TECTONIC PLATE BOUNDARIES

There are three main tectonic plate boundaries. Divergent, convergent, and transform. Each one of them cause slightly different things to result. Some cause earthquakes, some mountains, and others, volcanos. No single plate can move without 
affecting the other.

DIVERGENT PLATE BOUNDARIES

These plate boundaries occur when two plates shift away from each other. In the ocean, it generates an ocean ridge or a spreading ridge. On land, diverging plates are less common, and is called a rift valley. Plates diverge because magma is pushed to earth's surface due to convection in the asthenosphere, which creates long cracks in the lithosphere. Along a rift or ridge, rift eruptions transpire.



The place where magma reaches earths surface is called a spreading centre. As the magma cools, it forms 'new rock'. The new material pushes old material aside, making the area with a ridge (or rift) younger than the area without one. An example of this happening is in the Mid-Atlantic Ridge. The North American plate and the Eurasian Plate move further and further apart creating an oceanic ridge and a rift valley, as it runs through the middle of iceland.

CONVERGENT PLATE BOUNDARIES

 There are three types of convergent plate boundaries. Oceanic-oceanic, continental- oceanic, and continental- continental. Although they are all convergent boundaries, the collision can have various results.

OCEANIC-OCEANIC: 

When two oceanic plate collide, subduction occurs. One of the plates will be denser because of cooling, and the denser plate will slide underneath the other, deep into the mantle. This creates a deep underwater trench, like the Marianas Trench. This convergence also produces volcanic island arcs (a chain of island volcanos). Regions like this experience earthquakes of different magnitudes.

OCEANIC-CONTINENTAL:

Subduction also occurs when an oceanic plate meets a continental plate, because oceanic plates are much denser than continental ones. As the plate moves deeper into the mantle, pieces melt off, cool, and then crystallize into large land masses below the surface of the continental plate. Those masses can become cone volcanos if magma reaches the surface. Volcanic belts are not not uncommon. Sometimes those rock masses can stay trapped under the surface for long periods of time before moving suddenly and generating large earthquakes. Earthquakes also happen because colliding plates will resist convection currents, slab pull and ridge push. Converging plates also create mountain ranges as continental rock crumbles and folds.

CONTINENTAL-CONTINENTAL:

Subduction does not occur when two continental plates collide because their densities are too similar. instead the plates fold and crumble, forming high mountain ranges. The Himalayas, which is the youngest and highest mountain range, was formed when the Indian continent, collided with the Asian continent around 45 million years ago. Because the plates are still moving together, the elevation of the Himalayas increases by 5 cm every year.

TRANSFORM PLATE BOUNDARIES 

Transform boundaries are where two plates slide horizontally past each other. Since rock is gliding against rock, no mountains or volcanos form. Most transform boundaries are found in the ocean although they sometimes can be found on land too. Small earthquakes and faults may result since the sliding breaks down rock layers. A famous example of this is the San Andreas Fault which runs through California. The Pacific Plate and the North American Plate grind past each other which causes a 5 cm difference every year.