Unit 2PLATE TECTONICSCHAPTERS 10, 11, 12, 13 & 19 (SECT.1&2)

SES2. Students will understand how plate tectonics creates certain geologic features, materials, and hazards

a. Distinguish among types of plate tectonic settings produced by plates diverging, converging, and sliding past each other.

b. Relate modern and ancient geologic features to each kind of plate tectonic setting.

c. Relate certain geologic hazards to specific plate tectonic settings.

d. Associate specific plate tectonic settings with the production of particular groups of igneous and metamorphic rocks and mineral resources.

e. Explain how plate tectonics creates and destroys sedimentary basins through time.

Wegener’s Hypothesis

Continental drift the hypothesis that states that the continents once formed a single landmass, broke up, and drifted to their present location

The hypothesis of continental drift was first proposed by German scientist Alfred Wegener in 1912.

Wegener’s Evidence

Fossil Evidence: fossils of the same plants and animals could be found in areas of continents that had once been connected.

Evidence from Rock Formations: ages and types of rocks in the coastal regions of widely separated areas matched closely.

Climatic Evidence: changes in climatic patterns suggested the continents had not always been located where they are now.

Wegner could not explain HOW the continents moved.

Mid-ocean ridge a long, undersea mountain chain that has a steep, narrow valley at its center, that forms as magma rises from the asthenosphere, and that creates new oceanic lithosphere (sea floor) as tectonic plates move apart

1. The sediment that covers the sea floor is thinner closer to a ridge than it is farther from the ridge

Sea-floor Spreading

2. The ocean floor is very young. Rocks on land are as old as 3.8 billion years. None of the oceanic rocks are more than 175 million years old.

Sea-floor spreading the process by which new oceanic lithosphere (sea floor) forms as magma rises to Earth’s surface and solidifies at a mid-ocean ridge

Paleomagnetism

Paleomagnetism the study of the alignment of magnetic minerals in rock

As magma solidifies to form rock, iron-rich minerals in the magma align with Earth’s magnetic field. When the rock hardens, the magnetic orientation of the minerals becomes permanent.

Magnetic Reversals - Scientists have discovered rocks whose magnetic orientations point opposite of Earth’s current magnetic field.

Rocks with magnetic fields that point north (normal polarity) are all classified in the same time periods. Rocks with magnetic fields that point south (reversed polarity) also all fell into specific time periods

Scientists discovered a striped magnetic pattern on the ocean floor on each side of a mid-ocean ridge.

How Continents Move

plate tectonics the theory that explains how large pieces of the lithospehere, called plates, move and change shape

The lithosphere forms the thinouter shell of Earth and isbroken into several blocks ortectonic plates.

The tectonic plates ride onthe asthenoshpere in much the same way that blocks of wood float on water.

Convection is the movement of heated material due to differences in density that are caused by differences in temperatures.

Energy generated by Earth’s core and radioactivity within the mantle heat the mantle. This heated material rises through the cooler, denser material around it.

Effects of Plate Movement

Modern climates are a result of past movements of tectonic plates. When continents move, the flow of air and moisture around the globe changes and causes climates to change.

Geologic evidence shows that ice once covered most of Earth’s continental surfaces. As continents began to drift around the globe, however, global temperatures changed and much of the ice sheet melted.

As continents rift or as mountains form, populations of organisms are separated. When populations are separated, new species may evolve from existing species.

The Supercontinent Cycle

supercontinent cycle the process by which supercontinents form and break apart over millions of years

Pangaea the supercontinent that formed 300 million years ago and that began to break up beginning 250 million years ago

Panthalassa the single, large ocean that covered Earth’s surface during the time the supercontinent Pangaea existed

Evidence of Pangaea

Pangaea Animations http://www.youtube.com/watch?v=WaUk94AdXPA

https://www.youtube.com/watch?v=uGcDed4xVD4

Tectonic Plates

Scientists have identified about 15 major tectonic plates.

Scientists identify plate boundaries primarily by studying data from earthquakes.

The locations of volcanoes can also help identify the locations of plate boundaries.

Types of Plate Boundaries

Types of Plate Boundaries

Types of Plate Boundaries

Plate Movement

Deformation - the bending , tilting, and breaking of Earth’s crust; The change in shape of volume of rock in response to stress

Isostasy - a condition of gravitational and buoyant equilibrium between Earth’s lithosphere and asthenosphere. When the weight of the lithosphere changes, the lithosphere sinks or rises until a balance is reached once again.

