Destructive Boundaries (30) Flashcards
3 points to add in intro
> earths crust split up into slabs called plates that float on on partly melted rock in the upper mantle
they move from heat from the earths core which generates thermal convection currents which flow slowly in the upper mantle
convection currents drag the plates causing them to collide and separate
What is another word for destructive boundaries and upper mantle
Destructive - convergent
Upper mantle - asthenosphere
What happens when a oceanic and continental plate collide
> oceanic plate sinks because it is heavier and denser made of basalt
continental is made up of light alluvium rock eg granite
oceanic slides down and is destroyed and recycled (subduction)
during subduction oceanic crust melts and moves up throug continental crust to form explosive mountain ranges (Andes)
Name an explosive mountain range and how it was formed (o+c)
> during subduction oceanic crust melts and magma moves up through the continental crust to form explosive mountain ranges
the Andes
Where are deep trenches formed an example (o+c)
> they can be found at the point of subduction
Peru-Chile trench is over 8km deep
deep trenches are also associated with deep earthquakes
How are terraces formed (o+c)
> sediments carried on the seabed of the plate are scraped off and piled up against the edge of the continental plate
Andes Peru
What happens when two continental plates collide
> niether plate is subducted because they are both relatively light and resist downward movement
crust at the edge of these plates buckle and push upwards
both plates are destroyed by folding and uplifting to form fold mountains such as the Himalayas
When and what plates formed the Himalayas
About 50 mil years ago
Indian and Eurasian plate collided and still continue to grow
How do 2 continental plates form earth quakes
Continental plates tend to move upwards and sideways causing devastating shallow earth quakes at the boundary (Pakistan in 2005)
Example of shallow earthquake formed from 2 continental plates colliding
Pakistan in 2005 where over 89 thousand people died
What are fold mountains composed of 2C
Often composed of sedimentary rock, such as limestone, that formed on the seabed
What happen when 2 oceanic plates collide
> Usually one sinks beneath the other one and sinks into the mantle
the sunken plate is melted and the magma rises to form underwater volcanoes
these will eventually appear on the surface of the sea (the Philippine islands)
What are island arcs and when do they occur
> an island arc will form at a subduction zone
>they are a curved line of volcanic island (japan and the Philippine islands)
Example of a trench formed at a oceanic and oceanic boundary
> the marianas trench marks the place where fast moving Pacific plate and slower moving Philippine plate collide
marianas trench is over 11km deep
trenches that form as o+o subduction zones are some of the deepest parts of the ocean
