VOLCANOES

1. VOLCANOES Just the Facts

2. Hazards • Ash Falls (tephra falls) • Hot Ash Flows (pyroclastic flows) • Mudflows (lahars) • Volcanic Landslides (debris flows and debris avalanches) • Lava Flows • Volcanic Gases

3. Tephra falls • Tephra falls can cause the collapse of roofs and can affect areas far from the eruption. • Tephra falls blanket an area like snow, but are far more destructive • Tephra deposits have a density more than twice that of snow and tephra deposits do not melt like snow.

4. Tephra falls Pumice deposits from the ~13,000 year old Laacher Mt. Baker, WA Tephra falls destroy vegetation, including crops, and can kill livestock that eat the ash covered vegetation. Tephra falls can cause loss of agricultural activity for years after an eruption, a secondary or tertiary effect.

5. Damage to Planes Ash is also a great hazard to airplanes. Ash from the 1982 eruption of Galunggung Volcano in West Java, Indonesia caused engines in two jet airplanes to fail. Both aircraft dropped 25,000 feet before they could get their engines to start again. Ash end St. Elmo's fire entered the cabin and caused damage to the aircraft. Greater than sixty airplanes have been damaged by ash from various volcanic eruptions. Damage can include pitting of wind sheilds which causes them to look foggy. The fuselage, wings, engines, and light covers can also be damaged by ash and are very expensive for the airlines to repair. http://www.earthscape.org/t1/ric01/ric01a.html

6. Damage to Planes • Volcanic eruption clouds cause rerouting, cancellation, and delays in flights which is also expensive for the airlines. • The accumulation of ash can also load down a plane which may cause the plane to rest on its tail. • Ash can also clog airplane engines and cause them to catastrophically fail • Ash on runways is another problem because anytime a plane lands or takes off the ash is resuspended. • http://www.earthscape.org/t1/ric01/ric01a.html

7. Pyroclastic Flows • Ash falls and ash flows: Ash falls can bury the countryside. Ash flows can incinerate towns. • Pyroclastic flows can move very fast. • Small pyroclastic flows can move as fast as 10 to 30 m/s • Larger flows can move at rates of 200 m/s http://www.geology.ohio-state.edu/~vonfrese/gs100/lect10/xfig10_03.jpg

8. Pyroclastic Flows http://www.physorg.com/newman/gfx/news/UIUC31406_1.jpg Pyroclastic flowa have been recored to extend as far as 50 km to 200 km from their source depending on the type of flow They averaged 30 to 50 m thick in others but Pyroclastic flows have been known to top ridges 1000 m high At Mount Pinatubo in the Philipines, pyroclastic flow deposits were 220 m thick

9. Pyroclastic Flows Pyroclastic flows can be very hot. Pyroclastic flows from Mount Pelee had temperatures as high as 1075 degrees C Some Pyroclastic flows from Pinatubo had temperatures of 750 degrees C and pyroclastic flows from Mount St. Helens had temperatures of 350 degrees C Such high temperature flows can burn manmade structures, vegetation, and, for those unlikely enough to be caught by then, human skin.

10. Types of Eruptions St. Pierre in Caribbean was incinerated by an ash flow from Mt. Pelée in 1902. The event killed 40,000 people; only survivor was a prisoner in the dungeon. Pompeii was covered by ash from Vesuvius in 79 A.D.; The town was completely preserved by theash, for archeologists to find in the 19th century. In fact, we can still find the casts of victims. Can also get explosions when water gets into magma chamber and turns to steam

11. Lahars • Lahars (mud flows) are fast-moving slurries made from a mixture of water and ash (the water may come from melting snow on the volcano during the eruption). • Lahars rush down river valleys and wash away or bury everything in their path. http://vulcan.wr.usgs.gov/Imgs/Jpg/MSH/Images/MSH82_lahar_from_march_82_eruption_03-21-82_med.jpg

12. Lahars • Lahars usually travel down valleys. • Velocities varying from 1 m/s to 40 m/s. • Lahars can travel long distances. Some lahars have traveled hundreds of kilometers from their source • The deposits of a lahar that traveled 60 km from its source at Mount Rainier can be found near the large city of Seattle, Washington • Lahars have been known to transport very large boulders. At Mount Pinatubo, boulders measuring 1.5 m long were not uncommon in lahar deposits . The lahars from Nevado del Ruiz transported a boulder with a volume of 208 cubic meters, 300 m downstream . http://vulcan.wr.usgs.gov/Imgs/Jpg/MSH/Images/MSH82_lahar_from_march_82_eruption_03-21-82_med.jpg

