EOSC 114 Unit 4 Volcanoes.docx

6 Pages
Unlock Document

Earth and Ocean Sciences
EOSC 114
Leah May Ver

Unit 4: Volcanoes  Explain what magma density and magma viscosity are o Magma: mixture of molten rock, crystals and gas below the earth’s surface o Created by the melting of pre-existing rock in Earth’s interior (mantle + crust).  Reaches the surface through fractures, erupts as lava or pyroclastic material (tephra) o In order for magma to rise, it must be  List the different categories of volcanic rocks and Less dense than crust  Runny enough to flow  Hot enough to stay liquid o Main gases: H2O< Co2, SO2, Cl2  At a depth, <10% gas content. This decreases viscosity and density  As pressure decreases, the gases become less soluble and bubbles form o Viscosity = runninses, resistance to flow.  Explain the differences between the magmas they came from  Igneous rocks come from solidifying magma Mafic Rock Felsic Rock  Rich in denser minerals (olivine,  Rich in low density minerals (quartz, pyroxene), darker in colour feldspar) ls, light colour  Mafic rocks  Felsic rocks  Basalt (extrusive), Gabbro (intrusive)  Rhyolite (extrusive), Granite (intrusive)  Dacite (extrusive), Tonalite (intrusive) Intrusive Extrusive  Big crystals = intrusive aka plutonic  Small crystals = extrusive (Granite, Gabbro). Freezes in crust,  Rapidly cooled never erupted. Cools slowly. Intermediate rocks: Dacite (ext), Tonalite (int) Andesite (ext), Diorite (int)  Explain why some magmas erupt explosively (as pyroclastic material) and some magmas erupt effusively (as lava) Basalt Andesite Dacite Rhyolite Mafic (less silica) Felsic (more silica) Intermediate Hot (1200-1400 C) Cool (600-1000 C) Low viscosity High viscosity (RUNNY) (GOOEY) NON-EXPLOSIVE EXPLOSIVE LAVA PYROCLASTICS Love gas content High gas content  Viscosity and Gas Content are related to explosively o As pressure decreases, bubbles grow  Pressure reises inside bubbles until strength of liquid magma overcome. Bubble pops, fragmentation occurs  Pyroclastic material is produced  Mafic = low gas content + fluid, quiet, effusive eruptions  Gas escapes  Felsic = high gas content + gooey, explosive  Gas kept under increasing pressure  Explain the differences between pahoehoe and a'a lavas o Both are basaltic magmas  Pahoehoe erupted at high temperature, hardens with a smooth ropy texture (moves @ km/hr)  Cooler, more viscous moves slower (m / day), rough and blocky  Aa is more viscous and chunky because of lower temp  Describe the different types of volcanic eruptions and how they are related to magma properties Hawaain Strombolian Vulcanian Pelean Plinian Phreatomag matic  Low  Basaltic –  V.  Dome  Sustained  Water + viscosity mildly explosive collap column of magma,  Effusive explosive  Explosions se ash and violent  Bombs, of ash  Explo pyroclasti  Firefount ains lavas sive c flow, v  Block explosive and ash flow Basaltic Basaltic/And Andesitic/Rhy Andesitic/rhy Different lol (Mafic) esitic olitic olitic (Felsic)  Describe the distribution of the world's active volcanoes o Located near hotspots and tectonic plate boundaries o Pacific ring of fire  List the three types of plate boundaries and the different types of volcanoes that occur at these plate boundaries o Divergent Boundaries  Mantle rises linearly, pressure decreases. Mantle can melt the overlying crust.  Mantle rises linearly and pressure decrease. Mafic magma can melt the overlying crust.  On continental crust, mafic – int – felsic  Oceanic plates – mafic only o Subduction Zones  Beneath continental crust or beneath oceanic  Beneath continental crust - Mafic-int-felsic  Beneath oceanic crust – mafic – int – felsic o Hotspots  Mantle rises in a cylindrical plume, pressure decreases  Magma can also melt overlying crust  Under continental crust – mafic – int – felsic  Under oceanic crust – mafic  Describe the type of volcanoes that occur at hot spots o Emerge out of water, form island chains  Hawaiian Islands  Describe the tectonic setting of British Columbia and determine the dominant type of volcano that occurs here o Many stratovolcanoes o Cascadia subduction zone causes continental volcanic arc  Describe the morphology, dominant rock type and typical eruption style of the different types of volcanoes o Cinder Cones – mafic, explosive  Layers of pyroclastic ejecta from fire fountaining  Mafic (basalt)  Angle of repose = 30-40 o  Small volcanoes that never grow up. Usually erupt for a few years then never again.  Small. <2km wide, <500m tall o Shield volcanoes – mafic, non-explosive  Lava erupts from a fissure, runs down, cools  Mafic lava flows  Forms pahoehoe followed by a’a  Not explosive  ~100 km wide o Stratovolcanoes – intermediate, mixed  Interbedded lava flows, pyroclastic flows and lahars  Usually int fo felsic  Frequently explosive, often viscous magma  Can be active for a long time  ~10 km wide, <5 km tall  Erupt 10-1000 years o Cald
More Less

Related notes for EOSC 114

Log In


Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.