Understanding Volcanoes: Types, Hazards, and Safety Measures

2. Learning Objectives • Explain the relationship of volcanoes to plate tectonics. • Identify the different types of volcanoes and their associated features. • Locate on a map the geographic regions at risk from volcanoes.

3. Learning Objectives, cont. • Describe the effects of volcanoes and how they are linked to other natural hazards. • List the potential benefits of volcanic eruptions. • Discuss how humans can minimize the volcanic hazard. • Recommend adjustments we can make to avoid death and damage from volcanoes.

4. Eyjafjallajökull 2010 Eruption • Iceland home to more than 30 active volcanoes • Volcanic eruption in April 2010 • Ash plume 9.5 km (~6 mi) high • Caused shutdown of airspace throughout Europe • Largest aerial closure since WWII • Increased seismic activity in December 2009 • Future eruptions • 2010 eruption was small taste of what could happen if the more explosive Katla erupts

5. Volcanic Ash Shuts Down Air Travel

6. Fire and Ice

7. 5.1 Introduction to Volcanism • Volcanic activity is directly related to plate tectonics • Most volcanoes are near plate boundaries • Approximately 2/3 of active volcanoes within “Ring of Fire” • At plate boundaries, magma is created • Magma is molten rock • Lava is magma on the Earth’s surface • Volcanoes form around a vent • Not all volcanoes are the same • Different processes in formation • Depends on tectonic settings

8. The “Ring of Fire”

9. How and Where Magma Forms • Most magma come from the asthenosphere • Weak layer of rock that is close to melting temperature • Three principal magma generating processes • Decompression melting • Pressure exerted on hot rock is decreased • Divergent plate boundaries, continental rifts, and hot spots • Addition of volatiles • Chemical compounds that lower the melting temperature of the rock • Subduction zones – responsible for “Ring of Fire” • Addition of heat • Induces melting if temperature exceeds melting temperature • Continental hot spots

10. Magma Formation

11. Magma Properties • Described by silica content and amount of dissolved gasses • Three types of magma based on silica content (low to high) • Basaltic, andesitic, and rhyolitic • Magma less dense than surrounding rock • Rises toward the surface • Accumulates in magma chambers • Composition changes • Viscosity • Volatile content

12. Magma Properties, cont. • Viscosity • Resistance to flow • Affected by temperature and composition • As magma cools, viscosity increases • As silica content increases, viscosity increases • Affects • The flow of lava • Shape of resulting volcano • Correlated to the volatile content

13. Magma Properties, cont. • Volatile content • Determines how explosive the eruption will be • High concentration of dissolved volatiles will explode violently • Volatile-poor magma results in effusive eruptions • Volatile content increases with increasing silica content • Pyroclastic debris • Volcanic materials (like ash) that are explosively ejected

14. Volcano Characteristics

15. 5.2 Volcano Types, Formation, and Eruptive Behavior • Volcanoes vary greatly • Size, shape, composition • Number of eruptions in formation • How and where magma is formed • Amount of magma evolution • Volatile content • Viscosity and volatile content still primary control of eruption explosiveness • Volcanic explosivity index (VEI) • Relative scale to compare exlopsions

16. Volcano Characteristics

17. Volcanoes and Eruption Types

18. Volcanic Explosivity Index (VEI)

19. 5.2 Volcano Types, Formation, and Eruptive Behavior, cont. • Stratovolcanoes • Known for beautiful conical shapes • Result of high viscosity magma • Lava does not flow far resulting in steep sides • Mixture of explosive activity and lava flows • Produce combination of lava flows and pyroclastic deposits • Also called composite cones • Can be extremely explosive • Responsible for over 80% of eruptions • Responsible for most of the death and destruction • Common in the “Ring of Fire” • Examples: Mount St. Helens and Mount Rainer in United States, Mount Fuji in Japan

20. Stratovolcano

21. 5.2 Volcano Types, Formation, and Eruptive Behavior, cont. • Lava Domes • Small dome with steep sides • Often form in the vent of a stratovolcano after an explosive eruption • Can grow in single event or over decades • Made from highly viscous magma • Exhibit highly explosive eruptions • Common in the “Ring of Fire” • Examples: Mount Lassen in CA, Mt. Unzen dome in Japan

22. Lava Dome

23. 5.2 Volcano Types, Formation, and Eruptive Behavior, cont. • Shield Volcanoes • Largest volcanoes in the world • Thin lava flows build up volcano with gentle slopes • Wider than they are tall • Still among tallest mountains on Earth (measured from bases) • Associated with basaltic magma • Low viscosity, low volatile content • Gently flowing lava with non-explosive eruptions • Develop a cladera • Common at hot spots in the oceanic lithosphere and divergent plate boundaries, continental rifts • Hawaiian Islands, Iceland, and in the East African Rift • Examples: Mauna Loa and Kilauea in Hawaii

