today – 4/13 more volcanoes! more volcanoes!. first mars shot - hill
Post on 22-Dec-2015
218 views
TRANSCRIPT
Last Time
Hotspots – mantle plumes reach the surface; decompression melting to form basaltic magma; Hawaii, Mars, Venus; independent of plate boundaries
Intrusive v. extrusive: coarse v. fine texture depends on cooling rate
Three kinds of volcano: shield, stratovolcano, caldera – depends on magma type
Last Time – Shield Volcano
Built up from repeated basalt flows
Basalt has high Fe / Mg, high temperature, low Si, low gas content, low viscosity (stickiness)
MOR’s, hotspots, areas of continental extension
StratovolcanoStratovolcano Built from alternating Built from alternating
layers of pyroclastic & layers of pyroclastic & andesite lava flows andesite lava flows
Magma – intermediate Magma – intermediate temperature, gas temperature, gas content, composition, content, composition, viscosityviscosity
St. Helens, Monserrat, St. Helens, Monserrat, Pinatubo, TamboraPinatubo, Tambora
Form above subduction Form above subduction zones zones
Wet melting of the Wet melting of the mantlemantle
Mount Ngauruhoe, New Mount Ngauruhoe, New ZealandZealand
Classic Stratovolcano
--- 1000s of feet high.
PyroclasticPyroclasticFlowsFlows- - - - - - - - - - MayonMayon
PhilippinesPhilippines19681968- - - - -- - - - -
Hot: 600Hot: 600ooCCFast: Fast:
60 to 100 60 to 100 mphmph
Cascade Cascade Volcanic Volcanic
ArcArc ----------
Lassen PeakLassen Peak Crater Lake Crater Lake
Mt.St.Helens Mt.St.Helens
Mt. RainierMt. Rainier - - - -- - - -
Part of Pacific Part of Pacific Ring of Fire.Ring of Fire.
Mount St. Helens Mount St. Helens VolcanocamVolcanocam
http://http://www.fs.fed.us/gpnf/volcanocams/mshwww.fs.fed.us/gpnf/volcanocams/msh//
Space Needle Space Needle view Seattle, WA view Seattle, WA
and Mount and Mount Rainier:Rainier:
Most dangerous Most dangerous volcano in North volcano in North
America?America?
Mount Rainier, Most dangerous Mount Rainier, Most dangerous volcano in North America?volcano in North America?
Volcanoes – Agents of Climate Volcanoes – Agents of Climate ChangeChange
Mount Pinatubo, Philippines 1991
Mt. Pinatubo Ash Circles the Mt. Pinatubo Ash Circles the EarthEarth
Earth’s surface cooled 1 °F for two years.
Climatic Effects of Volcanism
Volcanic particles in stratosphere interact with man-made CFC’s to destroy ozone. Particles settle out in 2-3 years, ozone layer recovers.
Volcanoes add CO2 to the atmosphere (10% of anthropogenic emissions), contributing to long-term global warming
SO2 in the stratosphere reacts with water to form sulfuric acid, which absorbs solar energy and re-radiates it into space, creating short term cooling. Sulfuric acid droplets settle out after several years
Tambora, April 1815
Largest stratovolcano eruption in recorded history
1816 – year without a summer. June snow in New England, frost in July and August. Crop failure – oats from 12 cents to 92 cents. Settlers move to midwest, Mary Shelley writes Frankenstein. Famine in Europe.
Stratovolcano v. Caldera Stratovolcano v. Caldera ExplosionsExplosions
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
St Helens Tambora1815
Ystone1.2 Ma
Ystone0.6 Ma
Ystone2.2 Ma
La Garita28 Ma
Caldera ExplosionsCaldera Explosions
Caldera – LARGE volcanic crater Caldera – LARGE volcanic crater caused by the collapse of a magma caused by the collapse of a magma chamber after a big eruptionchamber after a big eruption
Convergent margins, hotspots Convergent margins, hotspots under continentsunder continents
Wet melting of the continental Wet melting of the continental crustcrust
Inconceivably cataclysmicInconceivably cataclysmic Often called “supervolcanoes”Often called “supervolcanoes” Magma – low temperature, high Magma – low temperature, high
gas content, high viscosity, high gas content, high viscosity, high silica content = HIGHLY explosivesilica content = HIGHLY explosive
CalderasCalderas Often Often
formed by formed by explosive explosive eruption.eruption.
