Volcanoesg110 lecture prepared by Bob Hall revised 7/31/2000
Points to Be Covered on Volcanos Products of eruptions Lava properties vs composition Fissure eruptions Types of volcanoes Distribution of volcanoes
World Famous Kilimanjaro Fujiyama Mt St Helens Mauna Loa Mt St Helens
Lava flows from some Range from mafic (e.g. basalt) to felsic, like all ign rx Water Gases Solids lofted into atm from others (called pyroclastics. Better than fireworks? You bet!!! Rocks may form from fusing of pyroclastics can range from dense (tuff) to light (pumice) What do we expect in a volcanic eruption?
VolcanoesVulcan’s Story • Magma/lava viscosity related to composition. • Less viscous lavas flow more easily. • This releases dissolved gases more easily. • Less likely to produce a violent eruption. • More likely to be distributed farther.
Gassy Volcanoes –Giving us atmosphere Sangay Kilauea Stromboli Paricutin
VolcanoesMore on Water and Gases What gas is overwhelmingly the most abundant volcanic gas? Water vapor. Over (95%) Isn’t that how we got our oceans, streams, etc. Our hydrosph, yes. And our atm Oxygen, nitrogen, carbon dioxide, carbon monoxide, hydrogen sulfide (stinky), hydrogen chloride (??), sulfur dioxide (bad guy?), ammonia
Fissure Eruptions Erupt basaltic lava. Low viscosity, moves fast and far. Where are these fissures? The ocean floor in spreading centers. Anywhere on land? Yes, wherever rifting has occurred. Check out the Colombia Plateau. Great thicknesses of basalt lava.
Shield Volcanoes Buildup primarily from basalt flows. Long, low-angle slopes. Form of an inverted shield. Mauna Loa
Cinder Cones Almost entirely pyroclastics. Short, steep slopes. Slopes at steepest angle possible for size of pyroclastics. Usually depression at top of cone. Paicutin
Stratovolcanoes(Composite Cones) Pyroclastics build up. Lava flows extend laterally. Alternating lava and pyroclastics. Mt Hood Cotopaxi
Spectacular VolcanicFeatures Crater Lake
Distribution of Volcanoes Convergent plate boundaries Circum-Pacific Ring of Fire Alpine-Himalayan Belt Divergent plate boundaries: oceanic ridges Mid-Atlantic Ridge
Technical Terms Cinder cone Convergent boundary Divergent boundary Fissure eruption Pyroclastics Rift Shield volcano Spreading center Stratovolcano (Composite cone) Non-technical terms Lava Viscosity Terms used in the study of volcanoes
Student Responsibilities on Volcanoes • What are the products of volcanic eruptions? • How do we interrelate magma/lava viscosity, stored gases, violence of an eruption, and distance of transport of the volcanic products? • What are fisssure eruptions, shield volcanoes, cinder cones, and stratovolcanoes? • How do we explain the global distribution of volcanoes?