1. One side of the continents usually has a subduction zone, while the other side doesn't.
Explanation:
It can be easily noticeable that some continents have high geological activity on one side, while they are much calmer on the opposite side. This is because of the different types of plate boundaries. Very often, one side of the continents has a subduction zone nearby, thus it is very active geologically. The other, opposite side, usually has another type of plate boundary, or the boundary is far away, making that side of the continent much less active.
- The subduction zones are places where one plate moves below another plate.
- The result of a subduction zone is intense volcanic activity and earthquakes.
- The absence of plate boundary near a continent's edge results in geologically stable area.
(a) No, not all continental coastlines are plate boundaries.
Explanation:
The majority of large plates on Earth's surface are continental tectonic plates. They are all different from each other though, be it in their size, their composition, the interaction with the other plates, the percentage of continental and oceanic crust they have etc. All continental plates have oceanic crust, thus their boundaries are strictly defined by the land mass. Some of continental plates have one boundary being further away in the ocean, while the other one actually to be roughly corresponding with the land mass.
- The North American plate is an example where one side of the plate has its boundary along the edge of the land mass, while the other one is further away in the ocean.
- The western boundary of the North American plate is with the Juan de Fuca and the Pacific plates, where there is subduction zones, and the boundary is roughly the same as the coastline.
- The eastern boundary is with the Eurasian and slightly with the African plate. It is a divergent boundary, found in the middle of the Atlantic Ocean.
(b) The west coast of Africa is geologically relatively calm, while the west coast of South America is geologically very active.
Explanation:
The west coasts of South America and Africa are very different. Apart from having different shape, which is nothing weird, there are several other crucial differences. The west coast of South America is actually the boundary of the plate, while the west coast of Africa is far away from the boundary of the plate. The west coast of South America has a subduction zone, thus it is very active geologically, while the west coast of Africa doesn't have a plate boundary nearby so it is relatively calm geologically.
- The west coast of Africa has a broader continental shelf than the west of South America, with the main reason being that there isn't a plate boundary nearby.
- The west coast of South America has very narrow continental shelf as there is a subduction zone nearby.
- Because of the subduction zone on its western boundary, the South American plate is also near several ocean trenches.
- The subduction zone and the intense geological activity along the west coast of South America contribute to lot of earthquakes, which can easily be seen by Chile's earthquake record.
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