The Natural Environment: earthquakes & volcanoes

How are volcanoes formed

When magma erupts onto the earths surface as lava through a vent in the earths crust

What is the magnitude of a volcanic eruption measured in?

Volcanic explosivity index (VEI)

What is a crater?

The mouth of a volcano which surrounds the vent

What is a vent?

An opening in the surface of the earth through which volcanic materials can escape

What is a magma chamber?

A large underground pool of molten rock found beneath the surface of the earth

What are 5 features of a strato-volcano

* Formed from alternating layers of ash and lava
* Steep-sided
* Viscous lava
* More explosive eruptions
* Tend to form on convergent (destructive) plate boundaries

What are 5 features of a shield volcano

* Gently sloping sides
* Runny lava
* Tends to form on divergent (constructive) plate boundaries
* Frequent eruptions
* Not very explosive eruptions/gentle eruptions

What is an active volcano

A volcano that has recently erupted and is likely to erupt again

What is a dormant volcano

A volcano that has erupted in the last 2000 years and may possibly erupt again

What is an extinct volcano

A volcano which has not erupted in human history

What features might you see in a volcanic eruption (6)

* Lava
* Ash
* Pyroclastic flow
* Lahars
* Earthquakes
* Volcanic bombs

What is pyroclastic flow

Fast moving v hot clouds of poisonous gases mixed with ash

average speeds of 100km/h but can go up to 700km/h

What are lahars

When volcanoes erupt snow and ice on the peak melts and combines with the ash. Creates fast moving lahars

How do volcanoes cause earthquakes

Magma rising to the surface through vents in volcano → increases pressure on the Earth’s crust → earth tremors

What are volcanic bombs

Fragments of molten rock which are ejected from the volcano . between 60mm and 5m in diameter

What is an earthquake

The sudden, violent shaking of the ground

What are earthquakes the result of

Pressure building when tectonic plates move

What is the epicentre

The point of the Earths surface directly above the focus

What is the focus

The point at which the earthquake starts below the earths surface

What is the magnitude

The amount of energy released by earthquakes

What is magnitude measured on

* Moment Magnitude scale
* Richter scale

What is the damaged caused by earthquakes measured on

* Mercalli scale

What happens to an earthquake at a constructive (divergent) plate boundary

Weaker - plates are moving apart

What happens to an earthquake at a destructive (convergent plate boundary) and conservative (transform) plate boundary

Stronger

Earthquake sequence

1) As the tectonic plates move they can get stuck

2) Pressure builds as the plates continue to try and move

3) Eventually, the plate jolts free and the pressure is released as energy

4) The energy passes through the Earth’s crust as seismic waves which is the earthquake

What can also cause earthquakes other than tectonics moving

Human activity like drilling into the crust or mining

What is a fault line

where there is a long break in the rock that forms the earths surface and where earthquakes are more likely to happen

Where do most earthquakes occur

Around the rim of the Pacific ocean called the ‘Ring of Fire’

Oceanic crust vs continental crust

oceanic = 5-10km but heavier and denser

continental = 25km-90km but older and denser

Why do tectonic plates move

Convection currents within the mantle

Where do volcanoes occur

Divergent and Convergent plate boundaries only

Volcanoes at constructive plate boundaries

* Often occur under the sea
* The lava escapes through the gap as the plates move apart
* Lava cools and hardens forming a new crust
* At constructive plate boundaries lava tends to be runny and eruptions less explosive
* Forms shield volcanoes

Volcanoes at destructive boundaries

* The plates are moving towards each other
* The heavier denser oceanic plate subducts under the lighter continental plate
* In the subduction zone the two plates come together causing friction


* Friction causes heat and the plate material melts forming magma
* Magma rises to the surface through cracks in the crust
* Cooling lava and ash build up forming a volcano
* Form strato-volcanoes

Primary effects of earthquakes

* ground shaking
* surface rupture

Secondary effects of earthquakes

* Liquefaction (when loose material like soil and rocks acts like a liquid due to an earthquake)
* Landslides
* Tsunamis
* Fires

Secondary effects of volcanoes

* Landslides
* Tsunamis
* Acid rain

Benefits of living in tectonically active areas

* Tourism
* Geothermal energy
* Fertile soils
* Minerals & precious stones
* Creating new land areas

In what ways can buildings be earthquake-proofed

* Shutters on windows - prevent falling glass
* Cross bracing of steel frames
* Rubber shock absorbers - reduce tremors
* Reinforce walls with concrete
* Reinforced/shatter proof glass
* Fire resistant materials