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GEOG 100 Lecture 14--Volcanoes
 

GEOG 100 Lecture 14--Volcanoes

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GEOG 100 Lecture 14--Volcanoes GEOG 100 Lecture 14--Volcanoes Presentation Transcript

  • VolcanoesVolcanoesEarth’s Interior in Action!Earth’s Interior in Action!
  • 22Volcanism:Volcanism:all phenomena associated with the origin andmovement of molten rock• all phenomena associated with the origin andmovement of molten rock⇐A volcanologistgeared up for work
  • 33What Constitutes AnWhat Constitutes An“Active” Volcano?“Active” Volcano?• Not fully agreed upon among scientists• Intervals between eruptions may be thousandsof years• On land, close to 1500 have erupted in the past10,000 years– Millions, if you count undersea eruptions• Over a thousand active magma systems havebeen identified on land• An accurate count of the world’s volcanoesremains elusive
  • Chaiten Volcano(southern Chile)May 3, 2008—Chaiten volcano erupts May 2nd and thousands flee; ash from thevolcano reaches Esquel, Argentina; last recorded eruption: over 9000 years ago(7420 BC ± 75 yrs)
  • 55What’s that stuff on the ground?What’s that stuff on the ground?• Lava– Magma that makes it to thesurface• Pyroclastic material– When lava erupts into the airand cools quickly, it can formmaterial the size of ash up tolarge rocks– Any of this solidified lava“spew” is called pyroclastics(pyro = fire; clast = rock)
  • 66EruptionsEruptions• Whether a volcanic eruption is explosiveor mild depends on the type of magmachemistry that is involved.– Felsic = explosive– Mafic = mild
  • 77Structures Associated WithStructures Associated WithExtrusive VolcanismExtrusive Volcanism• Volcanic peaks• Caldara• Volcanic neck• Flood basalt
  • 88Volcanic PeaksVolcanic Peaks• The type of peak that forms depends onthe type of magma– Felsic• Forms composite (strato) volcanoes– Magmas don’t flow far– Tall, steep-sided cones– Mafic• Forms shield volcanoes– Magmas flow for long distances– Broad, gently-sloping cones
  • 99Composite VolcanoComposite Volcano(also called a Stratovolcano)(also called a Stratovolcano)• Felsic magma, tall, steep-sided cone formed ofalternating layers of lava flows and pyroclasticmaterialMount MayonPhilippines, Island of Luzon, province of Albay,Bicol region, 15 km NW of Legazpi City
  • 1010Shield VolcanoShield Volcano• Mafic magma (basaltic), gentle slope (looks likea warrior’s shield laid on the ground)Mauna Loa Shield Volcano
  • 1111Other Types of Volcanic PeaksOther Types of Volcanic Peaks• Lava Dome—Formed from felsic magmas,like a bulge on the surface– Common where previous felsic eruptions haveoccurred– Material not well fused together (easily eroded)
  • 1212Lava domeLava domeNew lava dome forming inside Mount St. Helens
  • 1313Other Types of Volcanic PeaksOther Types of Volcanic Peaks• Cinder Cone– Usually less than 150 ft. high– Associated with flood basalts and shieldvolcanoes– Frothy, (usually) mafic magma under highpressure at a narrow vent– Tephra rains around the vent, forming small,rounded volcanoes made of ash and cinders
  • 1414Cinder conesCinder conesWizard Island—Crater Lake, OR
  • 1515CalderaCaldera• Collapsed and/orexploded volcanicpeak, producing acrater
  • Long Valley Caldera in California
  • 1717Volcanic NeckVolcanic Neck((Shiprock, NM)Shiprock, NM)• Solidified magma within the “neck” of a volcano• Surrounding material may later be eroded away,leaving a tall, standing structure of igneous rock
  • 1818Flood BasaltsFlood Basalts(also called Fissure Eruptions)(also called Fissure Eruptions)• No dome or cone-shaped structure• Magma flows out of breaks in the crust, usuallyin high volume, in layers that may be hundredsof feet deep and thousands of miles wide– Deccan Plateau in India• 200,000mi2– Columbia Plateau, crossing WA, OR, and ID borders• 50,000mi2
  • 1919Flood BasaltFlood BasaltColumbia Gorge, along the Columbia River in theCascade Mountains of Washington and Oregon
  • 2020Hazards Associated withHazards Associated withExtrusive VolcanismExtrusive Volcanism• Volcanic blast• Earthquakes• Avalanches andDebris Flows• Mudflows andLahars• Eruption columnand ashfall• Pyroclastic flows• Lava flows• Volcanic gases
  • 2121Volcanic BlastVolcanic Blast(also called Blowdown)(also called Blowdown)From Mount St. Helens:• A 600ºF blast of rocks, ash, and gases sweptacross the land at 670 miles an hour• The force of the blaststripped trees from hillsides 6 mi. away
