Other volcanic features Flood basalts Largest volcanic events in terms of volume Volatiles, viscosity are low, so not very explosive Cover large areas w/ thick layers of lava Lava domes Hardened dome/plug of magma cools quickly Can form in hours, continue for years, decades

Flood Basalts

Lava Dome, Mt. St. Helens Lava Domes

Volcanic Hazards

Outline Types of volcanic hazards

Volcano Classification Active: currently erupting or has erupted in historical time Dormant: presently inactive but may erupt again (examples: Cascades) Extinct: not active, not expected to be active for long time in future

Cumulative Deaths Due to Volcanic Hazards in past 2000 years

Causes of Deaths

How bad can it be? 1815 Indonesia 92,000 died* 1822 Indonesia 5,500 killed 1826 Indonesia 3,000 killed 1883 Indonesia 36,417 killed 1902 Martinique 29,025 killed 1902 Guatemala 6,000 killed 1919 Indonesia 5,110 killed 1951 New Guinea 2,942 killed 1982 Mexico 1,700 killed 1985 Columbia 23,000 killed

Pyroclastic Flow Most deadly of all hazards Superhot, fast moving cloud of volcanic gas, steam, debris 200-700 degrees C, 80 km/hr (hurricane speeds!)

Generation of pyroclastic flow Eruption column collapse Dome collapse Directed blasts

Pyroclastic flows Mayon, Philippines, 1984

Effects of Pyroclastic Flows Destroys nearly everything in path Structures Burial of sites Burn forests, crops, structures Melt snow to form lahars

Building destruction Remnant of building after eruption of El Chichon, Mexico in 1982 Note reinforcement rods bent in direction of flow

Effects of pyroclastic flows Mt. St. Helens - forest destruction

Effects on people Physical impact Burns Inhaling superhot gases Usually quick death

Examples Many examples of devastating pyroclastic flows Unzen, Japan Chichon, Mexico Mt. Pelee, Caribbean*

Mt. Pelee 1902-1903, 1929-1932 significant pyroclastic flows Many from directed blasts, deadliest in 1902 Viscous magma filled crater May 1902, several pyroclastic flows, traveling ~190 km/hr Destroyed St. Pierre (~30,000 people) and other towns in area

Mt. Pelee Large area affected by 1902 pyroclastic flows

Eruption Debris Includes cloud, bombs, ash fall Bombs kill small # of people every year Clouds Planes fly into cloud - dangerous Over 25 years, ~60 jets damaged Ash fall Bury cities

Ash fall hazards Roof collapse Mid-Afternoon - daylight gone Water systems can clog

Kamchatka eruption, seen by space shuttle Cloud Hazard Ash from Mt. Spurr traveled around for days (satellite image)

Example - Mt. Vesuvius 79 AD Cause of volcano: subduction Region near Pompeii also had earthquakes, but city of ~20,000 people not deterred to move Significant volume of material erupted (4 km3) in first wave Pompeii buried by ash/pumice 3 m deep Later pyroclastic flows continued to bury city

Vesuvius Remains of Pompeii after 79 AD eruption

Tsunami Wave caused by undersea vertical displacement (like earthquakes) Volcanic eruption can also cause tsunami Pyroclastic flow or lava dome avalanche Collapse of cone or crater

Example - Krakatau 1883 Stratovolcano between Java and Sumatra Subduction zone Collapse led to tsunami ~35 m (115 ft) Death toll ~36,000 New cone appeared in 1927

Collapse of Krakatau Anak Krakatau

Lahars Mudflow of volcanic debris, produced when pyroclastic debris or lava mix with rain, snow, ice, lakes Can travel quickly (40 mph) and significant distances (10s of miles)

Dark pathways - lahars triggered by Mt. St. Helens eruption, 1985 “Cloud” upriver: lahar traveling down riverbed in Guatemala

Home destroyed from lahar - Mt Home destroyed from lahar - Mt. Unzen, Japan lava dome collapse and later rains, 1993

Example - Nevado del Ruiz 1985 Colombian volcano, small glacier on top Small eruption caused melting, sending mud down the mountain Covered most of town of Armero with ~26 ft thick mud Killed ~22,000

Nevado del Ruiz, 1985 River valley with lahar remains Town of Armero

Famine Indirect hazard Eruptions change climate Can harm plants, animals

Iceland eruption, 1783 Fissure eruption of basalt Released gas rich in SiO2 and fluorine Slowed grass growth and added significant amounts of fluorine to grass Killed significant population of livestock ~20% of Iceland population died due to famine

Tambora, 1815 Indonesian volcano, most violent eruption in last 200 years Significant Plinian eruption Next pyroclastic flows (12mi3 of material) Deaths in region ~90,000 (10% during eruption, 90% later) 1816 - year without summer Affected global climate

Gas Gas can escape from basaltic magmas CO2 gas is common Depending on gas, can kill plants in region Can also be trapped in water

Example - Lake Nyos, Cameroon Area of failed rifts with some remaining volcanic activity 1986 - gas burp from the lake Sent rivers of gas down into valleys ~25 km (16 mi) Effects - ~1700 deaths, no animals alive Plants ok though

Why? CO2 gas leaking out of basaltic magma Dissolved in bottom waters of lake (held down by pressure) Some event caused overturn Eruption, earthquake, landslide, temp change all possible triggers Gas release “river” ~50 m thick

Lake Nyos

Lake Nyos Efforts to pump water, gas out of lake

Continued hazard? YES! Still some gas remaining Continues to build up Possible ways to pump gas out to reduce risk

Lava Flows Not big hazards in terms of fatalities Moves too slow to kill people Can destroy towns, villages

Kilauea, HI Few lives lost Mostly structural losses

1973 Flows in Iceland Lava flows threatened town, harbor Built diverters to control flow Sprayed water to harden flows, move to flow in other direction away from harbor

Man vs. volcano!

Actually gained land and improved harbor

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