Geog 1113 Exam 1 part 2

LECTURE 05: PLATE TECTONICS

What is plate tectonics?

Plate tectonics is the theory of global crustal dynamics in which the lithosphere is broken into plates that move because of convection and other forces in the upper mantle.

What evidence did Alfred Wegener use to support continental drift?

He used similarities in fossil records, climatic records, and geologic records between distant continents, especially South America and Africa.

What was Pangea?

Pangea was the large ancient landmass proposed by Wegener that later split into Laurasia and Gondwana.

Why was Wegener’s continental drift theory not fully accepted at first?

He could not explain a mechanism that moved the continents.

What idea eventually helped explain a possible mechanism for moving continents?

The Theory of Thermal Convection suggested that huge convective cells of magma in the asthenosphere could help drive continental movement.

What is seafloor spreading?

Seafloor spreading is the movement of oceanic crustal material caused by upwelling magma along mid-ocean ridges, which pushes crust apart and forms new seafloor.

Where is the youngest oceanic crust found relative to a mid-ocean ridge?

The youngest oceanic crust is at the ridge.

Where is the oldest oceanic crust found relative to a mid-ocean ridge?

The oldest oceanic crust is farthest from the ridge.

What is paleomagnetism or geomagnetic reversal evidence?

It is the symmetrical magnetic alignment pattern in rocks on both sides of a mid-ocean ridge, showing that new seafloor formed and moved away from the ridge over time.

Does paleomagnetism cause plate movement?

No. Paleomagnetism shows that plates have moved; it does not cause the movement.

What ideas are combined in the theory of plate tectonics?

Plate tectonics combines continental drift, seafloor spreading, paleomagnetism, and other crustal movement ideas.

What major tectonic processes are explained by plate tectonics?

Plate tectonics helps explain upwelling magma, plate movement, subduction, folding, faulting, warping, fracturing, earthquakes, and volcanic activity.

What are the eight major tectonic plates?

Pacific, North American, South American, Eurasian, African, Australian, Indian, and Antarctic.

What are some examples of minor tectonic plates?

Nazca, Cocos, Caribbean, Arabian, Somalian, Scotia, Caroline, Fiji, Philippine, and Juan de Fuca.

How can plate boundaries be identified from surface patterns?

They can be identified by mapping linear patterns of volcanic and earthquake activity.

What is the Pacific Ring of Fire?

It is a pattern of volcanoes and high earthquake activity around the Pacific Ocean, especially along western North and South America and eastern Asia down to New Zealand.

What are the three main types of plate boundaries?

Divergent, convergent, and transform boundaries.

What is a divergent plate boundary?

A divergent plate boundary is an area where plates move apart from each other under tensional stress.

What processes help form divergent boundaries?

Upwelling magma causes ridge push, and gravity creates slab pull.

What are examples of oceanic divergent boundaries?

The Mid-Atlantic Ridge and the formation of the Red Sea.

What is an example of a continental divergent boundary?

The Great Rift Valley of East Africa, where the Somalian plate is pulling away from the African plate.

What is a convergent plate boundary?

A convergent plate boundary is an area where plates move toward each other under compressional stress.

What is a subduction zone?

A subduction zone is an area where one plate is pushed or pulled beneath another plate and eventually remelted in the asthenosphere.

What are the three basic types of convergent plate boundaries?

Continental-oceanic, oceanic-oceanic, and continental-continental.

What happens at a continental-oceanic convergent boundary?

Denser oceanic crust subducts beneath less dense continental crust, forming a trench, mountain building, earthquakes, and volcanic activity.

What are examples of continental-oceanic convergence?

The Nazca and South American plates form the Peru Trench and Andes Mountains; the Juan de Fuca and North American plates form the Cascade Range.

What happens at an oceanic-oceanic convergent boundary?

One oceanic plate subducts beneath another, forming deep trenches, earthquakes, volcanic activity, and volcanic island archipelagos.

What are examples of oceanic-oceanic volcanic island archipelagos?

The Philippine Islands, Japanese Islands, and Aleutian Islands.

What happens at a continental-continental convergent boundary?

Two continental plates collide with little or no continental subduction, causing compression, mountain building, numerous earthquakes, and little or no volcanism.

What are examples of continental-continental convergence?

The Appalachian Mountains formed when North American, African, and Eurasian plates converged, and the Himalayas are forming where the Indian plate converges with the Eurasian plate.

