Transcript Earth’s Structural Key Elements

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
10 Supercontinent
The
Cycle
Earthquakes
• Note focus, epicenter,
direction of seismic waves
Shallow focus –
Surface to 40
mi. (60 km)
Wave properties
Wave characteristics
Intermediate – 60
– 300 km.
Deep focus – up to
700 km.
Body waves (P wave & S wave)
Surface waves (L waves)
Liquefaction of recent
sediments causes
buildings to sink
Landslides may
occur on hilly
ground
Two adjoining plates
move laterally along the
fault line
Earth movements
cause flooding in
low-lying areas
Shock
waves
Epicenter
Focus
Fig. 14-8, p. 350
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)
Tsunamis
• Caused by an epicenter located on the ocean
floor
• Also caused by underwater landslide which
was activated by an earthquake
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 wave
Bangladesh
Burma
India
Thailand
Earthquake
Sri Lanka
Malaysia
Indonesia
Sumatra
December 26, 2004, tsunami
Fig. 14-11, p. 352
Volcanoes
• Activity occurs when…(3 answers)
Extinct volcanoes
Eruption cloud
Ash flow
Ash
Acid rain
Lava flow
Mud flow
Landslide
Central vent
Magma conduit
Magma reservoir
Fig. 14-7, p. 349
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