GEOG 100--Lecture 13--Volcanoes

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  • http://volcano.und.edu/vwdocs/msh/mshindex.html\n
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  • GEOG 100--Lecture 13--Volcanoes

    1. 1. VolcanoesEarth’s Interior in Action!
    2. 2. Volcanism:all phenomena associated with the origin and movement of molten rock ⇐A volcanologist geared up for work
    3. 3. What Constitutes An “Active” Volcano?• Not fully agreed upon among scientists• Intervals between eruptions may be thousands of years• On land, close to 1500 have erupted in the past 10,000 years – Millions, if you count undersea eruptions• Over a thousand active magma systems have been identified on land• An accurate count of the world’s volcanoes remains elusive
    4. 4. Chaiten Volcano (southern Chile)May 3, 2008—Chaiten volcano erupts May 2nd and thousands flee; ash fromthe volcano reaches Esquel, Argentina; last recorded eruption: over 9000years ago (7420 BC ± 75 yrs)
    5. 5. What’s that stuff on the ground?• Lava – Magma that makes it to the surface• Pyroclastic material – When lava erupts into the air and cools quickly, it can form material the size of ash up to large rocks – Any of this solidified lava “spew” is called pyroclastics (pyro = fire; clast = rock)
    6. 6. Eruptions
    7. 7. Eruptions• Whether a volcanic eruption is explosive or mild depends on the type of magma chemistry that is involved.
    8. 8. Eruptions• Whether a volcanic eruption is explosive or mild depends on the type of magma chemistry that is involved.
    9. 9. Eruptions• Whether a volcanic eruption is explosive or mild depends on the type of magma chemistry that is involved. – Felsic = explosive
    10. 10. Eruptions• Whether a volcanic eruption is explosive or mild depends on the type of magma chemistry that is involved. – Felsic = explosive
    11. 11. Eruptions• Whether a volcanic eruption is explosive or mild depends on the type of magma chemistry that is involved. – Felsic = explosive – Mafic = mild
    12. 12. Structures Associated With Extrusive Volcanism
    13. 13. Structures Associated With Extrusive Volcanism
    14. 14. Structures Associated With Extrusive Volcanism• Volcanic peaks
    15. 15. Structures Associated With Extrusive Volcanism• Volcanic peaks
    16. 16. Structures Associated With Extrusive Volcanism• Volcanic peaks• Caldara
    17. 17. Structures Associated With Extrusive Volcanism• Volcanic peaks• Caldara
    18. 18. Structures Associated With Extrusive Volcanism• Volcanic peaks• Caldara• Volcanic neck
    19. 19. Structures Associated With Extrusive Volcanism• Volcanic peaks• Caldara• Volcanic neck
    20. 20. Structures Associated With Extrusive Volcanism• Volcanic peaks• Caldara• Volcanic neck• Flood basalt
    21. 21. Volcanic Peaks
    22. 22. Volcanic Peaks• The type of peak that forms depends on the type of magma
    23. 23. Volcanic Peaks• The type of peak that forms depends on the type of magma – Felsic
    24. 24. Volcanic Peaks• The type of peak that forms depends on the type of magma – Felsic • Forms composite (strato) volcanoes
    25. 25. Volcanic Peaks• The type of peak that forms depends on the type of magma – Felsic • Forms composite (strato) volcanoes – Magmas don’t flow far
    26. 26. Volcanic Peaks• The type of peak that forms depends on the type of magma – Felsic • Forms composite (strato) volcanoes – Magmas don’t flow far – Tall, steep-sided cones
    27. 27. Volcanic Peaks• The type of peak that forms depends on the type of magma – Felsic • Forms composite (strato) volcanoes – Magmas don’t flow far – Tall, steep-sided cones – Mafic
    28. 28. Volcanic Peaks• The type of peak that forms depends on the type of magma – Felsic • Forms composite (strato) volcanoes – Magmas don’t flow far – Tall, steep-sided cones – Mafic • Forms shield volcanoes
    29. 29. Volcanic Peaks• The type of peak that forms depends on the type of magma – Felsic • Forms composite (strato) volcanoes – Magmas don’t flow far – Tall, steep-sided cones – Mafic • Forms shield volcanoes – Magmas flow for long distances
    30. 30. Volcanic Peaks• The type of peak that forms depends on the type of magma – Felsic • Forms composite (strato) volcanoes – Magmas don’t flow far – Tall, steep-sided cones – Mafic • Forms shield volcanoes – Magmas flow for long distances – Broad, gently-sloping cones
    31. 31. Composite Volcano (also called a Stratovolcano) • Felsic magma, tall, steep-sided cone formed of alternating layers of lava flows and pyroclastic materialMount Mayon Philippines, Island of Luzon, province of Albay, Bicol region, 15 km NW of Legazpi City
    32. 32. Shield Volcano• Mafic magma (basaltic), gentle slope (looks like a warrior’s shield laid on the ground) Mauna Loa Shield Volcano
    33. 33. Other Types of Volcanic Peaks
    34. 34. Other Types of Volcanic Peaks• Lava Dome—Formed from felsic magmas, like a bulge on the surface
    35. 35. Other Types of Volcanic Peaks• Lava Dome—Formed from felsic magmas, like a bulge on the surface – Common where previous felsic eruptions have occurred
    36. 36. Other Types of Volcanic Peaks• Lava Dome—Formed from felsic magmas, like a bulge on the surface – Common where previous felsic eruptions have occurred – Material not well fused together (easily eroded)
    37. 37. Lava domeNew lava dome forming inside Mount St. Helens
    38. 38. Other Types of Volcanic Peaks• Cinder Cone – Usually less than 150 ft. high – Associated with flood basalts and shield volcanoes – Frothy, (usually) mafic magma under high pressure at a narrow vent – Tephra rains around the vent, forming small, rounded volcanoes made of ash and cinders
    39. 39. Cinder cones Wizard Island—Crater Lake, OR
    40. 40. Caldera• Collapsed and/or exploded volcanic peak, producing a crater
    41. 41. Long Valley Caldera in California
    42. 42. Volcanic Neck (Shiprock, NM)• Solidified magma within the “neck” of a volcano• Surrounding material may later be eroded away, leaving a tall, standing structure of igneous rock
    43. 43. Flood Basalts (also called Fissure Eruptions)• No dome or cone-shaped structure• Magma flows out of breaks in the crust, usually in high volume, in layers that may be hundreds of feet deep and thousands of miles wide – Deccan Plateau in India • 200,000mi2 – Columbia Plateau, crossing WA, OR, and ID borders • 50,000mi2
    44. 44. Flood BasaltColumbia Gorge, along the Columbia River in the Cascade Mountains of Washington and Oregon
    45. 45. Hazards Associated with Extrusive Volcanism
    46. 46. Hazards Associated with Extrusive Volcanism• Volcanic blast
    47. 47. Hazards Associated with Extrusive Volcanism• Volcanic blast• Earthquakes
    48. 48. Hazards Associated with Extrusive Volcanism• Volcanic blast• Earthquakes• Avalanches and Debris Flows
    49. 49. Hazards Associated with Extrusive Volcanism• Volcanic blast• Earthquakes• Avalanches and Debris Flows• Mudflows and Lahars
    50. 50. Hazards Associated with Extrusive Volcanism• Volcanic blast • Eruption column• Earthquakes and ashfall• Avalanches and Debris Flows• Mudflows and Lahars
    51. 51. Hazards Associated with Extrusive Volcanism• Volcanic blast • Eruption column• Earthquakes and ashfall• Avalanches and • Pyroclastic flows Debris Flows• Mudflows and Lahars
    52. 52. Hazards Associated with Extrusive Volcanism• Volcanic blast • Eruption column• Earthquakes and ashfall• Avalanches and • Pyroclastic flows Debris Flows • Lava flows• Mudflows and Lahars
    53. 53. Hazards Associated with Extrusive Volcanism• Volcanic blast • Eruption column• Earthquakes and ashfall• Avalanches and • Pyroclastic flows Debris Flows • Lava flows• Mudflows and • Volcanic gases Lahars
    54. 54. Volcanic Blast (also called Blowdown)From Mount St. Helens:• A 600ºF blast of rocks, ash, and gases swept across the land at 670 miles an hour• The force of the blast stripped trees from hillsides 6 mi. away
    55. 55. Earthquakes and Debris flows• The movement of magma up through the crust creates earthquakes• The Mount St. Helens eruption began with a magnitude 5.1 earthquake. The entire north flank of the mountain broke loose in three separate blocks, which slid down the mountain at 100 mph.• An avalanche of rock, ice, snow, and soil, like this one, is called a debris avalanche
    56. 56. Debris Flow• Rocks and mounds of debris filled river valleys for 14 miles, as much as 600 feet deep in some places, damming streams and forming new lakes
    57. 57. Mudflows and Lahars• Superheated ash and magmas melt and mix with snow and ice, then speed down the volcano’s flanks – Nevado del Ruiz, Colombia, 1985 – Melted ice and snow mixed with volcanic ash and mud, sending a 130 foot (40 m) high mud-flow down the Lagunilla River
    58. 58. Mudflows and Lahars• Superheated ash and magmas melt and mix with snow and ice, then speed down the volcano’s flanks – Nevado del Ruiz, Colombia, 1985 – Melted ice and snow mixed with volcanic ash and mud, sending a 130 foot (40 m) high mud-flow down the Lagunilla River
    59. 59. Mudflows—Mt. St. Helens• …sloshing from side-to-side as it rushes through forests and clearcuts, ripping trees, houses, and bridges from the ground, devastating downstream environments and communities
    60. 60. Eruption Column and Ashfall
    61. 61. Eruption Column and Ashfall • Can reach the stratosphere, where it is transported long distances
    62. 62. Eruption Column and Ashfall • Can reach the stratosphere, where it is transported long distances • Can block insolation, altering weather and climate
    63. 63. Eruption Column and Ashfall • Can reach the stratosphere, where it is transported long distances • Can block insolation, altering weather and climate • Ash and gases mix with water in atmosphere, producing acid precipitation
    64. 64. Eruption Column and Ashfall • Can reach the stratosphere, where it is transported long distances • Can block insolation, altering weather and climate • Ash and gases mix with water in atmosphere, producing acid precipitation • May produce enough ash to bury the landscape and kill residents
    65. 65. Eruption Column and Ashfall • Can reach the stratosphere, where it is transported long distances • Can block insolation, altering weather and climate • Ash and gases mix with water in atmosphere, producing acid precipitation • May produce enough ash to bury the landscape and kill residents • Can cause electrical failure in jet engines
    66. 66. Mt. Mayon, Island ofLuzon, Phillipeans,1984 Pyroclastic Flows (Nueé Ardant) • Swift, destructive cloud of hot ash and gases that flows rapidly downhill and burns all in its path – Ash weighs down the gases, which would otherwise rise into the atmosphere – Nueé Ardant—French for “glowing avalanche” • Mont Pelée in Martinique
    67. 67. Mt. Pelée, Island of Martinique, CaribbeanMay 8,1902—The town of St. Pierre was obliterated by a nuée ardante; over 28,000 lost their lives
    68. 68. Mt. Pelée, Island of Martinique, CaribbeanMay 8,1902—The town of St. Pierre was obliterated by a nuée ardante; over 28,000 lost their lives St. Pierre today….
    69. 69. Pyroclastic FlowFrom Mount St. Helens:• Within a few hours of the lateral blast, hot mixtures of volcanic gas, pumice, and ash swept down the north flank of the volcano at speeds up to 100 miles an hour and temperatures of over 1200ºF
    70. 70. Soufriere Hills Pyroclastic Flow The Soufrière Hills Volcano, Montserrat, West Indies, began erupting on July 18, 1995.
    71. 71. Soufriere Hills Pyroclastic Flow The Soufrière Hills Volcano, Montserrat, West Indies, began erupting on July 18, 1995.
    72. 72. Lava Flows• Can travel long distances, burning and burying everything• Lava does not need to actually touch an object to set it on fire
    73. 73. Volcanic Gases• Volcanic gases, some of which are colorless and odorless like CO2, can cause suffocation, killing plants, animals, and humans alike
    74. 74. Volcanic Gases• Volcanic gases, some of which are colorless and odorless like CO2, can cause suffocation, killing plants, animals, and humans alike
    75. 75. Volcanic Gases• Such an incident happened at Mammoth Mountain in early 2006, where CO2 emanating from faults at the edge of Long Valley Caldera killed one member of the local ski patrol
    76. 76. Volcanic Gases• Ash and gases (such as SO2—sulfur dioxide) can mix with cloud droplets near the ground to form “vog” (a volcanic fog that causes health problems)• Hydrogen from lava combines with chlorine in sea water to form hydrochloric acid, which becomes airborne as steam, forming corrosive lava haze, or “laze” Hawaiian vog
    77. 77. Hazards Associated with Extrusive Volcanism
    78. 78. Structures Associated With Intrusive Volcanism• Pluton--a massive body of intrusive igneous rock which solidifies deeply within the crust• Batholith • Dike• Laccolith • Sill• Stock • Vein
    79. 79. Intrusive Igneous Structures and Their Formation
    80. 80. Structures Associated With Intrusive Volcanism• Batholith— >40 mi2 (100 km2) in diameter, amorphous, forms deep in the crust – granite often forms batholiths • Sierra Nevada Mountains• Stock—A few mi2 in diameter, amorphous, forms deep in the crust, may be an offshoot of a batholith• Laccolith—Similar to a stock, but intrudes just beneath the surface, warping surface rocks and forming a hill; may form the base of small mountain chains – The Black Hills, South Dakota – Devil’s Tower, WY
    81. 81. Batholiths inWestern North America
    82. 82. Laccolith:Devil’s Tower, WY
    83. 83. Dike

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