What is a transform plate boundary?

A transform boundary is an area where plates slide laterally past each other under shear stress.

What is a major example of a transform plate boundary?

The San Andreas Fault Zone in southern California.

What activity is common at transform boundaries?

High earthquake activity and some crustal deformation, but no subduction or volcanism.

What is slab-pull?

Slab-pull is the process of a subducting plate edge pulling the rest of the plate as it sinks into the asthenosphere.

What is ridge-push?

Ridge-push is gravity causing a plate to slip away from an elevated mid-ocean ridge.

What is basal drag?

Basal drag is resistance to flow exerted on the bottom of a plate by the asthenosphere beneath it.

What is mantle resistance?

Mantle resistance is frictional resistance to the movement of a subducting plate.

What is friction in plate movement?

Friction is resistance along fault planes and between plates.

LECTURE 06: VOLCANIC LANDSCAPES

What is volcanism?

Volcanism is the process by which magma and gases are transferred from Earth’s interior to near or on the surface.

What are the two basic types of volcanism?

Extrusive volcanism and intrusive volcanism.

What is extrusive volcanic activity?

Extrusive volcanic activity occurs when magma flows onto Earth’s surface and cools to form igneous rock.

What is intrusive volcanic activity?

Intrusive volcanic activity occurs when magma cools below Earth’s surface within the crust, forming intrusive igneous rock that is exposed later by erosion or uplift.

What is a volcano?

A volcano is a landform with a vent or fissure at the surface connected to a conduit from below the crust in the asthenosphere or mantle.

What is a magma chamber?

A magma chamber is an underground area where magma collects below a vent or fissure before being expelled.

What is a crater?

A crater is the surface depression at the summit of a volcano, often containing the vent or opening.

What is the difference between magma and lava?

Magma is molten rock underground, while lava is molten rock that has reached the surface.

What is an active volcano?

An active volcano is currently erupting, has erupted during recorded history, or still has a high potential to erupt.

What is a dormant volcano?

A dormant volcano is at rest but still has the potential to erupt in the future.

What is an extinct volcano?

An extinct volcano has little or no potential to erupt again.

Where is volcanic activity most common?

Volcanic activity is common at convergent and divergent plate boundaries and at hot spots.

What is mafic or basaltic lava?

Mafic or basaltic lava is high in magnesium and iron, has less than 50% silica, is less viscous, flows more easily, traps less gas, and produces less explosive eruptions.

What is felsic lava?

Felsic lava has more than 50% silica, is more viscous, flows more slowly, traps more gas, and produces more explosive eruptions.

What are pyroclastics or tephra?

Pyroclastics or tephra are solid fragments of magma explosively expelled from a volcano, common with felsic magma and explosive eruptions.

How is tephra classified by size?

Tephra is classified by size, including bombs, pumice, scoria, cinders, lapilli, ash, and dust.

What is an effusive eruption?

An effusive eruption is a relatively gentle, nonviolent eruption associated with mafic magma that flows readily and releases gas more easily.

What volcanic cone is commonly associated with effusive eruptions from a vent?

A shield volcano.

What are examples of shield volcano settings?

Hawai’i, the Galápagos Islands, and Iceland.

What feature may form from an effusive eruption through a fissure?

A plateau or flood basalt.

What is an example of a flood basalt?

The Columbia Plateau in Washington and the northwestern United States.

What is an explosive eruption?

An explosive eruption is a violent eruption usually associated with felsic magma that traps gas, increases pressure, and commonly produces pyroclastics.

Where are explosive eruptions most commonly found?

They are most common along subduction zones.

What volcanic cone is commonly associated with explosive eruptions through a vent?

A composite volcano or stratovolcano.

What are examples of composite volcanoes?

Mt. St. Helens, Mt. Rainier, Mt. Pinatubo, Mt. Vesuvius, Nevado del Ruiz, Mount Shishaldin, and Mount Etna.

What four related ideas go with mafic lava?

Mafic lava is associated with effusive eruptions, shield volcanoes, and Hawai’i as an example.

What four related ideas go with felsic lava?

Felsic lava is associated with explosive eruptions, composite volcanoes, and examples such as Mt. St. Helens, Mt. Vesuvius, and Mt. Pinatubo.

How do shield volcanoes usually look compared with composite volcanoes?