Isostatic adjustments The surfaces of mountains are worn away by erosion over millions of years, resulting in a

reduction of height and weight of the mountain range. The surrounding crust becomes lighter, and the area rises by isostatic adjustment in process called uplift.

Rivers carry a large load of sediment into large bodies of water, such as an ocean. The added weight to the area causes the ocean floor to sink by isostatic adjustment in a process called subsidence.

The growth and retreat of glaciers and ice sheets causes the lithosphere to sink, while the ocean floor rises because the weight of the overlying water is less. When glaciers or ice sheets melt, the land rises and the ocean floor sinks.

Plate Movement - Stress

Stress the amount of force per unit area that acts on a rock As Earth’s lithosphere moves, or when tectonic plates collide, these actions exert force on the rock

called stress.Compression is the type of stress that squeezes and shortens a body of rock. It reduces the amount of space that rock occupies, and pushes rocks higher up or deeper down into the crust.

Compression occurs at or near convergent boundaries. Tension is stress that stretches and pulls a body of rock apart. When rocks are pulled apart by tension, the rocks tend to become thinner.

Tension occurs at or near divergent boundaries.Shear stress distorts a body of rock by pushing parts of the rock in opposite directions. Sheared rocks bend, twist, or break apart as they slide past each other.

Shear stress occurs at transform boundaries

Plate Movement - Strain

strain any change in a rock’s shape or volume caused by stress. When stress is applied slowly, the deformed rock may regain its original shape when

the stress is removed. The amount of stress that rock can withstand without permanently changing shape is limited. If a stress exceeds the rock’s limit, the rock’s shape permanently changes. Materials that respond to stress by breaking or fracturing are brittle. Brittle strain appears as cracks

fractures. Ductile materials respond to stress by bending or deforming without breaking. Ductile strain is a

change in the volume or shape of rock in which the rock does not crack or fracture.

fold a form of ductile strain in which rock layers bend, usually as a result of compression. When rock deforms in a ductile way, folds form. Although a fold commonly results from compression, it can also from as a result of shear stress. Folds vary greatly in size. Some folds are small enough to be contained in a hand-held rock specimen. Other folds cover thousands of square kilometers can be seen only from the air.

Plate Movement - faults

fault a break in a body of rock along which one block slides relative to another; a form of brittle strain

Breaks in rock along which there is no movement of the surrounding rock is called a fracture.

A break along which the surrounding rock moves is called a fault.

A normal fault is a fault in which the hanging wall moves downward relative to the footwall. Normal faults commonly form at divergent boundaries.

When compression causes the hanging wall to move upward relative to the footwall, a reverse fault forms.

In a strike-slip fault, the rock on either side of the fault plane slides horizontally in response to shear stress. Strike-slip faults commonly occur at transform boundaries.

Great Rift Valley

Eastern Africa

Example of a Normal Fault

Resulting from Tension as the here three plates are pulling away from one another: the Arabian Plate and two parts of the African Plate - the Nubian and Somali—splitting along the East African Rift Zone.

San Andreas Fault, CA

Transform fault line

extends roughly 1300 km (810 miles) through California.

Forms boundary between the Pacific Plate and the North American Plate

Strike-slip fault

Steep Mountain

The Alps mountains were formed over tens of millions of years as the African and Eurasian plates collided.

The Himalaya's were formed as a result of a continental collision along the convergent boundary between the Indo-Australian Plate and the Eurasian Plate.

Plate movement results in compression and reverse Faults

Alps

Himalaya

Mountain formation Convergent Boundaries

Types of Mountains – folded mountains

folded mountain a mountain that forms when rock layers are squeezed together and uplifted

The highest mountain ranges in the world consist of folded mountains that form when continents collide.

The same stresses that form folded mountains also uplift plateaus, which are large, flat areas of rock high above sea level.

Most plateaus form when thick, horizontal layers of rock are slowly uplifted so that the layers remain flat instead of faulting and folding.

Colorado Plateau

Types of Mountains – fault-block mountains

fault-block mountain a mountain that forms where faults break Earth’s crust into large blocks and some blocks drop down relative to other blocks.

