Volcanoes

Volcanic Hazards Smith Ch 7 Another tectonic hazard Occurrence controlled by plate tectonics

Types of Volcano Subduction (edge of continent) Rift (oceanic) Hot-Spot (oceanic)

Subduction Volcanoes Silica-rich magma, viscous –steep slopes –gassy, explosive, intermittent –ash/lava layered volcanoes

Mt St Helens Explosive eruptionExplosive eruption

Pompeii

Rift Volcanoes Mg & Fe-rich magma, basaltic, less viscous –Lava flows important –eruptions more continuous –gently-sloping volcanoes

Hot-Spot Volcanoes Like Rift volcanoes Found on oceanic “hot spots” like Hawaiian islands

Primary Volcanic Hazards Pyroclastic flows Airfall tephra Lava Gases

Pyroclastic Flows Dense clouds of hot, glowing solid lava fragments ejected from volcano –“nuee ardente” or glowing cloud flows fast downhill –30m/sec for km especially dangerous if blast is lateral –responsible for 70% of C20th volcano deaths

Mt Pelee, Martinique, 1902 Eruption of Mt Pelee Nuee ardente –travelled 6 km at 33m/sec (approx. 120 km/h) –temperature: 700 degrees C –Destroyed town of St Pierre –Killed 29,000 people in 3 minutes –2 survivors in St Pierre

Air-fall Tephra Tephra: volcanic dusts and solids –A feature of explosive eruptions especially Dust-fall can cover 100s of Kms Dust can rise into upper atmosphere –affect climate globally

Mt St Helens 1980 Ash-fall over 400 km Night-like darkness in Yakima & Spokane Traffic disrupted Vehicle engines clogged Breathing problems

Mt Pinatubo 1991 Ash-fall disrupted 500,000 farming people Ash-fall thick for 30km radius 1 million affected by ash-fall significantly reduced global temperatures

Pintaubo: crater

From Clark AFB

Clark AFB

After ash fall and lahar

Karakatoa 1883 Explosive eruption audible at 5000 km Global dustcloud created golden sunsets in 1880s

Tambora 1815 Killed 12,000 directly blew 1400m off the top 80,000 die in famine and disease locally global cooling caused global crop failure –riots and famine in Europe

Tambora 519 CE Eruption caused global cooling for a decade Global crop failures, famine, social breakdown

Lava Can kill, usually doesn’t –silica-rich lavas solidify too quickly –basaltic lavas move faster 15 m/s (54 km/h)

Nyirangongo Zaire 1977 Volcano sides crack draining lava lake –kills 72

Goma volcano 2002

Lava Ruins agricultural land –1783 eruption in Iceland causes death of 10,521 in famine

Mauna Kea

Kilauea

Gases Potentially fatal Carbon Dioxide the most likely to kill

1979 Java eruption 142 people being evacuated from eruption asphyxiated by carbon dioxide

Cameroon tragedies 1984 Lake Monoun –Carbon dioxide released by eruption kills Lake Nyos –Carbon dioxide released by eruption kills 1746

1986 Lake Nyos disaster International effort shipped inappropriate relief supplies: –22000 blankets supplied (5 each!) –1430 tents, 5000 gas masks –5000 kg of jam –11000 frozen chickens

Secondary Volcanic Hazards Ground deformation –Lahars –Flooding –Tsunamis

Ground Deformation Pre-eruption buildup of magma distorts ground –triggers avalanches, debris flows

Mt St Helens 1980 Triggers debris avalanche 20km down North Fork of Toutle R fills valley to 40m depth

Lahars Mudflows triggered by volcanoes –saturation of old and new ash-falls –melting snowpack

1919 Kelut Volcano, Java 5500 killed by Lahar

Nevado del Ruiz 1985 Lahar brings largest loss of life in C20th since Mt Pelee, Eruption generates lahar Overwhelms town of Armero, 50km downstream –3-8 m depth of mud –5000 buildings damaged –22,000 killed in minutes

Nevado del Ruiz 1985

Tsunamis Volcanic-origin tsunamis can do significant damage Karakatoa eruption 1883 –Tsunamis kill 36,000

Volcanic Hazards Normally have their worst effects nearby Intermittent Can have global impact –serious with large populations depending on finite global farmland