volcanoes. prepare for quiz print name: bill shields lab section: 12 ta: ryan 1. 2. 3. 4. 5....
TRANSCRIPT
Prepare for Quiz
Print Name: Bill Shields
Lab Section: 12
TA: Ryan
1.2.3.4.5.
Signature: #&$*&(*&)*(&
1. Igneous rocks high in silica are dark in color.A. true B. false
2. Igneous rocks which cool slowly have coarse-grains, (large crystals).A. true B. false
3. Volcanic igneous rocks are fine-grained, (small crystals).A. true B. false
4. Extrusive igneous rocks are plutonic.A. true B. false
5. Mafic igneous rocks are low in iron and magnesium.A. true B. false
Felsic/ Silicic Mafic
light colored intermediate dark colored
high in SiO2 low in SiO2
Phaneritic Plutonic (magma)
(coarse grained) Intrusive
Aphanitic Volcanic (lava)
(fine grained) Extrusive
Igneous Rock Classification
Granite
Rhyolite
Diorite Gabbro
Andesite Basalt
Increasing Fe and Mg
Increasing silica (SiO2)
Types of Volcanoes*Based on type of eruption
Nonexplosive – shield volcano
Explosive – composite (strato) volcano
Largely a function of - viscosity - dissolved gases
Volcanism at Divergent Margins
Few actual volcanoes, lava erupts from fissures.
Molten results from decompression melting.
Mafic in chemical composition.
Volcanism at Convergent Margins
Volcanoes form in a line parallel to the subduction zone.
Molten material is generated by heating "wet" rocks that are being subducted.
Volcanism at Convergent Margins
Stratovolcanoes
- steep-sided
- alternating layers of lava, ash and pyroclastics
- explosive (due to high magma viscosity and gas content
Silicic magma chemistry
Mantle Plumes (Hot Spots)
Molten material rising from deep within the Earth.
Mafic magma chemistry.
Can form shield volcanoes – broad and gently sloping sides, non-violent eruptions, built by repeated layers of lava flows (Hawaiian Islands).
Hazardous Volcanic Geologic Processes
1. Tephra Fall2. Pyroclastic Flows3. Pyroclactic Surges4. Explosive Ejection of Ballistic Projectiles5. Lateral Blasts6. Lava Flows7. Lahars
Pyroclastic Flows
Avalanches of hot, dry, volcanic rock fragments and gases
• Denser than air • 600 - 1500O F• Up to 200 mph• Tends to channel into valleys
Pyroclastic Surges
Avalanches of hot, dry, volcanic rock fragments and gases
• Less dense than air • 600 - 1500O F• Up to 200 mph• Not confined to channels
Pyroclastic Surge Hazards
•Incineration
•Destruction by high-velocity
ash-laden winds
•Impacts by rock or flying material
•Exposure to noxious gases (SOx) (CO2)
Explosive Ejection of
Ballistic Projectiles
• Not constrained by wind direction
• Not dependent on eruptions
• Large projectiles thrown 1/2 mile
Lava Flows
• Flow controlled by topography
• Destructive, but not life threatening
• Speed related to slope and viscosity
Predicting Eruptions
• Ground tilt and displacement
• Increases in surface temperature
• Monitoring earthquakes
• Changes in gas composition