Wednesday February 24, 2010 Volcanic Activity. Basic Information All volcanoes are fueled by magma...
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Transcript of Wednesday February 24, 2010 Volcanic Activity. Basic Information All volcanoes are fueled by magma...
Basic Information
All volcanoes are fueled by magma deep beneath Earth’s surface
Magma = • Mixture of molten rock, suspended
mineral grains and dissolved gases deep beneath Earth’s surface.
• Formed when temperatures are high enough to melt the rocks involved.
Lava = Magma that has reached the Earth’s surface
Volcanic Gases
The expansion of gases brings the magma closer to the surface and drives eruptions.
The interaction between the viscosity and temperature of the magma and the gas content determines if an eruption will be effusive or explosive.
http://volcano.oregonstate.edu/education/gases/index.html will be effusive or explosive.
Magma is less dense than its surrounding rock. This density difference causes magma to move
upward (float) and eventually come in contact with (intrude) the crust
Intruding magma can affect the crust in several ways• Force the crust apart• Break blocks of rock off which sinks into the
magma• Melt the rocks that it intrudes with (IGNEOUS)
Magma Meets Crust
Vent
Crater
Volcano
Magma Chamber
http://www.msnucleus.org/membership/html/k-6/pt/volcanoes/2/images/pt2v01_.gif
Anatomy of a Volcano
Vent = Opening in the crust where lava exits. Volcano
• As lava erupts it flows out onto the surface where it cools and solidifies around the vent
• Over time the lava accumulates to form a mountain, aka the volcano
Crater = Bowl shaped depression at the top of the volcano around the vent
Magma Chamber = Storage area for magma that fuels the volcano
Emitted Volcanic Material 1
Ash Cloud = • Volcanic ash consists of tiny jagged
pieces of rock and glass. Ash is hard, abrasive, mildly corrosive, conducts electricity when wet, and does not dissolve in water. Ash is spread over broad areas by wind.
• Falling ash can turn daylight into complete darkness
Emitted Volcanic Material 2
Tephra• Rock fragments thrown into the air
during a volcanic eruption
Volcanic bombs • Blobs of lava that can harden in the air
or hit the ground, flatten then solidfy
http://facweb.bhc.edu/academics/science/harwoodr/GEOG102/Study/images/volc1.jpg
http://www2.sfu.ca/soils/people/tephra.jpg
http://www.ngdc.noaa.gov/seg/image/titlethumb/73900210.jpg
Pyroclastic flows Mixtures of hot gas, ash and tephra traveling very
quickly down the slopes of volcanoes.
They are one of the most dangerous hazards posed by volcanoes.
Pyroclastic flows are so hot and choking that if one is caught in one the person will certainly be killed. Because these flows are very fast they cannot be out run!
Types of Volcanoes
Based on • The material that
forms the volcano• Type of Eruption
that occurs
Shield Volcanoes Cinder-cone
Volcanoes Composite
Volcanoeshttp://www.ugs.state.ut.us/education/tc/images/volcanos.gif
Shield Volcano• The widest in size • Gentle sloping sides• Least explosive• Form as layers of lava accumulate from non-
explosive eruptions Cinder Cone Volcano
• Smallest in size, often found next to large volcanoes
• Steepest sides• Intermediate explosiveness• Form when tephra falls back to Earth and piles
around the vent
Composite• Tallest• Steep sides• Most dangerous; very explosive• Form when layers of volcanic fragments
alternate with lava
Composite
http://home.flash.net/~alanm52/VolcanoTypes.jpg
Where Do Volcanoes Occur
Most form at plate boundaries• Convergent and divergent boundaries - 95%
Hot Spots – 5%• Unusually hot regions of the mantle that rise to
the surface, melting everything in its path all the way through the crust
• Far from plate boundaries• The magma moves vertically but NOT laterally..• As a result, a trail of progressively older
volcanoes forms as the plate moves over a hot spot