1 Plutons are formed from the cooling and hardening of magma beneath the earths crust. 2 A sill is formed when magma is injected along sedimentary bedding surfaces at shallow depths. Laccoliths are formed when magma is intruded between sedimentary layers close to the surface. Dikes are formed when magma is injected into fractures, cutting across preexisting rock layers mainly magma from a large magma chamber invades the fractures to form the dikes. Batholiths are the largest intrusive igneous bodies for the intrusive igneous body to be called a batholith it must have over 100 square kilometers or more of exposure. 3 Intrusive features are classified by size, the way they are formed and the relationship to the surrounding rock layers. 4 A sill is formed by magma being injected along sedimentary bedding underground while a dike is formed by magma is injected into fractures across preexisting rock layers and made by magma in a large magma chamber but a dike can be seen on the earths surface unlike a sill. 5 Intraplate volcanism is caused when a mass of hotter than normal mantle material called a mantle plume rises toward the surface, which is not near a plate boundary. 6 One difference between volcanic island arcs and volcanic arcs is the continental crust in a volcanic arc, the continental crust is thicker and has a higher silica content than oceanic crust does. The second difference is volcanic island arcs are formed by oceanic -oceanic plate boundaries and are formed in the middle of the ocean, while volcanic arcs are made by continental –oceanic plate boundaries, they are made on land because of the continental crust that made the oceanic crust subduct but they volcanic arc is near the ocean. 7 One example of intraplate volcanism is how the large lava plateau called the Columbia Plateau was formed.