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Understanding Volcanic Eruptions and Hazards

Learn about different types of volcanoes, how they erupt, and the hazards they pose. Discover the causes of volcanic activity and the signs scientists look for to predict eruptions. Explore explosive and effusive eruptions, as well as the impact of volcanic ash, pyroclastic flows, and lahars.

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Understanding Volcanic Eruptions and Hazards

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  1. Warm Up • 1. What is an earthquake? • 2. What are the different types of earthquakes? • 3. What are the different types of boundaries? • 4. What are the layers of the atmosphere? • 5. What are the layers of the Earth?

  2. Volcanic Eruptions and Hazards

  3. Mt. St. Helen

  4. What is a volcano? • A mountain or hill, typically conical, having a crater or vent through which molten rock (magma), rock fragments, hot vapor, and gas are or have been erupted from the earth's crust • The volcano includes the surrounding cone of erupted material. vent cone conduit magma chamber

  5. What causes the magma to escape the mantle and come up through the crust of Earth? • Subduction Zone Volcanoes • Remember that subduction happens at convergent plates • Divergent Zone Volcanoes • This results in ridges • Hot Spots • These can pop up anywhere the crust is weak and thin, even in the middle of plates

  6. What are Hotspot Volcanoes? • A hotspot is a location on the Earth's surface that has experienced active volcanism for a long period of time The Hawaiian island chain are examples of hotspot volcanoes. Photo: Tom Pfeiffer / www.volcanodiscovery.com

  7. The tectonic plate moves over a fixed hotspot forming a chain of volcanoes. The volcanoes get younger from one end to the other.

  8. How and why do volcanoes erupt? • Hot, molten rock (magma) is buoyant (has a lower density than the surrounding rocks) and will rise up through the crust to erupt on the surface. • Same principle as hot air rising, e.g. how a hot air balloon works • When magma reaches the surface it depends on how easily it flows (viscosity) and the amount of gas (H2O, CO2, S) it has in it as to how it erupts.

  9. How and why do volcanoes erupt? • Large amounts of gas and a high viscosity (sticky) magma will form an explosive eruption! • Think about shaking a carbonated drink and then releasing the cap. • Small amounts of gas and (or) low viscosity (runny) magma will form an effusive eruption • Where the magma just trickles out of the volcano (lava flow).

  10. Types of Volcanoes • An active volcano is a volcano that has had at least one eruption during the past 10,000 years. An active volcano might be erupting or dormant. • An erupting volcano is an active volcano that is having an eruption... • A dormant volcano is an active volcano that is not erupting, but supposed to erupt again. • An extinct volcano has not had an eruption for at least 10,000 years and is not expected to erupt again in a comparable time scale of the future.

  11. Why do volcanoes stop erupting? all the trapped volatile gasses have degassed and there is no longer sufficient pressure to drive the magma out of the Earth. OR enough heat is lost so that the magma cools and is no longer buoyant

  12. Pacific Ring of Fire Volcanism is mostly focused at plate margins

  13. Ring of Fire • The Ring of Fire has 452 volcanoes and is home to over 75% of the world's active and dormant volcanoes • The Ring of Fire is a direct result of plate tectonics and the movement and collisions of crustal plates

  14. Explosive Eruptions • Explosive volcanic eruptions can be catastrophic • Erupt 10’s-1000’s km3 of magma • Send ash clouds > up to 25 km into the stratosphere • Have severe environmental and climatic effects • Hazardous!!! Mt. Redoubt Above: Large eruption column and ash cloud from an explosive eruption at Mt Redoubt, Alaska

  15. Explosive Eruptions • Three products from an explosive eruption • Ash fall • The fallout of rock, debris and ash • Pyroclastic flow • Pyroclastic flows are hot, turbulent, fast-moving, high particle concentration clouds of rock, ash and gas. • Pyroclastic surge • they don’t have a high concentration of particles and contain a lot of gas Pyroclastic flows on Montserrat, buried the capital city.

  16. Direct measurements of pyroclastic flows are extremely dangerous!!!

  17. Pyroclastic Flow - direct impact Courtesy of www.swisseduc.ch

  18. Pyroclastic Flow - burial

  19. Pyroclastic Flow - burns

  20. Pyroclastic Flow - lahars • Hot volcanic activity can melt snow and ice • Melt water picks up rock and debris • Forms fast flowing, high energy torrents • Destroys all in its path

  21. From above you can see their fine grainsize and the distinctive slight ridges and grooves that show which way the mass of hot dusty air was moving.

