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Chapter 4 . ROCKS “The Mixture of Minerals”. Rock – a naturally occurring solid mixture of crystals of one or more minerals. Rock Cycle – the continual process by which new rock forms from old rock material. Rocks are always changing. The Rock Cycle.

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Chapter 4

ROCKS “The Mixture of Minerals”

  • Rock – a naturally occurring solid mixture of crystals of one or more minerals.

  • Rock Cycle – the continual process by which new rock forms from old rock material.

    • Rocks are always changing.

The Rock Cycle

  • Weathering – the process in which water, wind, ice, and heat break down rock.

    • Weathering is very important:

      • Breaks down rock into fragments called sediment.

      • The fragments are the materials that are used to make sedimentary rocks.

Weathering, Erosion, and Deposition

  • Physical Weathering – Any process in which rocks are broken down by contact with the Earth’s atmosphere and water.

  • Chemical Weathering – Occurs when chemical reactions break down the bonds holding the rocks together.

    • Most common in areas that contain large amount of water.

Types of weathering

  • Erosion – the process by which sediment is removed from its source.

    • Different types of erosion:

      • Wind

      • Ice

      • Water

      • Gravity

Weathering, Erosion, and Deposition

  • Deposition – the process in which sediment moved by erosion is dropped and comes to rest.

    • Once deposited, sediments may be compressed and cemented to form a sedimentary rock.

Weathering, Erosion, and Deposition

Heat and pressure may cause a rock to chemical change into a metamorphic rock.

If the rock gets too hot it will melt which eventually cools to form igneous rocks.

Heat and Pressure

  • Foliation – The set of layers visible in many metamorphic rocks as a result of flattening and stretching of mineral grains during metamorphism.


  • Bedding – layers of sedimentary rock.

    • This can also be referred to as strata.


The relationship of heat and pressure:

Heat and Pressure

  • ^Pressure ^ Heat

  • ^ Heat ^ Pressure

Gravitational Potential Energy – is the potential energy associated with gravitational forces, as work is required to elevate objects against Earth’s gravity.

Mechanical energy

  • Rock is exposed at the Earth’s surface by a combination of uplift and erosion.

    • Uplift – is the movement within the Earth that causes rocks inside the Earth to be moved to the Earth’s surface.

    • After uplift, the rock reaches the surface, and the cycle continues.

How the Cycle Continues

Round and Round It Goes

You are going to need your notebook for this activity.

In the output section record 10 rolls of the dice. (Write down what the dice said.)

You may never move from a station but continue to roll the dice at that station and write down what the dice said.

Once you have finished return to your seat.

A Trip around the rock cycle

  • Three main classes of rock:

    • Igneous

    • Sedimentary

    • Metamorphic

      In order to identify rocks scientist break the rocks up into two categories:

      Composition and Texture

Rock Classification

  • Composition – the chemical makeup of a rock; describes either the minerals or other materials in the rock.

    • Determined by the minerals contained in the rock.

    • Ex. A rock made of mostly the mineral quartz will have a composition very similar to that of quartz.


  • Texture – is the quality of a rock that is based on the sizes, shapes, and positions of the rock’s grains.

  • There are three different grains of texture:

    • Fine-grained

    • Medium-grained

    • Coarse-grained


  • The amount of time that a igneous rock is allowed to cool determines the texture of the rock.

    • If the rock cools quickly then it will be fine grained.

    • If the rock cools slowly then it would be coarse grained.

    • The texture of a rock can reveal the processes that formed it.


Fine Grained “Silkstone”

Medium Grained “Granite”

Coarse Grained - conglomerate


Your assignment: Create a children’s story, comic strip, or some other creative story about Roger the Rock.

Roger is a rock that has been a part of the rock cycle for millions of years. Your job is to tell Roger’s story. You must describe how Roger was “born” and at least three transitions that occurred during Roger’s life. (For example, changing from igneous to sedimentary, sedimentary to metamorphic, and metamorphic to igneous.)

Your grade will be based on in-class work, the accuracy of your information, creativity, and neatness/effort. This should be a story appropriate for a children’s story (think back to 2nd grade here!), including pictures.

