GLOSSARY

When you click on words in the glossary, you will access the text that is relevant to it.

aa lava - lava that has a rough surface when cooled

active volcano - a volcano that might erupt at any time

ash (or tephra) - tiny rock fragments that are ejected from a volcano during an eruption

asthenosphere - the uppermost ÒplasticÓ part of the earthÕs mantle, about 600 km thick (the layer below the lithosphere that is marked by low seismic wave velocities and high seismic wave attenuation)

basalt - an igneous rock formed when runny lava cools and hardens

caldera - a large crater (usually at least 5 km in diameter) formed when a volcano explodes

continent - One of the seven main land masses on earth: Asia, Africa, Europe, North America, South America, Australia and Antarctica

convection - in seismology, a form of motion in the mantle which occurs when hot matter rises and colder matter sinks

core - the hard centre of the earth, consisting of solid iron surrounded by liquid iron and nickel

crater - the funnel-shaped opening at the summit of a volcano, usually 1 km or less in diameter

crater lake - a lake which forms in a crater when the lava has cooled

crust - the outer ÒskinÓ of the earth

dormant volcano - a volcano that is not active but is expected to erupt again

epicentre - the point on the earthÕs surface which is immediately above the focus (the point at which the rock broke) of an earthquake

extinct - a volcano that is not expected to erupt again

fault - a break in the earthÕs crust which may range from centimetres to kilometres in length

foreshock - a tremor that occurs prior to an earthquake

geothermal energy - energy produced by harnessing the water or steam from hot rocks

geyser - a hot spring that erupts hot or boiling water and steam

hotspot volcano - a volcano that occurs in the middle of a plate above a hotspot of magma

hot spring - a pool or spring that is formed when seeping water that has been warmed by magma or heated rocks is returned to the surface

island arc - a chain of volcanic islands formed when magma rises from a subduction zone (e.g. Japan)

lahar - another name for a mudflow

lava - magma or molten rock that has erupted onto the surface of the earth

lithosphere - the earthÕs crust

lithospheric plate - a section of the earthÕs crust that ÒfloatsÓ on the mantle

L waves or Love waves - the third and most destructive energy waves to be released in an earthquake

magma - molten rock in the mantle that forms igneous rocks when cooling

magma chamber - a pocket of magma in the earthÕs crust

mantle - the main bulk of the earth between the core and the crust

Mercalli Scale - the scale which measures the intensity of an earthquake dependent on observation of damage caused

mid-ocean ridge - an oceanic mountain range occurring where plates are moving apart

mudflow - a fast-moving mixture of ash and water during or following a volcanic eruption (sometimes called a lahar)

mud pot - a hot spring in which water has mixed with mud

outer core - the liquid iron and nickel that surround the earthÕs solid core

pahoehoe lava - a type of lava that cools to give a twisted, rope-like appearance

pillow lava - lava which erupts underwater and cools into characteristic pillow shapes

primary waves (or P waves) - the first energy waves released in an earthquake

pumice - a volcanic rock formed by cooled frothy lava which contains so much air that it can float in water

pyroclastic flow - a fast-flowing cloud of hot gases and ash which is blown from the mouth of a volcano

Richter Scale - a scale of measurement of seismic intensity in an earthquake

Ring of Fire - an area  of volcanic activity which rings the Pacific Ocean

secondary waves (or S waves) - the second set of energy waves released in an earthquake

seismic activity - any of the effects caused by an earthquake

seismology - the study of seismic activity and earthquakes

spreading ridge - a ridge formed when magma rises to fill the rift when two plates move apart

subduction - the process of one plate sinking beneath the other into the earth and pulling the ocean lithosphere

surface waves - the third and most destructive energy waves to be released in an earthquake (there are 2 types - Love waves and Rayleigh waves)

tephra - volcanic ash

volcano - you should know what this means by now! A volcano is an opening in the surface of the earth from which molten rock, called magma, and gases escape