  22. Pyroclastic Fall • Ash load • Collapses roofs • Brings down power lines • Kills plants • Contaminates water supplies • Respiratory hazard for humans and animals

  23. Effusive Eruptions • Effusive eruptions are characterized by outpourings of lava on to the ground. Hawaii Courtesy of www.swisseduc.ch

  24. Lava Flow • It is not just explosive volcanic activity that can be hazardous. Effusive (lava) activity is also dangerous. • Lava flows have temperatures in excess of 200 degrees Celsius

  25. How can scientists tell if there is going to be an eruption?

  26. Volcanoes Give Signs • "These signs may include very small earthquakes beneath the volcano, slight inflation, or swelling, of the volcano and increased emission of heat and gas from vents on the volcano," • said U.S. Geological Survey (USGS) Volcano Hazards Program coordinator John Eichelberger.

  27. Deformation Monitoring • “Tiltmeters” are used to measure the deformation of the volcano • The tiltmeters measure changes in slope as small as one part per million. A slope change of one part per million is equivalent to raising the end of a board one kilometer long only one millimeter!

  28. Deformation Monitoring • Tiltmeters can tell you when new material enters the magma chamber. A Note the presence of earthquakes in relation to the deformation. Often it is a combination of events that fore-warns of an eruption. B

  29. Gas Monitoring • Commonly gas output from a volcano increases or changes composition before an eruption. • As magma rises to the surface it releases (exsolves) much of its gas content. • This can be measured

  30. Types of volcanoes: • Composite Volcanoes-are a mixture between shield volcanoes and cone volcanoes, their eruptions are explosive.

  31. Types of volcanoes: • Composite Volcanoes • Shield Volcanoes-are low and flat and have small, flowing eruptions

  32. Types of volcanoes: • Composite (Strato) Volcanoes • Shield Volcanoes • Cinder Cones - Cones are the tallest and largest volcanoes, and they have VERY explosive eruptions.

  33. Types of volcanoes: • Composite Volcanoes • Shield Volcanoes • Cinder Cones • Spatter Cones

  34. Types of volcanoes: • Composite Volcanoes • Shield Volcanoes • Cinder Cones • Spatter Cones • Super (Complex) Volcanoes

  35. In Summary.. • Volcanoes are extremely hazardous. • However, the volcano can be studied, monitored and understood. • Each volcano is different, and offers a unique set of dangers • Plans may be emplaced to help control potential damage.

  36. Post-lecture Question: • What should geologists do about volcanic eruptions in the future? Study volcanoes to find out more about how and why they erupt Monitor the volcanoes Develop hazard mitigation plans Understand the population around volcanoes, i.e. why do people choose to live near volcanoes? Education

  37. Warm Up • 1. What is a divergent boundary? Draw one. • 2. What is a convergent boundary? Draw. • 3. What is subduction? Draw. • 4. What is a transform boundary? Draw. • 5. What is the lithosphere? • 6. What are the layers of the atmosphere?

  38. Earthquakes

  39. Figure showing the distribution of earthquakes around the globe • As with volcanoes, earthquakes are not randomly distributed over the globe • At the boundaries between plates, friction causes them to stick together. When built up energy causes them to break, earthquakes occur.

  40. Where do they happen? • Most often they happen where the plates meet (fault lines) • Sometimes in the middle of the plate where the crust becomes very heavy and drops like a sink hole. Ex: Mississippi River delta

  41. Friction causes the plates to get stuck, building pressure and when the pressure if released, an earthquake occurs. • The point where the earthquake starts is called the focus.

  42. Where do earthquakes form? Figure showing the tectonic setting of earthquakes

  43. Earthquake key terms: • Foot wall: The plate that doesn’t move during an Earthquake. • Hanging wall: The plate that moves during an Earthquake. • Fault plane: The plane along which the break between two plates occurs. • Fault line: The line in the surface of the Earth caused by the fault plane.

  44. How do they move? • 5 ways • Strike-Slip Quake (happen at transform boundaries) • Normal- Hanging wall moves down. (divergent boundaries) • Reverse/Thrust Quakes- hanging wall moves up (convergent boundaries.)

  45. How do they move? • Horst Quakes • A horst represents a block pushed upward by the faulting, and a graben is a block that has dropped due to the faulting. • Graben Quakes

  46. Strike-slip Earthquakes

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