Wednesday February 24, 2010 Volcanic Activity

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.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.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.  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 apartForce the crust apart Break blocks of rock off which sinks into the magmaBreak blocks of rock off which sinks into the magma Melt the rocks that it intrudes with (IGNEOUS)Melt the rocks that it intrudes with (IGNEOUS) Magma Meets Crust

Vent Crater Volcano Magma Chamber

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 ventAs 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 volcanoOver 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.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 darknessFalling ash can turn daylight into complete darkness

Volcanic Ash

Emitted Volcanic Material 2  Tephra Rock fragments thrown into the air during a volcanic eruptionRock 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 solidfyBlobs of lava that can harden in the air or hit the ground, flatten then solidfy

Pyroclastic flows  Mixtures of hot gas, ash and tephra traveling very quickly down the slopes of volcanoes.  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!  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!

Pyroclastic flows can travel at 200 km/hr and exceed 700ºC!

Types of Volcanoes  Based on The material that forms the volcanoThe material that forms the volcano Type of Eruption that occursType of Eruption that occurs  Shield Volcanoes  Cinder-cone Volcanoes  Composite Volcanoes

 Shield Volcano The widest in sizeThe widest in size Gentle sloping sidesGentle sloping sides Least explosiveLeast explosive Form as layers of lava accumulate from non- explosive eruptionsForm as layers of lava accumulate from non- explosive eruptions  Cinder Cone Volcano Smallest in size, often found next to large volcanoesSmallest in size, often found next to large volcanoes Steepest sidesSteepest sides Intermediate explosivenessIntermediate explosiveness Form when tephra falls back to Earth and piles around the ventForm when tephra falls back to Earth and piles around the vent

 Composite TallestTallest Steep sidesSteep sides Most dangerous; very explosiveMost dangerous; very explosive Form when layers of volcanic fragments alternate with lavaForm when layers of volcanic fragments alternate with lava Composite

Where Do Volcanoes Occur  Most form at plate boundaries Convergent and divergent boundaries - 95%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 crustUnusually hot regions of the mantle that rise to the surface, melting everything in its path all the way through the crust Far from plate boundariesFar from plate boundaries The magma moves vertically but NOT laterally..The magma moves vertically but NOT laterally.. As a result, a trail of progressively older volcanoes forms as the plate moves over a hot spotAs a result, a trail of progressively older volcanoes forms as the plate moves over a hot spot