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 (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