geography: ch 11

11.3, 11.5-11.9

mid-ocean ridges

huge mountain ranges that form a continuous chain down the centre of the ocean floors

ocean trenches

long, narrow, and deep depressions near the edges of some countries

mountain belts

a long chain of mountains that share similar features, structures, and formation processes

destructive/convergent plate boundaries

happens when oceanic or continental plates collide, causing earthquakes, forming volcanoes and mountains

constructive/divergent plate boundaries

occurs when two lithospheric plates are forced apart, causing earthquakes and forming mountains

conservative/transform plate boundaries

happens when two plates slide past each other, causing earthquakes

earthquake

a sudden violent movement of the Earth’s surface

seismometer

an instrument that records earthquakes as waves on a graph

magnitude

the amount of energy an earthquake gives out, shown on the Richter scale

epicentre

the area on the surface directly above the earthquake

focus

the location below the Earth’s surface where the earthquake starts

seismic wave

waves of energy caused by the sudden movement of the plates

foreshocks

smaller earthquakes that occur before a larger earthquake that follows

mainshock

the largest, main earthquake

aftershocks

a smaller earthquake following the main shock of a large earthquake

volcanoes

openings or cracks in the lithosphere where magma from inside the Earth can escape onto the surface

magma

can erupt as flowing lava, volcanic bombs, hot ash and dust, or as steam and poisonous gases.

shield volcano

a volcano with gentle slopes, formed from runny lava which spreads far from its source

composite volcano

a tall volcano with steep sides and a symmetrical cone shape, formed from very thick, sticky lava

active volcano

is erupting or has erupted recently, and is likely to erupt again

dormant volcano

has not erupted for 10 000 years but could be active again

extinct volcano

has not erupted for 1 million years and will probably never erupt again