The same type of faulting that forms fault-block mountains also forms long, narrow valleys called grabens.

Grabens develop when steep faults break the crust into blocks and one block slips downward relative to the surrounding blocks.

Grabens and fault-block mountains commonly occur together.

The Hanging Hills of Connecticut

Types of Mountains – dome mountains

dome mountain a circular or elliptical, almost symmetrical elevation or structure in which the stratified rock slopes downward gently from the central point of folding

Dome mountains are rare, and form when magma rises through the crust and pushes up the rock layers above the magma.

Black Hill, South Dakota

Types of Mountains – volcanic mountains

Volcanic Mountains

Mountains that form when magma erupts onto Earth’s surface are called volcanic mountains, which commonly form along convergent plate boundaries.

Mt. St. Helen’s, WA

Types of Mountains in US

Earthquakes

earthquake a movement or trembling of the ground that is caused by a sudden release of energy when rocks along a fault move

elastic rebound the sudden return of elastically deformed rock to its undeformed shape

Earthquakes occur when rocks under stress suddenly shift along a fault. Geologists think that earthquakes are the result of elastic rebound. In this process, the rocks on each side of a fault are moving slowly. If the

fault is locked, the rock deforms, and stress in the rocks increases. When rocks are stressed past the point at which they can maintain their

integrity, they fracture. The rocks then separate at their weakest point along the fault and

rebound, or spring back to their original shape.

Anatomy of an Earthquake

epicenter the point on Earth’s surface above an earthquake’s starting point, or focus

focus the location within Earth along a fault at which the first motion of an earthquake occurs

Seismic Waves

As rocks along a fault slip into new positions, the rocks release energy in the form of vibrations called seismic waves.

Seismic waves travel outward in all directions from the focus through the surrounding rock.

body wave a seismic wave that travels through the body of a mediumP wave a primary wave, or compression wave; a seismic wave that causes particles of rock to

move in a back-and-forth direction parallel to the direction in which the wave is traveling P waves are the fastest seismic waves and can travel through solids, liquids, and gases. The more rigid the material is, the faster the P wave travels through it.S wave a secondary wave, or shear wave; a seismic wave that causes particles of rock to move

in a side-to-side direction perpendicular to the direction in which the wave is traveling S waves are the second-fastest seismic waves and can only travel through solids.

surface wave a seismic wave that travels along the surface of a medium and that has a stronger effect near the surface of the medium than it has in the interior

Although surface waves are the slowest-moving seismic waves, they can cause the greatest damage during an earthquake.

Seismic Waves and Earth’s Interior

Earth’s Internal Layers In 1909, Andrija Mohorovičić discovered that the speed of seismic waves increases abruptly at

about 30 km beneath the surface of continents, where the crust and mantle meet. By studying seismic waves, scientists have discovered Earth’s three composition layers (the

crust, the mantle, and the core) and Earth’s five structural layers (the lithosphere, the asthenosphere, the mesosphere, the outer core, and the inner core).

shadow zone an area on Earth’s surface where no direct seismic waves from a particular earthquake can be detected

Shadow zones exist because the materials that make up Earth’s interior are not uniform in rigidity.

When seismic waves travel through materials of different rigidity, they change in both speed and direction.

S waves do not reach the S wave shadow zone because cannot pass through the liquid outer core.

P waves do not reach the P wave shadow zone because of the way the P waves bend and they travel through Earth’s interior.

Shadow Zone

Earthquakes and Plate Tectonics

Most earthquakes occur at or near tectonic plate boundaries, where stress on the rock is greatest.

Convergent Oceanic Environments At convergent plate boundaries, plates move toward each other and collide. The denser plate moves down, or subducts, into the asthenosphere under the other plate, causing

earthquakes.

Divergent Oceanic Environments At the divergent plate boundaries that make up the mid-ocean ridges, plates are moving away from

each other. Earthquakes occur along mid-ocean ridges because oceanic lithosphere is pulling away from both

sides of the ridge.

Continental Environments Earthquakes also occur at locations where two continental plates converge, diverge, or move

horizontally in opposite directions. As the continental plates interact, the rock surrounding the boundary experiences stress, which

causes earthquakes.

Earthquakes Away from Plate Boundaries

Not all earthquakes result from movement along plate boundaries.