24. Shield Volcano and Volcano Dimensions

25. 5.2 Volcano Types, Formation, and Eruptive Behavior, cont. • Cinder Cones • Cone shaped with summit crater • Built from an accumulation of tephra • Small pieces of black or red lava • Formed when lava meets groundwater • Associated with basaltic eruptions • Low to intermediate explosivity • Also called scoria cones • Common on larger volcanoes, normal faults, or along cracks and fissures • Examples: SP Crater in AZ, Parícutin in Mexico, Eldfell in Iceland

26. Cinder Cone

27. 5.2 Volcano Types, Formation, and Eruptive Behavior, cont. • Continental Caldera • Large summit depression • Collapse of the land surface or volcanic edifice • Associated with rhyolite eruptions • Violent explosions • ultra-Plinian extrude a great deal of pyroclastic debris on mainly ash • Largest known as the supervolcanic type • Very rare • Examples: Mount Mazama (Crater Lake), Yellowstone caldera

28. Large Calderas Form by Explosion and Collapse

29. Crater Lake Caldera

30. Ash Fall Hazard

31. 5.3 Geographic Regions at Risk from Volcanoes • Direct volcanic risk • Ring of Fire: surrounds Pacific Ocean basin • Hot spots: Hawai’i and Yellowstone Park • Mid-ocean ridges: Iceland • Rift valleys: East Africa • Indirect volcanic risk • Ash fall and ash clouds: all locations in path

32. United States Volcanic Hazards

33. 5.4 Effects of Volcanoes • 50 to 60 volcanoes erupt each year worldwide • In the United States, 2 to 3 per year, mostly in Alaska • Most eruptions are in sparsely populated regions • 500 million people live close to volcanoes • Japan, Mexico, Philippines, and Indonesia and several U.S. cities are vulnerable • Primary Effects • Lava flows, ash fall, pyroclastic flows, lateral blasts, and release of volcanic gases • Secondary Effects • Debris flows, mudflows, landslides or debris avalanches, floods, fires, and tsunamis • Global cooling of the atmosphere in a large eruption

34. Selected Historic Volcanic Events

35. Locations of Volcanoes in the United States

36. Lava Flows • One of most familiar products of volcanic activity • Results when magma reaches the surface through crater or from a vent • Three types: basaltic, andesitic, rhyolitic • Basaltic is the most abundant • Can form lava tubes • Can move slowly or more rapidly • Basaltic lavas are the most rapid at 15–35 km/h (10–30 mph) • Pahoehoe lavas are smooth and ropey • AA are blocky flows • Move slow enough for people to get out of the way

37. Lava Flows

38. Lava Tubes

39. Pyroclastic Activity • Explosive volcanism that blasts magma and rocks from a vent • Known as tephra • Fine dust to sand-sized ash (less than 2mm) • Small gravel-sized lapilli (2 to 64 mm) • Large angular blocks and smooth-surfaced bombs (greater than 64mm) • Falls cool and lightly like snow or hat, fast, and heavy like a freight train • Accumulation forms a pyroclastic deposit

40. Pyroclastic Activity

41. Pyroclastic Activity, cont. • Ash Fall • Explosive fragmentation of magma during an eruption • Can cover hundreds or thousands of square kilometers • Direct hazards • Vegetation may be destroyed • Surface water may be contaminated by sediment • Fine particles clog the gills of fish and kill other aquatic life • Ash accumulation on roofs may cause structural damage • Irritation of the respiratory system and eyes • Engines of jet aircraft may “flame out”

42. Volcanic Tephra on Buildings

43. Pyroclastic Activity, cont. • Pyroclastic Flows • One of the most lethal aspects of volcanic eruptions • Hot and race down side of volcano at speeds exceeding 400 km/hr (~250 mph) • Hot expanding gases carry low-density ash upward • Base of flow contains larger debris • Also known as ash flows, hot avalanches, or “glowing clouds” • Catastrophic if populated area in path • Responsible for more deaths than any other hazard • Formation • Large ash-generating eruptions (VEI>3) • Lateral blasts: explosion destroys part of the volcano • Lava dome collapse: most common

44. Pyroclastic Flow

45. Plaster Casts of Volcano Victims

46. Poisonous Gases • Emitted gases • Carbon dioxide and water vapor account for 90 percent of emissions • Carbon dioxide gas is odorless and heavy • It can accumulate suffocating people • Sulfur dioxide • Can produce acid rain • Others: carbon monoxide and hydrogen sulfide • Toxic concentrations rarely reach populated areas • Chemicals can contaminate soil and plants • Can cause air pollution known as vog (volcanic smog)

47. Debris Flows, Mudflows, and Volcanic Landslides • Also known as lahars • Loose volcanic ash becomes saturated with water, becomes unstable, and moves down volcano • Can occur in the absence of an eruption • Debris flows • Glaciers and ice are melted by volcano and mix with sediment and rock • Similar to wet concrete

48. Debris Flows, Mudflows, and Volcanic Landslides, cont. • Mud flows • Finer than debris flows • Populous areas of Pacific Northwest are built on old mudflows • Not unlikely for new flows to occur • Landslides • May be triggered outside of an eruption • May affect areas far from their source • Can cause tsunamis

49. Volcanic Mudflow Catastrophe

50. Mount Rainier Volcanic Hazard Map