Hazards key terms Flashcards
Destructive plate margin - two types
Subduction
1) Two plates move toward each other, one oceanic and one continental.
2) The denser, heavier oceanic curst subducts under the lighter, less dense continental crust. This creates an ocean trench and a subduction zone.
3) In the subduction zone, friction from the contact of the two plates can cause earthquakes (when they lock and release) and heat.
4) The subducting oceanic crust melts to produce magma. This expands, becomes less dense, and rises through weaknesses in the continental crust, erupting on the surface as a volcano.
5) Where the oceanic crust subducts under the continental crust, ocean sediment is scraped off the ocean bed and onto the continental crust forming fold mountains.
The Earthquakes are severe.
Produces composite volcanoes which are explosive.
Produces ocean trenches and fold mountains.
Collision
1) Two continental plates of the same density move toward each other.
2) Due to their similarity, little or no subduction takes place, but instead the sediment and rocks at the plate margin crumple and fold.
3) This creates mountainous ridges.
4) Over time, these mountains may be weathered, and eroded by the effects of glaciers and rain.
Some of the Earthquakes are severe.
Produces fold mountains.
Constructive plate margin
1) Two plates of oceanic crust pull apart (diverge).
2) The rising magma plume forces the ends of the plate to push up and buckle.
3) Magma is squeezed into the gap between the two plates and cools to form new, solidified rock (basalt).
4) Submarine volcanoes (shield volcanoes) are formed on the ocean floor.
5) With successive eruptions over millions of years, they can grow until they break the surface of the ocean and become a volcanic island (e.g., Iceland).
The Earthquakes are gentle.
Produce shield volcanoes which are gentle.
Produces rift valleys and ocean ridges.
Conservative plate margin
1) Two plates moving in either opposite or the same direction (at different speeds). There is no subduction or creation of new rock.
2) Movement is not smooth, and friction is generated between the two plates.
3) This causes the plates to lock together so there is an increase in potential energy.
4) At some point, pressure overcomes friction and the plates are suddenly released, jolting past one another.
5) This sudden release of energy causes earthquakes.
The Earthquakes can be severe.
Produces upland ridges - e.g., San Andreas fault.
Crustal evolution
the formation, destruction and renewal of the rocky outer shell at the planet’s surface.
Tectonic plate
a broken section or piece of Earth’s crust.
Two types of tectonic plates
- Oceanic - more dense
- Continental - older
Plate margin
the boundary between two plates where they meet or come together.
Gravitational sliding
movement away from a spreading ocean ridge takes place with plate movement driven because of the higher elevation of plates at ocean ridges.
Ridge push
newly-formed plates at oceanic ridges are warm, and so have a higher elevation at the oceanic ridge than the colder, more dense plate material further away. Gravity causes the higher plate to push away from the other plate that lies further from the ridge.
Slab pull
The older, colder plate sinks at the subduction zone because as they cool, they become more dense than the underlying mantle. Therefore, the sinking plate pulls along the rest of the plate along behind it.
Convection currents
occurs within the molten rock in the mantle with the rising and sinking of molten material acting like a conveyor belt caused by the application of heat.
Seafloor spreading
caused by mantle convection currents as tectonic plates split apart from each other to often cause mid ocean ridges.
Subduction
the process of the denser oceanic plate colliding with and descending beneath the less dense continental plate.
Young fold mountains
two or more plates push together, compressing and causing the land to become warped and folded to form fold mountains. Usually found at destructive plate boundaries where the oceanic crust sinks below the continental crust at a subduction zone or two continental plates collide and push together at a collision zone.
Rift valleys
a lowland region forming when tectonic plates move apart, found both on land and at the bottom of the ocean where seafloor spreading is the cause.
Mid ocean ridges
the fracture zone along the ocean bottom where molten mantle material comes to the surface, thus creating new crust. This fracture can be seen beneath the ocean as a line of ridges that form as molten rock reaches the ocean bottom and solidifies.
Deep ocean trenches
deep ocean trenches are formed at destructive plate boundaries where the oceanic plate subducts below the continental plate forming long, narrow depressions on the seafloor.
Island arcs
long chains of active volcanoes with intense seismic activity found along destructive tectonic plate boundaries.
Volcanoes
vents in the Earth’s crust through which lava, tephra and gases erupt.
Destructive plate boundaries form composite volcanoes.
Constructive plate boundaries form shield volcanoes.
Nuees ardentes
billowing masses composed of incandescent dust and ash,
buoyed up by hot gases
Lava flows
Factors for speed of lava
streams of molten rock that pour or ooze from an erupting vent. The speed of lava flow depends on: type of lava and viscosity; steepness of ground it travels over; whether the lava flows as a broad sheet, through a confined channel, or down a lava tube; rate of lava production at the vent.
Mudflows
a wet, viscous fluid mass of fine-to-coarse-grained material flows rapidly and turbulently downslope, usually in a drainageway.
Pyroclastic flow and ash fallout
contains a high-density mix of hot lava blocks, pumice, ash and volcanic gases, moving at very high speeds down volcanic slopes. They typically follow valleys and flow in two parts: 1) the lower basal flow of coarse fragments that move along the ground; 2) a turbulent cloud of ash that rises above the basal flow.
Gases
gases are released from the liquid part of the magma with significant amounts of harmful GHGs like CO2 and SO2 released alongside water vapor which is harmless.
Acid rain
increased levels of SO2 can lead to acid rain and air pollution downwind from a volcano.
Lahars
mudflows and debris flows composed mostly of volcanic materials on the flanks of a volcano, typically entering a river valley.
Tephra
fragments of rock that are produced when magma or rock is explosively ejected.
Fatalism
optimistic or accepting approach, where people may believe that hazards are part of life and for many viewed as an “act of god”.
Prediction
monitoring the risk/cause of a hazard.
Adaptation
this perspective suggests that hazards are influenced by natural and human events and so we can change our lives to reduce the impacts.
Management
reducing the impacts of a disaster through prior planning and effective response and recovery.
Domination
this perspective suggests that hazards are predictable and that they can be better understood and overcome to an extent through scientific research.
Capacity
a combination of all the strengths and resources available within a community, society or organization that reduce the level of risk, or the effects of disaster.
Vulnerability
the condition determined by physical, social, economic, and environmental factors or processes, which increase the susceptibility of a community to the impact of hazards.
Mitigation
minimizing the effects of a disaster - e.g., building codes and zoning; vulnerability analyses; public education.
Preparedness
planning how to respond - e.g., preparedness plans; emergency exercises/training; warning systems.
Response
efforts to minimize the dangers created by the disaster - e.g., search and rescue; emergency relief.
Recovery
returning the community to normal - e.g., temporary housing; grants; medical care.