Crater Lake fills Crater Lake fills caldera formed caldera formed by collapse by collapse during massive during massive eruption eruption of Mt. Mazama of Mt. Mazama 6600 years ago.6600 years ago.
Caldera FormationCaldera Formation
Figure 7.12: Sequence of events in the formation of Crater Lake.
Eruption Collapse
Last Big One – 74 Ka, Toba, SumatraLast Big One – 74 Ka, Toba, Sumatra
2,800 cubic kilometers of material 2,800 cubic kilometers of material ejectedejected
Cause of the human genetic Cause of the human genetic bottleneck?bottleneck?
Long Valley Caldera, Long Valley Caldera, California California - A very dangerous - A very dangerous
volcanovolcanohttp://http://
quake.wr.usgs.gov/recenteqs/Maps/Long_Valley.hquake.wr.usgs.gov/recenteqs/Maps/Long_Valley.htmltml
Right: Lasers monitor ground swelling at Long
Valley Caldera
Left: Cross section of Long Valley Caldera.
Internal Heat Generation
Earth
Remnant heat from formation, much of which is stored in the liquid core
Decay of radioactive elements
Satellites of large planets
Gravitational energy turned into heat – “tidal friction”
Io – Most Io – Most Volcanically Active Volcanically Active Spot in the Solar Spot in the Solar
SystemSystem
Io v. Titan
Io – moon of Jupiter
Sulfur / silicate magma
Titan – moon of Saturn
Ammonia-water solution magma
Igneous Rock Bodies
Small ones
Sill – horizontal tabular body
Dike – vertical tabular body
Volcanic neck – pipelike remains of a vent
Big ones
Pluton – large igneous intrusion
Batholith – really large igneous intrusion
Igneous intrusive Igneous intrusive landformslandforms
Plutons and Batholiths: Large igneous intrusive rock bodies.Crystallized deep within crust. Exposed by uplift and erosion.
QuickTime™ and aPhoto - JPEG decompressor
are needed to see this picture.
Sills
Dikes
Volcanic Necks
Igneous intrusive rocks formed
close to surface: Dikes, Sills,
Volcanic Necks
Beneficial Aspects of Volcanoes
Outgassing formed oceans, atmosphere
Ash produces rich, fertile soil
Mineral deposits
Geothermal energy
Beautiful sunsets!
Geyser, New Geyser, New ZealandZealand
Water circulates through cooling magma bodies.Water circulates through cooling magma bodies.
Hot brines Hot brines
deposit deposit minerals minerals
with with copper, copper,
lead, zinc, lead, zinc, gold, gold, silver.silver.
Gold & Quartz Gold & Quartz VeinsVeins
Deposited in fractures by hot water (50 to 200 Deposited in fractures by hot water (50 to 200 ooC).C).
gold
quartz
Volcanic Hazards
Ash falls – choke people, animals, kill animals that eat it, collapse roofs – worsened by rain
Pyroclastic flows – suffocation and burning, knock over anything in their way
Mudflows (lahars) – ice and snow melt, rain on ash flow
Volcanic landslide
Lava flow
Poisonous gas emission – Lake Nyos in Cameroon, 1700 CO2 suffocation deaths
http://perso.wanadoo.fr/mhalb/nyos/webcam.htm
Igneous Rocks Tell Their Story
Just as sedimentary strata record the environments of their deposition, igneous rock bodies and layers record the history of magmatism and volcanism in and on the Earth. Rock types and rock distribution tell what kind of activity occurred and radioisotopic dating tells when