2.1 Plate tectonics

Oceanic crust: younger, heavier, can sink and is constantly being destroyed and replaced

Continental crust: older, lighter, cannot sink and is permanent

Earthquake, volcano and fold mountain distribution:

	Plate Boundary	What happens	Volcanoes?	Earthquakes?	Fold mountains?
A.	Constructive margins	2 plates move away from each other forming new oceanic crust	Gentle	Gentle	No
B. i)	Destructive margins	Oceanic crust moves towards continental and sinks under it, and is destroyed	Violent	Violent	Yes
B. ii)	Collision zones	2 continental crusts collide, neither can sink so forced upwards	None	Yes there is	Yes
C.	Conservative margins	2 plates move sideways past each other	none	violent	no

Earthquake distribution (in terms of places, not boundary types):

-encircle the whole of the Pacific Ocean

-extend down the entire length of the mid-Atlantic Ocean

-stretch across southern Europe and Asia, linking the Atlantic and Pacific Oceans

Volcanoes:

-encircle the whole of the Pacific Ocean

-extend down the entire length of the mid-Atlantic Ocean

-smaller areas in southern Europe, the Caribbean, east Africa and the mid-Pacific Ocean

Fold mountains:

Plate movement is caused by convection currents in the mantle

Volcano features/vocab:

-The eruption column can collapse & flow down the volcano at over 200km/hr incinerating everything it touches. This is a pyroclastic flow (a)

-large crater called a caldera (b)

-crater

-poisonous gases

-blast wave

-volcanic bombs (ejected rocks)

-plume (ash cloud)

-Explosive eruption can produce mud flows called lahars. They are formed from ash mixed with water which can come from heavy rain, melted snow & ice or rivers (c)

lahars can be caused by:

• melting snows;

• heavy rainfall/water content of magma;

• mix with ash;

• flow down steep slopes/gravity;

• triggered by earthquakes

They are problematic because:

• loss of life;

• destroy buildings/homes;

• inundate farmland/destroy crops/livestock;

• disrupt communications;

• bring down power lines/damage water pipes;

• destroy workplaces/damage factories;

• occur without warning/at great speed etc.

-Most volcanoes at constructive boundaries erupt under the ocean. The lava cools quickly to form ball shapes – pillow lava. These volcanoes usually occur along a rift, not from one main vent (d)

 -a bulge (before eruption)

-Volcanic plugs are formed when lava solidifies in the pipe of an extinct volcano.  Over time, the volcanic cone made up of less resistant rocks wears away, leaving behind the solidified volcanic plug (e)

-ash and steam (f)

-lava flow (g)

Earthquake features/vocab:

-focus: point of earthquake

-epicenter: point directly above the focus, on the ground surface

-seismic waves

-shaking ground

A subduction zone occurs at a destructive plate boundary, it is where one plate goes under the other

Causes:

Earthquakes – 2 plates ‘stick’; pressure builds up; one plate jerks forward sending shock waves to the surface

Volcanoes –

At constructive margin: plates move away from each other; magma rises to fill the gap; there might be steam or ash ejections, explosions

At destructive margin: oceanic crust melts from friction and heat from mantle; newly formed magma is lighter so it rises to the surface

A composite or stratovolcano

• Found at destructive plate boundaries.
• Formed by viscous (thick) lava.
• Eruption starts violently creating ash & pulverised rock. Later lava flows out.
• Have alternating layers of lava and rock fragments
• Usually large and conical

• alternate layers;

• ash/cinders and lava;

• slopes steeper at summit;

• main cone;

• crater;

• secondary cones;

• vent/pipe;

• magma chamber;

• dyke  

Preventing damage or deaths by earthquake:

• Move away from areas of instability;

• Forecasting/warning to public;

• build earthquake proof buildings/or specific references to structures to 

• awareness/what action to take;

• practise drills;

• emergency services organised;

• emergency food/supplies

Effects/difficulties of earthquakes:

• cost;

• may occur in country with low GNP;

• devastation may cover a wide area/large-scale/affects many people;

• magnitude of disaster/intensity;

• damage to infrastructure;

• damage to economy;

• impacts on food supplies/famine;

• impacts of disease on recovery;

• lack of hospitals/health care hinder recovery;

• homelessness;

• psychological impacts