Convergent Plates
Convergent plates are when two plates push against each other and collide. They are also known as destructive boundaries as rock is lost and melted in the process. The two plates must be an oceanic plate and a continental plate. When the two plates collide, a process called subduction occurs. Subduction is the process where two tectonic plates push against each other and the oceanic crust sinks below the continental crust, where it is melted in the mantle. This process occurs because the continental plate is denser than the oceanic plate. This means that the continental crust is lighter and therefore moves on top of the oceanic crust. This collision can cause powerful earthquakes as well as the creation of volcanoes where the cold sea water meets the hot magma from the melted crust.
There are also two other types of convergence boundaries. These are oceanic-oceanic convergence and continental-continental convergence. During oceanic-oceanic convergence, the denser plate is usually subducted beneath the other. A deep oceanic trench is formed when this occurs. Undersea volcanoes are also formed due to oceanic-oceanic convergence. However, after millions of years, these undersea volcanoes erupts lava which slowly piles up until the volcano breaks the surface and forms an island volcano. These volcanoes are typically strung out in chains and are called island arcs. One example are the Hawaiian islands.
During continental-continental convergence, neither plate is subducted. This is because both plates have a similar density so one cannot be pushed downwards. Instead, the plates tend to buckle or be forced upwards or sideways. This process can create mountains such as the Himalayas after millions of years.
There are also two other types of convergence boundaries. These are oceanic-oceanic convergence and continental-continental convergence. During oceanic-oceanic convergence, the denser plate is usually subducted beneath the other. A deep oceanic trench is formed when this occurs. Undersea volcanoes are also formed due to oceanic-oceanic convergence. However, after millions of years, these undersea volcanoes erupts lava which slowly piles up until the volcano breaks the surface and forms an island volcano. These volcanoes are typically strung out in chains and are called island arcs. One example are the Hawaiian islands.
During continental-continental convergence, neither plate is subducted. This is because both plates have a similar density so one cannot be pushed downwards. Instead, the plates tend to buckle or be forced upwards or sideways. This process can create mountains such as the Himalayas after millions of years.
Divergent Plates
Divergent plates are when two plates move away from each other and create trenches or ocean ridges. They are also known as constructive boundaries as new rock is created in the process. This process usually happens at the plate boundaries in the ocean. As the two plates move apart, magma from the mantle rises to the surface, forming underwater volcanoes and creating new oceanic crust as the cold sea water cools it. As the crust moves apart further, more volcanoes appear and more crust is formed. New crust is constantly formed at these ocean ridges.
When two plates diverge on a continental plate, there is not enough force to pull apart the plates in a clean, single break. Instead, there are multiple fractures in the plate and it creates a rift-shaped structure. The central blocks of land which are in this structure slowly slide downwards and this causes earthquakes to occur. As this occurs, water may seep into the trench left by the land and as it grows deeper, ocean water can flow in and create a new ocean basin. One example of this type of boundary is the Red Sea.
When two plates diverge on a continental plate, there is not enough force to pull apart the plates in a clean, single break. Instead, there are multiple fractures in the plate and it creates a rift-shaped structure. The central blocks of land which are in this structure slowly slide downwards and this causes earthquakes to occur. As this occurs, water may seep into the trench left by the land and as it grows deeper, ocean water can flow in and create a new ocean basin. One example of this type of boundary is the Red Sea.