To earn an “A”, you need to include many details-the names of specific rock types, descriptions about what causes the changes to occur, etc.

This project will be due on the day of Chapter 4 Test. These projects will be presented by you and your partner.


End of Section 4.1

  • Mantle Convection – the slow creeping motion of Earth’s rocky mantle caused by convection currents carrying heat from the interior of the Earth to the surface.

  • Convection Currents – the uneven heating of rock in the Earth’s asthenosphere that causes rock to rise and sink.

Mechanisms that drive lithospheric plates

Mantle Convection

Ridge Push – Gravitational force that causes a plate to move away from the crest of an ocean ridge, and into a subduction zone.

Mechanisms that drive lithospheric plates

  • Gravity Pull/Slab Pull – another force where the weight of a sub-ducting slab pulls the plate at the surface down.

    • Colder ocean plates are denser.

Gravity Pull

Wegener’s Continental Drift Hypothesis

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

    • Alfred Wegener proposed the theory in the early 1900’s.

Wegener’s Continental Drift Hypothesis

  • Supporting Evidence

    • Plates Fit together like a puzzle.

    • Fossil Evidence across continents.

    • Rocks matched across seas.

    • Glacial striations on rocks matched on Africa and South America proving a once super continent.

    • Coal on Antarctica proves that it was once warm.

Wegener’s Continental Drift Hypothesis

Wegener’s Continental Drift Hypothesis

Wegener’s Continental Drift Hypothesis

  • Inconclusive Evidence

    • No credible evidence that explained why the continents moved.

      • Wegner thought that the continents just “plowed” through the rocks.

      • Many scientist concluded that the continents would have broken into several different pieces if this were to true.

The Drifting Continents

  • 245 million years ago

  • Pangaea (Means entire Earth) existed when some of the earliest dinosaurs were roaming the Earth.

  • Panthalassa (all sea) The ocean that once covered the Earth.


The Drifting Continents

  • 180 Million Years ago Pangaea gradually breaks up into two pieces.

    • Laurasia

    • Gondwana

The Drifting Continents

  • 65 million years ago.

  • Dinosaurs became extinct and Laurasia and Gondwana split into two smaller pieces.

Mid-Ocean Ridges and Sea-Floor Spreading

  • Sea-floor spreading – the process in which new oceanic lithosphere forms as magma rises toward the surface and solidifies.

    • A chain of submerged mountains runs through the center of the Atlantic Ocean.

      • Also known as Mid-ocean Ridges

Mid-ocean ridges and Sea-Floor Spreading

  • As tectonic plates move away from each other, the sea floor spreads apart and magma fills in the gap.

  • New crust forms, older crust gets pushed away from the mid-ocean ridge.

Mid-ocean Ridges and Sea-Floor Spreading

Evidence for Sea-Floor Spreading: Magnetic Reversals

  • Biggest evidence comes from magnetic reversals recorded in the ocean floor.

    • North and South poles have changed places many times.

  • Magnetic Reversal – the process in which magnetic poles change places.

How magnetic reversal works.

  • Tiny grains of magnetic minerals are found at the mid-ocean ridges.

  • Mineral grains contain iron and are like compasses.

  • They align with the magnetic field of the Earth.

  • When the rock cools, the record of theses tiny compasses remains in the rock.

Magnetic Reversals and Sea-Floor Spreading

  • Rock is slowly taken away from the spreading center of the ridge as sea-floor spreading occurs.

Evidence for Sea-Floor Spreading: Magnetic reversals

Seafloor Spreading

  • Activity on seafloor spreading.

The Theory of Plate Tectonics

  • Plate Tectonics – the theory that explains how large pieces of the Earth’s outermost layer called tectonic plates, move and change shape.

Tectonic Plate Boundaries

  • Boundary – a place where tectonic plates touch.

  • There are three different types of boundaries:

    • Convergent

    • Divergent

    • Transform

Convergent Boundaries

  • Convergent Boundary – the boundary formed by the collision of two lithospheric plates.

  • There are three different types of convergent boundaries:

    • Oceanic – Oceanic

    • Oceanic – Continental

    • Continental - Continental

Oceanic – Oceanic Plate Boundaries


Oceanic – Oceanic Convergent Boundary

  • Normally one of the oceanic plates will subduct below the other.

