A2 Geography – Earth Hazards glossary

Shear strength  the strength of a material or component against the type of yield or structural failure where the material or component fails 

Shear stress the form of stress in a body, part, etc., that tends to produce cutting rather than stretching or bending

Slope failure The downward sliding of a relatively dry mass of earth and rock.Dynamic equilibrium

A condition in which all acting influences are canceled by others, resulting in a stable, balanced, or unchanging system.

Primary impacts Occur as a result of the process itself. For example water damage during a flood or collapse of buildings during an earthquake, landslide, or hurricane

Secondary impacts

Occur only because a primary effect has caused them. For example, fires ignited as a result of earthquakes, disruption of electrical power and water service as a result of an earthquake, flood, or hurricane, or flooding caused by a landslide into a lake or river

Tertiary impacts Are long-term effects that are set off as a result of a primary event. These include things like loss of habitat caused by a flood, permanent changes in the position of river channel caused by flood, crop failure caused by a volcanic eruption etc

Creep Is the slowest form of mass movement. the expansion and contraction of the water within soil is the main cause of it. wetting causes the soil to expand and to move downslope under the influence of gravity.

Avalanche is a sudden, drastic flow of snow down a slope, occurring when either natural triggers, such as loading from new snow or rain, or artificial triggers, such as snowmobilers, explosives or backcountry skiers, overload the snowpack. 

Slump A form of mass wasting event that occurs when loosely consolidated materials or rock layers move a short distance down a slope

Tectonics On Earth, there are seven or eight major plates (depending on how they are defined) and many minor plates. Where plates meet, their relative motion determines the type of boundary: convergent, divergent, or transform

Destructive margin

A convergent boundary, also known as a destructive plate boundary (because of subduction), is an actively deforming region where two (or more) tectonic plates or fragments of lithosphere move toward one another and collide

Constructive margin

A divergent boundary or divergent plate boundary (also known as a constructive boundary or an extensional boundary) is a linear feature that exists between two tectonic plates that are moving away from each other

Conservative margin

transform boundary, also known as conservative plate boundary since these faults neither create nor destroy. It is a type of fault whose relative motion is predominantly horizontal.

Subduction The process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate, sinking into the Earth's mantle, as the plates converge

Focus depth of focus refers to the depth at which an earthquake occurs. Earthquakes occurring at a depth of less than 60 km are classified as

'shallow-focus' earthquakes, while those with a focal-depth between 60 and 300 km are commonly termed 'mid-focus' or 'intermediate-depth' earthquakes

Epicentre the point on the Earth's surface that is directly above the focus, the point where an earthquake originates

Lahars Is an Indonesian term that describes a hot or cold mixture of water and rock fragments flowing down the slopes of a volcano and (or) river valleys

Tephra When a volcano erupts it will sometimes eject material such as rock fragments into the atmosphere. This material is known as tephra. The largest pieces of tephra (greater than 64 mm) are called blocks and bombs

Pyroclastic flows Is a fluidized mixture of solid to semi-solid fragments and hot, expanding gases that flows down the flank of a volcanic edifice

Tsunamis is a series of water waves caused by the displacement of a large volume of a body of water, typically an ocean after an earthquake

D. Drake 2012@djdhums