Convergent Oceanic/Continental Flashcards
What happens at an oceanic/continental convergence
The denser oceanic plate is forced under the lighter continental one- subduction.
How is an ocean trench formed
The downwarping of the oceanic plate forms a very deep part of the ocean.
Example of an ocean trench
Off the Western coast of South America where the Nazca plate is subducting under the South American plate, forming the Peru-Chile trench.
How are fold mountains formed
Sediments that have accumulated on the continental shelf on the margin of the land mass are deformed by folding and faulting. Along the edge of the continental plate, these are uplifted to form fold mountains.
Example of fold mountains
The Andes along the pacific side of south america.
What happens as the oceanic plate descends
The increase in pressure can trigger major earthquakes along the line of the subducting plate.
What are the earthquakes like
Shallow, intermediate or deep focus
What happens in the Benioff zone
The further the rock descends, the hotter the surroundings become. This together with the heat generated from friction, begins to melt oceanic plate into magma in a part of the subduction zone known as the Benioff zone.
How are volcanoes formed
The Benioff zone is less dense than the surrounding asthenosphere, this molten material begins to rise as plutons of magma. Eventually these reach the surface and form volcanoes.
How do different lava types form different volcanoes
The andesitic lava, which has a viscous nature (flows less easily), creates complex, composite, explosive volcanoes (contrast this to the basaltic emissions on constructive margins which tend to be gentle eruptions).
How is an island arc formed
If the eruptions take place offshore, a line of volcanic islands known as an island arc can appear
Example of an island arc
The West Indies