    • The older plate is usually the one that gets pushed down because it has a greater density.

  • Eventually magma is formed because of the increased pressure causing volcanoes to form over the top of the layer.

    • Eventually the volcanoes will peak out of the water and if they continue to grow the will form island chains.

      • Ex. Japan

Oceanic – Oceanic Plate Boundary

Continental – Oceanic Plate Boundaries “Mt. Adams”


Continental – Oceanic Plate Boundaries

  • When the two plates collide the less dense continental plate will rise up on top of the more dense oceanic plate.

    • The subducted plate will become molten due to the increase in temperatures.

    • The magma will then rise because it is less dense than the mantle that is surrounding it.

      • As the magma rise it will cause volcanic and earthquake activity.

Continental – Oceanic Plate Boundaries

Continental – Continental Plate Boundaries


Continental – Continental Plate Boundaries

  • The process in which two land masses collide together. Normally the landmass that is the least dense will subduct only slightly below the other.

    • Mountains will form because the two colliding plates are very light in comparison to the mantle.

Divergent Plate Boundaries

  • Divergent Boundary – the boundary between two tectonic plates that are moving away from each other.

    • New Sea floor forms at divergent boundaries.

    • Mid-ocean ridges is the most common type of divergent boundary.

Divergent Plate Boundaries

Transform Boundaries

  • Transform Boundary – The Boundary between tectonic plates that are sliding past each other.

  • Ex. San Andreas Fault in California.

    • One of the few faults that can be visibly seen.

    • One of the major causes of Earthquakes.

Output: Pushing and Pulling Mountains

  • Draw an example of the five different plate boundaries.

  • Label and describe what happens at each different plate boundary.

Transform Plate Boundaries

Plate Summary

Possible Causes of Tectonic Plate Motion

  • Asthenosphere flows very slowly.

  • This movement occurs because of the change in density within the asthenosphere.

    • Density changes because of the outward flow of energy within the Earth.

      • Hot rock expands and rises.(Less Dense)

      • Cool rock contracts and sinks. (More Dense)

Possible Causes of Tectonic Plate Motion

Tracking Tectonic Plate Motion

  • Tectonic plates move roughly 5cm per year.

    • The rate is so slow that it cannot be seen nor felt except during an Earthquake.

  • Plate movement is tracked by GPS.

Fall Zone

  • The fall zone marks the geologic boundary of hard metamorphosed terrain and the sandy, relatively flat outwash plain of the upper continental shelf.

    • The transition from the harder metamorphosed rock to the softer sediment creates water falls.

  • Formed from the erosion of the mountain regions of NC to help form the Sandy coastal plain regions.

Volcanic Eruptions

  • Volcanoes – are areas of Earth’s surface through which magma and volcanic gases pass.

    • Explosion of a volcanic eruption can turn an entire mountain into a billowing cloud of ash and rock in a matter of seconds causing global climate temperatures to drop.

    • Help form fertile land.

    • Create some of the largest mountains on earth.

Volcanic Eruptions

  • Magma – melted rock below the Earth’s surface.

  • Lava – Melted rock above the Earth’s surface.

Mt. Cleveland- Aleutian Islands, Alaska

Stromboli Volcano - Sicily

Mount Redoubt - Alaska

Types of Lava Flows

  • Pahoehoe lava flows – sheet like lava flows that result in continuous surfaces.

    • Flow smoothly

    • Move forwards in tongues or lobes and are characterized by a glassy, plastic skin.

Pahoehoe Lava Flow

Types of Lava Flows

  • Aa – lava pours out quickly and forms a brittle crust.

    • The crust is torn into jagged pieces as molten lava continues to flow underneath.

    • Got its name because of the painful experience of walking barefoot across the jagged surfaces.

    • Associated with lava fountaining.

Aa Lava Flow

Lava Fountaining

  • Lava Fountaining – spraying of lava into the air pulsing with the pressure of escaping gases.

Types of Lava Flows

  • Pillow lava – forms when lava erupts underwater.

    • Lava forms rounded lumps that are the shape of pillows.

