Flashcards
Destructive (convergent) Margins
Cards in this deck (24)
- 1There are two types of plates, so there are three different convergent situations:.Oceanic plate moves towards continental plate
. Oceanic plate moves towards oceanic plate
. Continental plate moves towards continental plate - 2Oceanic/Continental Convergence: . What happens here? . What is this known as?Continental plate meets denser oceanic plate – ocean plate is forced under continental plate = process called subduction
The down-warping of the oceanic plate forms a deep part of the ocean know as a trench - 3Oceanic/Continental Convergence: . What are fold mountains?Sediment that has accumulated on the continental shelf are deformed by folding and faulting
Along the edge of the continental plate these are uplifted to form fold mountains - 4Oceanic/Continental Convergence: . How are earthquakes triggered?Major earthquakes along the line of the sub-ducting plate can be triggered by an increase in pressure as the oceanic plate descends; these may be shallow, intermediate or deep focus.
- 5Oceanic/Continental Convergence: . What happens as these surroundings get hotter?The surroundings become hotter, the further the rock descends; this combined with the heat from friction starts to melt the oceanic plate into magma in a part of the subduction zone known as the Benioff zone.
- 6Oceanic/Continental Convergence: . What happens to the magma at this point?As it 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.
- 7Oceanic/Continental Convergence: . What type of volcanoes are these?The andesitic lava (viscous) creates composite explosive volcanoes
- 8Oceanic/Continental Convergence: . What are other landforms associated with this convergence?If volcanic eruptions take places offshore; a line of volcanic islands can appear – these are called island arcs
- 9Oceanic/Continental Convergence: . Ocean trench exampleOceanic trench example: where the Nazca plate is subducted under the South-American plate forming the Peru-Chile trench
- 10Oceanic/Continental Convergence: . Fold mountain exampleFold mountain example: The Andes along the pacific side of South America
- 11Oceanic/Continental Convergence: . Island arcsIsland arcs: West Indies
- 12What is Oceanic/Oceanic Convergence?This is similar to oceanic-continental convergence in that one of the plates is subducted under the other during the collision. At the subduction zone a very deep trench is formed in the ocean floor.
- 13Oceanic/Oceanic Convergence: . What does this result in?Oceanic and oceanic plate convergence result in the formation of volcano chains. The crust that is pulled under or subducted melts to form magma.
- 14Oceanic/Oceanic Convergence: . What happens to the magma?This magma rises to the top of the overriding oceanic plates and erupts on the ocean floor. Over millions of years, the lava and debris from the volcanic eruptions pile up on the ocean floor until the volcano rises above sea level to form a volcanic island.
- 15Oceanic/Oceanic Convergence: . Are these formed in chains?These types of islands are usually formed as chains called island arcs, which run parallel to the trench at the subduction zone.
- 16Oceanic/Oceanic Convergence: . Do these convergences experience earthquakes?Oceanic-oceanic plate convergence experience similar powerful earthquakes to oceanic-continental convergences.
- 17Oceanic/Oceanic Convergence: . Landforms?. Island Arcs
. Trench - 18Oceanic/Oceanic Convergence: . Island Arcs, what are they? And what happens?Island arcs are a feature of oceanic/oceanic convergence. They are a chain of volcano's which are aligned in an arc shape and sit close to the boundary where two tectonics meet. Where oceanic plates meet one if forced under the other, this process is called subduction. Hot, re melted material from the sub ducting slab rises and leaks into the crust, forming a series of volcanoes. These volcanoes can make a chain of islands called an island arc
- 19Oceanic/Oceanic Convergence: . Island Arcs exampleKuril Islands in Japan.
The islands themselves are summits of volcanoes that are a direct result of the subduction of the Pacific Plate under the Okhotsk Plate, which forms the Kuril trench some 120 miles east of the islands . The chain has as around 100 volcanoes, some 40 of which are active, and many hot springs. - 20Oceanic/Oceanic Convergence: . Example of a trenchThe Marianas Trench, which runs parallel to the Mariana Islands, has formed where the relatively fast-moving Pacific Plate converges with the less speedy Philippine Plate.
- 21Oceanic/Oceanic Convergence: . Facts of the trenchAt nearly 11,000 m below sea level (7 miles long), the Challenger Deep, at the southern end of the Marianas Trench, is the deepest known point. For comparison, Mount Everest rises a mere above 8,854 m above sea level.
- 22Continental/Continental Convergence: . Why is there not much subduction where they meet?The plates forming continental crust have a much lower density than the underlying layers, so there is not much subduction where they meet.
- 23Continental/Continental Convergence: . What happens instead?Instead, these plates more towards each other, their edges and the sediment between them are forced up into a fold mountain.
- 24Continental/Continental Convergence: . Why is there no volcanic activity? However what can be triggered?As there is little subduction, there is no volcanic activity, but the movement of the plates can trigger shallow-focus earthquakes. Material is also forced downwards to form deep mountain roots.
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- A2 A2 Geography (Tectonics) Flashcards on Destructive (convergent) Margins, created by Alice Kimpton on 08/12/2016.
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