EARTHQUAKES

&

VOLCANOES

When plates move, they bump into each other

Depending on the type of plate boundary, different

deformations result

Two special events/formations happen as well:

Earthquakes

Volcanoes

EFFECTS OF PLATE TECTONICS

EARTHQUAKES Earthquake: shaking of the ground that results from

the movement of rock beneath Earth’s surface

Stress on rocks from pushing/pulling changes its

shape/volume of the rock

Types of Stress:

Shearing – causes rocks to slip

Tension – stretches rock

Compression – pushes rocks together

Fault: a break in Earth’s crust where slabs of crust

slip past each other.

Rocks on both sides of a fault can move up or down

or sideways

Usually occur along plate boundaries, where the

forces of plate motion compress, pull or shear the

crust so much that it breaks.

FAULTS

Strike-Slip Faults: where rocks on either side of the fault slip past each other sideways with little up or down motion

Occurs at transform plate boundaries

Ex: San Andreas Fault, California

Normal Faults: a fault at an angle so one block of rock lies above the fault and the other block of rock lies below the fault, caused by tension

Occurs where plates diverge

Hanging wall – half that lies above

Footwall – half that lies below

TYPES OF FAULTS

Reverse Faults: have the same structure as a normal

fault, but the blocks move in the opposite direction

(toward each other)

Produced by compression forces

Ex: produced part of the Appalachian Mountains in the

eastern US

TYPES OF FAULTS

Friction is the force that opposes motion between surfaces

When friction along a fault is low, the rocks pass easily without sticking

When friction along a fault is high, the rocks lock together and do not move.

Energy continues to build until it’s strong enough to overcome friction.

When they jerk free, you get an earthquake

The strength of the quake depends on the amount of energy built up (how much friction there was)

FRICTION ALONG FAULTS

Two things we need to know

when earthquakes happen:

Where they’re located

How “big” they were

MEASURING EARTHQUAKES

Focus – the point beneath the Earth’s surface where

stressed rock breaks

Epicenter – the point on the surface directly above

the focus

Found by measuring the difference between arrival times

of P and S waves.

EARTHQUAKE LOCATION

Earthquakes produce vibrations called waves, which

carry energy as they travel through solid material

Seismic Waves– vibrations that carry the energy of

an earthquake away from the focus, through Earths’

interior, and across the surface

EARTHQUAKE STRENGTH

Primary Waves (P Waves) – first waves to arrive;

compress and expand the ground like an accordion

Move through solids & liquids

Secondary Waves (S Waves) – come after P waves;

vibrate from side to side, as well as up and down,

shaking the ground violently

Cannot move through liquids

Surface Waves – P and S waves that reach the

surface; move more slowly but produce the most

severe ground movements

TYPES OF SEISMIC WAVES

Magnitude: measuring earthquake strength based on

the seismic waves and movement along faults

Three ways to measure:

Mercalli Scale

Richter Scale

Moment Magnitude Scale

MEASURING EARTHQUAKE

MAGNITUDE

Measures intensity (strength of ground motion in a

given place)

Not precise

12 steps describe how quakes affect people,

buildings and land surface

Same quake can have different ratings because it

has different amounts of damage at different

locations

MERCALLI SCALE

Rates the size of seismic waves measured by a

seismograph

Developed in 1930’s and used for about 50 years

Provides accurate measurements for small, nearby

quakes

Does not work well

for large or distant

earthquakes

RICHTER SCALE

More commonly used

today

Rating system that

estimates the total

energy released by an

earthquake

MOMENT MAGNITUDE SCALE

Can be used to rate earthquakes near or far

Does not work well for large or distant earthquakes

Building damage

Liquefaction : earthquake’s shaking causes loose soil

to turn to liquid mud; often causes landslides

Tsunamis: when earthquake jolts ocean floor, this

causes the floor to rise and push water; can form

large waves called tsunamis

DAMAGE DONE BY

EARTHQUAKES

VOLCANOES

Volcano: a weak spot in the crust where molten

material (magma) comes to the surface

Constructive force (builds land)

Magma: molten mixture of

rock-forming substances,

gases, and water from the

mantle

Lava: magma that reaches

the surface; when cooled,

it forms solid rock

WHAT IS A VOLCANO?

