1. C: Ocean-continent convergence
The island arcs are most often formed near a convergent plate boundary between oceanic and continental plates. The denser and lower oceanic plate is moving below the continental plate, thus creating a subduction zone.
The plates create a lot of pressure on each other, and that immense pressure makes lot of cracks in the crust near the boundary. The magma from the mantle is then able to move upwards through the crust, and as it gets deeper it also manages to melt the rocks, so gradually it manages to reach the surface at some points.
Once the magma reaches the surface, it pushes the crust up until it reaches a breaking point. This often results in the crust moving from the seafloor and above the sea level, thus creating a volcanic island. This is not just happening at only one point though, but it is happening at multiple places along the plate boundary, so many volcanic islands pop out of the sea, creating an island arc.
2.
Cinder cone
Composite cone
There are three basic types of volcanoes on Earth:
- startovolcanoes/composite volcanoes
- cinder cone volcanoes
- shield volcanoes
They each form in their own specific way, have their own specific shape, and their own specific eruptions.
The cinder cone volcanoes for example can be found pretty much everywhere where there is volcanic activity. They are the smallest and simplest of volcanoes. The cinder cones have explosive eruptions through which material is thrown and built up on the sides in the shape of a cinder, thus the name.
The composite volcanoes, on the other hand, are most commonly found at oceanic-continental convergent boundaries, thus near subduction zones. These volcanoes are much larger than the cinder cones. The composite volcanoes have steep sides and a summit crater. The eruptions tend to be periodical and they can be explosive or effusive.
