Volcanoes and Volcanic Hazards
View From Space - Klyuchevskaya, Russia
Cleveland Volcano, Alaska
Mount Etna From Space
Mount Etna From Space
Mount Etna From Space
Mount Etna
Shiveluch, Russia
Magma – molten rock beneath
the surface
Lava – molten rock on the
surface
Where Does Magma Come From?
• Earth’s interior is hot (25 C/km near surface
= 1000 C at 40 km)
• Pressure inhibits melting
– Mantle is solid
– Never far below melting point
• Volcanoes fed by small pockets 0-100 km
deep
– Rising hot material may melt
– Water can lower melting point
Why Igneous Rock Classification
Matters
• Silica Content = Viscosity
• Silica Content Governs Violence of
Eruptions
– Silica Poor (Basalt): Fluid lavas, generally little
explosive activity
– Intermediate Lavas (Andesite): Pasty lavas,
explosive eruptions common
– Silica-Rich Lavas (Rhyolite): Extremely
viscous lava and explosive eruptions
Basalt (45-52% SiO2)
• Slightly modified planetary raw material
• Derived directly from mantle
–
–
–
–
–
Oceanic crust
Hot Spots and Flood Basalts
Oceanic volcanic arcs
Early stage of continental volcanic arcs
Rift zones with rapid spreading
• Fluid lava with little explosive activity
• Shield volcanoes, Cinder Cones
Plate Tectonics and Volcanoes
A Cinder Cone:
Wizard Island, Crater Lake, Oregon
Paricutin,
Mexico
1943-1952
Shield Volcano: Haleakala,
Hawaii
Andesite (52-66% SiO2)
• Mixture of mantle material and continental
crust
• Continental volcanic chains
• Pasty lava with significant explosive
activity
• Stratovolcanoes
Plate Tectonics and Volcanoes
Stratovolcano: Mount Shasta,
California
Stromboli
Rhyolite (>66% SiO2)
• Mostly remelted continental crust
• Settings where magma has a long time to
react with continental crust
– Late stage of continental volcanic arcs
– Slow-spreading Continental Rifts
– Continental Hot Spots (Yellowstone)
• Catasrtophic explosive activity common
• Obsidian domes, magma chamber collapses
Lava Dome, California
Some Igneous Rocks Are
Named on Textural Criteria
•
•
•
•
Pumice - Porous
Obsidian - Glass
Tuff - Cemented Ash
Breccia - Cemented Fragments
Classes of Eruption
Effusive
• Icelandic
• Hawaiian
Explosive
• Strombolian
• Vulcanian
• Plinian
• Caldera-Forming (Ultra-Plinian)
• Phreatic:
Classes of Eruption
Type
Lava
Volcano
Effects
Icelandic
Basalt
None or Shield
Fissure Flows
Hawaiian
Basalt
Shield
Strombolian
BasaltAndesite
Small
Stratovolcano
Mild, Continuous
Vulcanian
Andesite
Stratovolcano
Large eruption
cloud
Plinian
Andesite –
Rhyolite
Stratovolcano
Pyroclastic Flows
Caldera-Forming Rhyolite
Stratovolcano or
None
Large Pyroclastic
Flows
Phreatic
Any
Steam Blast
Any
Products of Eruptions
Lava Flows
Pyroclastic Debris
• Bombs
• Lapilli
• Ash
Mudflows
Landslides
Gases
• Steam
• Carbon Dioxide
• H 2S
• SO2
• HCl
• HF
Environmental Hazards of
Volcanoes
Pollution
• SO2, HCl in
Water
Lava Flows
Falling Ejecta
Ash Falls
• Building Collapse
• Crop Destruction
Mudflows
• Direct Damage
(Colombia, 1985)
• Floods (Several Types)
