Plate layers convection distribution_movement

CHAPTER 1

LIVING WITHTECTONIC HAZARDS Risk or Opportunity?

CHAPTER 1 LIVING WITH TECTONIC HAZARDS

Gateway 1: Why are some area more prone to tectonic hazards?

a. What is a natural hazard? b. What is the internal structure of the Earth?

• A natural hazard is a natural event that threatens human lives and causes damage to property.

a. What is a natural hazard?

Examples of natural hazards

• Tectonic hazards

• Earthquakes• Volcanic eruptions• Tsunamis

• Climate-related hazards

• Droughts• Floods• Storms

a. What is a natural hazard?

Distribution of natural hazards

a. What is a natural hazard?

b. What is the internal structure of the earth?

• Makes up the Earth’s rigid outer shell• When the rocks in the lithosphere melt,

hot molten rock called magma is formed.

Lithosphere = Crust + Uppermost mantle

b. What is the internal structure of the earth?

• A tectonic plate is made up of the lithosphere (i.e. crust + uppermost mantle).

• The earth’s crust is broken into several pieces of tectonic plates.

• These plates move in relation to one another.• Tectonic plates can be made up of: – oceanic crust– continental crust or – a combination of both

c. What is a tectonic plate?

Oceanic crust vs Continental crust

Oceanic Crust• Located beneath deep

ocean

• Very thin — between 5 and 8 km

• Denser (e.g. basalt)

Continental Crust• Located beneath land

masses and under shallow seas

• Very thick — between 30 and 60 km

• Less dense (e.g. granite)

c. What is a tectonic plate?

1. Convection currents•Convection currents are movements of heat within the mantle.•Material in the mantle is heated by the core.•This causes convection currents in the molten mantle material.•Mantle expands, rises and spreads out beneath the plates.•Plates are dragged along and move away from each other.

d. Why do tectonic plates move?

1. Convection currents•Subsequently, the hot molten mantle cools slightly and sinks, pulling the plates along •Hence plates move towards each other. •The sinking mantle material heats up again as it nears the core and the whole process repeats.

d. Why do tectonic plates move?

Tectonic plates float on molten mantle, driven by heat energy/convection currents

Plates moving away from each other

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Ocean floor

d. Why do tectonic plates move?

2. Slab-pull force• This occurs when an oceanic plate (denser) subducts

under a less dense plate and pulls the rest of the plate along.• The subducting plate drives the downward-moving

portion of convection currents.• While mantle material away from the subduction zone drives the rising portion of convection currents.

d. Why do tectonic plates move?

Changing positions of the earth’s continents• Plate movements have altered the distribution of the earth’s land masses over several hundred million years.

d. Why do tectonic plates move?