Plate Tectonics Theory of Continental Drift • Alfred Wegener suggested that continents had once been part of

supercontinent named ________, that later broke up. • The pieces moved apart over ________ of years and formed the separate

________ we know today. • These ideas are known as the Theory of ________________. • Evidence of continental drift includes:

• ________ in mountain ranges of eastern North America and western Europe are similar.

• ________ found in South America and South Africa suggest these continents were once joined.

• ________ and ________ living only in South America, Africa and Australia suggest that these continents were once linked but moved apart.

Theory of Plate Tectonics Tectonic Plates

• The lithosphere is made up of the ______ and the upper layer of the ______;

• It is ________ and ________, and can fracture during earthquakes;

• The lithosphere is divided into pieces called ________ plates;

• These plates float on the hot, plastic __________ (lower region of the mantle), which is too hot to ever fracture (although it can be stretched);

• Tectonic plates can either contain both __________ and ________ crust, or only ________ crust;

• There are a dozen ________ plates and many ________ plates.

Plate Movement • Tectonic plates move because of _________ currents in the mantle;

• Magma is heated up near the core and becomes less ______ and ________;

• Rising magma pushes plates apart at ________ centres in oceans, called __________ boundaries;

• Where oceanic plates collide with continental plates, the oceanic plate will ________ under the continental plate and be _____________ into the mantle (subducted).

• Continental crust is less ________ than oceanic crust and never ________.

• Continental crust is forever pushed around the ________ of the earth, and consequently contains the ________ rocks on earth.

• Oceanic crust is continually being ________ and is much ________.

Video: Plate Tectonics

1. The _________ _________ theory is the theory that the Earth’s outer layer is made up of plates that have moved throughout history.

2. Tectonics comes from the greek work “one who _________”.

3. About 250 million years ago, the Earth had one unified supercontinent

(landmass) called ___________.

4. Continental drift was first proposed by a scientist named

________________.

5. Evidence for continental drift includes:

a. common __________________

b. __________________ remains

c. old __________________ belts

d. __________________ and __________________ deposits

6. Submarines noticed a pattern of __________________ stripes on the

ocean floor. These represent magnetic __________________, which

occur when the Earth’s magnetic field flips.

7. __________________ spreading is when 2 plates move away from each

other, allowing magma to rise from the Earth’s interior and making new ocean floor.

8. In summary, 2 pieces of evidence that give rise to plate tectonics are:

a. ____________________________________

b. ____________________________________ 9. The crust and upper mantle form a rigid outer shell called the

______________.

10. The weak, mushy, partially melted layer beneath the lithosphere is called

the __________________.

11. The rigid __________________ floats on the __________________ .

12. The lithosphere is broken up into __________________ that slide about.

13. There are about __________________ major plates, and several minor

ones.

14. Plates may contain both ______________ crust and _______________ crust.

15. The Earth’s plates move at a rate of about _________ per year.

16. We can measure plate movement directly using __________________.

17. Inside the Earth, molten material is able to flow, causing __________________.

18. Convection drives the __________________ of the plates.

Plate Boundaries • Plate boundaries are marked by ________, ________, ________ ranges and

ocean ________.

• There are three main types of plate boundaries: 1) __________ Boundaries (or Spreading Centres)

• Where plates are spreading apart;

• Huge mountain ranges found beneath the Earth’s oceans known as mid-ocean ________;

• Basaltic ________ pours out from the ridges and spreads out to form new oceanic crust.

__________ Boundaries

• Where two plates collide;

• When continental plates collide, neither plate is ________ enough to be pushed down, so the land ________ like a car hood in a car crash (“uplifting”), forming ________ ranges;

• When continental plates collide with oceanic plates, ________ occurs – the oceanic plate sinks beneath the continental plate;

• ________ are found beneath the ocean where the oceanic crust subducts;

• When two oceanic plates collide, usually one plate ________ beneath the other.

3) Transform Boundaries:

• Where two plates ______ by each other instead of subducting and

uplifting;

• Results in frequent __________.

INSERT BOUNDARY MAP ACTIVITY

Continental Growth

• The ancient core of a continent is called the ________.

• The cratons are much smaller than the __________ we see today.

• Growth material for the continents comes from:

1) deep sea ________ (scraped off subducting plates)

2) ________ rock

3) sediments deposited by ________ that flow across the continent.

VOLCANOLOGY – THE STUDY OF VOLCANOES

Magma – forms wherever ________ and ________ are high enough to melt

rock.

• Some magma forms at the ______________

• Magma also forms at plate __________, where intense heat and pressure

develops from ________ between the plates.

