Volcanoes
Chapter 7
Volcanoes of the World
Relationships of Volcanic Activity to Plate Tectonics
Fissure Eruption: Cracks through which Lava Flows
Hot Spots around the World
Magma Types
• What type of Magma influences what type of eruption 1. 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
2. Felsic Magma-Silica Rich (common crust)
Pahoehoe Lava Kalapana Hawaii
Ignited Pahoehoe
More Pahoehoe (solidified)
Basalt and Pumice
Lava can move underground in a Tube forms a lava tube
After cooling crystallize to form rock
Lava-Formation of Lava Trees near Kilauea- Effect of Quenching Lava
Lava-Wahalua Visitor Center in Hawaii Volcanoes National Park engulfed by lava1989
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 Material
Enormous amount of rock fragments, volcanic glass fragments, and volcanic bombs Volcanic Ash (<2mm), Dust (<.25mm) Lapilli- “Little Stones” (<64mm)
Pyroclastic Flow-Ash Cloud over Plymouth On July 27, 1996 from Soufri`ere Hills West Indies
Mount Pinatubo (Phillipines)June 15–16, 1991 Pyroclastic Flow Killed 350 people and destroyed a U.S. military baseNearly 1-ft depth of ash covered buildings over a 40-km radiusHuge cloud of ash 400 km wide into nearly 40 km elevationAffected global climate (cooler summer the nextyear; global temp differences −0.5°C, ~1°F)
Pyroclastic Flows -St. Pierre, Martinique West Indies Destroyed by a from Mont Pele’e 1902 Explosion-A convicted murderer sole survivor
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.
Pyroclastic Flow From Mount St. Helens
Mount St. HelensMount St. HelensMay 18, 1980, erupted after a 120-year dormancyEarthquake (4–5 magnitude)
Lateral blast impacted 19 miles at 1000 km/hMudflows 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
Volcanic Materials - Pyroclastics
Volcanic Ash from Mt. St. Helens
Blocks from Kilauea
Volcanic Breccia at Mt. Lassen
Bombs may form streamline shape in the air from Mt. Kea
Volcanic Bomb
Kilauea threw a 14 ton bomb ½ mile !!!!! Stromboli threw a 2 ton bomb 2 miles!!!
Lapilli (“little stones”)
Types of Volcanoes1. Shield volcanoes
2. Cinder Cones
3. Composite (Stratovolcanoes)
1. Shield Volcanoes and Their Characteristics
Shield Volcano
Very Thin Lava Flows Kilauea in Hawaii
Fluidity of Hawaiian Lavas is evident even after they solidified- Pahoehoe
(Pa hoy hoy) ropy-texture
1. Shield Volcano
Mauna Loa-gentle slope
Hawaii
Mauna Kea Shield Volcano
2. Cinder Cone
Paricutin Mexico pyroclastics flung out vent
Typical Symmetric Form
Stromboli Eruption of October 2005 at night
http://www.volcanodiscovery.com/volcano-tours/stromboli_updates.html
3. Composite or Stratovolcano
Alternating layers of lava and pyroclastics
Two Composite volcanoes of the Cascade Range, Mt. St. Helens and Mt. Rainier before 1980
Mt. St. Helens
April 29, 2007 Mt. Etna (Italy)
Caldera-The magma chamber below a volcano is emptied and the cone collapses and leaves a large basin shaped depression
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
Alaskan EruptionThe Novarupta Volcano
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