Tectonic Processes and Hazards Flashcards
Asthenosphere
The part of the mantle, below the lithosphere, where the rock is semi-molten.
Benioff zone
The area where friction is created between colliding tectonic plates, resulting in intermediate and deep earthquakes.
Collision plate boundary
Where two plates move towards each other causing a very slow collision which is likely to cause folding and faulting of crustal rocks and the uplift of continental crust to form fold mountains.
Community adaptation
People within communities, either whole or parts of settlements, work together to change their way of life so that the impact of a tectonic hazard event is not as hazardous.
Community preparedness
People within communities, either whole or parts of settlements, work together to change their way of life so that the impact of a tectonic hazard event is not as hazardous.
Conservative plate movement
Where two plates meet and move alongside each other in a similar direction or opposite direction, usually at different speeds. Friction between the two plates is great and stresses and strains build up to create shall earthquake foci.
Also transform plate boundary.
Constructive plate boundary
Where two plates move in opposite directions, leaving a zone of faulting and a gap into which magma from the asthenosphere rises.
Also divergent plate boundary.
Constructive plate boundary
Where two plates move in opposite directions, leaving a zone of faulting and a gap into which magma from the asthenosphere rises.
Also divergent plate boundary.
Convection currents
Hot, liquid magma currents moving in the asthenosphere.
Convergent plate boundary
Where two plates move towards each other and at the boundary the denser oceanic plate (basaltic) is subducted beneath the less dense continental plate (granitic), creating surface features such as a trench, and deep features such as the Benioff zone.
Also destructive plate boundary.
Crustal fracturing
When energy released during an earthquake causes the Earth’s crust to crack.
Disaster
The realisation of a hazard when 10 or more people are killed or 100 or more are affected
Epicentre
The point on the Earth’s surface directly above the focus of an earthquake.
Focal depth
The depth at which an earthquake starts (focus). It is divided into shallow, intermediate and deep. Shallow earthquakes have the greatest impacts, as the seismic waves have not lost as much of their energy by the time they reach the surface.
Focus
The point inside the Earth’s crust from which the pressure is released when an earthquake occurs.
Also hypocentre.
Geological structure
The arrangement of rock in layers, or folds and the joints and bedding planes within them.
Governance
The many ways that institutions and individuals manage their common affairs
Hazard
A perceived natural event that has the potential to threaten life and property
Hazard-management cycle
A theoretical model of hazard management as a continuous four-stage cycle involving mitigation, preparation, response and recovery.
Hazard profile
A technique used to understand and compare the physical characteristics of different types of hazard e.g. duration
Hot spot
Points within the middle of a tectonic plate where plumes of hot magma rise and erupt.
Hydrometeorological hazards
Natural hazards caused by climate processes (including droughts, floods, hurricanes and storms).
Intra-plate earthquakes
Earthquakes which occur in the middle or interior of tectonic plates, rather than on plate margins.
Jokulhlaups
Glacial outburst floods caused by volcanic activity melting ice
L waves
The slowest seismic waves, which focus all their energy on the Earth’s surface.
Lahar
A mixture of meltwater from snow and ice on top of an active volcano and tephra (volcanic material such as ash) from eruptions that travels very quickly down existing river valleys, reaching some distance away from the volcano.
Land-use zoning
A process by which local government regulates how land in a community may be used.
Landslide
A mass movement of rock and soil down a steep slope under the influence of gravity, perhaps triggered by an earthquake loosening material.
Lava flow
Molten magma that reaches the Earth’s surface is known as lava. It will flow down the sides of a volcano until it cools and solidifies. Basaltic lavas flow faster than andesitic lavas, for example, because of the different velocities.
Liquefaction
When the violent shaking during an earthquake causes water-saturated material to lose its strength and behave like a liquid.
Lithosphere
The solid layer, made from the crust and upper mantle, from which tectonic plates are formed.
Magnitude
The amount of energy releases by a tectonic event. For earthquakes this is best measured on the Moment Magnitude Scale (MMS) and for volcanoes the Volcanic Explosivity Index (VEI).
Mass movement
The downward movement of material under the influence of gravity. It includes a wide range of processes such as rockfalls, landslides and solifluction.
Mega-disaster
When a major hazardous event becomes catastrophic and more than a disaster. For example, the scale of the impacts are unusually great or very sever with huge numbers of deaths, loss of buildings and infrastructure, or long-lasting impacts on normal social and economic systems.
Mercali scale
An earthquake intensity scale based on 12 levels of damage to areas.
Mitigation
Action to reduce the impacts of an event.
Modify loss
Action to reduce the impacts of an event.
Modify the event
Alter the natural hazards itself in order to change its likely impacts. Earthquakes cannot be changed, but some volcanic activity can be modified, such as by diverting lava flows.
Modify vulnerability
Vulnerability is a key factor in determining the impact of a hazard, so making people less vulnerable will reduce the scale of a disaster.
Moment Magnitude Scale (MMS)
The most accurate earthquake magnitude scale, it measures the total energy released by an earthquake.
Multiple-hazard zone
An area that is at risk from multiple natural hazards such as hurricanes and earthquakes (hydro-meteorological and tectonic)
P (Primary) waves
The fastest seismic waves which travel through both solids and liquids.
Palaeomagnetism
The study of past changes in the Earth’s magnetic field.
Park model
Shows how a country or region might respond after a hazard event.
Plate tectonics
A theory developed to explain the large scale movements of the lithosphere
Pressure and release (PAR) model
A tool used to work out how vulnerable a country is to hazards.
Pyroclastic flow
Clouds of hot gas, ash and other volcanic materials which travel at high speeds and are extremely hot
Resilience
The ability of a community to resist the impacts of a hazard by adapting and recovering.
Richter scale
A measurement of the height of the waves produced by an earthquake
Risk
The exposure of people to a hazard event, or the probability of a hazard occurring and causing damage.
S (secondary) waves
Seismic waves which only travel through solids and move with a sideways motion.
Seismic hazards
Generated when rocks within 700m of the Earth’s surface come under such stress that they break and become displaced
Sea floor spreading
The movement of the oceanic crust away from a constructive plate boundary, as recorded by the magnetic stripes in the basaltic rock (palaeomagnetism).
Slab pull
When newly formed oceanic crust sinks into the mantle, pulling the rest of the plate further down with it.
Subduction
Where two plates move together, and often a thinner, denser plate descends beneath a continental plate.
Subduction zone
The area in the mantle where a tectonic plate melts.
Tephra
Material ejected from a volcano from large rock fragments to ash.
Transform fault
A fault created on a large scale when two plates slide past each other.
Volcanic Explosivity Index (VEI)
The scale used to measure the magnitude of a volcanic eruption.
Water column displacement
The movement of a volume of seawater above the point at which the seabed was moved up or down by an earthquake, such as a thrust.