In 1811 and 1812 the most widely felt series of earthquakes in United States history occurred in the middle of the continent near New Madrid, Missouri.

In the late 1970s scientists discovered an ancient fault zone deep within the crust of the Mississippi River region.

Earthquakes and Tectonic Plates

Seismology

The study of earthquakes and seismic waves is called seismology.

seismograph an instrument that records vibrations in the ground

seismogram a tracing of earthquake motion that is recorded by a seismograph

Seismographs record three types of ground motion—vertical, east-west, and north-south.

Because they are the fastest, P waves are the first seismic waves to be recorded by a seismograph.

S waves are the second seismic waves to be recorded, and surface waves are the last to be recorded by a seismograph.

Locating an Earthquake

To determine the distance to an epicenter, scientists consult a lag-time graph and analyze the arrival times of the P waves and S waves.

The start time of an earthquake can also be determined by this graph.

Scientists use computers to perform complex triangulations based on information from several seismograph stations. These calculations help determine the location of an earthquake.

Before computers were widely available, scientists used simpler, less precise calculations together with maps to locate earthquakes.

Earthquake Measurement

magnitude a measure of the strength of an earthquake

Magnitude is determined by measuring the amount of ground motion caused by an earthquake.

While the Richter scale was widely used for most of the 20th century, scientists now prefer to use the moment magnitude scale.

intensity the amount of damage caused by an earthquake

Before the development of magnitude scales, the size of an earthquake was described in terms of the earthquake’s effects.

Tsunami

tsunami a giant ocean wave that forms after a volcanic eruption, submarine earthquake, or landslide

A tsunami may begin to form when the ocean floor suddenly crops or rises because of faulting associated with undersea earthquakes.

A tsunami may also be triggered by an underwater landslide caused by an earthquake.

volcano a vent or fissure in Earth’s surface through which magma and gases are expelled

magma liquid rock produced under Earth’s surface

Magma can form under three conditions.

First, if the temperature of the rock rises above the melting point of the minerals the rock is composed of, the rock will melt.

Second, rock melts when excess pressure is removed from rock that is above its melting point.

Third, the addition of fluids, such as water, may decrease the melting point of some minerals in the rock and cause the rock to melt.

lava magma that flows onto Earth’s surface; the rock that forms when lava cools and solidifies

Volcanoes and Plate Tectonics

Volcanic Eruptions

mafic describes magma or igneous rock that is rich in magnesium and iron and that is generally dark in color

felsic describes magma or igneous rock that is rich in feldspar and silica and that is generally light in color

Mafic rock commonly makes up the oceanic crust, where as felsic and mafic rock commonly make up the continental crust.

The viscosity, or resistance to flow, of magma affects the force with which a particular volcano will erupt.

Magma that contains large amounts of trapped, dissolved gases is more likely to produce explosive eruptions than is magma that contains small amounts of dissolved gases.

pyroclastic material fragments of rock that form during a volcanic eruption

Eruptions from oceanic volcanoes, such as those in Hawaii, are usually quiet.

Types of Volcanoes: Shield Volcanoes

Broad at the base and have gently sloping sides

Cover a wide area

Malfic lava flow out, cool and harden and slowly build up to form the cone

Quiet eruptions

Hawaiian islands form a chain of shield volcanoes that build up around a hot spot

Mauna Kea, Hawaii

Types of Volcanoes: Cinder Cones

Very steep slopes

Rarely more than a few hundred meters high

Explosive eruptions containing pyroclastic material.

Pu’u O’o Hawaii

Types of Volcanoes: Composite

Made of alternating layers of hardened lava flows and pyroclastic material.

Quiet and explosive eruptions

Also known as stratovolcanoes

Usually form large volcanic moutnains

Mt. Vesuvius, Naples, Italy

Types of Volcanoes: Caldera

Large, circular depression that forms when the magma chamber below a volcano partially empties and causes the ground above to sink

Eruptions that discharge large amounts of magma can also cause a caldera to form.

Calderas may later fill with water to form lakes.

Predicting Volcanic Eruptions

One of the most important warning signals of volcanic eruptions is changes in earthquake activity around the volcano.

Before an eruption, the upward movement of magma beneath the surface may cause the surface of the volcano to bulge outward.