Volcanoes • Melted rock ______ as it heats up, becoming less dense than surrounding

rock.

• Magma moves upwards through __________;

• If magma reaches the surface, it erupts through an opening called a

________.

Magmas

• Felsic magmas: high ________, thick, ________-coloured, slow-moving

• Mafic magmas: low ________, thinner, ________-coloured, flow more easily

Volcanic Eruptions

• Magmas contain ________ gases (i.e., water vapour, carbon dioxide)

• As magma reaches the surface, ________ is reduced and dissolved gas

comes out of solution as ________ of gas.

• Bubbles expand and ________…therefore…

LOTS OF GAS = MORE EXPLOSIVE ERUPTIONS!

• Mafic magmas are more _______ and let gases escape more easily than

felsic magmas

MAFIC MAGMAS = LESS EXPLOSIVE

FELSIC MAGMAS = MORE EXPLOSIVE

Lava and Lava Fragments

• If magma reaches the surface of the earth, it is called ________

• Explosive eruptions produce lava fragments called ________

TEPHRA CLASSIFICATION:

________ < 2mm

________ 2 mm – 64 mm

________ >64 mm

• ___________ FLOW: in explosive eruptions, tephra combines with gases to

form a dense, superheated _______ traveling at very high speeds (> 100

km/h)

Volcano Hazards

1. Ash • Gritty ________-sized particles blasted from erupting volcano • Can reach very high ________. • Large amounts can block sunlight, causing world __________ to

drop. • Can destroy ________, ________, clog ________, damage

_______.

2. Lava • Molten rock may ______ over large areas, destroying everything in

its path.

3. Pyroclastic flow • Destructive mix of ____________ gas, ash and debris, which can

move > 100 km/h.

4. Lahar • Flow of mud, water, ash and debris that can result when _____-

covered volcanoes erupt.

Mount Baker—Living with an Active Volcano

1. a) Name and briefly describe the four possible volcano hazards at Mt. Baker.

b) Which hazard is considered to be of greatest concern? Why?

2. Describe the two ways that lahars can form.

3. When did volcanic activity begin in the Mt. Baker area? ________________ 4. In recent Mt. Baker history, when did:

a) Lava flow from the summit vent? ______________ b) Pyroclastic flows pour down its side? ______________ c) Mt. Baker have its last major eruption? ______________ d) Mt. Baker have its last lahar flow? ______________

5. What observations had scientists worried that Mt. Baker might erupt in 1975?

6. What signs did scientists look for that would have confirmed that magma was rising under the volcano?

7. What monitoring is currently being done at Mt. Baker?

TYPES OF VOLCANOES There are three main ways volcanoes are formed: 1. __________ boundaries

(composite volcanoes):

• As ocean plate sinks beneath the ________ plate, increasing heat melts the rock, forming magma.

• Magma is lighter than the surrounding solid rock, so it rises up through the edge of the continental plate to form a ________.

• Form classic, _____-shaped volcanoes that erupt ____ and ______ • Cone shape results from ________ of ash and lava building up over time • Magma is usually __________ (very thick), and traps gas producing

__________ eruptions • i.e, Mt. Baker

2. Divergent boundaries (rift eruptions):

• Magma flows out of volcanoes at __________ ridges; • occasionally, volcanoes grow high enough to rise above the ________ of

the ocean and produce ________ • i.e, Iceland

3. Hot Spots (shield volcanoes):

• Sometimes extremely high temperatures are found beneath the ________ of oceanic plates, in areas called _____________.

• At these locations, the melting of crustal rock produces magma that rises up to form a volcano. As the plate moves, it carries the hot spot with it, so that ________ of volcanic islands are formed

• Magma is usually ______, so eruptions are not ________ and volano’s sides have a ________ slope.

• i.e., Hawaii

Plutons and Volcanism Magma squeezes through __________ and rock _________ as it rises. • Igneous rock masses that form inside other rocks are called _________. • Structures are named according to their _______ and __________. __________ • sheets of igneous rock that cut across the rock layers they intrude

(usually mafic) __________ • sheets of igneous rock that are parallel to the rock layers they intrude (also

usually mafic) __________ • dome-like masses of igneous rock formed by stiff magma which, instead of

spreading, bulges upwards (usually felsic). __________ • plug of magma that hardened inside the vent of a volcano __________ • largest of intrusions; forms the core of many mountain ranges (usually felsic) __________ • small batholith ( < 100 square kilometers exposed at the surface).

Chapter 14 Review – Volcanoes Name: _____________

1. For each of the following, choose the phrase in Column B that best describes the term in Column A, and mark its letter in the blank space.

