Landforms at Plate Margins

There are 2 main types of landform that occur at plate boundaries (in addition to volcanoes but information on these can be found here).  These are fold mountains and ocean trenches.

Fold Mountains

Fold mountains occur at collision plate boundaries where 2 pieces of continental crust meet.  They often occur after destructive plate margins have ‘dragged’ continental crusts towards each other but due to their similar densities, neither can really be subducted.  This means that rock gets folded up into mountains.  The whole process can be summarised in 3 stages:

  1. Rivers carry sediments into the sea where they are deposited on the sea bed with a large geological dip called a geosyncline.
  2. As the sediment on the sea bed accumulates (builds up) it causes the lower layers to be compressed so much they form into sedimentary rock.  These rock layers continue build up to form hundreds of different strata (layers of rock).
  3. While all this is going on, the continental plates either side of the sea are being moved towards each other by convection currents within the mantle.  As they get closer and closer they causes the sedimentary rock to buckle and fold up into mountains.  The incredible force with which the continental plates collide causes the newly made fold mountains to continue to grow into the largest mountains in the World.

During the formation of fold mountains, several features are created with the rock.  Upward folds are called Anticlines (they look like an A) and downward folds are called Synclines.

Image courtesy of Wikipedia

Ocean Trenches

Ocean trenches occur at destructive plate margins where oceanic plate is subducted beneath continental plate.  They are most common around the Pacific Ring of Fire and can reach in excess of 10,000m deep, the deepest points on Earth (Challenger Deep at 10,916m being the deepest).  Ocean trenches are very important scientifically given the range of species, some yet undiscovered, that live in them.  They are also important for human uses, commonly used for dumping of waste, which obviously conflicts with scientific interests.

Map of Challenger Deep courtesy of Wikipedia

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