Volcano Notes PDF

VOLCANO NOTES  Zones of Volcanism Volcanism on Earth occurs along convergent plate boundaries, divergent plate boundaries, and at hot spots. 1. At an oceanic-continental subduction zone parts of the mantle above the subducting plate melt and magma rises, eventually leading to the for...

VOLCANO NOTES  Zones of Volcanism Volcanism on Earth occurs along convergent plate boundaries, divergent plate boundaries, and at hot spots. 1. At an oceanic-continental subduction zone parts of the mantle above the subducting plate melt and magma rises, eventually leading to the formation of a volcano. Most volcanoes located on land result from oceanic-continental (convergent) subduction. These volcanoes are characterized by explosive eruptions. 2. Eruptions at divergent boundaries tend to be nonexplosive. At the divergent boundary on the ocean floor, eruptions often form huge piles of lava called pillow lava. 3. A hot spot is an unusually hot area in Earth’s mantle where high-temperature plumes of mantle material rise toward the surface. Hotspots and Plate Motion Chains of volcanoes that form over stationary hotspots provide information about plate motions. Flood basalts form when lava flows out of long cracks in Earth’s crust called fissures.  ANATOMY OF A VOLCANO CRATER A bowl shaped depression at the top of the volcano that surrounds VENT (SIDE VENT) the vent The opening where lava will emerge It is referred to as lava once it reaches CALDERA the Earth’s Surface LARGER depressions at the top of a volcano CONDUIT Tube-like structure in which magma will move through MAGMA CHAMBER Stores magma, which is molten material below Earth’s surface TYPES OF VOLCANOES The appearance of a volcano depends on two factors: the type of material that forms the volcano and the type of eruptions that occur. SHIELD VOLCANOES CINDER CONES COMPOSITE VOLCANOES  Shield Volcanoes A shield volcano is a mountain with broad, gently sloping sides and a nearly circular base. Shield volcanoes form when layers of lava accumulate during nonexplosive eruptions. They are the largest type of volcano.  Cinder Cone Volcanoes Cinder cones have steep sides and are the smallest type of volcano. When eruptions eject small pieces of lava into the air, cinder cones form as this material, called tephra, falls back to Earth and piles up around the vent.  Composite Volcanoes Composite volcanoes are formed of layers of ash and hardened chunks of lava from violent eruptions alternating with layers of lava that oozed downslope before solidifying. These volcanoes are generally cone-shaped with concave slopes. ERUPTIONS MAKING MAGMA Pressure increases with depth because of the weight of overlying rocks. As pressure increases, the temperature also increases. This explains why most of the rocks in Earth’s lower crust and upper mantle are solid and in the core and outer core are liquid.  TYPES OF MAGMA A volcano’s explosivity depends on the composition of the magma. BASALTIC ANDESITIC RHYOLITIC Forms when rock in the found along When molten material upper mantle melts result oceanic-continental rises and mixes with the in the volcano having subduction zones. the overlying continental crust. quiet eruptions. volcanoes it fuels are said Volcanoes fueled by this to have intermediate type of magma are very explosivity. explosive.