The volcanic eruptions are often violent, with lots of steam, gas and ash. If two continental plates collide , neither can sink and so the land buckles upwards to form fold mountains. This is called a collision boundary. Earthquakes can occur at collision boundaries. At a divergent plate boundary , the plates move apart from one another. When this happens the magma from the mantle rises up to make or construct new land in the form of a shield volcano.
The movement of the plates over the mantle can cause earthquakes. At a conservative plate boundary , the plates move past each other or side by side, moving at different speeds.
This is an earthquake. Some of the plates have ocean water above them. Other plates include continents, and some plates include both continents and ocean. The movements of the plates help shape the geological features of our planet. The three main types of plate movements include:. Divergent Spreading :This is where two plates move away from each other.
Molten rock from the mantle erupts along the opening, forming new crust. The earthquakes that occur along these zones, called spreading centers, are relatively small. Convergent Colliding : This occurs when plates move towards each other and collide. When a continental plate meets an oceanic plate, the thinner, denser, and more flexible oceanic plate sinks beneath the thicker, more rigid continental plate. This is called subduction. Subduction causes deep ocean trenches to form, such as the one along the west coast of South America.
The rocks pulled down under the continent begin to melt. Sometimes the molten rock rises to the surface, through the continent, forming a line of volcanoes. Another form of convergent boundary is a collision where two continental plates meet head-on. Since neither plate is stronger than the other, they crumple and are pushed up. This can lead to the formation of huge, high mountain ranges such as the Himalayas. Louth and at the Giant's Causeway in Co. Antrim, formed at the opening of the North Atlantic approximately 60 million years ago.
See volcanoes for more on the effects of divergent plate boundaries redirect to Topics section. Convergent or d e s t ruc t iv e pla te boundarie s This is when two tectonic plates move toward each other and collide. The result depends on the type of plates involved.
It is possible to have the collision of two oceanic plates, an oceanic plate and a continental plate or two continental plates. Subduction occurs when there is a difference in the density of the plates. Oceanic crust is typically denser than continental crust and is forced downwards into the hot mantle when it collides with continental crust.
The less dense conitinental crust is forced upward. At the start the Iapetus oceanic crust was subducted beneath continental crust, but eventually the oceanic crust was gone and continents collided. The Caledonian mountains formed at this time and it is thought they were as high as the modern Himalayas when they formed.
The Himalayas are an example of the collision of two continental plates where the Indian plate is crashing into the Eurasian plate and is being forced upwards. They are continually growing at an average rate of 1cm per year, this will be 10km in 1 million years. See earthquakes , tsunami , and volcanoes for more on the effects of convergent plate boundaries redirect to Topics section.
Passive plate bo u ndarie s. This is when two plates slide past each other. When the plates move, the jagged edges of the plate boundaries snag and catch each other and can get jammed.
This causes a build-up of pressure. When the plates eventually pass each other, the pressure is released in the form of an earthquake. The closest passive plate boundary to Ireland is the boundary between the African and Eurasian plate south of Portugal.
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