Shield volcanoes are broader with gentler slopes, while composite volcanoes are narrower and steeper-sided.

What is a lahar?

A lahar is a volcanic mudflow formed when volcanic material mixes with water, often from melted snow and ice during an eruption.

What is the named lahar example from the lecture?

The 1985 Nevado del Ruiz eruption in Colombia created a lahar that covered Armero and killed more than 20,000 people.

What is a nuée ardente or pyroclastic flow?

A nuée ardente or pyroclastic flow is a cloud or flow of hot volcanic gas, ash, and dust that moves down a volcano’s flanks.

What is the named nuée ardente example from the lecture?

The 1902 Mount Pelée eruption in Martinique destroyed St. Pierre and killed about 30,000 people.

What is a phreatic eruption?

A phreatic eruption is a violent explosive eruption made stronger when water enters a magma chamber and turns to steam, increasing pressure.

What are named examples of phreatic eruptions?

Krakatau, Tambora, and Santorini.

What is a cinder cone?

A cinder cone is a volcano made mostly of cinder-sized tephra, with little or no lava, and is usually small.

What is a named example of a cinder cone?

Sunset Crater in Arizona; Capulin Volcano in New Mexico is also shown in the slides.

What is a volcanic dome?

A volcanic dome is a mound of lava that may form inside a crater, cap a vent, or be the only surface feature from an eruption.

What is a caldera?

A caldera is a large, roughly circular depression or basin associated with a volcanic vent, much larger than the original vent.

What are the two caldera examples from the lecture?

Crater Lake in Oregon is a collapse caldera, and Yellowstone National Park is an explosive caldera.

What is a mantle plume?

A mantle plume is a buoyant mass of hot mantle material that rises to the base of the lithosphere and may produce volcanism and structural deformation.

What is a hot spot?

A hot spot is the surface expression of a mantle plume that creates or finds an opening in the crust and forms volcanic features as a plate moves over it.

What is an oceanic hot spot example?

Hawai’i.

What is a continental hot spot example?

Yellowstone National Park.

Why is Iceland a special hot spot example?

Iceland is related to a mantle plume associated with the Mid-Atlantic Ridge, a divergent plate boundary.

What are hydrothermal or geothermal features?

They are features formed when water below the surface is heated by the geothermal gradient or by contact with shallow magma.

What are examples of hydrothermal features?

Hot springs, geysers, fumaroles, mud pots, and other geothermal features.

What is a plutonic landscape?

A plutonic landscape is a landscape made of intrusive volcanic features formed when magma cools below the surface and is later exposed by erosion or uplift.

What is a pluton?

A pluton is the exposed portion of a mass of intrusive igneous rock.

What is a discordant pluton?

A discordant pluton disrupts or changes the existing geologic structure into which it intrudes.

What is a concordant pluton?

A concordant pluton does not melt the existing geologic structure; it may move rock or fill existing spaces.

What is a batholith?

A batholith is a large discordant mass of intrusive igneous rock with a surface exposure of at least 100 square kilometers.

What are examples of batholithic features?

Stone Mountain in Georgia, the Black Hills of South Dakota, and the Sierra Nevada Mountains.

What is a stock?

A stock is a relatively small, roughly circular discordant pluton, usually less than 100 square kilometers in surface exposure.

What is a dike?

A dike is a narrow mass of cooled magma that cuts across preexisting strata in a vertical orientation.

What is the large dike example from the lecture?

A large dike in Zimbabwe is about 600 kilometers long and averages 10 kilometers wide.

What is a volcanic neck or plug?

A volcanic neck or plug is solidified magma that once filled the vent or neck of an ancient volcano and was later exposed by erosion.

What are examples of volcanic necks or plugs?

Shiprock in New Mexico, Mount Coonowrin and Mount Cooroora in Australia, and Saint Michel d’Aiguilhe chapel in France.

What is a laccolith?

A laccolith is a concordant pluton that arches the strata above it into a lens-shaped body with a horizontal floor.

What is a sill?

A sill is a relatively narrow mass of cooled magma injected horizontally between existing rock strata.

LECTURE 07: EARTHQUAKES

What is an earthquake?

An earthquake is a sharp release of energy that creates seismic waves when stress along a fault exceeds the elastic limit of rock and sudden movement occurs.

What are seismic waves?

Seismic waves are pulses of energy generated by an earthquake that pass through Earth as shock waves.