1
GEOLOGY
I LIKE TO MOVE IT MOVE IT
Part 1 Age of Earth and scientific classification
Part 2 Plate tectonics and water
CONTINENTAL DRIFT
Theory
1912 Alfred Weagner proposed the theory that Earth's crust is
slowly drifting on a liquid core.
His theory was not accepted in his lifetime...but now there is a
lot of evidence
National Geographic Continental Drift
http://www.youtube.com/watch?v=3uBcq1x7P34
Pangea
250 million years ago
Evidence
Fit of continents
Evidence
Distribution of rocks &
mountains
Evidence
-Paleoclimates- Rocks deposited at the Earth's surface
(sedimentary) reflect the climate and latitude of which they form
-Glacial sediments
-Fossils
Plate Movement

“Plates” of lithosphere are moved around by
the underlying hot mantle convection cells
Divergent Boundaries

Spreading ridges


As plates move apart new material is erupted to fill the gap
Effect: Underwater mountains
Age of Oceanic Crust
Courtesy of www.ngdc.noaa.gov
Evidence:Earth’s Magnetic Field



Movement of Fe (l) in the outer core as the planet
rotates.
Behaves like permanent magnet near center of
Earth
Magnetic north (compass measures) differs from
geographic north of planet’s axis of rotation.
How can it be monitored?



Basaltic lava with iron minerals act like compasses.
When they cool, they are magnetized in the
direction of the surrounding magnetic field.
Paleomagnetism = Study of ancient magnetism
Earth’s Magnetic Field
http://nsdl.org
BUT…..Magnetic North is NOT
at the North Pole
http://nsdl.org
AND…the Magnetic Field
Reverses
• Field reverses ~1 time
every 200,000 years on
average.
• 400 times in last 330
million years.
• Last reversal was
780,000 years ago.
NORMAL
REVERSE
WHICH FAULT IS AT FAULT?!
What is a fault?
A fault is a fracture in the Earth's crust that occurs when stress is
applied to quickly or when stress is too great.
It can be either vertical or horizontal
A vertical fault is comprised of a footwall and a hanging wall
Normal Fault
Tension pulls rocks apart
causing the hanging wall
block to be pulled down.
Normal does not mean
most common!
Why do you think it is called a normal fault?
At what type of plate boundary do normal faults occur?
Reverse Fault
Opposite of the
normal fault
Compression pushes
rocks together and
causes the hanging
wall to be pushed up
At what plate boundary do reverse faults occur?
Strike-Slip Fault
A strike-slip fault happens
when rocks slide past
each other (shearing)
Moves left or right laterally
with very little horizontal
movement
At which plate boundary do strike slip faults occur?
What is a common example of a strike slip fault?
The Himalaya Mountains contain many of these faults.
EARTHQUAKES
Earthquakes

Earthquake is the vibration of Earth caused by a
rapid release of energy
 Often
caused by slippage along a break in Earth’s
crust

Focus & Epicenter
 Focus
is point w/in Earth where earthquake starts
 Energy is released in waves
 Epicenter is location on surface directly above the focus

Faults
 Earthquakes
are usually associated w/large fractures in
Earth’s crust & mantle called faults
 Faults are fractures in Earth where movement has
occurred
Causes of Earthquakes

Scientists studied 1906 San Francisco quake along
San Andreas fault
 Some
areas moved 4.7 m on one side of fault
compared to the other
 Hypothesis was developed – force causes rocks to bend
& store elastic energy, eventually friction which holds
rocks together is overcome, rocks slip at the weakest
point (focus) releasing energy allowing rocks to return
to original shape

Elastic rebound hypothesis
 Explains
that when rocks are deformed, they bend then
break, releasing stored energy
 Most earthquakes are produced by the rapid release
of elastic energy stored in rock that has been subjected
to great forces
 When strength of rock is exceeded, it suddenly breaks,
causing vibrations of an earthquake

Aftershocks & foreshocks
 Aftershocks
are smaller earthquakes produced after a
major earthquake
 Foreshocks are small earthquakes produced before a
major earthquake; can be days or years before quake
Earthquake waves

Surface waves
 Travel
along Earth’s outer layer
 Move up-down & side-to-side
 Causes ground & anything on it to move
 Most destructive
 AKA L waves or Rayleigh waves
Earthquake waves

