Science of Natural Disasters: Volcanoes!
13 April 2016
Rebecca ClottsDepartment of Geology, University of St Thomas
“…and it was then I saw how, in the hole, the ground swelled and raised itself 2 or 2.5 meters high, and a kind of smoke or fine dust -- grey, like ashes -- began to rise up in a portion of the crack that I had not previously seen . .”-Dionisio Pulido, 1943
Volcano Types: CINDER CONE
5 Misconceptions about YELLOWSTONE
1) When Yellowstone erupts, it will be a catastrophe.
2) The magma chamber is growing.3) It’s overdue for a SUPER eruption.4) The land is rapidly rising.5) Earthquakes mean moving magma.
https://volcanoes.usgs.gov/volcanoes/yellowstone/faqs_misconceptions.html
But… What IF?!
Check out the docu-drama “Supervolcano” by BBC
and the Discovery Channel (2005)
• http://www.npr.org/2013/09/13/222101240/worlds-largest-volcano-discovered-on-pacific-seafloor (5.5 minutes) 13
Largest Volcano!
Volcanic Hazards: Volcanic Gas
• Mainly water vapor (H2O) and carbon dioxide (CO2)
• Also sulfur dioxide (SO2), hydrogen sulfide (H2S)
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1) Mafic
Pahoehoe – ropey, fast flowing
• Low viscosity = flows freely• Low amount of Silica (Si)• Very hot (>950°C or ~1700°F)• http://www.youtube.com/watch?v=eoPz5O6_-d0
2) Intermediate
• Higher viscosity = poor flow (erupts more explosively)
• More of Silica (Si)• Hot (>750°C or ~1400°F)
3) Felsic
• High viscosity = does not flow• High Silica (Si) content• “Cool” Temperature (>650°C or ~1200°F)
Lava Flows
• Typically less than 1km/hour on gentle terrain• Basaltic lavas tend to be faster:
– Fastest ever• 30-60 km/hr Hawaii (18 to 40 mph)• 8-75 km/hr Vesuvius (5 to 47 mph)
• Siliceous lavas are typically slower:– 10’s to 100’s of m/hr (<1 mph)
24http://volcanoes.usgs.gov/vhp/lava_flows.html
Hawaii Kilauea Volcano Lava Flow Destroys 1st House:https://www.youtube.com/watch?v=U-3B7vO3tRI
Pyroclastic flows
• High-density mixture of hot, dry rock
fragments and hot gases, maybe water
– Density
– Gravity
What is it REALLY like?http://www.youtube.com/watch?v=Cvjwt9nnwXY1:12 minutes
Destroys by direct impact Melt snow and ice to form lahars
Burns forest, crops and buildingsBuries sites with hot rock debris
Pyroclastic flows
• How fast? Speed depends on: gradient and size
– >80 km/hr; max 700km/h (450 mph)
• How hot?
– 200-1,000°C (1,830°F)
• How far?
– Gravity, most follow topography
– 8 km, max=10-20 km (12 mi)
http://www.arch.virginia.edu/struct/pompeii/pyroclastic-6.html
How bad?
• 1902 eruption of Mont PeléeMartinique, West Indies
• 4 mi to St. Pierre
– killing ~30,000 inhabitants
The good news?
• Reinforced concrete shelters
• Occasional survivors
• Instant death
• Active volcanoes
Th
e b
ad
ne
ws?
• Determining Run Out distance?
– Run-out distance: ∆H/L = 2.03V-0.15
• L= run-out distance
• ∆H = change in elevation
• V = volume of pyroclastic flow
• Determining Maximum Potential Velocity?
– Max potential vel: v = 0.38∆h0.68
• v = velocity
• ∆h = change in elevation
What is the worst volcanic hazard?
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Deaths Volcano When Major Cause of Death
92,000 Tambora, Indonesia 1815 Starvation
36,417 Krakatau, Indonesia 1883 Tsunami
29,025 Mt. Pelee, Martinique 1902 Ash flows
25,000 Ruiz, Colombia 1985 Mudflows
14,300 Unzen, Japan 1792 Volcano collapse, tsunami
9,350 Laki, Iceland 1783 Starvation
5,110 Kelut, Indonesia 1919 Mudflows
4,011 Galunggung, Indonesia 1882 Mudflows
3,500 Vesuvius, Italy 1631 Mudflows, lava flows
3,360 Vesuvius, Italy 79 Ash flows and falls
2,957 Papandayan, Indonesia 1772 Ash flows
VISCOSITY (Composition and Temperature) help determine how violently the molten material will erupt
http://libraryphoto.cr.usgs.gov/cgi-bin/show_picture.cgi?ID=ID.%20HVO%20140ct
Will it FLOW?
http://libraryphoto.cr.usgs.gov/cgi-bin/show_picture.cgi?ID=ID.%20CVO-A.%20%20%204ct
Will it BLOW?
Different eruptive styles!
Eruption Styles
Eruption Styles
1. Molten material viscosityViscosity depends ona) Temperatureb) Composition (amount of Si)
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Oceanic Crust
(Low Silica
content)
Continental
Crust (High Silica
content)
Depends on:2. Gas Content
http://w3.salemstate.edu/~lhanson/gls110/images_GLS110/Cascades_images/VocanClasses.gif
http://science.uniserve.edu.au/school/virtexps/vftkiama/pheasant/gasholes.jpg
Eruption Styles
What type of lava would you associate with a violent eruption?
33%
33%
33%
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A. AndesiteB. BasaltC. Rhyolite
Based on:– Volume of
erupted material
– Plume Height
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Volcanic Explosivity Index (VEI)
Eruption Styles
Economic Deposits• Bauxite,
Diamonds, Gold, Nickel
• Base Metals: Lead, Zinc, and Copper
What’s so good about volcanoes?
• The USGS monitors US Volcanic Hazards: http://volcanoes.usgs.gov/
• There are over 160 US volcanoes that have erupted in the past 10,000 years
• http://volcanoes.usgs.gov/about/volcanoes/volcanolist.php
• 57 are Priority, including:– Mt Rainier, Mt St Helens in Washington– Kilauea, Mauna Loa in Hawaii– Others in California and Oregon 70
http://volcanoes.usgs.gov/index.html
NYT 1/12/2016The 40,000-mile Volcano
Vol
cano
es in
the
New
s
http://www.nytimes.com/2016/01/12/science/midocean-ridges-volcano-underwater.html
Vol
cano
es in
the
New
s
Olympus Mons, MARS (NASA photo)
Recent World News 3/3/2016Volcanic Activity TIPPED Mars
Tharsis dome
http://recentworldnews.org/news/science/649491/mars-mega-volcano-red-planet
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Midcontinent rift – a divergent margin –started to form, then failed
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But a long, long time ago……about 1.1 BILLION years ago…