600 active on land, with many more beneath the sea

Form along the boundaries of Earth’s plates

Weak, fractured crust allows magma to reach the surface

Most volcanoes occur along diverging plate

boundaries (mid-ocean ridges) or subduction zones

at the edges of oceans

Some volcanoes form at “hot spots,” far from plate

boundaries

LOCATION OF VOLCANOES

LOCATION OF VOLCANOES

Divergent boundary: plates divide; magma rises

Volcanoes form along the mid-ocean ridge

Rarely, these volcanoes rise above the ocean surface

Iceland

Azores Islands

VOLCANOES @ DIVERGENT

PLATE BOUNDARIES

Convergent boundary: plates collide; oceanic crust melts/returns to mantle; magma rises

Volcanoes form where magma erupts through the surface as lava

Many occur on islands where two oceanic plates collide

Island arc: a string of volcanoes that form islands at converging oceanic crusts Japan

New Zealand

Caribbean

Philippines

Indonesia

VOLCANOES @ CONVERGENT

PLATE BOUNDARIES

Hot Spot: an area where magma from deep in the mantle melts through the crust like a blow torch

Often lie in the middle of plates, far from edges

Not a result of subduction (crust sinking/melting/rising)

Hot spots can produce a series of volcanic mountains as the plate drifts over the hot spot

Hawaii

Yellowstone National Park

HOT SPOT VOLCANOES

Magma is formed in the asthenosphere, where the

rock becomes liquid

Magma rises because it is less dense than the

surrounding solid rock

During a volcanic eruption, the gases dissolved in the

magma rush out, carrying magma with them

VOLCANIC ACTIVITY

Magma Chamber: the pocket of magma beneath a volcano

Pipe: a long tube in the ground that connects the magma chamber to Earth’s surface

Vent: an opening in the volcano through which gases leave

Lava Flow: the area covered by lava as it pours out of a vent

Crater: a bowl-shaped area that may form at the top of a volcano around the central vent

INSIDE A VOLCANO

INSIDE A VOLCANO

TYPES OF VOLCANIC

ERUPTIONS The silica content of magma determines whether the

volcanic eruption is quiet or explosive

Quiet Eruptions: magma flows easily and relatively

constantly

Explosive Eruptions: trapped gases build up pressure

and explode

QUIET ERUPTIONS

The most common type of volcanic activity on Earth

Runny lava oozes from vent quietly and builds land

over thousands of years

Ex: Mount Kilauea, Hawaii

Produce two different types of lava:

Pahoehoe – fast moving, hot lava; looks like wrinkles

Aa – slow moving; forms a rough surface with jagged

chunks

EXPLOSIVE ERUPTIONS

Thick sticky magma clogs up the volcano pipe like a

cork in a bottle

Trapped gases build pressure until they explode into

fragments of lava

Volcanic ash – fine rocky particles

Cinders – pebble-sized particles

Bombs – larger particles of lava from

baseball to car-sized

Pyroclastic Flow: occurs when an explosive eruption

hurls out ash, cinders, bombs, and gases

LANDFORMS FROM LAVA &

ASH Shield Volcanoes – wide, gently sloping mountain

made up of thin layers of lava that pour out and

harden on top of previous layers

Cinder Cone Volcanoes – a steep, cone-shaped

mountain made up of ash, cinders, and bombs piled

up from explosions of thick magma

LANDFORMS FROM LAVA &

ASH Composite Volcanoes – tall, cone-shaped mountains

with alternating layers of lava and ash from

alternating quiet and explosive eruptions

Lava Plateaus – high, level areas of lava that floods

and area and cools

LANDFORMS FROM LAVA &

ASH Calderas – a huge collapse of a volcanic mountain

after an enormous eruption empties the magma

chamber beneath the volcano; appears like a crater,

but much larger