What erupts from a Volcano?

  • Lava – liquid magma that flows from a volcanic vent.

  • Pyroclastic material - forms when magma is blasted into the air and hardens.

    • Nonexplosive eruptions produce mostly lava.

    • Explosive eruptions produce mostly pyroclastic material.

    • Volcano’s eruptions may alternate between lava and pyroclastic eruptions.

Pyroclastic Material

Volcanic Bombs

  • Volcanic Bombs – large blobs of magma that harden in the air.

    • The shape of the bomb was caused by the magma spinning through the air as it cooled.


  • Lapilli – pebblelike bits of magma that hardened before they hit the ground.

    • Means “little stones”

Volcanic Ash

  • Volcanic Ash – forms when the gases in stiff magma expand rapidly and the walls of the gas bubbles explode into tiny, glasslike slivers.

    • Makes up most of the pyroclastic material in an eruption.

Volcanic Ash

Pyroclastic Flows

  • Pyroclastic Flow – produced when enormous amounts of hot ash, dust, and gases are ejected from a volcano.

    • Can move downhill at 200km/h.

    • Center of the flow can exceed 700 C.

End of Section 9.1

Effects of Volcanic Eruptions

June 10, 1816 Connecticut

“Dear Diary, The clothes my wife had laid out to dry the day before had frozen during the night.”

Volcanic Eruptions and Climate Change

  • 1815, Mount Tambora blanketed most of Indonesia in darkness for more than 3 days.

    • 12,000 people died directly from the explosion.

    • 80,000 people died from the resulting hunger and disease.

Mauna Kea - Shield Volcano

Cinder Cone Volcanoes

Mt. St. Helens

Mt. St Helens

Mt. Fuji


  • Crater – funnel-shaped pit found around the central vent at the top of many volcanoes.

    • When eruption stops, lava drains back underground making a larger collapsed crater.

    • Next eruption may blast it away creating a larger and deeper crater.

Kamchatka, Russia


  • Caldera – a large, semicircular depression that forms when the magma chamber below a volcano partially empties and causes the ground above to sink.

    • Much larger than a crater.

Crater Lake, Washington

Lava Plateaus

  • Lava Plateau – a wide, flat landform that results from repeated nonexplosive eruptions of lava that spread over a larger area.

    • Formed from seepage of magma from long cracks or rifts.

    • Lava can pour out for millions of years and spread over huge areas.

Lahar (mud) Flows

  • A type of mudflow or debris flow composed of a slurry of pyroclastic material, rocky debris, and water.

    • Typically occurs along a river.

    • Has the density and consistancy of concrete.

Possible Causes of a Lahar

  • Melted glaciers

  • Mixture with wet soil to create a viscous material.

  • Water from a crater lake.

Columbia River Plateau

End of Section 9.2

Where Volcanoes Form

  • Most volcanoes are found directly on tectonic plate boundaries.

    • 80% of active volcanoes on land form where plates collide.

    • 15% form where plates separate.

  • Other rare and few volcanoes form far away from plate boundaries known as hotspots.

Ring of Fire

  • The location of the worlds most active volcanoes.

  • The ring is entirely located along plate boundaries in which many earthquakes occur as well.


  • Hotspot – is a location on the Earth’s surface that has experienced active volcanism for a long period of time.

    • Often located in the middle of oceanic plates.

    • Hawaii is an example of an active hotspot.

When Tectonic Plates Separate

  • Rift zone – an area of deep cracks that forms between tectonic plates that are pulling away from each other.

    • Mantle rock lifts up to fill the gap.

    • As mantle rises the pressure decreases allowing the rock to melt and form magma.

End of Volcanoes


What Are Earthquakes?

  • Seismology – the study of earthquakes.

  • Seismologist – scientist who study Earthquakes.

  • Earthquake – the shaking of the Earth’s surface due to the movement of tectonic plates.

Where Do Earthquakes Occur?

  • Most if not close to all Earthquakes occur near the edges of tectonic plates.

    • Due to the movement of tectonic plates, numerous features called faults exist in the Earth’s crust.

  • Fault – is a break in the Earth’s crust along which blocks of the crust slide relative to one another.

