volcanoes and volcanic hazards
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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• HawaiianExplosive• Strombolian• Vulcanian• Plinian• Caldera-Forming (Ultra-Plinian)• Phreatic:
Classes of EruptionType Lava Volcano Effects
Icelandic Basalt None or Shield Fissure Flows
Hawaiian Basalt Shield
Strombolian Basalt-Andesite
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 Any Steam Blast
Products of Eruptions
Lava Flows
Pyroclastic Debris
• Bombs
• Lapilli
• Ash
Mudflows
Landslides
Gases
• Steam
• Carbon Dioxide
• H2S
• 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 70-
hundreds• 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, Greece
Santorini, Greece
Ash Layer, Santorini
Ash Layers, Santorini
What Really Destroyed the Minoan Civilization
Volcanic Explosivity IndexVEI Classification Description Plume Ejecta
volume Frequency Example
0 Hawaiian non-explosive < 100 m < 104m³ daily Mauna Loa
1 HawaiianStrombolian gentle 100-1000 m > 104 m³ daily Stromboli
2 StrombolianVulcanian explosive 1-5 km > 106 m³ weekly Galeras 1993
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 mega-colossal > 25 km > 1,000 km³ ≥ 10,000 yrs 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
• Historical Records of Unusual Cold
• Optical Effects
• Persistent “Dry Fog”
• Frost Rings in Trees
Frost Ring, 536 AD, Mongolia
Recorded Large Distant Eruptions
• 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
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