Earth’s Structural Key Elements & the Hazards of Plate Movement
AICE EM: Lithosphere Key Content 1 & 2
Before We Begin, You Need to Understand These Terms:
• Convection Currents• Density
Convection Currents Cause Motion
• Demo – through water• Demo – through air
Picture drawing an arrow from the base of the fountain up and out in any direction that the water flows. This is the possible path for convection currents. When you see the next slide, it is a cross section of the planet.
The Earth’s Crust Is Made Up of a Mosaic of Huge Rigid Plates: Tectonic Plates
The Evidence• In 1912 Alfred Wegener -
hypothesis of continental drift – Fossil Evidence (dinosaurs &
coal measures)– Evidence form rock formations– Climatic Evidence
Originally opposed b/c the mechanism was disproved
Mid-Ocean Ridges
MORs – How They Cause Sea-Floor Spreading
More Evidence
• Paleomagnetism– Normal polarity– Reversed polarity– MORs have alternating
magnetic fields
Continents in Motion
Sea-floor Spreading Also Causes Motion
Lithosphere sits on top of moving asthenosphere
Boundary Types
• Convergent• Divergent• Transform
• Constructive• Destructive• Conservative
Note location of MOR, rift valley, oceanic & continental crust
Note: ocean trench, active volcano, magma, subduction zone.•Why subduction occurs•Oceanic & Continental plates•Oceanic & Oceanic Plates
What type of boundary is found between the South American plate and the African plate? What surface features are most often at boundaries of this type?
Chapter 10The Supercontinent Cycle
Earthquakes
Wave propertiesWave characteristics
Body waves (P wave & S wave)Surface waves (L waves)
• Note focus, epicenter, direction of seismic waves
Shallow focus –
Intermediate – 60 – 300 km.Deep focus – up to 700 km.
Surface to 40 mi. (60 km)
Fig. 14-8, p. 350
Liquefaction of recent sediments causes buildings to sink
Two adjoining plates move laterally along the fault line
Earth movements cause flooding in low-lying areasLandslides may
occur on hilly ground
Shock waves
EpicenterFocus
Seismic Waves
P waves S
Earthquakes Occur at All Boundaries
Fig. 14-5, p. 348
Earthquake scales• Richter scale
– Measures ground motion to determine strength (magnitude)• Moment magnitude scale
– Measures strength based on area size that the fault moved, average distance that fault blocks move, and rigidity of blocks in fault zone
– The greater the number, the stronger the (E). < 2.5 not felt by people
– 6.9 Kobe, Japan 1995• Modified Mercalli scale
– Based on intensity and effect felt / damage to structure (I – XII)
9.5
Tsunamis
• Caused by an epicenter located on the ocean floor
• Also caused by underwater landslide which was activated by an earthquake
Fig. 14-11, p. 352
Earthquake in seafloor swiftly pushes water upwards, and starts a series of waves
Waves move rapidly in deep ocean reaching speeds of up to 890 kilometers per hour.
As the waves near land they slow to about 45 kilometers per hour but are squeezed upwards and increased in height.
Waves head inland causing damage in their path.
Undersea thrust fault
Upward waveBangladesh
IndiaThailand
Sri Lanka MalaysiaEarthquake
SumatraIndonesia
December 26, 2004, tsunami
Burma
Volcanoes• Activity occurs when…(3 answers)
Fig. 14-7, p. 349
Extinct volcanoes
Eruption cloud
AshAsh flow
Lava flow
Mud flow
Landslide Central vent
Magma conduit
Magma reservoir
Solid
lithosphere
Upwelling magma
Partially molten
asthenosphere
Acid rain
VOLCANIC ERUPTIONS• Difference between magma & lava is…– Oceanic crust tends to create Mafic lava (Mg & Fe)
• Low viscosity quiet eruptions (basaltic eruptions)– Continental crust tends to make Felsic lava (silicates)
• Sticky, high viscosity explosive eruptions
• Explosive eruptions:– Trapped dissolved gasses
• Leads to acidic atmospheric pollution (SO2, H2S, CO2)
– Pyroclastic material• Volcanic ash, dust, stones, bombs, blocks
Volcanic eruption sequence• Steam explosions
(phreatic explosions)• Explosive eruption of
magma• Eruption cloud• Pyroclastic flows• Lava flows• Lava fountains• Volcanic debris &
mudflow (lahars)
Predicting Eruptions & Reducing Loss
• Earthquake activity– Magma pressure– Temperature changes
• Activity patterns– Geologic measurements– Measuring Devices
• Historical records
• Don’t live there at all• Evacuate