Download Volcano!

12/12/2014
5.1 notes:
Volcanism and Plate Tectonics
What is a Volcano?
When…liquid “HOT MAGMA” (Austin Powers)…reaches
the surface it erupts through an opening called a…
Volcano!
Video 5.1a –
How do Volcanoes form?
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Volcanoes of the World
Volcano vs. Mountain
How do we know the difference?
Compositional differences…
Types of Volcanoes
i. Cinder Cone
- Found along subduction boundaries
- very STEEP sided
- very EXPLOSIVE eruptions
- produces LAVA fragments (Tephra)
- pronounced crater
MOST ACTIVE volcanoes in the WORLD!
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Cinder Cone – Arizona, U.S.A
Types of Volcanoes
ii. Composite Cone or Strato-Volcanoes
- form along Subduction boundaries
- contain alternating layers of ash and gas
- EXTREMELY violent eruptions
- make up Cascade Mountain Range
ex. Mt. Baker and Mt. St. Helens
Mt. Baker, Washington State
Volcano Arenal, Costa Rica
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Types of Volcanoes
iii. Rift Eruptions
- occur at long, narrow, fractures in the crust
- non-violent eruptions basaltic lava flows smoothly and fluidly
- ex. Washington State, Iceland and East Africa
Types of Volcanoes
Basalt Plateau or Rift Eruptions
- occur at spreading centres (i.e. Mid-Atlantic Ridge)
- Oceanic: lava oozes out and cools rapidly
- Rift eruptions, on land, spread lava evenly over 1000s of Km’s
(i.e. Columbia Plateau of Washington, Oregon and Idaho)
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Basalt Plateaus
Basalt Plateaus
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Types of Volcanoes
iv. Shield Volcanoes
- Made up of several fine layers of hot basalt lava
- Broad base and gently sloping sides
- Lava produced is VERY fluid
- Lava flows great distances
Like a warrior’s shield…
Shield Volcano
Extremely W-I-D-E!
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How lava flows…
Types of Volcanoes
v. Hot Spot
- Can be found in the middle of an Oceanic Plate
- Basaltic MAGMA forces its way through oceanic crust (POW!)
- Hawaiian Island Chain (U.S.A.)
Oldest
Youngest
Plume remains stationary while overlying plate moves…
Video clip: 5.1 – hotspot volcanoes
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Video 5.1b – Types of volcanoes
5.1 volcano types – magma rising
MAGMA vs. LAVA
What’s the difference?
MAGMA – molten rock underneath the earth’s surface
LAVA – molten rock that reaches the earth’s surface
MAGMA: What’s the difference?
vs.
MAFIC
FELSIC
•LOW SILICA CONTENT
• HIGH SILICA CONTENT
•THINNER (low viscosity)
• THICK (high viscosity)
•DARK-COLOURED
• LIGHT-COLOURED
•FLOW EASILY
• SLOW MOVING (Slow = Felsic)
Gabbro
Rhyolite
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LAVA: What’s the difference?
Pahoehoe (ok to walk on)
Aa (hurts to walk on)
• Smooth and Rope-like
• Rough and Jagged
• Cools slooowly…
• Cools VERY quickly!
• Flows easily
• Does NOT flow easily
Hotter lava flows
underneath cooled lava
Pahoehoe
causing twists and ropy
surface appearance
Pahoehoe or Aa?
Solidified Pahoehoe Lava Flow
Copyright P. Lambert - 2009
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Aa or
Pahoehoe?
A typical aa flow
Aa Lava Flow - Mt. Etna, Greece
Slow Flow
Aa or
Pahoehoe?
Lava cools quickly – rough
and jagged surface texture
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Video 5.1c - Pahoehoe and Aa Lava
Flows
How does Pillow Lava form?
- When fluid basaltic lava flows into the ocean
- Rapidly cools – gases cause expansion – creating bulbous pillow lava…
- Commonly found along coastal margins
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Video 5.1d – Pillow Lava
Pillow Lava
Oozing lava that cools
quickly into rounded shapes
Kilauea Crater , Hawaii
Solidified Pillow Lava Field
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Volcanic Eruptions:
What are the chances?
I don’t think it will erupt…
Ooops! Maybe it will…
Eruptive Stages
1) Active
2) Dormant
3) Extinct
Eruptive Stages
ACTIVE - currently erupting volcano or one that
has erupted recently.
Rinjani, Lombok, Indonesia
Kilauea, Hawaii
Eruptive Stages
DORMANT - has not erupted in past 2000-3000 years,
but has potential to erupt.
Mt. Baker, WA
Mt. Rainier, WA
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Eruptive Stages
EXTINCT – No historical record of eruption or are badly
eroded
Extinct Volcano, Philippines
Crater Lake, Oregon
Video:Kilaeau, Hawaii (2011)
Video: Iceland Eruption
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HW:
• P. 262 #1,3
• P. 264 #1,2,3
• Describe the difference between an active,
dormant, and extinct volcano.
• List one real world example of each type of
volcano listed above.
Speaking of volcanoes:
Mount Saint Helens was a small Volcano by volcano
standards…
Tambora 1815
(Sambawa Indonesia)
• The largest eruption known:
– more than 50 cubic kilometers of magma.
– Caldera collapse at the end of the eruption destroyed 30
km3 of the mountain and formed a 6 km wide and 1250 m
deep caldera.
– killed more than 100,000 people
– Global temperatures dropped 5o
– Giant ash cloud of 80 km3 caused the “year without
summer”
• Bizarre weather in 1816. Spring brought cold temperatures. The
sky seemed permanently overcast which caused a lack of sunlight
= farmers lost their crops and food shortages were reported even
in Europe and the United States.
http://www.volcanodiscovery.com/tambora.html
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• Excessive pressure built
up, explosion heard
4500 km away
• Eruption caused
volcano to collapse into
the sea = 120 ft
tsunami.
• 45 km3 of debris caused
darkness for 3 days
• Global temps dropped
1o
• More than 37000 killed
http://www.livescience.com/28186-krakatoa.html
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