___1. Magma a. rock mass crystallized within another rock ___2. Lava b. large piece of solid rock thrown into the air during an

explosion ___3. Felsic c. largest of all igneous intrusions ___4. Mafic d. solid fragments of lava produced in explosive eruptions ___5. Ash e. flat sheet of igneous rock that cuts across rock layers. ___6. Tephra f. Molten rock within the Earth ___7. Sill g. Type of molten rock on Earth’s surface that is thick and stiff ___8. Lapilli h. Fragment of lava that solidifies in the air ___9. Dike i. Flat sheet of igneous rock parallel to the intruded rock layer ___10. Block j. Sill that forms a domelike mass ___11. Neck k. Molten rock on Earth’s surface ___12. Stock l. The smallest piece of tephra ___13. Batholith m. Pluton whose exposed area is less than 100 sq. km ___14. Bomb n. Piece of tephra between 2 and 64 mm ___15. Laccolith o. Type of molten rock on Earth’s surface that is thin and fluid ___16. pluton p. Hardened lava in the vent of an eroded volcano

2. What are the names of the three “types” of volcanoes? a) __________ b) ____________ c) _____________ 3. Explain what a “Hot Spot” is, and give an example: _____________________________________________________________________________________________________________________________ 4. a) Which type of magma is the “explosive” type? __________________

b) What makes this type of magma so explosive?_________________________ ______________________________________________________________

5. During eruptions, many different types of lava fragments occur:

a) The general term for the fragments is ___________. b) Name the different types of fragments:

- less than 2 mm in diameter: _____________ - up to 64 mm in diameter: _____________ - more than 65 mm in diameter: _____________

6. Fill in the blanks with the most correct response. Each word may only be used once.

Less dense felsic subduction zones Gases tephra composite Lava rifts mafic Aesthenosphere magma silica

a) Volcanoes are caused by a surge of _________ to the Earth’s surface. b) Melted rock that comes to the surface is called _________. c) The magma rises because the liquid is ___________ than the surrounding rock. d) Magma is formed both in the _________, and at __________________. e) Fast-flowing magma is made of a _________type of molten rock, while a slow-

flowing magma is made of a _________ type of molten rock. f) Felsic magma contains a lot of _________, while mafic magma contains little. g) Violent eruptions are mostly due to _________ inside the liquid rock. h) The most common type of volcano, the _________ type, form at subduction

zones. i) The type of volcanoes that occur at _________ are shield type. j) _________ are the solid rock fragments that are released from volcanoes.

7. Name and describe the four main hazards of a volcanic eruption:

1) ___________ _______________________________________________ 2) ___________ _______________________________________________ 3) ___________ _______________________________________________ 4) ___________ _______________________________________________

_________________________________________________________

8. Sketch a composite volcano, and label its parts.

9. Sketch and label the different plutonic structures that form within the Earth.

Seismology – The Study of Earthquakes

• Earthquakes occur when rock masses in the Earth’s outer layer move along ______ lines.

• Focus – the location on a fault where there is the __________ amount

of movement, __________ the surface of the earth. • Epicentre – point on the __________ that is directly __________ the

focus.

Causes of Earthquakes:

• Rock masses on either side of a _______ are pushing past one another.

• Rock masses ______ and __________ until there is enough stored energy to overcome __________ between the rock masses;

• this energy is then is quickly released as kinetic ________ during an earthquake – Elastic Rebound Theory.

Earthquake Waves

P waves – longitudinal wave; - particles move _________ to the direction of the wave. - Almost twice as ______ as S waves. - Travel through ______ and ______ (crust, mantle and core)

S waves – transverse wave;

- particles move _____________ to the direction of the wave. - Travel ______ than P waves. - Travel only through ______ (lithosphere)

Love waves - Surface waves:

- ground motion is a _________ action, like ripples on a pond.

- Travels along __________of the Earth.

IMPORTANT: P Waves almost ____ as fast as S Waves

Locating an Earthquake:

The seismometer

• Instrument used to measure the ground _________ resulting from earthquakes.

• Produces a _________ tracing on a paper by a pen • Tracing is called a _______________

Determining the Distance to the Epicentre

• P waves are _________ than S waves; therefore, P waves arrive at a

seismograph station _________ the S waves. • The time interval between the _________ of P and S waves at a

seismograph is used to determine the _________ to epicenter. • Time-distance graph is used as a tool to calculate distance to epicenter

(p. 235, text) Locating the Epicentre • Need _________ different locations using the time-distance graph to

calculate the epicenter. • Draw a _________ around each seismograph with a _________ equal

to the distance to the epicenter. • The location where the three circles _________ is the epicenter.

