VOLCANOES AND IGNEOUS ROCKS WHAT IS A VOLCANO? A volcano is a geological structure where the release of magma takes place. MAGMA is molten rock that originates deep in the Earth’s crust and Mantle. LAVA is molten rock on the Earth’s surface (under natural atmospheric conditions). VOLCANIC FORMATIONS/LANDFORMS Volcanic activity can be described as INTRUSIVE or EXTRUSIVE. INTRUSIVE EXTRUSIVE * Below ground or underneath * Above the surface or ground the surface * Not visible * Features a Magma chamber * Rocks formed from this feature are called PLUTONIC ROCKS * Visible (Volcanic peak) * Rocks formed are called VOLCANIC ROCKS INTRUSIVE VOLCANIC FORMATIONS Intrusive volcanic formation can be described based on their vertical and horizontal features: HORIZONTAL * Formation is called a “Sill” * Always occurs between sedimentary layers VERTICAL * Formation is called a “Dyke” * It can be straight or on an incline * Cuts through a number of sedimentary layers OTHER INTRUSIVE VOLCANIC FORMATIONS LOPOLITH – Saucer shaped intrusive formation PHACOLITH – Convex shaped formation i.e. bulges outwards in anticlines and synclines OTHER TYPES OF VOLCANIC FORMATIONS LACCOLITH is a large blister or igneous mound with a ‘domeshaped’ upper surface and a level base fed by a pipe-like conduit from below. It arches up the overlying strata of sedimentary rocks BATHOLITH - It is a huge mass of igneous rocks, usually granite, which after removal of the overlying rocks forms a massive and resistant upland region. BATHOLITH EXTRUSIVE FORMATIONS * Depends on the type of magma (Basic or acidic) BASIC MAGMA ACIDIC MAGMA * Mid-oceanic ridge * Ash-cinder Volcano * Shield Volcano * Basalt lava plateau * Composite Volcano * Caldera Volcano BASIC MAGMA Comes from OCEANIC crust that forms at the MID-OCEANIC RIDGES BASIC MAGMA SHIELD VOLCANOES – Results in formation of islands under the ocean e.g. Hawaii BASIC MAGMA FISSURE VOLCANO – Results in basaltic lava plateau on continents. E.g. Deccan traps in India, Snake Plateau in USA BASIC MAGMA DOME VOLCANO – Similar to shield volcano but found on continent ACIDIC MAGMA ASH-CINDER VOLCANO – Slightly acidic. Does not form very high peaks (about 400m). E.g. Naples,Mt. Paricutin in Mexico ACIDIC MAGMA COMPOSITE VOLCANO: • More acidic than ash-cinder volcanoes • Known as Strato-Volcanoes due to their different types of layers • Have side vents known as branch pipes or parasitic cones where magma will exit as well • Produces some of the highest volcanic peaks Examples: Mt Etna, Stromboli,Vesuvius, Fujiyama, Krakatoa, Chimborazo ACIDIC MAGMA CALDERA VOLCANO – Most explosive of all volcanoes collapsing in on itself. Selfdestructive. Over time once the depression solidifies it turns in to a caldera lake (bigger) or crater lakes (smaller) due to rainfall. E.g.