Volcanoes and Plate Tectonics Earth Science Chapter 7

• Temperature and pressure in the lower part of the mantle keeps rocks above melting point • This means that it is liquid!

• Magma – Liquid Rock – Surrounding rock exerts less than normal pressure

• Lava – Magma that erupts onto the earth’s surface http://www.engineering.uiowa.edu/~cfd/gallery/images/flo12.jpg

• Vent – Opening in which molten rock flows through

• Volcano – Any area surrounding a vent

Volcanism: movement of magma towards the Earth’s surface

http://www.uwsp.edu/geo/faculty/ritter/images/lithosphere/volca nism/shield_volcano_2.gif

Volcanic zones occur near….

Divergent Boundaries Convergent Boundaries http://www.gly.fsu.edu/~salters/GLY1000/Chapter5/Slide45.jpg

http://www.geo.lsa.umich.edu/~crlb/COURSES/117IntroductiontoGeology/Lec19/div.jpeg

Subduction Zone • Where one plate is forced under another

Ring of Fire (Major volcanic zone in the pacific ocean)

http://pubs.usgs.gov/gip/dynamic/fire.html

Island Arc • String of volcanic islands which form along a trench

Mid-Ocean Ridges (undersea mountain ranges)

http://www.photolib.noaa.gov/nurp/nur09764.htm

Characteristics of Mid-Ocean Ridges • Rifts- large openings or cracks usually along the seafloor through which magma flows through • Fissures- small pressure cracks through which magma flows

Hot Spots Example: Hawaiian Islands

http://www.dukelabs.com/images/HawaiianTrackwAge s.jpg

• When magma works its way to the earth’s surface within the interiors of lithospheric plates • Magma remains stationary as plate above it continues to drift slowly

Volcanologists

• Scientists who study volcanoes http://landsat.gsfc.nasa.gov/graphics/hawaii1.jpg

Three Types of Lava • Mafic • Felsic • Other

Mafic • Dark colored when it hardens • Rich in iron (Fe) and magnesium (Mg) • Most often associated with “Quiet Eruptions” • Example: Pahoehoe http://www.aeic.alaska.edu/Input/sanchez/csav03/hawaii_41.jpg

– “Ropey” – Hardens with a wrinkled surface

Felsic • Light colored • Contain high values of silica, lower values of Mg and Fe • Most often associated with “violent” eruptions • Example: AA – Lava cools, breaks into jagged chunks as liquid continues to flow

http://www.ctahr.hawaii.edu/soilsurvey /Hawaii/Htm/DescriptionSoils/Image1 7.jpg

Other • Consist of a range of compositions • Found usually only on ocean floor • Example: Pillow Lava – Common at MidAtlantic Ridge – Cools in rounded shapes

http://www.gly.fsu.edu/~salters/GLY1000/9Volcanoes/Slide25.jpg

Eruptions • Quiet – Mafic lava – Gases escape easily – Flows Like red-hot river – Ocean Floor & Island Volcanoes

• Explosive – Felsic lava – Continental Volcanoes – Contain large amount of gases

Rock Fragments • Tephra (Pyroclastics)- Volcanic rocks ejected from volcanoes – 5 types of Tephra (Classified by size) • Volcanic Ash – tiny millimeter pieces • Volcanic Dust – along with ash, pollute atmosphere • Lapilli – little stones or pebbles • Volcanic Bombs – “grenade” or rock-size • Volcanic Blocks – boulder-size or bigger

3 types of Volcanic Cones • Shield • Cinder • Composite (Stratovolcanoes)

Shield Volcanoes • • • •

Broad Base Gently sloping sides Composed of lava flows (Mafic Lava) Associated with Quiet eruptions

http://wapi.isu.edu/EnvGeo/EG6_volcano/images/shield3.gif

Cinder Cone Volcanoes • • •

Steep Slopes, short, narrow Composed of Cinders Usually associated with explosive eruptions (Felsic Lava)

http://erg.usgs.gov/isb/pubs/teachers-packets/volcanoes/poster/poster.html

Composite (Stratovolcanoes) • • •

High Volcanic Mountains – widest and tallest of all cones Composed of alternating layers of lava and cinder Can have both Quiet or Explosive Eruptions (mafic and/or felsic lava)

http://wapi.isu.edu/EnvGeo/EG6_volcano/images/stratovolcano.gif

Craters • Formed when material is blown out by volcanic explosions – bowl-shaped depression

Kiluaea http://volcanoes.usgs.gov/Products/Pglossary/PitCrater.html

Caldera • Formed by an explosion or collapse of a volcanic cone (most violent of eruptions)

Example: Krakatoa http://www.geokem.com/images/pix/Krakatau.jpg

Volcanic Eruptions: What do we look for? • • • • •

Seismographs – earthquake activity Slight bulges in the slope of the volcano Study of previous eruptions Strange Animal Behavior Change in Water Quality (Sulfur content) • Change in gas composition

Seismograph

http://www.calstatela.edu/faculty/acolvil/quakes/seismograph_vert.jpg

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Bulges in Slope

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Extraterrestrial Volcanism

http://mars.jpl.nasa.gov/gallery/atlas/images/oly-az.jpg

Moon • Covered with basaltic lava flows • Craters (meteorites) • Also has fissures and a once active volcano

http://grin.hq.nasa.gov/IMAGES/LARGE/GPN-2000-000473.jpg

Mercury and Venus • Mercury – Evidence of volcanism found – Long dormant

• Venus – Active? – Still needs to be verified……

Mars • Olympus Mons – Largest Shield Volcano – Seismically active, may be volcanically active

Comparison of Volcanoes on Earth and Mars

IO

• Moon of Jupiter • 10 active Volcanoes • Spews sulfur & sulfur dioxide rather than containing Magnesium or Iron http://antwrp.gsfc.nasa.gov/apod/ap020327.html