Earth’s Structural Key Elements & the Hazards of Plate Movement

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