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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. 

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GeologyI 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


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


http://nsdl.org

Earth’s Magnetic Field


http://nsdl.org

BUT…..Magnetic North is NOT at the North Pole


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 Chamber- molten rock that feeds a volcano

  • Vents- cracks in the crust

  • What is the difference between magma and lava?


Types of Volcanoes

  • Shield Volcano

  • Built from layers of lava

  • Non-explosive eruptions

  • Not very steep, but can be big


Types of Volcanoes

  • Cinder Cone Volcano

  • Built from pyroclastic material

  • Moderately explosive, short eruptions

  • Small in size, steep slopes


Types of Volcanoes

  • 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?

  • Magma Chamber- molten rock that feeds a volcano

  • Vents- cracks in the crust (chimney)

  • What is the difference between magma and lava?

vent

cone

conduit

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.

    • 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

  • 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

  • Pyroclastic flow

  • Lahars/Mud flows

  • Pyroclastic fall

  • Lava flow

  • Noxious Gas

  • Earthquakes

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!

Naples

Vesuvius

Bay of Naples

Courtesy of www.swisseduc.ch


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.


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