video below:

Ground Water

Key Terms

Aquifer -A body of rock or sediment which contains significant quantities of groundwater.

Groundwater -Any liquid water that lies beneath the ground surface. Groundwater usually fills the pore spaces and fractures in rocks and sediments.

Hydrology - The study of water, particularly how it circulates through the water cycle. Hydrogeology- is the study of how water moves through geologic materials.

Infiltration- The percolation of water into the subsurface.

Permeability -The ability of a rock or sediment to transmit a fluid, such as water. A permeable substance must not only have significant pore spaces within it, but those pore spaces must be interconnected.

Porosity - The percentage of the total volume of a rock or sediment that is open space. Porosity is used as a measurement of the ability of a rock or sediment to hold fluid.

Recharge -The addition of surface water to an aquifer.

Saltwater Intrusion -Contamination of an aquifer by salt water.

Saturated Zone -The underground region where all of the spaces in a rock or sediment are filled with water.

Subsidence - Sinking or settling of the earth's surface that can occur in response to removal of groundwater or oil.

Unsaturated Zone -The underground region where the spaces in a rock or sediment are not filled entirely with water; the unsaturated zone lies above the saturated   zone.

Water Table- The boundary between the saturated zone and the unsaturated zone.

Ground Water

Shows how ground water is distributed, and assesses its importance to human life.

Brill, Kirby Orange County Water District

Goodrick, Jim Orange County Water District

Sadd, James Ph.D. Occidental College

Download the transcript for this video below:

Running Water

Rivers and  Streams

Key Terms

Abrasion –A process of erosion in which particles of sediment grind away at the river banks and each other and the friction and impact wear the particles down. Abrasion causes the round­ ing of rocks and pebbles that is commonly observed in streams.

Braided Stream -A stream that forms when the stream is heavily laden with sedimentary mate­ rial and develops a series of channels and sedimentary accumulations on the valley floor. The stream has no main channel and the channels change course frequently, responding to changes in runoff and sedimentary load.

Delta –An accumulation of sediments that results from the deposition of sediments as the velocity of a stream decreases when the stream enters a body of still water. The sediments form a generally triangular body called a delta, named by Herodotus in the fifth century BC for the Nile delta that resembled the Greek letter "delta".

Deposition -The settling of sedimentary material that has been transported by moving water.

Dissolution -A process of weathering and erosion that breaks down solid rock, especially lime­ stones, into the chemical components, or ions, that are soluble in water. The dissolved components are then carried away in the stream water.

Erosion -The physical breakdown and removal of solid rock by an erosive agent such as moving water. Glacial ice and wind are also effective agents of erosion.

Flood Plain - A broad area that results from erosion by migrating streams. Repeated floods blanket some flood plains with sediments.

Hydraulic Action -The ability of turbulent water to pick up and move rocks and sediments in the river channel.

Meandering River- A stream that has developed a series of curves in a twisting, winding course of looping bends.  From the Latin word meandere meaning "to wander''.

Turbulence -A swirling flow of water in which water flows along erratic paths. Turbulent flow is usually very rapid and chaotic.

Running Water

Analyzes the role of running water in sculpting Earths surface, discusses tectonic and hydrologic cycles, and identifies the roles human activity can play in impacting flood danger.

Powell, Nancy P.E. U.S. Army Corps of Engineers

Rhodes, Dallas Ph.D. Whittier College

Sadd, James Ph.D. Occidental College

Download the transcript for this video below:

Weathering and Soils

Weathering

Key Terms

Exfoliation -A process of physical breakdown of rocks where the outermost layer of rock separates and leaves a dome feature. The concentric layers of exfoliating rock resemble the layers of an onion.

Humus - The dark-colored, well-decomposed organic matter found in the upper horizons of fertile soils. It supplies nutrients to growing plants Humus usually contains particles of decayed leaves, roots, twigs, animal remains, and abundant microorganisms.

Ice Wedging - The physical breakdown of rocks caused by the expansion of water as it freezes.

Leaching - The removal of fine particles and soluble materials by rain water percolating downward through the upper soil horizon. Leaching may deplete the upper horizon of certain minerals which will be deposited in the lower, or B, horizon of the soil profile.

Soil -A relatively thin layer of unconsolidated, weathered rock and decayed plant material that lies on top of bedrock.

Soil Horizons - The layers within the soil that are recognizable by their characteristic physical properties.

Weathering- Surface processes that act upon rocks to change or destroy them.

