Notes Volcano Notes
Transcript of Notes Volcano Notes
Volcanoes
BIG Questions1 – What plate settings do volcanoes occur at?
2 - Volcanoes aren’t equally dangerous....how do their hazards differ, and why?
VOLCANOES
Volcano
•an opening in a planet's
crust, which allows hot molten rock,
ash, and gases to escape from
below the surface.
What comes out of a volcano? Ash
What comes out of a volcano? GasMost common:
H2OCO2
SO2
HCl
What comes out of a volcano?Lava
So...Why are there different types of
Volcanoes•Viscosity of the magma controls the type of volcano.
•Viscosity – a liquid’s resistance to flow
•Low viscosity – flows easily
•High viscosity – flows slowly
•Viscosity is controlled by the composition and temperature of the magma.
•Silica (SiO2) content controls viscosity.
What are the different types
of Magma?
•Basaltic
•Andesitic
•Rhyolitic
Composition
Magma Source
Viscosity Gas % Silica %Explosive
nessLocation
BasalticUpper Mantle
Low 1-2 % ~ 50 %Least / Mild
Divergent Boundaries and Hot Spots
AndesiticOcean Crust & Sediments
Medium - High
3-4 % ~ 60 %Intermedi
ate
Convergent
Subduction Zones
RhyoliticContinental Crust
High - Extreme
4-6 % ~ 70 % Greatest
Convergent
Subduction ZonesHigh silica = high viscosity = explosive
eruptionLow silica = low viscosity = quiet
eruption
Viscosity and Silica content
Shape
•Shapes of volcanoes are due to the viscosity of the magma.
•Runny lava forms relatively flat shield volcanoes with quite eruptions.
•Thick lava forms steep cones with explosive eruptions.
Explosiveness
Explosiveness of the volcano
is controlled by
- the silica content of the magma
- the viscosity of the magma
- the release of gases
Types of Eruptions
Explosive “clogged”Plate Setting: Convergent Boundary Subduction Zones
Type of Volcano: Composite volcanoes and Cinder Cones
Type of Magma: Andesitic or Rhyolitic composition
Quiet “runny”Plate Setting: Divergent Boundaries and Hot Spots
Type of Volcano: Shield volcanoes
Type of Magma: Basaltic composition
Quiet Eruptions•Magma flows easily
•Gasses bubble out gently
Plate Setting: Divergent BoundaryDivergent boundary volcanoes have very low viscous magma
and non-explosive eruptions
Plate Setting: Hot SpotHot spot volcanoes form when mantle plumes rise
through the crust like a blow torch Characterized by low viscous magma and non-explosive
eruptions
Type of Volcano: Shield
•Usually start under water
•resembles a Roman shield lying on the ground
•characterized by relatively quiet eruptions with lava flows that harden on top of each other
Examples: - Hawaiian Islands - Iceland
Type of Magma: Basaltic
• runny, low viscosity lava
• relatively little explosive activity
Kilauea, Hawaii: A typical shield volcano
Basaltic eruptions produce
2 types of lavaPahoehoe – hot, fast moving lava. Surface looks like
wrinkles and rope-like coils
Pahoehoe Lava
Pahoehoe Lava
Basaltic eruptions produce
2 types of lavaAa– cooler, slow moving lava. Hardens to form rough,
jagged lava chunks
Anatomy of a Shield Volcano
Explosive Eruptions•Magma is thick and “sticky”
•Magma slowly builds up in the volcano's pipe
•Gasses cannot easily escape from the magma
•Trapped gasses build up pressure until the volcano explodes
•More dangerous and have more hazards such as pyroclastic flows
Pyroclastic Flows•Pyroclastic flows - fast-moving hot gas and rock fragments which travel away from the volcano
•speeds generally as great as 450 miles/hr
•Can reach temperatures of 1,830 °F
Plate Setting: Convergent BoundaryExplosive volcanoes form at
convergent subduction zones and have highly viscous magma
Type of Volcano: Cinder Cone•relatively small (less than 300 m or 1000 ft high)
•relatively steep slopes (30 - 40 degrees)
•made of pyroclastic material
Type Of Magma: Andesitic
- high silica content - highly viscous magma - explosive eruptions
Examples - Paracutin, in Mexico
Anatomy of a Cinder Cone
Type of Volcano: Composite
•large (1 - 10 km across)
•Also called a Stratovolcano
•layered structure, consisting of alternating layers of lava and pyroclastic material
•These volcanoes make up the largest percentage of the Earth's volcanoes (about 60%)
Type Of Magma: Rhyolitic - high silica content - highly viscous - explosive eruptions
Examples: Mt. Vesuvius,
Mt. St. Helens and Mt. Rainier in the
Cascade Range
Mt. St. Helens: Before the 1980 eruption
Mt. St. Helens after its 1980 eruption
Anatomy of a Composite Volcano
Pyroclastic flow
Status of a Volcano
•Active – currently erupting or showing signs of an imminent eruption. Risk is high
•Dormant – does not show signs of an erupting in the near future or has not erupted in the recent past
•Extinct – unlikely to ever erupt again
Signs a volcano is about to erupt
•When a volcano begins to show new or unusual signs of activity, it is possible it is about to erupt
•Increased Earthquake Activity
•Ground Deformation
•Change in water composition
•Gas emissions
•Monitoring from space
Volcanic Hazards
Volcanic Hazards• Lava flows
• Ash fall
• Pyroclastic flows
• Mudflows
• Volcanic Gases
• Tsunami
Volcanic Hazards
Volcanic Hazards
Volcanic Hazards
•Volcano Hazards program
•http://volcanoes.usgs.gov/activity/alertsystem/icons.php