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GEOLOGYI LIKE TO MOVE IT

MOVE ITPart 1 Age of Earth and scientific classificationPart 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

Spreading ridges As plates move apart new material is erupted to fill the gap

Effect: Underwater mountains

Divergent Boundaries

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 apartcausing the hanging wallblock to be pulled down. 

Normal does not meanmost 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 thenormal fault

Compression pushesrocks together and causes the hangingwall 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 laterallywith very little horizontalmovement

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

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

Earthquake waves

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

Chamber- molten rock that feeds a volcano

Vents- cracks in the crust

What is the difference between magma and lava?

Types of Volcanoes Shield Volcanoa) Built from layers

of lavab) Non-explosive

eruptionsc) Not very steep,

but can be big

Types of VolcanoesCinder Cone Volcano

a) Built from pyroclastic material

b) Moderately explosive, short eruptions

c) Small in size, steep slopes

Types of VolcanoesComposite Volcanoes

a) Most common type

b) Explosive eruptions and lava flow

c) Built from pyroclastic material AND lava

Types of Volcanoes

VOLCANIC ERUPTIONS AND HAZARDS

What is a volcano?

Magma Chamber- molten rock that feeds a volcano

Vents- cracks in the crust (chimney)

What is the difference between magma and lava?

vent

cone

magma chamber

conduit

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. Same principle as hot air rising, e.g. how a hot air balloon works

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! 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

Mt. Redoubt

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!!!

Above: Large eruption column and ash cloud from an explosive eruption at Mt Redoubt, Alaska

Three products from an explosive eruption Ash fall Pyroclastic flow Pyroclastic surge

Explosive Eruptions

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

Pyroclastic flow Lahars/Mud flows Pyroclastic fall Lava flow Noxious Gas Earthquakes

Volcanic Hazards

Courtesy of www.swisseduc.ch

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

Vesuvius remains a hazardous volcano with heavily populated flanks: 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!

Bay of Naples

Vesuvius

Naples

Courtesy of www.swisseduc.ch

An eruption of Mt Peleé in 1902 produced a pyroclastic flow that destroyed the city of St. Pierre.

before after

Mt Peleé, Martinique (1902)

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.