other volcanic features flood basalts –largest volcanic events in terms of volume –volatiles,...

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 DomesLava Dome, Mt. St. Helens

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

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

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







Mid-Afternoon - daylight gone

Roof collapse

Water systems can clog

Cloud Hazard




are needed to see this picture.QuickTime™ and a

TIFF (Uncompressed) decompressorare needed to see this picture.

Ash from Mt. Spurr traveled around for days (satellite image)

Kamchatka eruption, seen by space shuttle

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. 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

Next Time

• U.S. volcanoes and related hazards

other volcanic features flood basalts –largest volcanic events in terms of volume –volatiles,...

Documents

area slide

city slide

future slide

ad eruption slide

direction of flow slide

quick death slide

space shuttle slide

effects of pyroclastic