GEOL 101 1nd Edition Lecture 10 Outline of Last Lecture I Intro to Volcanoes II The Nature of Volcanoes III General Features IV Stratovolcanoes Outline of Current Lecture I Cinder Cones II Shield Volcanoes III Other Landforms IV Igneous Activity Current Lecture Cinder Cones Built of ejected lava that formed cinder sized fragments Usually small in sized 1000 ft Scoria intermediate to mafic vesicular rock Creates a steep angle and can form in short periods of time Very abundant everywhere and more than often happen in a stratovolcano It can be called parasitic cone Shield Cones Largest of volcanoes even though slopes are long not steep Dome shaped with long slopes Mauna Loa is over 30 000 feet from the base to the peak Created by huge amounts of low viscosity basaltic lava It usually has less explosive eruptions low silica mean low gas content Located on the hot spots and on divergent boundaries Can form where sea floor spreading centers at peak above sea level The greatest volume of volcanic rock is produced along the oceanic ridge How it spreads o Lithosphere falls apart o Less pressure on rocks and makes it melt These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute o Large amounts of basaltic magma is made Ex Iceland Can form by hot spots Magma in the lower mantel rise up towards oceanic crust These make pools of magma that punch through the crust making volcanoes Hot spots NOT associated with plate boundaries are called interplate volcanism As the plate moved across the hot spot new volcanoes are formed while the ones already made are shut off of the magmas supply o Ex Hawaii Continental Rift Zones If plates are diverging it can cause a rift in the continental crust that results in decompression melting o Ex East African rift zone Can create rare volcano that has carbonate lava o Ol Doinyo Lengai in Tanzania is only active carbonate volcano Other Landforms Calderas Steep walled depressions at the summit of a volcano Usually 1 km in diameter For after massive eruption drains the magma chamber and the crater fall in on itself o Ex Crater Lake Oregon and Yellowstone Fissure eruptions and flood basalts Fluid basaltic lava extruded from crustal fractures called fissures Lava Domes Viscous masses of lava that produce a dome Most are from explosive eruptions of gas rich magma o Mt St Helen has a lava dome that has continued to grow since 1980 Volcanic pipes and necks Pipes short conduits that connects the magma chamber to the surface o Can extend several tens of km below surface Necks resistant vents left standing after erosion has removed the volcanic cone o Ex Devil s Tower Igneous Activity Most magma is emplaced deep in the Earth Underground igneous body cooled and solidified that is called pluton o Plutons are classified by shape Tabular thin sheet like Massive bulbous o And by orientation Discordant cuts across sedimentary rock units Concordant parallel to sedimentary rock units Dike tabular AND discordant pluton o Usually a vertical intrusion Sill tabular AND concordant o Usually a horizontal intrusion Laccolith lens or round intrusion Batholith largest intrusive body granite o Usually from the cores of mountains after overlying material was eroded
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