Key words Flashcards
Lithosphere
The section of Earth’s profile which includes the crust and upper (solid) mantle
Asthenosphere
The uppermost part of the mantle roughly 80-200 km beneath the Earth’s surface. This is the layer than tectonic plates rest and move.
Below the lithosphere
Plate tectonics theory
Theory that the crust is divided up into smaller sections which all float on top of the mantle, and all move
Sea-floor spreading
Process by which oceanic plates split apart and new crust is formed through the rising of basaltic magma
Convection currents
Material in the mantle rises up and down. Hot material, which is less dense, moves upwards. As it cools, density increases and it sinks once again
Ridge push (gravitational sliding)
Secondary form of plate movement, caused by the heavy weight of new oceanic crust at ocean trenches
As the crust moves away from a mid-ocean ridge, it cools and becomes denser and thicker. This causes the lithosphere to slope away from the ridge and gravity pulls the lithosphere down this slope, pushing it forwards.
Slab pull
Process by which dense and old oceanic crust is pulled down under less dense continental crust at subduction zones
The pulling force exerted by a cold, dense oceanic plate plunging into the mantle due to its own weight. The theory is that because the oceanic plate is denser than the hotter mantle beneath it, this contrast in density causes the plate to sink into the mantle
Convergent boundary
Land is destroyed as two plates collide. The denser (oceanic) plate is forced (subducted) below the lighter plate and melted in the mantle
Divergent boundary
Two plates pull apart creating new land- ocean ridges or rift valleys (constructive)
Conservative boundary
Plates move past each other, but no land is destroyed. Pressure builds and is suddenly released, often as powerful earthquakes
Magma plume
Upward flow of hotter magma, than the surrounding mantle
Young fold mountains
Mountains made of thick accumulations of sedimentary rock which form along the edges of continents where two plates collide e.g. the Himalayas
Rift valley
Narrow depression between an upland area on each side, sometimes seen at divergent plate boundaries as the two plates pull apart
Ocean ridge
Area of raised seabed, where the two tectonic plates are spread apart at a divergent plate boundary
deep-sea trench
Deep depression found along the seaward edge of convergent plate boundaries.
Trenches are formed through subduction, which occurs when tectonic plates collide and push one plate beneath the other. Trenches can be found all over the surface floor of the ocean at subduction zones
Island arc
Often crescent shaped line of volcanoes protruding from the ocean along a convergent plate boundary
Plate boundary
The boundary between two tectonic plates
Hotspot
Site of a volcano away from a plate boundary as hot magma rises and melts through the crust
Shield volcano
Landform with a central vent and gently sloping sides, built up by layers of basaltic lava flows e.g. Mauna Load, Hawaii
Composite volcano
Steep-sided, pyramid-shaped landform built up from alternating layers of ash and lava flows e.g. Mount Vesuvius, Italy
High-viscosity magma
Underground material that is very sticky and silica rich e.g rhyolite and andesite, formed from melted crust at convergent boundaries
Low-viscosity magma
Underground material that flows relatively freely, with low silica content e.g. basaltic, often formed of mantle material, not melted crust
Effusive eruption
Low-magnitude volcanic ejection, such as runny basaltic lava which flows away from a vent- little height of ejecta is maintained
Explosive eruption
Violent ejection of volcanic material due to a great build-up of pressure, trapped gases and viscous magma often at a convergent plate boundary
Super volcano
Volcano capable of the largest type of eruption- 1,000km^3 or more of material is erupted
Volcanic Explosivity Index (VEI)
Classification of volcanoes based on the volume of material ejected, the eruption height and duration of the eruption
Pyroclastic flows
A mixture of volcanic rock, ash and gases, heated to upwards of 800degrees C which flows rapidly downslope, sometimes at 700km/h
Lahar
Volcanic mudflow composed of pyroclastic material and water which flows down a volcano and along a river channel
Tephra
Generic name for material ejected from a volcano; can be subdivided into size, from largest- volcanic bombs, to smallest-ash
Volcanic gases
Sulphur dioxide and carbon dioxide and others ejected from a volcano
Jokulhlaups
Glacial outburst flood caused by a heating or volcanic eruption below ice, releasing water from a subglacial lake
Tsunami
High wave at the shore with potentially devastating consequences. Undersea earthquakes, volcanoes and landslides are triggers
Focus
The point within earth’s crust from which a sudden pressure release occurs
Epicentre
The point on Earth’s surface above the focus where an earthquake originated
Benioff zone
Part of the subduction zone where the descending oceanic crust begins to melt into magma. The increased heat and friction at the region create a zone of earthquake hypocentres
Seismic wave
Pressure oscillation propagating through the ground, as energy is released via an earthquake
Shallow-focus
Earthquake with a focus depth of 0-70km
Deep-focus
Earthquake with a focus depth of 300-700km
Intermediate focus
Earthquake with a focus depth of 70-300km
Magnitude
The amount of energy, for example, delivered by a seismic event
Seismometer
Device used to measure earthquakes- the movement of the ground
Moment magnitude scale
Scale of the amount of energy (magnitude) derived from an earthquake, a replacement of the Richter scale.
It is the main scale now used by seismologists
Includes additional parameters (size of fault rupture and rock strength)
Each increase on the magnitude scale represents a 10-fold increase in shaking and a 32-fold increase in energy released.
Modified Mercalli scale
A 12 point scale which measures the impact of an earthquake.
Measures intensity, based on qualitative data
Ranges from level 1 (detected by instruments not felt by people) to Level XII
Escarpment
Differential land height along a fault line caused by horizontal and movement; for example a high ridge remaining after an adjacent fall down
Primary hazard
Damage and danger caused by the direct shaking of the ground
Includes ground shaking, liquefaction, landslides and avalanches
Secondary hazard
Damage caused after the earthquake as a result of ground shaking
Includes tsunamis and flooding
Liquefaction
Saturated or partially saturated sediments (such as soil) lose mechanical strength during an earthquake and act like a fluid
Perception
The way that a person sees hazard risk- dependant on personal experience and circumstances
Mitigation
Reducing the effects of a disaster- such as building strong earthquake resistant buildings
Adaptation
Coping with the effects of a tectonic hazard and changing the way of life after the event
Planning
Preparation for an event- covering responses to immediately spring into action as soon as a disaster occurs in order to deal with the event as quickly as possible
Hazard risk equation
Risk=hazard likeliness x level of vulnerability
Park model
Graph displaying the speed and magnitude at which quality of life declines after a hazard and the speed and level of recovery afterwards
Viscosity
How well a substance flows. More viscous material is thicker and flows less easily
Caldera
A basin-shaped depression, 2-50km in diameter formed by the collapse of a volcano following a highly explosive eruption
Lava plateaux
Flat, elevated landforms created by extremely large volume effusive eruptions called flood basalts
Richter Scale
Assesses energy release using maximum amplitude of seismic waves recorded on a seismogram.