13. www.uccs.edu/~geogenvs/ges199/rainier/lahars.htm

14. Historical Lahar • Nevado del Ruiz, Colombiais the northernmost volcano of the Andean Volcanic Belt. It is a stratovolcano. Nevado del Ruiz has been active for about two million years. • Nevado del Ruiz usually generates Plinian eruptions, which produce swift-moving currents of hot gas and rock called pyroclastic flows. These eruptions often cause massive lahars http://www.geo.mtu.edu/volcanoes/hazards/primer/lahar.html

15. Historical Lahar • On November 11, 1985, a small eruption produced an enormous lahar that buried and desolated the town of Armero , causing an estimated 23,000 deaths. • This event later became known as the Armero tragedy—the deadliest lahar in recorded history. Similar but less deadly incidents occurred in 1595 and 1845, consisting of a small explosive eruption followed by a large lahar. • The volcano is part of Los Nevados National Park, which also contains several other volcanoes. The summit of Nevado del Ruiz is covered by large glaciers, although these have retreated significantly since 1985 due to atmospheric warming. The volcano continues to pose a threat to the nearby towns and villages, and it is estimated that up to 500,000 people could be at risk from lahars.

16. Volcanic Landslides • Explosive blast: The blast of an exploding volcano can flatten everything within range. • Slope material can be destabilized and come crashing down. http://www.geocities.com/CapeCanaveral/Hangar/7195/blastt.jpg http://library.thinkquest.org/17457/volcanoes/blast4.jpg http://www.eoearth.org/upload/thumb/e/e6/Mt_st_helens_blast.jpg/200px-Mt_st_helens_blast.jpg

17. Lava Flows • Lava Flows: Basaltic (lava-dominated) eruptions may emit flows that can bury highways and towns. http://volcanoes.usgs.gov/Hazards/What/Lava/lavaflow.html

18. Lava Flows • Lava flows are common in Hawaiian and Strombolian type of eruptions, the least explosive. • Although lava flows have been known to travel as fast as 64 km/hr, most are slower and give people time to move out of the way. • Thus, in general, lava flows are most damaging to property, as they can destroy anything in their path.

19. Poisonous Gas Emissions • Volcanoes emit gases that are often poisonous to living organisms. Among these poisonous gases are: Hydrogen Chloride (HCl), Hydrogen Sulfide (H2S), Hydrogen Fluoride (HF), and Carbon Dioxide (CO2). • In 1984, CO2 gas escaping from the bottom of Lake Monoun, a crater lake in the African country of Cameroon, killed 37 people. • In 1986 an even larger CO2 gas emission from Lake Nyos in Cameroon killed more than 1700 people and 3000 cattle.

20. Types of Volcanic Hazards: • Volcanic Lakes and Gas Releases • Only three lakes in the world are known to contain high concentrations of dissolved gas in their bottom waters: Lakes Nyos and Monoun in Cameroon and Lake Kivu in East Africa. • The release of large quantities of gas from lakes is very rare; however, massive carbon dioxide gas (CO2) releases from Lake Monoun in 1984 (Bulletin v. 9, no. 8) and Lake Nyos in 1986 (Bulletin v.11, no. 8) resulted in the loss of nearly 1,800 lives. http://vulcan.wr.usgs.gov/Glossary/Lakes/description_volcanic_lakes_gas_release.html

23. Lake Nyos • Numerous maars and basaltic cinder cones lie on or near the deeply dissected Mount Oku massif along the Cameroon volcanic line. Two of these crater lakes, Lake Nyos to the north and Lake Monoun to the south (~100 kilometers ESE of Lake Nyos, part of the Bambouto Volcanic Field), have produced catastrophic gas release events. • The 15 August 1984 gas release at Lake Monoun that killed 37 people (Sigurdsson and others, 1987) was attributed to overturn of stratified lake water, triggered by an earthquake and landslide. • The Lake Nyos event on 21 August 1986 caused at least 1,700 fatalities. The emission of around 1 cubic kilometer of magmatic CO2 has been attributed to overturn of stratified lake waters as a result of a non-volcanic process, or to phreatic explosions or injection of hot gas into the lake.