Body waves
P
waves
 Push-pull
waves
 Compression waves
 Change volume of material they pass through
Earthquake waves
S
waves
 Most
particles @ right angles to their travel
 Transverse waves
 Change shape of material they pass through, SOLIDs only
Earthquake waves

Seismogram shows all 3 types of waves
P
waves arrive first – fastest traveling
 S waves arrive second
 Surface waves (L waves) arrive last – slowest traveling
Locating an Earthquake

Compare arrival times of P & S waves


Greater the difference = greater distance to focus
Earthquake distance




Developed using seismograms from earthquakes w/identifiable
epicenters
2 steps
1. Find time interval btwn 1st P wave & 1st S wave
2. Find on travel-time graph the equivalent time spread btwn P &
S wave curves

Earthquake direction
 Travel-time
graphs from 3 or more seismographs can
be used to find exact location of earthquake’s
epicenter
 Draw circle w/diameter in distance, where they
intersect = epicenter

Earthquake zones
 95%
of earthquakes occur in narrow zones
 Most on outer edge of Pacific called circum-Pacific belt
 Second belt Mediterranean-Asian belt
TSUNAMIS
Tsunamis


Wave caused by earthquake on ocean floor
Causes of tsunamis
 Slab
of ocean floor is displaced vertically along a fault
 Vibration can also set an underwater landslide into
motion
 Waves travel 500-950 km/hr
 Height in ocean is less than 1m but can reach 30m when
it hits land

Tsunami warning system
 Tsunami
warning center in Honolulu HI
 Receives
info about large earthquakes in Pacific
 Use water level in tide gauges
 Warnings are issued w/in 1 hr of report
 Only 1-2 destructive tsunamis per year
Other Dangers

Landslides
 Greatest
damage to structures is from landslides &
ground subsidence, or sinking of ground triggered by
the vibrations

Fire
 Start
when there’s damage to gas & electric lines
Emergency Situations






What should you do in a Tsunami?
Follow the evacuation order issued by authorities and evacuate
immediately. Take your animals with you.
Move inland to higher ground immediately. Pick areas 100 feet (30 meters)
above sea level or go as far as 2 miles (3 kilometers) inland, away from
the coastline. If you cannot get this high or far, go as high or far as you can.
Every foot inland or upward may make a difference.
Stay away from the beach. Never go down to the beach to watch a
tsunami come in. If you can see the wave you are too close to escape it.
CAUTION - If there is noticeable recession in water away from the shoreline
this is nature's tsunami warning and it should be heeded. You should move
away immediately.
Save yourself - not your possessions.
Remember to help your neighbors who may require special assistance infants, elderly people, and individuals with access or functional needs.
Emergency Situations




What should you do in an Earthquake?
If Indoors
DROP to the ground; take COVER by getting under a sturdy table or other
piece of furniture; and HOLD ON until the shaking stops. If there isn’t a
table or desk near you, cover your face and head with your arms and
crouch in an inside corner of the building.
Stay away from glass, windows, outside doors and walls, and anything that
could fall, such as lighting fixtures or furniture.

If Outdoors

Stay there.

Move away from buildings, streetlights, and utility wires.

Once in the open, stay there until the shaking stops. The greatest danger
exists directly outside buildings, at exits and alongside exterior walls.
VOLCANOES
Vulcan- Roman God of Fire
What is a volcano?


Volcano- Areas of earth’s surface through which
magma and volcanic gases pass
Volcano comes from the Roman word Vulcan, which
means “fire”
What’s inside a volcano?



Magma Chambermolten rock that
feeds a volcano
Vents- cracks in the
crust
What is the
difference
between magma
and lava?
Types of Volcanoes

a)
b)
c)
Shield Volcano
Built from layers of
lava
Non-explosive
eruptions
Not very steep, but
can be big
Types of Volcanoes
a)
b)
c)
Cinder Cone Volcano
Built from pyroclastic
material
Moderately explosive,
short eruptions
Small in size, steep
slopes
Types of Volcanoes
a)
b)
c)
Composite Volcanoes
Most common type
Explosive eruptions
and lava flow
Built from pyroclastic
material AND lava
Types of Volcanoes
VOLCANIC ERUPTIONS
AND HAZARDS
What is a volcano?
vent

cone

conduit

Magma Chambermolten rock that feeds
a volcano
Vents- cracks in the
crust (chimney)
What is the
difference between
magma and lava?
magma chamber
How and why do volcanoes erupt?