Major Volcanic Zones

Like earthquakes, most active volcanoes occur in zones near both convergent and divergent boundaries of tectonic plates.

A major zone of active volcanoes encircles the Pacific Ocean.

This zone, called the Pacific Ring of Fire, is formed by the subduction plates along the Pacific coasts of North America, South America, Asia, and the islands of the western Pacific.

Many volcanoes are located along subduction zones, where one tectonic plate moves under another.

Major Plates & Ring of Fire

Hot Spots

hot spot a volcanically active area of Earth’s surface, commonly far from a tectonic plate boundary

Most hot spots form where columns of solid, hot material from the deep mantle, called mantle plumes, rise and reach the lithosphere.

As magma rises to the surface, it breaks through the overlying crust. Volcanoes can then form in the interior of a tectonic plate.

However, the lithospheric plate above a mantle plume continues to drift slowly.

So, the volcano on the surface is eventually carried away from the mantle plume.

The activity of the volcano stops because a hot spot that contains magma no longer feeds the volcano.

However, a new volcano forms where the lithosphere has moved over the mantle plume.

Hawaii – hot spot

Ocean Basin

74% of Earth’s surface is covered with water

97% of all Earth’s water is in the oceans.

Oceanography – study of Ocean water and ocean floor

Mountains and volcanoes are found on the ocean floor

Earthquakes occur on the ocean floor

Deepest place in the Earth’s crust is in the ocean floor – Mariana’s Trench

Mapping the Ocean Floor

Sonar

sonar sound navigation and ranging, a system that uses acoustic signals and returned echoes to determine the location of objects or to communicate

Scientists measure the time that the sound waves take to travel from the transmitter, to the ocean floor, and to the receiver in order to calculate the depth of the ocean floor.

Scientists then use this information to make maps and profiles of the ocean floor.

Continental and Oceanic Crust

Continental Margin

continental margin the shallow sea floor that is located between the shoreline and the deep-ocean bottom

Continental Shelf Continents are outlined in most places by a zone of shallow water where the ocean

covers the end of the continent. The shelf usually slopes gently from the shoreline and drops about 0.12 m every 100

m. The average depth of the water covering a continental shelf is about 60 m.

Continental Slope and Continental Rise At the seaward edge of a continental shelf is a steep slope called a continental slope. The collection of sediments form a wedge at the base of the continental slope called

a continental rise.

Deep Ocean Basin

deep-ocean basin the part of the ocean floor that is under deep water beyond the continental margin and that is composed of oceanic crust and a thin layer of sediment

These features include broad, flat plains; submerged volcanoes; gigantic mountain ranges; and deep trenches.

In the deep-ocean basins, the mountains are higher and the plains are flatter than any features found on the continents are.

Deep Ocean trenches & abyssal plain

trenches a long, narrow, and steep depression that forms on the ocean floor as a result of subduction of a tectonic plate, that runs parallel to the trend of a chain of volcanic islands or the coastline of a continent, and that may be as deep as 11 km below sea level; also called an ocean trench or a deep-ocean trench

Earthquakes occur near trenches. Volcanic mountain ranges and volcanic island arcs also form near trenches

abyssal plain a large, flat, almost level area of the deep-ocean basin

Abyssal plains cover about half of the deep-ocean basins and are the flattest regions on Earth.

Layers of fine sediment cover the abyssal plains. The thickness of sediments on the abyssal plains is determined by three factors.

Mid-Ocean Ridges & Seamounts

Mid-Ocean Ridges most prominent The most prominent features of ocean basins are the mid-ocean ridges, which form

underwater mountain ranges that run along the floors of all oceans.

Mid-ocean ridges rise above sea level in only a few places, such as in Iceland.

The largest amount of magma comes to the surface where plates are moving apart at mid-ocean ridges.

Seamounts

Submerged volcanic mountains that are taller than 1 km are called seamounts. Seamounts form in areas of increased volcanic activity called hot spots.

Seamounts that rise above the ocean surface form oceanic islands.

As tectonic plate movements carry islands away from a hot spot, the islands sink and are eroded by waves to form flat-topped, submerged seamounts called guyots or tablemounts

Continental and Oceanic Crust

Ocean Floor Feature

Tectonic Plate Boundary

Trench

Mid-ocean ridge

Gyout & seamount