24. Atmospheric Effects • Since large quantities of tephra and volcanic gases can be injected into the atmosphere, volcanism can have a short-term effect on climate. • Volcanic ash can cause reflection of solar radiation, and thus can cause the temperatures to be cooler for several years after a large eruption. • The 1815 eruption of Tambora volcano in Indonesia, was the largest in recorded history.  The year following the Tambora eruption (1816) was called the "year without summer".  Snow fell in New England in July.

25. Atmospheric Effects • Volcanic gases like SO2 also reflect solar radiation.  Eruptions in 1981 at El Chichón Volcano, Mexico, and 1991 at Pinatubo, Philippines, ejected large quantities of SO2 into the atmosphere.   The effects of the El Chichón eruption were masked by a strong El Niño in the year following the eruption, but Pinatubo caused a lowering of average temperature by about 1oC for two years following the eruption. • Volcanic gases like CO2  are greenhouse gases which help keep heat in the atmosphere.  During the mid-Cretaceous (about 90 to 120 million years ago) the CO2 content of the atmosphere was about  15 times higher than present.  This is thought to have been caused by voluminous eruptions of basaltic magma on the sea floor.  Average temperatures were likewise about 10 to 12oC warmer than present.

27. Tsunami • Debris avalanche events, landslides, caldera collapse events, and pyroclastic flows entering a body of water may generate tsunami. • During the 1883 eruption of Krakatau volcano, in the straits of Sunda between Java and Sumatra, several tsunami were generated by pyroclastic flows entering the sea and by collapse accompanying caldera formation.  The tsunami killed about 36,400 people, some as far away from the volcano as 200 km.

28. Famine and Disease • Tephra falls can cause extensive crop damage and kill livestock.  This can lead to famine. • Displacement of human populations, breakdown of sewerage and water systems, cut off of other normal services can lead to disease for years after an eruption, especially if the infrastructure is not in place to provide for rapid relief and recovery.

29. Predicting Eruptions and Decreasing Consequences • If there is enough warning, the region can be evacuated. People must also get out of could fill with lahars. • NOTE: Volcano prediction is much more possible than earthquake prediction. • All we can do with earthquakes is estimate recurrence interval (statistically average time between events). We cannot exactly say when or where an earthquake will occur. But we can with a volcano.

30. Predicting Eruptions and Decreasing Consequences Geologists are able to determine if a volcano is about to erupt, based on several clues: • Ground Deformation • Increase in local seismicity • Changes in Gas Compositions • Changes in Magnetic Field • Changes in Electrical Resistivity • Changes in Heat Flow

31. Predicting Eruptions and Decreasing Consequences Ground Deformation • As magma moves into a volcano, the structure may inflate.  • This will cause deformation of the ground which can be monitored.  • Instruments like tilt meters measure changes in the angle of the Earth's surface. • Other instruments track changes in distance between several points on the ground to monitor deformation. 

32. Predicting Eruptions and Decreasing Consequences Increase in local seismicity • As the magma chamber fills, rocks crack and break, causing small earthquakes. • There may be underground explosions due to the release of gas from the magma.

33. Predicting Eruptions and Decreasing Consequences Changes in Gas Compositions • The composition of gases emitted from volcanic vents and fumaroles often changes just prior to an eruption. • In general, increases in the proportions of hydrogen chloride (HCl) and sulfur dioxide (SO2) are seen to increase relative to the proportion of water vapor.

34. Predicting Eruptions and Decreasing Consequences Changes in Magnetic Field • If a magma body enters a volcano, the body itself will show no magnetism, and • If it heats the surrounding rocks to temperatures greater than the Curie Temperature (about 500oC for magnetite) the magnetic field over the volcano will be reduced.  • Thus, by measuring changes in the magnetic field, the movement of magma can sometimes be tracked.

35. Predicting Eruptions and Decreasing Consequences Changes in Electrical Resistivity • Rocks have resistance to the flow of electrical current which is highly dependent on temperature and water content.  • As magma moves into a volcano this electrical resistivity will decrease.  • Making measurements of the electrical resistivity by placing electrodes into the ground, may allow tracking of the movement of magma.