Hot, molten rock (magma) is buoyant (has a lower density
than the surrounding rocks) and will rise up through the crust
to erupt on the surface.



When magma reaches the surface it depends on how easily it
flows (viscosity) and the amount of gas (H2O, CO2, S) it has in
it as to how it erupts.
Large amounts of gas and a high viscosity (sticky) magma will
form an explosive eruption!


Same principle as hot air rising, e.g. how a hot air balloon works
Think about shaking a carbonated drink and then releasing the cap.
Small amounts of gas and (or) low viscosity (runny) magma
will form an effusive eruption

Where the magma just trickles out of the volcano (lava flow).
Explosive Eruptions





Explosive volcanic eruptions
can be catastrophic
Erupt 10’s-1000’s km3 of
magma
Send ash clouds >25 km into
the stratosphere
Have severe environmental
and climatic effects
Hazardous!!!
Mt. Redoubt
Above: Large eruption column and ash
cloud from an explosive eruption at Mt
Redoubt, Alaska
Explosive Eruptions

Three products from an
explosive eruption
 Ash
fall
 Pyroclastic flow
 Pyroclastic surge
Pyroclastic flows on
Montserrat, buried the
capital city.
Direct measurements
of pyroclastic flows
are extremely
dangerous!!!
Effusive Eruptions

Effusive eruptions are
characterised by outpourings of
lava on to the ground.
Hawaii
Courtesy of www.swisseduc.ch
Volcanic Hazards






Courtesy of www.swisseduc.ch
Pyroclastic flow
Lahars/Mud flows
Pyroclastic fall
Lava flow
Noxious Gas
Earthquakes
Pyroclastic Flow


Hot, fast moving, high
particles concentration
flows of gas, rock and
ash
For example, eruption of
Vesuvius, Italy in 79 AD
destroyed the city of
Pompeii
Pompeii (79AD)
On August 24, 79AD Mount Vesuvius literally
blew its top, erupting tonnes of molten ash,
pumice and sulfuric gas miles into the
atmosphere. Pyroclastic flows flowed over the
city of Pompeii and surrounding areas.
Pompeii (79AD)
Pyroclastic flows of poisonous gas and hot
volcanic debris engulfed the cities of Pompeii,
Herculaneum and Stabiae suffocating the
inhabitants and burying the buildings.
Pompeii (79AD)
The cities remained buried
and undiscovered for almost
1700 years until excavation
began in 1748. These
excavations continue today
and provide insight into life
during the Roman Empire.
Vesuvius today

Naples
Vesuvius remains a
hazardous volcano with
heavily populated flanks:

Vesuvius
Bay of
Naples


Courtesy of www.swisseduc.ch
around 1.5 million
people live in the city of
Naples alone
Naples is situated
approx. 30 km from
Vesuvius
Pyroclastic flows can
flow up to 100 km from
source!
Mt Peleé, Martinique (1902)

An eruption of Mt Peleé in 1902 produced a
pyroclastic flow that destroyed the city of St. Pierre.
before
after
29,000 people died….
Only 2 survived! Why?
Pyroclastic Flow - direct impact
Courtesy of www.swisseduc.ch
Pyroclastic Fall
• Ash load
–
–
–
–
Collapses roofs
Brings down power lines
Kills plants
Contaminates water
supplies
– Respiratory hazard for
humans and animals
Lava Flow

It is not just explosive volcanic activity that can be
hazardous. Effusive (lava) activity is also dangerous.
Earthquakes


Large volumes of magma moving through the
shallow crust can cause large earthquakes.
This can lead to building collapse, slope
failure and avalanches
So….
How do we minimize the risk of active
volcanoes?
*Volcano Monitoring
Volcano Observatories
are set up on all active
volcanoes that threaten
the human population.
These are designed to
monitor and potentially to
predict the eruptive
behaviour of the volcano
in question.