Volcanoes

• What is volcanism?

  The eruption of magma and gases at the surface.
• How can volcanism be constructive?

  It can be an origin for many oceanic islands, fertile farm lands, and critical atmosphere gases.
• How can volcanism be destructive?

  Can be deadly and destroys property.
• What is the most volcanically active body in the solar system?

  Jupiter’s moon Io.
• What is the tallest volcano in the solar system?

  Olympus Mons (Mars).
• Olympus Mona have the size of the state of Arizona.
• Volcanoes and flood basalts are present in Venus.
• Mercury has widespread flood basalts covering its surface from extensive volcanic eruptions.
• Moon’s mare (dark spots) are flood basalts.
• A volcano is the hill/mountain tha forms around a vent where lava, pyroclastic materials, and gases erupt.
• A vent is surrounded by the volcano.
• Crater


  A roughly circular depression located near the top of a volcano.
• Caldera


  A huge circular depressions that are formed from collapse of rock above an empty magma chamber.
• An example of a caldera is the Crater Lake in Oregon and Satorini.
• Fissure eruption


  Most common eruptions in mid-ocean ridges, but also occurs on land.
• Volcanic gases are primarily water vapor. Chlorine contributes to the deterioration of ozone layer. Sulfur gases from large eruptions may cool global climates for 1-2 years.
• Shield Volcano


  They have gentle slopes and largely composed of basalt (and scoria ash).

  It is non-explosive and pose little danger to humans.

  It can be found in Hawaii, Iceland, and Mars.
• Cinder (Scoria) Cone

  Scoria and other pyroclastic materials.

  Accumulate as steep-sloped cones that rarely exceed 300m high.

  It has mafic composition.

  Mostly found with shield volcanoes.
• Composite volcano (stratovolcano)

  Composed of layers of lava plows, pyroclastic debris, and volcanic mud flows (lahars).

  Explosive

  Intermediate composition
• Lava Domes

  Bulbous lava domes form when viscous lavas are forced up through the conduits of some volcanoes.

  Solidified lava with volcanic ash and rock fragments.

  Usually felsic/intermediate

  Can erupt explosively
• How do gases affect magma?

  As magma rises, pressure decreases and gases come on of solution.

  Soda as reference.
• How viscosity affects magma

  More viscous (felsic) traps gas so it builds up resulting in explosive eruptions. Less viscous (mafic) allows gas to escape when it erupts as lava flows.
• Shield volcanoes have basaltic (mafic) eruption [often begins with lava/fire fountain].

  Fragments cool as they fly through the air, forming scoria around the vent.

  Basaltic lava flows downhill or from the base of scoria cone.
• Rock types that emerge from shield volcanoes

  Basalt, vesicular basalt, scoria.
• Basalt lava flow: Lava tube

  The top of lava flow solidifies and acts as an insulator, keeping the lava below war and liquid.

  Can be found in Hawaii, Moon and Mars.
• Basalt Lava Flows: Pahoehoe Lava (Hawaii)

  Smooth surfaces creates small folds. Usually fed by a lava tube.
• Basalt Lava Flows: AA Lava (Hawaii)

  Consists if angular blocks and fragments.

  It breaks apart into fragments as it flows.

  Forms from rapidly flowing lava.
• Basalt Lava Flows: Columnar joints

  Forms in response to the cooling and contraction of lava.

  Three-pronged cracks form that grow and intersect to form four to seven-sided columns.

  Most commonly occur in thick basalt and andesite lava flows.
• What are some hazards of basaltic eruptions?

  Lava flow

  Lava/fire fountain

  Volcanic ash
• Pyroclastic material are magma fragments that are explosively ejected by volcanoes. Most pyroclastic materials are solid.
• Pyroclastic materials includes ash, lapili, bombs, and blocks.
• Eruption column is tephra and gas that rises upwards.
• Tephra is pyroclastic material that is ejected during eruption
• Pyroclastic flows: violent eruptions of hot gases, ash, and angular rock fragments.
• Lahar: mudflow consisting of liquid water and pyroclastic materials.

  May be hot or cold. Often formed from rain during eruption.
• Rock types that emerge from stratovolcanoes

  Andesite, Tuff, Obsidian, Pumice
• Hazards of Composite eruptions

  Lahar

  Pyroclastic Flow (Pompeii)
• Tonga

  Built by undersea eruptions.

  It was two pre-existing island; joined by the 2015v eruption.
• Distribution of Volcanoes

  ~ 60% in circum-pacific belt (Ring of Fire)

  ~ 20% in the Mediterranean belt

  ~ 20% are at or near mid-oceanic ridges.
• Alaska’s volcanoes

  Mostly composite, some with huge calderas.

  Extremely active with many explosive eruptions.