Blast (Mt. St. Helens, 1980)
Pyroclastic Flow (St. Pierre,
1902)
Gas (Lake Nyos,
Cameroon, 1986)
Volcanic
Hazards,
Congo
Nyiragongo, Congo
• At least 34 eruptions since 1982
• Semi-permanent lava lake
• Area accounts for 40% of Africa’s historic
eruptions
• Steep-sided but unusually fluid lava: unique
• 1977: Lava lake drains at night, killing 70hundreds
• 2002: Lava invades city of Goma: 400,000
evacuated, 45 killed, 4500 buildings
destroyed, 120,000 homeless
Pyroclastic Flow or Nuee
Ardente (French: Fiery Cloud)
Welded Tuff, California
How Calderas Form
Crater Lake, Oregon
Mount Mazama: After
Mount Mazama: Before
Jemez Caldera, New Mexico
Valles Caldera, New Mexico
Tuff, Valles Caldera, New Mexico
Santorini
(Thera),
Greece
Santorini (Thera), Greece
Santorini, Greece
Santorini, Greece
Ash Layer, Santorini
Ash Layers, Santorini
What Really Destroyed the Minoan
Civilization
Volcanic Explosivity Index
VEI Classification
Description
Plume
Ejecta
volume
Frequency
Example
0
non-explosive
< 100 m
< 104m³
daily
Mauna Loa
gentle
100-1000 m > 104 m³
daily
Stromboli
explosive
1-5 km
> 106 m³
weekly
Galeras 1993
1
2
Hawaiian
Hawaiian
Strombolian
Strombolian
Vulcanian
3
Vulcanian /Pelean
severe
3-15 km
> 107 m³
yearly
Lassen 1915
4
Pelean/Plinian
cataclysmic
10-25 km
> 0.1 km³
≥ 10 yrs
Soufrière Hills
1995
5
Plinian
paroxysmal
> 25 km
> 1 km³
≥ 50 yrs
St. Helens 1980
6
Plinian/Ultra-Plinian colossal
> 25 km
> 10 km³
≥ 100 yrs
Pinatubo 1991
7
Plinian/Ultra-Plinian super-colossal
> 25 km
> 100 km³
≥ 1000 yrs
Tambora 1815
8
Ultra-Plinian
> 25 km
> 1,000 km³ ≥ 10,000 yrs
mega-colossal
Toba (73,000
BP)
Collapsing Volcanoes – Mount Rainier
Shastina and Landslide Deposit
Mount Shasta and Landslide Deposit
Collapsing Volcanoes - Hawaii
Volcanoes and Climate
• Stratospheric Ash
• Sulfuric Acid Aerosols
– Colorful sunset effects
– Large amounts can block sunlight
• Carbon Dioxide
Dating Large Remote Eruptions
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•
•
•
Historical Records of Unusual Cold
Optical Effects
Persistent “Dry Fog”
Frost Rings in Trees
Frost Ring, 536 AD, Mongolia
Recorded Large Distant Eruptions
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•
•
•
•
•
•
1627 BC: Thera?
536 AD: Krakatoa?
626: Unknown
934: Eldgja, Iceland
1258: Unknown
1783: Laki, Iceland
1815: Tambora, Indonesia
Tambora 1815
1816: “Year Without A Summer”
• 100 cubic km of ash erupted
• Global sunset color effects for months
• New England
– Snow in June and August, Frost in July
– Exodus to Midwest
• Europe: High prices, food riots
Tambora
Flood Basalts
• Siberian Traps and Permian Mass
Extinction?
• High Sulfur Content
– Aerosols may block significant sunlight
– Surface crust may trap sulfur
Supervolcanoes?
• Magma Chamber Collapse (Yellowstone?)
–
–
–
–
Destruction of crops
Destruction of high technology
Economic Disruption
Climatic Effects
• Flood Basalts
– Climatic Effects
– Toxicity
Long Valley Caldera
Long Valley Caldera
Bishop Tuff
Compaction of Bishop Tuff
Toba, Sumatra