Where Do Earthquakes Occur?

What Causes Earthquakes?

  • Deformation – the bending, tilting, and breaking of the Earth’s crust; the change in the shape of rock in response to stress.

  • This process occurs in two ways:

    • Plastic deformation.

    • Elastic deformation.

Plastic Deformation

  • Plastic Deformation – a rock that deforms in a stretching gentle manner.

    • Example: Pulling apart a piece of molded clay.

Elastic Deformation

  • Elastic Deformation – rock is stretched until it can no longer stand the force in which the rock springs back to its original location.

    • Rock can stretch farther than steel without breaking.

  • Example: Stretched rubber band.

Elastic Rebound

  • Elastic Rebound – the sudden return of elastically deformed rock to its undeformed shape.

    • Occurs when more stress is applied to the rock than the rock can stand.

  • Energy is released during the rebound.

    • Energy is released as seismic waves.

Visualizing Elastic Rebound


How Do Earthquake Waves Travel?

  • Seismic Wave – a wave of energy that travels through the Earth, away from an earthquake in all directions.

  • Body Waves – seismic waves that travel through the Earth’s interior.

  • Surface waves – seismic waves that travel along the Earth’s surface.

Types of Waves

  • P-waves or Primary Waves – Types of seismic waves that move in a compression manner.

    • Ex. A slinky moving back and forth from end to end.

    • Has the ability to move through all materials.

    • Fastest moving wave.

Types of Waves

  • P-waves are always the first waves of an earthquake to be detected.

Types of Waves

  • S-Waves or Secondary waves – are waves that move up and down.

    • Ex. Stretching a slinky outward and then pulling down on the center so that it would bounce up and down.

    • Cannot move through a liquid.

    • Waves are very damaging to surface objects.

Types of Waves

  • S-waves are also known as shear waves because of the damage they cause to the Earth’s rocks at the surface.

  • S-waves cannot travel through parts of the Earth that are completely liquid.

  • S-waves are slower than P-waves and always arrive later than P-waves.

Surface Waves

  • Surface Waves – are waves that move along the Earth’s surface and produce motion mostly in the upper few kilometers of Earth’s crust.

  • Two types:

  • Rayleigh Wave - Produces up, down, and around motion.

  • Love Waves - Back and forth motion much like S-waves.

    These waves are more destructive than body waves and move more slowly

Surface Waves

Locating Earthquakes

  • Seismographs – instruments located at or near the surface of the Earth that record seismic waves.

  • Seismogram – tracing of earthquake motion recorded by a seismograph.

Determining Time and Location of Earthquakes

  • Seismologists find an earthquake’s start time by comparing the differences in arrival times of P waves and S waves.

Determining Time and Location of Earthquakes

  • Epicenter – the point on the Earth’s surface directly above an earthquake’s starting point

  • Focus – the point inside the Earth where an earthquake begins.

The S-P Time Method

  • S-P time method – the way in which seismologists find an earthquake’s epicenter.

    • Collect several seismograms of the same earthquake from different locations.

    • Seismograms are placed on a time-distance graph.

    • By reading the horizontal axis the distance from the earthquake can be determined.

The S-P Time Method

The Richter Magnitude Scale

  • Richter scale – a scale used to measure the strength of an earthquake.

Earthquake Ground Motion

  • Magnitude – the strength of an earthquake.

  • Every time that the Richter scale increases by one it will produce 10x as much ground motion.

    • Ex. 5 on the scale will be 10x stronger than an earthquake that is a 4.

Modified Mercalli Intensity Scale

  • Intensity – a measure of how much damage caused by the earthquake.

    • The Scale uses roman numerals I-XII

    • Shows the type of damage caused by an earthquake.

Strength and Frequency

  • Earthquakes vary in strength.

  • Earthquakes don’t occur on a set schedule.

    • But, the strength of an earthquake is related to how often they occur.

Strength and Frequency

The Gap Hypothesis

  • Gap hypothesis – a hypothesis that states that sections of active faults that have had relatively few earthquakes are likely to be the sites of strong earthquakes in the future.

  • Seismic Gap – areas along a fault where relatively few earthquakes have occurred.

What causes change in sea-level?

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