Natural systems internal and external forces Flashcards
crustal plate
a large block of the lithosphere that reacts to tectonic forces.
Why do plates move?
The temperature is high deep in the earth and spreads out, flowing towards the surface forming large convection cells known as convection currents. They rise from deep in the mantle and towards the surface. They then spread below the crustal plates, cool and descend back into the mantle.
Three types of boundaries
divergent,convergent and transform.
Convergent
the plates move toward each other. At convergent plate boundaries (also called destructive plate boundaries), crustal plates collide in super slow motion causing earthquakes, folding and volcanic activity.
Subduction
Many convergent boundaries occur along the edges of our oceans. In these regions, oceanic crust collides with continental crust. The denser oceanic crust is pushed under the less dense continental crust.
Divergent
crustal plates are moving away from each other. At divergent plate boundaries the slow separation of the plates creates a small space through which magma rises and cools, creating or constructing new crust. (constructive plate boundaries). Earthquakes sometimes occur at divergent plate boundaries. Also the magma rising through weaknesses in the crust near divergent plate boundaries causes volcanic activity. Divergent plate margins often occur beneath our oceans.
Transform
they simply slide past each other. earthquakes sometimes occur.
Earthquakes
An earthquake is a shock or series of shocks caused by a sudden movement of crustal rocks.They are caused by a sudden release of pressure within the Earth’s crust.The Earth’s crustal plates do not always move smoothly against each other. Sometimes they may get stuck and this causes pressure or tension to build up. When this pressure is released, a massive amount of energy travels through the earth’s crust as seismic waves causing the ground to shake, sometimes violently.
Folding
The rocks at or near convergent plate boundaries are placed under tremendous pressure. As the plates collide, these rocks may be compressed, causing them to fold.
Extrusive volcanic features
Formed by lava and ash at the surface
Shield volcano
Composite cones
Caldera
Intrusive volcanic features
formed by magma which cools and hardens before it reaches the surface
sill- when magma forces its way in between beds of rock, horizontally
dyke- formed when magma passes through cracks or joints that cut across layers of rock, perpendicular to the ground.
batholith- enormous mass os igneous rock that forms when magma cools deep within the earth’s crust.
Definition of weathering
the deterioration of rocks, soils and minerals
Definition of erosion
the removal of soil and rock by wind, water and ice.
Definition of mass wasting
the downhill movement of soil and rock under the influence of gravity.
Frost Action
in daytime, when temperature is above freezing point, cracks and fissures in the rock fill with water from rain, dew and melting ice. At night, the temperature falls below freezing point, water turns to ice and expands by 9%. This process is repeated many times and the ice crystals press against the rock creating pressure causing rocks to split.