  • 2222Earthquakes and Debris flowsEarthquakes and Debris flows• The movement of magma up through thecrust creates earthquakes• The Mount St. Helens eruption began witha magnitude 5.1 earthquake. The entirenorth flank of the mountain broke loose inthree separate blocks, which slid down themountain at 100 mph.• An avalanche of rock, ice, snow, and soil,like this one, is called a debris avalanche
  • 2323Debris FlowDebris Flow• Rocks and mounds ofdebris filled rivervalleys for 14 miles,as much as 600 feetdeep in some places,damming streamsand forming newlakes
  • 2424Mudflows and LaharsMudflows and Lahars• Superheated ash andmagmas melt and mixwith snow and ice, thenspeed down thevolcano’s flanks– Nevado del Ruiz,Colombia, 1985– Melted ice and snow mixedwith volcanic ash and mud,sending a 130 foot (40 m)high mud-flow down theLagunilla River
  • 2929Mudflows—Mt. St. HelensMudflows—Mt. St. Helens• …sloshing from side-to-side as it rushes throughforests and clearcuts, ripping trees, houses, andbridges from the ground, devastatingdownstream environments and communities
  • 3030Eruption Column and AshfallEruption Column and Ashfall• Can reach the stratosphere,where it is transported longdistances• Can block insolation, alteringweather and climate• Ash and gases mix with waterin atmosphere, producing acidprecipitation• May produce enough ash tobury the landscape and killresidents• Can cause electrical failure injet engines
  • Pyroclastic Flows(Nueé Ardant)• Swift, destructive cloud of hot ash andgases that flows rapidly downhill andburns all in its path– Ash weighs down the gases, which wouldotherwise rise into the atmosphere– Nueé Ardant—French for “glowing avalanche”• Mont Pelée in MartiniqueMt. Mayon, Island ofLuzon, Phillipeans,1984
  • 3232Mt. Pelée, Island of Martinique, CaribbeanMt. Pelée, Island of Martinique, CaribbeanMay 8,1902—The town of St. Pierre was obliteratedMay 8,1902—The town of St. Pierre was obliteratedby a nuée ardante; over 28,000 lost their livesby a nuée ardante; over 28,000 lost their livesSt. Pierre today….
  • 3333Pyroclastic FlowPyroclastic FlowFrom Mount St. Helens:• Within a few hours ofthe lateral blast, hotmixtures of volcanicgas, pumice, and ashswept down the northflank of the volcano atspeeds up to 100miles an hour andtemperatures of over1200ºF
  • 3434Soufriere Hills Pyroclastic FlowSoufriere Hills Pyroclastic FlowThe Soufrière Hills Volcano,Montserrat, West Indies,began erupting on July 18,1995.
  • 3535Lava FlowsLava Flows• Can travel longdistances, burning andburying everything• Lava does not need toactually touch an objectto set it on fire
  • 3636Volcanic GasesVolcanic Gases• Volcanic gases, some of which are colorless andodorless like CO2, can cause suffocation, killingplants, animals, and humans alike
  • 3737Volcanic GasesVolcanic Gases• Such an incident happened at MammothMountain in early 2006, where CO2emanating from faults at the edge of LongValley Caldera killed one member of thelocal ski patrol
  • 3838Volcanic GasesVolcanic Gases• Ash and gases (such as SO2—sulfur dioxide) can mixwith cloud droplets near the ground to form “vog” (avolcanic fog that causes health problems)• Hydrogen from lava combines with chlorine in sea waterto form hydrochloric acid, which becomes airborne assteam, forming corrosive lava haze, or “laze”Hawaiian vog
  • 3939Hazards Associated withHazards Associated withExtrusive VolcanismExtrusive Volcanism
  • 4040Structures Associated WithStructures Associated WithIntrusive VolcanismIntrusive Volcanism• Pluton--a massive body of intrusive igneousrock which solidifies deeply within the crust• Batholith• Laccolith• Stock• Dike• Sill• Vein
  • Intrusive Igneous Structuresand Their Formation
  • 4242Structures Associated WithStructures Associated WithIntrusive VolcanismIntrusive Volcanism• Batholith— >40 mi2(100 km2) in diameter, amorphous,forms deep in the crust– granite often forms batholiths• Sierra Nevada Mountains• Stock—A few mi2in diameter, amorphous, forms deep inthe crust, may be an offshoot of a batholith• Laccolith—Similar to a stock, but intrudes just beneaththe surface, warping surface rocks and forming a hill;may form the base of small mountain chains– The Black Hills, South Dakota– Devil’s Tower, WY
  • 4343Batholiths inBatholiths inWestern North AmericaWestern North America
  • 4444Laccolith:Laccolith:Devil’s Tower, WYDevil’s Tower, WY
  • 4545DikeDike