1. Volcanoes
Chapter 7

2. Volcanoes of the World

4. Relationships of Volcanic Activity to Plate Tectonics

5. Fissure Eruption: Cracks through which Lava Flows

6. Hot Spots around the World

8. Magma Types What type of Magma influences what type of eruption
Mafic Magma–Hot and Thin: Magnesium and Iron (common ocean)
Cools Rapidly and crust slowly deforms (Like pudding crust) Ropy Lava and rock called Pahoehoe
Cools Rapidly and crust quickly deforms or is thick forms chunky lava and rock called Aa
Lava Flows out of fissures ocean floor forms blobs and rock called Pillow lava
Gas escapes easily and flows like a river
Felsic Magma-Silica Rich (common crust)

9. Pahoehoe Lava Kalapana Hawaii

11. Ignited Pahoehoe

12. More Pahoehoe (solidified)

13. Basalt and Pumice

14. Lava can move underground in a Tube forms a lava tube
After cooling crystallize to form rock

15. Lava-Formation of Lava Trees near Kilauea- Effect of Quenching Lava

16. Lava-Wahalua Visitor Center in Hawaii Volcanoes National Park engulfed by lava1989

17. Magma Type Influences eruption style
2. Felsic Magma-Silica Rich (common crust)
Large amount of Trapped gases-water vapor and CO2
Explosive! Volcano Ejects Pyroclastic Material (Pyroclastic Flow)
Pyroclastic Material
Enormous amount of rock fragments, volcanic glass fragments, and volcanic bombs
Volcanic Ash (<2mm), Dust (<.25mm)
Lapilli- “Little Stones” (<64mm)

18. Pyroclastic Flow-Ash Cloud over Plymouth On July 27, 1996 from Soufri`ere Hills West Indies

19. Mount Pinatubo
(Phillipines)
June 15–16, 1991
Pyroclastic Flow Killed 350 people and destroyed a U.S. military base
Nearly 1-ft depth of ash covered buildings over a 40-km radius
Huge cloud of ash 400 km wide into nearly 40 km elevation
Affected global climate (cooler summer the next year; global temp differences −0.5°C, ~1°F)

20. Pyroclastic Flows -St. Pierre, Martinique West Indies Destroyed by a from Mont Pele’e 1902 Explosion-A convicted murderer sole survivor

21. Harry Glicken at Mt. St. Helens Observation Site in 1980 before the eruption that blew off the top of the mountain. He is looking toward the bulge on the flank of the volcano. This is the post that when it erupted the observation post was destroyed and the geologist at the site was killed.

22. Pyroclastic Flow From Mount St. Helens Mount St
Pyroclastic Flow From Mount St. Helens Mount St. Helens May 18, 1980, erupted after a 120-year dormancy Earthquake (4–5 magnitude)
Lateral blast impacted 19 miles at 1000 km/h Mudflows reached nearly 100 km (60 miles) away Ash/tephra materials spread over WA, ID, and west MT
Its maximum altitude (peak) reduced by 450 meters (over 1476 ft)
Killed 57 people, damaged 100 homes, 800 million feet of timber: Total cost $3 billion

23. Volcanic Materials - Pyroclastics
Blocks from Kilauea
Volcanic Ash from Mt. St. Helens
Bombs may form streamline shape in the air from Mt. Kea
Volcanic Breccia at Mt. Lassen

24. Volcanic Bomb
Kilauea threw a 14 ton bomb ½ mile !!!!! Stromboli threw a 2 ton bomb 2 miles!!!

25. Lapilli (“little stones”)

26. Types of Volcanoes Shield volcanoes Cinder Cones
Composite (Stratovolcanoes)

27. 1. Shield Volcanoes and Their Characteristics
Very Thin Lava Flows Kilauea in Hawaii
Shield Volcano
Fluidity of Hawaiian Lavas is evident even after they solidified- Pahoehoe
(Pa hoy hoy) ropy-texture

28. 1. Shield Volcano
Mauna Loa-gentle slope
Hawaii

29. Mauna Kea Shield Volcano

30. 2. Cinder Cone Paricutin Mexico pyroclastics flung out vent
Typical Symmetric Form

31. Stromboli Eruption of October 2005 at night

32. 3. Composite or Stratovolcano
Two Composite volcanoes of the Cascade Range, Mt. St. Helens and Mt. Rainier before 1980
Alternating layers of lava and pyroclastics
Mt. St. Helens

33. April 29, 2007 Mt. Etna (Italy)

34. Caldera-The magma chamber below a volcano is emptied and the cone collapses and leaves a large basin shaped depression

35. June 1912 eruption of Novarupta Volcano altered the Katmai area dramatically
the largest eruption in the 20th century
Severe earthquakes rocked the area for a week before Novarupta exploded with cataclysmic force
more than 40 square miles of lush green land lay buried beneath volcanic deposits as much as 700 feet deep !
for two days a person could not see a lantern held at arm's length

36. Alaskan Eruption The Novarupta Volcano

37. Predicting Volcanic Eruptions
Classification by activity: Knowledge of previous eruptions can help predict future
Active:
Dormant:
Extinct:
Volcanic Activity
Small Earthquakes
Temperature changes
Number of Earthquakes
Increase In strength of earthquakes
Bulging at the surface