Other Volcanic Landforms Calderas Large depression in a volcano Collapse of the top of a composite volcano after an explosive eruptions From the collapse of the top of a shield volcano after the magma chamber is drained Lava Plateaus Fissures: low viscosity basaltic lava flow covering a wide area

Intrusive Igneous Activity Plutons Structures that result from the cooling and hardening of magma at depth Classified according to their shape, size, and relationship to the surrounding rock layers Sills Forms when magma is injected along sedimentary bedding surface parallel to the bedding plane

Types of Igneous Intrusive Features Laccolith Magma is intruded between sedimentary layers close to the surface (lens shape) Dike Magma injected into fractures, cutting across preexisting rock layers Batholith Large intrusive igneous body must have a surface exposure greater than 100 square kilometers

Plate Tectonics and Igneous Activity The basic connections between plate tectonics and volcanism is that plate motion provide the mechanisms by which mantle rock melt to generate magma Ring of Fire: area around the pacific ocean with extreme volcanic activity

Intraplate Activity Occurs within a plate, not plate boundary Most intraplate volcanism occurs where a mass of hotter than normal mantle material called mantle plumes rise toward the surface

Hot Spots Small volcanic region a few hundred kilometers across within a plate Ex: Hawaiian Island