Volcanoes Chapter 7. Volcanoes of the World Relationships of Volcanic Activity to Plate Tectonics.

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