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Discuss the various tectonic settings at which volcanism occurs, and describe the kind of activity that takes place.

Introduction
There has always been an interest as to why volcanism is found in certain places over the earth’s surface and has been deeply studied over the years. When trying to figure out why volcanic activity occurs in certain tectonic settings it’s important to understand the structure of the earth and then by looking at how tectonic plates move and where they collide, we can see a pattern of volcanism emerge. This essay looks at the theory of plate tectonics leading to areas of volcanism and the kind of volcanic activity that occurs along the plate boundaries.
Plate Tectonic Theory
The earth as we know it is a sphere and divided into layers, almost like an onion. From the surface to the centre there is the crust, the mantle and the core reaching down to a depth of 6,370km (Grotzinger et al. 2007*1). The core is made up of two layers – the inner core ( from a depth of 5,155 km down to the earth’s centre at 6,370km) and the outer core (between 2,900 and 5,155 km deep) (Marshak 2005*2). The inner core is solid while the outer core is liquid, both composed primarily of iron. The mantle is 2,885km thick and is primarily composed of the ultramafic rock peridotite. It can be divided into three layers: the upper mantle, the transition zone and the lower mantle, most of which is solid rock*1. However, the partly molten layer which is found below a depth of 100 to 150 km flows extremely slowly at less than 15cm per year which allows the mantle to change shape without breaking*2. The crust is the outermost layer and is made of low-density felsic and intermediate rock so is light weight especially over the continents where it is up to 40km thick*2. The crust at the oceanic floor is considerably thinner than the continental crust (around 7 km in depth*2) which means it is much denser, which results in the...