Chemical Weathering - Weathering processes that chemically breakdown or change the rocks to rocks of a different composition.

Physical Weathering -Weathering processes that physically fragment or change the rocks.

Weathering and Soils

Demonstrates how minerals and rocks change when subjected to the physical and chemical conditions that exist on Earths surface.

Hazlett, Richard Ph.D. Pomona College

Sadd, James Ph.D. Occidental College

Download the transcript for this video below:

Mass Wasting

Key Terms

• Creep -Extremely slow downslope movement of soil, rock, or debris. Although the downslope movement may be essentially imperceptible, over time creep can cause extensive damage.
• Debris -Sediments and any other unconsolidated material that is found above the bedrock at the
• Debris Flow - A mass wasting event in which all of the moving material (debris) is flowing rapidly downslope. Most debris flows have a high water content in addition to loose sedimentary material.
• Hummocky Topography - Irregular, almost bumpy, landscape that is the result of ancient landslide activity.
• Landslide -A general term that refers to the downslope movement or rock, soil, or other debris. Essentially synonymous with mass wasting.
• Mass Wasting -The downslope movement of a mass of rock, soil, or other debris which results from the force of gravity acting on unstable slopes.
• Mudflow-A flowing mixture of relatively fine sedimentary debris (mud) and water.
• Pore Spaces -The total amount of empty space that occurs between sedimentary grains or in fractures in a rock.
• Rock Fall - Rock fragments falling down a cliff.
• Rock Slide -A mass of rocks and rock fragments sliding down a steep mountain slope.
• Slump -A type of mass wasting that is characterized by an arcuate scarp (or cliff) at the top and an irregular surface at the base.
• Talus -Accumulation of large, angular rock fragments at the base of a steep slope.

Mass Wasting

Studies the causes, types and effects of mass wasting.

Meeker, Ann Engineering Geologist

Wells, Wade U.S. Forest Service

Download the transcript for this video below:

Deserts

Key Terms

• Alluvial Fans -Depositional features composed of rocks and mud eroded during heavy dash floods or rainstorms. These sediments are deposited at the base of the mountains where the gradient of the stream abruptly flattens, forming a fan shaped deposit.
• Desert -Regions that receive less than 25 centimeters (10 inches) of rainfall per year. Evaporation rates are generally very high.
• Desertification - The expansion of deserts into regions that were previously more temperate. Desertification is most problematic when deserts expand into populated regions.
• Rain Shadow - The region on the lee side of hlgh mountain ranges. Moist air blows in from the ocean and causes precipitation on the windward side of the mountains. The dry air then con­ tinues an and descends, causing intense evaporation and arid conditions in the rain shadow.
• Sand Dunes -Accumulations of loose sand grains that have been deposited by wind action.

Deserts

Addresses the formation and location of deserts, and identifies their geologic features.

Montana, Art Ph.D. University of California Los Angeles

Sadd, James Ph.D. Occidental College

Download the transcript for this video below:

Glaciers

Key Terms

• Drumlin -An elongated hill formed of till and oriented parallel to the direction of ice-flow.
• Esker -A long, winding sedimentary ridge deposited by glacial meltwater.
• Firm -Granular material that is transitional between snow and ice.
• Glacier - A large, slowly moving, mass of ice that persists over time. Glaciers form by the compaction and recrystallization of snow.
• Continental Glacier or lee Sheets - A large mass of ice that flows under its own weight and covers an extensive continental region.
• Valley Glacier - A glacier that forms in a valley and flows down the valley. After melting, the valley shows the U shape characteristic of glacial erosion.
• Kettle -A basin that forms after glacial retreat from the melting of an isolated block of ice that was buried in till.
• Loess - Extremely fine grained sedimentary deposit of wind-blown glacial dust.
• Moraine -A mass of till (see below) left behind after a glacier has receded or melted.
• End Moraine -A moraine that forms at the front edge of a glacier.
• Lateral Moraine -A moraine that forms along the sides of a glacier.
• Medial Moraine -A single moraine that forms when two glaciers come together and the lateral moraines are combined.
• Striations-Straight scratches or grooves left on a rock by the action of a moving glacier.
• Till- Rock debris carried by a glacier. Till typically includes a large range of grain sizes jumbled together in an unsorted heap.

Glaciers

Presents the properties of glaciers, and assesses their importance in sculpting Earths surface.

Anderson, Lawford J. Ph.D. University of Southern California

Sadd, James Ph.D. Occidental College

Zumberge, James Ph.D. University of Southern California

Download the transcript for this video below: