Volcanoes

1. Volcanoes Chapter 10

2. Vent or fissure through which solids, liquids, & gases move to the surface • Vent – straw-like opening through which magma flows • Lava moves radially (in all directions) to produce conical land form

3. Fissure – cracks in ground through which lava moves to surface • Lava travels in 2 directions to make flat landform

4. Cross-section of a volcano

5. Crater – forms when rocks break off at the end of eruption • Flank eruption – eruption from side of mountain (flank opening) • Caldera – when magma is released, a void is left in magma chamber • Volcano sinks (collapsed structure) • Example: Crater Lake, Oregan • Magma/lava – liquid solution of ions @ high temps (800-1100 °C) • O, Fe, Si, Ca, Al, K, Mg, Na

6. Caldera

7. Magma Composition

8. Viscosity • Resistance to flow • The more viscous a substance the slower the flow • Explosive volcano is more viscous than quiet volcano • Temperature: the warmer the lava, the less viscous it is • As it cools it hardens into rock – viscosity increases

9. Silica Content • The more silica the more viscous

10. Dissolved Gases • Gases trapped in mama provide force to eject lava • Mostly water vapor and carbon dioxide • Basaltic magma (thin) allows for bubbling, gases escape • Highly viscous magma doesn’t allow gas to escape, rather it keeps expanding until eruption occurs

11. Pyroclastic Materials • Particles produced in eruption • As gases expand, pulverized rock and lava are blown from vent

12. Volcanic Products • Solids – formed from land material, sharp & irregular shapes • Formed from cooled lava, teardrop & rounded shapes • Ash - <2 mm • Bombs - >64 mm • Bombs – rounded obsidian & basalt • Blocks – blocky (from landforms) hummice • Gases – water vapor (steam), ground water, and any combination of Cl, F, H, oxides of C, and oxides of S (ex. HCl, H2SO4)

14. Gas Flow from Volcano

15. Volcanic Plug • Creates pressure as gas builds up • Pressure can push out plug in one piece or cause the sides to swell out and gas escapes from cracks in side of volcano. • Example: Shiprock, NM

16. Volcanic Landforms • Vents: • Shield volcanoes • Low viscosity basaltic lava • Slopes less than 5 • Most grown from ocean to form islands • Example: Hawaiian Islands & Iceland Mauna Loa, Hawaii, is an excellent example of a shield volcano

17. Cinder Cones • Gas rich, basaltic magma • Composed of mostly loost pyroclastic material • Steep sided slopes (30-40) • Usually product of single eruption • Magma solidifies after eruption • Can form on side of other volcanoes • Examples American Southwest

18. Composite cones (Stratavolcano) • Large nearly symmetrical structure • Composed of layers of lava and pyroclastic material • Gas rich magma with andesitic composition • Low slopes increase toward peak • Mostly located in the ring of fir • Huge amount of pyroclastic material (most explosive) • May generate mudflows called lahars (snow and ice melt or heavy precipitation) Mt. Hood, a beautifully symmetric stratavolcano

19. Lava Dome • Lava is so sticky that it doesn’t flow • Rhyolitic lava, lots of silica • Volcanic plugs are typical • May have multiple flows East Butte, on the eastern Snake River Plain in Southern Idaho (USA), is a rhyolitic volcanic dome

20. Fissures • Lava Plateaus • Rock units are horizontal flows that stack up • Makes large flat plains

22. Volcanoes & Climate Change • As volcanoes erupt, they blast large clouds of gases, particles, water vapor, and aerosols into the atmosphere. As a result, they affect the Earth's atmosphere and global climate. • When large masses of gas from an eruption reach the stratosphere, it can produce a large, widespread cooling effect. This is sometimes referred to as an “Volcanic Winter.” This “winter” occurs because volcanic ash and droplets of sulfuric acid obscure the sun, causing the temperatures to drop. • Here are some examples: • In 1783, Benjamin Franklin blamed the unusually cool summer on volcanic dust coming from Iceland, where the eruption of Laki volcano had released enormous amounts of sulfur dioxide. • The eruption killed much of Iceland's livestock and lead to a catastrophic famine, killing a quarter of the population. Temperatures in the northern hemisphere dropped by about 1 °C in the year following the Laki eruption. • Known as the “year without a summer,” the summer of 1816, unexpected climate changes left countries in the Northern Hemisphere suffering from devastating famine and epidemic outbreaks. These weather patterns were the result of the volcanic eruption of Mount Tambora in Sumbawa, Indonesia, on 10th April 1815. • It snowed in June in the United States and Europe: Crops failed, there was starvation, people lost their farms, and it touched off a wave of emigration that led to the settlement of what is now the American Midwest. In the meantime, hundreds of thousands more starved around the world.  • New England and Europe were hit exceptionally hard. Snowfalls and frost occurred in June, July and August and all but the hardiest grains were destroyed. Destruction of the corn crop forced farmers to slaughter their animals. Soup kitchens were opened to feed the hungry. Sea ice migrated across Atlantic shipping lanes, and alpine glaciers advanced down mountain slopes to exceptionally low elevations. • In 1991 explosion of Mount Pinatubo, another stratovolcano in the Philippines, cooled global temperatures for about 2–3 years, interrupting the trend of global warming which had been evident since about 1970. • Another possible effect of a volcanic eruption is the destruction of stratospheric ozone. • Researchers suggest that ice particles containing sulfuric acid from volcanic emissions may contribute to ozone loss. When chlorine compounds resulting from the breakup of chlorofluorocarbons (CFCs) in the stratosphere are present, the sulfate particles may serve to convert them into more active forms that may cause more rapid ozone depletion.