36. Predicting Eruptions and Decreasing Consequences Changes in Heat Flow – • Heat is everywhere flowing out of the surface of the Earth.  • As magma approaches the surface or as the temperature of groundwater increases, the amount of surface heat flow will increase.  • Although these changes may be small they be measured using infrared remote sensing.

37. REVIEW

38. Definition: • - A vent at which lava, pyroclastic debris (ash and fragments of previously solidified rock), and gas erupt. • - Eruption may build a mountain around the vent. (Mountain is also called a volcano). • - Anatomy of a volcano: see a magma chamber at depth, and a vent to the surface.

39. Where do Volcanoes Occur? • - Rifts (e.g., East African rift) www.imagico.de/pov/earth2.html http://teach.fcps.net/trt20/projects/EKU/plate%20tectonics/tectonic%205.htm

40. Where do Volcanoes Occur? • - Hot spots (e.g., Hawaii; Yellowstone Park)

41. Where do Volcanoes Occur? • - Mid-ocean ridge (but we don't see them)

42. Where do Volcanoes Occur? • - Convergent Margins (the majority of major volcanoes; e.g., the Andes, Japan, Aleutians)

43. Nature of lava: • Characteristics of lava depend on its temperature and viscosity. (viscosity is a measure of the ability of a • fluid to flow; high viscosity means sticky and slow, low viscosity means watery and fast).

44. Nature of lava: • * The higher the temperature of a lava, the lower its viscosity (i.e., the easier it flows) • * The lower the silica content, the lower the viscosity, because silica polymerizes and the chains get • tangled up. So mafic lavas are less viscous than silicic lava. • * The greater the gas content, the lower the viscosity. Frothy lava flows more easily.

45. Nature of lava: • - Typically mafic lava (rich in Mg and Fe, low in silica) is also at high temperature (1100°C). Thus • mafic lavas tend to flow very easily, so basalt flows in widespread thin sheets. • - But silicic lava is also at low temperature (750°C). So silicic lavas are very sticky and plug up • volcanoes, unless they are very gassy.

46. Types of Eruptions • The nature of an eruption depends largely on the type of magma (high viscosity vs. low viscosity) that the volcano erupts.

47. Types of Eruptions • 1) Lava dominated eruption: • * Characteristic of low viscosity eruptions. Basaltic composition. • *If lava has low viscosity, it fountains out easily. You will see lava fountains, lakes and rivers, that flow long distances.

48. Types of Eruptions • 2) Explosive eruptions: • * Characteristic of silicic volcanoes. Sticky, very viscous lava clogs up the vent. Also, these lavas • contain gas (CO2 and H2O) that come out of solution and make bubbles, like the bubbles in a can of soda. Gas pressure builds up and the volcano explodes. • * Result is a cloud of ash that blankets countryside (air fall ash); or an ash flow (nuée ardent) that rushes • down the volcano side at 100 km/h, incinerating everything in its path. • * Ash fall creates a tuff, ash flow creates an ignimbrite (welded tuff).

49. Types of Eruptions • - St. Pierre in Caribbean was incinerated by an ash flow from Mt. Pelée in 1902. The event killed 40,000 • people; only survivor was a prisoner in the dungeon. • - Pompeii was covered by ash from Vesuvius in 79 A.D.; The town was completely preserved by theash, for archeologists to find in the 19th century. In fact, we can still find the casts of victims. • * Can also get explosions when water gets into magma chamber and turns to steam

50. Types of Eruptions • - this happened at Krakatoa (1883); the explosion was heard 3000 km away, and the waves it generatedkilled 40,000 people; great sunsets for a year. • The island exploded with the force of 100 megatons (the Hiroshima bomb was about 20 kilotons). The explosion was heard as far away as Madagascar (2,200 miles). Ash from the explosion rose 50 miles in altitude, into the stratosphere, where it affected weather patterns for the next year. Large amounts of ash which reach the stratosphere can have a cooling effect on weather because the ash remains in the sky and reduces the amount of sunlight reaching the surface. Tsunamis from the explosion were raised to 131 ft, destroying 163 villages along the coast of Java and Sumatra, and drowning 36,000 people. (http://www.windows.ucar.edu/tour/link=/earth/interior/Krakatoa.html&edu=high) • - this happened at Mt. Ste. Helens in 1980 (as much energy as an A-bomb). Flattened the forest like itwas made of toothpicks. Ash mixed with meltwater to create a slurry (lahar) that washed away bridges and houses far away.