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.