Measuring an Earthquake - Earthquake Magnitude • The Richter Scale is a standardized scale of earthquake _________

(amount of shaking) • Each point represents vibrations that are ___ times greater than the

point below it. • Each tenfold increase in vibrations means ___ times more energy

released.

Richter Magnitude

Earthquake Effects Estimated no. per year

<2.5 Generally not felt, but recorded 900 000 2.5 – 5.4 Often felt, but only minor damage

detected 30 000

5.5 – 6.0 Slight damage to structures

500

6.1 – 6.9 Can be destructive in populous regions 100 7.0 – 7.9 Major earthquakes.

Inflict serious damage 20

>8.0 Great earthquakes. Produce total destruction to nearby communities

One every 5-10 years

Earthquake Damage • The Mercalli Scale is used to estimate the _________ of an earthquake by

comparing amount of damage • Damage done is not always an adequate means for comparison – depends

on: o _________ from epicenter o Nature of _________ materials o Building _____________

Modified Mercalli Intensity Scale I Not Felt II Felt only be persons at rest III – IV Felt by persons indoors only V – VI Felt by all, some damage to plaster, chimneys VII People run outdoors, damage to poorly built structures VIII Well-built structures slightly damaged; poorly-built structures

suffer major damage IX Buildings shifted off foundations X Some well-built structures destroyed XI Few masonry structures remain standing; bridges destroyed XII Few masonry structures remain standing; bridges destroyed

Earthquake Hazards

1. Ground shaking • The result of the waves set in _________ by the earthquake • Some _________ move up and down while others move side to side • Most buildings can withstand large ___-and-______ vibrations, but not

_____-to-____ (cause collapse) 2. Liquifaction

• Vibrations cause __________ to rise, turning solid ground into a liquid-like material.

• Buildings built on solid rock experience little damage; buildings located on bog muds or soft fill suffer severe damage

3. Tsunamis

• Large sea waves produced when earthquakes occur under _________. • Caused by a large _______________ in the water column

Earthquake Waves inside the Earth As waves travel through earth, P- and S- waves change velocity, bend, or get reflected At 2900 km:

• Boundary between mantle (_____) and outer core (______) • P-waves _________ down • S-waves _________ (don’t travel through liquids)

At 5200 km: • P-wave velocity _________ • (approaches inner core – _________)

Mohorovicic Discontinuity (The Moho)

• Another abrupt change in P - and S-wave velocities occurs at the boundary between the _________ and the _________

• Discovered in 1909 by Andrija Mohorovicic : • Found that seismograms showed _________ distinct groups of P- and

S-waves • One of the groups traveled at an average velocity of ___km/s • The other group of waves traveled at ___ km/s • Mohorovicic reasoned that the faster wave group had one through

_________ material below the crust • This is the boundary between the crust and the mantle – named “The

_________” • The Moho is about 32km deep under _________but only 8km deep

below the _____

Shadow Zone • Even though an earthquake sends waves

throughout Earth’s _________, not all seismograph stations receive information.

• Seismic stations that don’t receive P or S-waves are said to be in the _________ zone

• Caused by Earth’s _________ core • P-waves refract (_________) when they pass

through the mantle • S-waves cannot travel through the outer core

(______)

Vancouver’s Next “Big Earthquake” • The Juan de Fuca Plate, Explorer Plate, and Gorda Plate are all

_________ under the North American Plate • Each of the three plates have _________ fault lines • Will most likely be produced by _________ and _________ generated

at a transform fault or along a subduction zone

Mountain Building • Mountain ranges form wherever tectonic plates _________. • Where oceanic crust _________ under continental crust, magma deforms the

continental crust forming mountains and volcanoes. • Where two continental tectonic plates collide, the plates _________ like car

hoods in a crash, forming vast mountain ranges. Faults • Faults are _______or cracks in the

Earth’s crust along which movement has occurred.

• The surface that separates two moving pieces of crust is called the fault ______.

Three types of Faults: 1) _________: rocks on one side

of fault plane drop down below rocks on the other side.

2) _________: rocks on one side are driven up over the other side.

3) _________ : rocks on opposite sides of fault plane move horizontally past each other.

Folds • During plate collisions, rock layers along

continental margins sometimes crumple into folds: • Anticlines: _________ in the rock layers • Synclines: _________ in the rock layers Uplifting • At some plate boundaries, sedimentary layers are

_________ to high levels with little deformation – end up with aquatic fossils and beaches at high _________.

Tilting/Overturning • Most sedimentary rocks are formed in _________ layers • Folding and uplifting may result in layers being _________

• Sometimes rocks are tilted over on themselves and end up _________ – “overturned”.

FAULTS WORKSHEET