• Pompeii ruins today – The quick burial by volcanic ash highly preserved the towns buildings and other artifacts
Eruption of Vesuvius 79 A.D. • Upon excavation, archeologists discovered voids in the volcanic ash. • They filled these molds with plaster and discovered that they were from bodies of people in Pompeii that were buried by the eruption.
low viscosity low SiO2 high temp flows quickly ~30 km/h (100 km/h max, Congo) flows typically gas pressure builds -> explosions – Typically have more dissolved gasses
Mafic (Basaltic) – Low viscosity -> effusive eruptions – Gas pressure provides push like a can of soda
Eruptive Styles • Effusive Eruptions – emits fluid lava flows – lava lakes near vent, – If enough gas pressure then fire fountains and cinder cones
• Explosive / Pyroclastic Eruptions – emits ash clouds, – pyroclastic flows, – expanding gasses cause explosion and fragmentation of magma into fine grained, glassy ash. – Sometimes can destroy much of the volcano
Eruptive Styles • Phreatomagmatic eruptions – Less common style. – Volcanic eruption where magma interacts with water. – Some phreatomagmatic eruptions can be cataclysmic. • A magma chamber breaches and admits water. • Water flashes to steam and blows the entire volcano apart. • Examples: Santorini, Krakatau.
Eruptive Style Also Depends on Tectonic Environment!
Volcanoes of the World and Their Tectonic Environments
Oceanic Hot Spot Volcanoes • Melting oceanic crust • Typically begin underwater (pillow basalts) • Effusive eruptions of basalt build up over time, forming a shield volcano • May slump under its own weight causing earthquakes and landslides
Continental Hot Spot Volcanoes • Melts continental crust • wide array of compositions from felsic to mafic. E.g. Yellowstone
Iceland – A Hot Spot on a Ridge
Volcanic Hazards • Highly predictable (relative to other natural disasters)
• Devastating to wide areas and many people • What Type depends on tectonic environment – Lava flows – Pyroclastic flows – Tephra/Ash Fall
• Secondary Hazards
Goma, (Dem Republic of Congo)
Lava flows • Slow moving but highly destructive • Evacuate people • Divert flow
Hawaii
– Heimaey, Iceland – Mt. Etna, Sicily
Iceland
Pyroclastic flows • Hot (~1000oC) gas, ash, and volcanic fragments • Fast (> 100 miles/hour) • Destructive – Mt. St. Helens, WA – Pompeii, Italy – Mayon, Philippines
Mt. Unzen, Japan
Tephra • Material ejected into the air from the volcano • Classified by size – Bombs -> Ash • Destructive – Weight of ash destroys buildings – Kills crops, blocks roads and streams – Problem for air traffic
Mt. Pinatubo, Philippines
Secondary Hazards • Lahars – volcanic mudflows
• Volcanic landslides – Volcanic cone becomes unstable – e.g. Mt St. Helens
• Tsunamis – e.g. Krakatoa
Amero, Colombia
Secondary Hazards • Volcanic gases – Fluorine absorbed by plants – CO2 release • e.g. Cameroon
• Earthquakes
What can we do? • • • •
Understand volcano recurrence Avoid building on previous flows/deposits Look for the pre-eruption signs Develop emergency plan
