GEOSCIENCE 91191 — KEY VOCAB

Subduction

one tectonic plate forced beneath another into mantle.

Subduction zone

region where one plate is being pushed beneath another.

Oblique plate boundary

plates move past each other at an angle, combining sideways movement with compression/extension.

Transform boundary

plates move horizontally past each other.

Fault

fracture in crust where movement can occur.

Elastic rebound

sudden release of stored elastic energy when rocks move toward less-stressed state.

Stress

force acting on rocks that can deform/break them.

Strain

deformation/change in shape/size caused by stress.

Friction

force resisting movement between surfaces, helping faults remain locked.

Focus/hypocentre

underground point where earthquake begins/energy first released.

Epicentre

point on surface directly above focus.

Seismic waves

energy waves released by earthquake.

P waves

fastest seismic waves; travel through solids, liquids, gases.

S waves

slower; travel through solids, not liquids.

Magnitude

measure of energy released by earthquake.

Aftershock

smaller earthquake after main event as crust adjusts.

Partial melting

only some minerals in rock melt, producing magma different from original.

Mantle wedge

mantle above subducting plate and below overriding plate where melting can occur.

Volatiles

water, carbon dioxide etc. dissolved in magma and can form gases as pressure decreases.

Silica content

amount of silica in magma, strongly affects viscosity.

Viscosity

resistance to flowing.

Degassing

dissolved gases escaping magma as pressure decreases.

Magma chamber

underground region where magma accumulates before an eruption.

Magma ascent

movement of magma upward.

Explosive eruption

violent release of gases/material due to pressure in viscous magma.

Effusive eruption

relatively fluid lava flows rather than violently exploding.

Pyroclastic flow

fast-moving hot mixture of gas, ash, rock.

Lahar

fast mixture of volcanic material and water down volcanic slopes/valleys.

Tephra

rock/magma fragments ejected during eruption.

Tsunami

series of long-wavelength ocean waves from sudden displacement of large water volume.

Seafloor displacement

sudden vertical/horizontal movement of ocean floor, displacing water above.

Water displacement

movement of water from original position due to disturbance.

Wavelength

distance between corresponding points on consecutive waves.

Wave height

vertical distance between crest/trough.

Shoaling

tsunami changes entering shallow water: slows, wavelength decreases, height increases.

Inundation

flooding of normally dry land by tsunami water.

Run-up

maximum vertical height above sea level reached by tsunami water on land.

Hazard

potentially damaging natural process/event.

Exposure

people/buildings/infrastructure/environment in area that could be affected.

Vulnerability

susceptibility to harm.

Risk

potential for hazard to cause damage/loss, influenced by hazard, exposure, vulnerability.