Volcanic Hazardsp. 138-140, web reading

• Volcano Facts• Volcano Hazards

• Fall processes• Flow processes• Other types

• Predicting Volcanic Eruptions

YellowstoneOld Faithful

Giant Caldera Volcano: Yellowstone

Ground collapse ~ Area of NYCMaterial ejected ~1000 km3

Ash Fall

Toba, IndonesiaThe Biggest Eruption?

• 75,000 years ago

Toba, IndonesiaThe Biggest Eruption?

• Caldera diameter 100x35 km• Volume erupted 2,800 km3

– 10 cm of ash fell in India, 3000 km away

• Volcanic winter for a decade– With global cooling 3-5°C

• Might have affected human evolution

Volcanic Eruptions over the last 10,000 years

• 1300 active volcanoes• 550 eruptions (< 2000 yrs)• <10% potentially destructive volcanoes

have been studied in detail

~800 million people worldwide @ risk>50% of world’s volcanoes in nations with per capita GDP <20% US

Volcanic Hazards

Fall ProcessesFlow Processes

Web reading

Lava FlowsBasaltic lava (low viscosity)Usually slow moving (<10 mph)Rarely life threatening

Nyiragongo volcano, CongoGoma, Jan. 19, 2002

Nyiragongo volcano, CongoGoma, Jan. 19, 2002

Pyroclastic Flows

High density mixture of hot ash, rock, and hot gases Temp. >500CVelocity > 80-100 mph

Pyroclastic Flows

Mt Unzen, Japan• Pyroclastic flows• Eruption in June,

1991, killed 40 journalists and 3 experienced volcanologists

Ash Falls (Tephra Falls)

Mount Pinatubo, Philippines June 1991

•can cover large areas for days to weeks•ash will last on the ground for months to years•making land and water unusable•provide material for future hazards (lahars)

Ash fall in Rabaul, Papua New Guinea, 1994

Volcanic Ash–Danger to Aircraft

Volcanic ash can be a serious hazard to aviation even thousands of miles from an eruption. Airborne ash can diminish visibility, damage flight control systems, and cause jet engines to fail.

USGS

Part of a 747 engine

Poisonous Gas Emissions

Lake Nyos, Cameroon

CO2, SO2, HCl, HFH2S

Volcanic Smog-Vog

CO2 gas from Magma

Bottom of lakeSaturated in CO2

Lake Nyos

Poisonous Gas EmissionsLake Nyos, Cameroon (1986)

“River” of CO2

50 m thick layer

Controlled degassing, 1995

Volcanic LandslidesMt. St. HelensMay 18, 1980Debris Flow2.3 km3 of material

Largest debris landslide in recorded history

The avalanche traveled approximately 15 miles downstream at a velocity exceeding 150 mph. It left behind a hummocky deposit with an average thickness of 150 feet and a maximum thickness of 600 feet.

Figure 5.10

Mt. St. Helens May 18, 1980

Mt. St. Helens

Lahars (Mudflows)

• A mixture of volcanic fragments and water

• Mudflows are channeled along valleys on the flanks of volcanoes.

• Mudflows have the consistency of wet concrete and move at high speeds (up to 20-60 mph).

Pinatubo

Nevado del RuizNov. 13, 1985Canyon that

channeled the lahar that destroyed Armero and killed 23,000 people

The November 13, 1985 lahar from Nevado del Ruiz

Town of Armero

Volcano Monitoring and Prediction

Goal: Prevent a Volcanic Crisis from turning into a Volcanic Disaster

Volcanoes of the “Lower

48”

Volcano Monitoring and Prediction

Long-Term based on Historical Records and Geologic History

Age-dating ofvolcanic deposits Eruption Frequency

Types and amounts oferuption products Size of Eruption

Volcano Monitoring and PredictionShort Term: systematic observations of volcano’s visible and subsurface activity

SeismicityGround tiltGas emissions

Rising MagmaGround DeformationRising magma and increasing pressure exerted by

gases often cause volcanoes to deform, or swell, before an eruption

Rising Magma

Magma rises into reservoir beneath volcano

Rising magma and volcanic gases exert pressure

Moving Magma and Volcanic Fluids Trigger Earthquakes

High pressure causes rocks to break, triggering earthquakes

Forecasting Volcanic Activity• Ideal Forecast includes

– Location– Timing– Character of eruption and

magnitude

Forecasting Volcanic Activity• Ideal Forecast includes

– Location– Timing– Character of eruption and

magnitude

•Effective Forecasting involves•Scientists•Public officials•News media•Informed Public

Friday VideoPath of a Killer VolcanoMt. Pinatubo eruption of 1991