Plate Tectonics L.O: To know about different plate margins and what happens when they push together or move apart.

Plate Margin The meeting place of one plate (plates make up the top layer of the Earth's structure) with another plate. There are four types of plate margin – destructive, constructive, collision, and conservative. A volcano may be found along two of the types of plate margin, and an earthquake may occur at all four plate margins.

Destructive

Destructive At a destructive margin an oceanic plate moves towards (and disappears into the mantle of) a continental plate or another oceanic plate. This is the subduction zone. As it is forced downwards, pressure at the margins increases, and this can result in violent earthquakes. The heat produced by friction turns the crust into magma (liquid rock). The magma tries to rise to the surface and, if it succeeds, violent volcanic eruptions occur.

Destructive

Conservative

Conservative plate margins At a conservative margin two plates try to slide past each other slowly. Quite often, the two plates stick and pressure builds up; the release of this pressure creates a severe earthquake. There are no volcanic eruptions along conservative plate margins because the crust is neither being created nor destroyed. The San Andreas Fault in California lies above the North American and Pacific plates, and is an example of a conservative plate margin.

Conservative

Constructive

Constructive plate margins At a constructive margin the Earth's crust is forced apart. Magma rises and solidifies to create a new oceanic crust and forms a mid-ocean ridge. This ridge is made from igneous rock; such ridges usually form below sea level on the sea bed (an exception to this is in Iceland).

Constructive

Mid Atlantic Ridge

Collision

Collision Two Continental crusts move together. Neither goes under the other, and they therefore buckle, or 'fold'. Over a large period of time, this creates mountains, such as the Himalayas. This may cause severe earthquakes, but not volcanoes.

Collision – India

Collision – India

Plate Movement