Introduction and Plate Tectonics

Natural hazard

The potential for negative interaction between people and extreme natural events.

How are hazard events classified?

By processes

• weather and climate

• hydrological

• geological

• extraterrestrial

Physical aspects

• mechanisms (duration, magnitude)

• timing

• location

• warning

What causes a hazard to become a disaster?

Poor scientific understanding, communication, and warning. Vulnerability of people, lack of community and education.

Vulnerability when it comes to natural hazards

Lack of access to resources = poverty and poor living conditions. These conditions increase vulnerability to natural hazards, reinforcing poverty in vulnerable communities.

Risk when it comes to natural hazards

Combination of likelihood, vulnerability, and probability.

Formation of the solar system

The nebular hypothesis states that the solar system formed from rotating clouds of gas and fine dust, with the rotation drawing in more matter and mass.

The cloud contracts under gravitational force causing it to flatten into a disc. Mass drifts to the centre and compresses under its own weight. Compression of matter raises internal temperature to one million degrees, this starts nuclear fusion.

Nuclear fusion forms the proto-sun, the remaining disc of gas and dust around the proto-sun flattens and heats. As the solar nebula cools, gas and dust sticks together to form planetary bodies (plantessimals).

Formation of planets

Cooling of the solar nebula causes gas and dust to stick together to form planetary bodies (plantessimals). Inner planets are terrestrial, made of rock and metal with lighter material vaporized by the sun. Outer planets are gas giants with rocky cores.

Formation of the moon

Melosh theory states that 4.5 billion years ago a Mars sized planetary body collided with the Proto-Earth. This melted a part of the Earth and the colliding body, causing the colliding body core to fold into the Earth and create a magma ocean, melting Earth.

The lighter crust of both bodies shoots into space, forming the moon, this also tipped Earth onto an angle.

Earth composition

Core

• metallic

• dominated by iron and nickel

Mantle

• olivine and pyroxene minerals

• rich in iron, magnesium, and calcium

Crust

• quartz, feldspar, and other light minerals

• rich in silica and aluminium

Lithosphere

Thicker than the crust, made of low density material and the upper part of high density material. Cold and brittle.

Asthenosphere

Below the lithosphere. A sweet spot of high temperature and low pressure, creating a weak and partially molten layer that behaves as fluid. This layer slides and allows plate tectonics to occur.

How does convection drive plate tectonics

Heat drives upward toward the surface, creating magma.

Divergent plate boundaries

Pull apart from one another, creating new crust.

Continental rifting - plates pull apart, creating cracking zone which thins the crust, hot mantle can rise and fill fractures with magma, creating new crust.

Seafloor spreading - mid ocean ridge has thin oceanic crust, new mantle erupts and creates magma that cools to form crust.

Convergent plates

Push together, destroy crust.

Subduction zone (ocean-ocean)

Oceanic crust into oceanic crust. Older and denser crust subducts below the other, generating island arc and volcanic arc.

Subduction zone (ocean-continent)

Continental crust is low density (does not subduct). Oceanic crust forced downward. Continental arc generated - mountain range.

Continent-continent zone

Continental crust is squeezed up and down to create thick patch of continental crust, mountain ranges form.