Volcanoes

BY: Kristina Scapin

Amy Schneider

Hillary Barter

How are volcanoes formed?How are volcanoes formed?

• One way is in the ‘subduction zones’ (Earth’s crust), which is made up of a series of tectonic plates that move over the molten mantle, which is relative to each other.

• One plate is forced under another when the collision occurs, and it melts while being pushed into the hot mantle.

• Magma is the molten rock which makes its way up to the top while pushing through the crust.

• Some of the magma cools and then is trapped in the crust, but the rest shoots upwards, thus forming the volcano.

When a Volcano erupts…When a Volcano erupts…

• Lava flows- usually they are slow enough so that people can get out of the way.

• Falling Ash- magma breaks into pieces and bursts from the volcano.

• Glowing Avalanches- very hazardous.

• Mud and Debris flows

Hot SpotsHot Spots

• Hot Spots are places on Earth where the crush is heated strongly by the mantle below.

• As the crustal plates move over them, a string of volcanoes begins to develop.

A Volcanic Eruption!A Volcanic Eruption!

• In this photograph, a volcano is erupting. This occurred in Mt. Etna, Sicily.

PahoehoePahoehoe

• Below is a picture of pahoehoe, which is what the lava looks like once the volcano is done erupting.

Lava…Lava…

• In this picture, lava is flowing upwards to the top of the volcano.

3 Main Types of Volcanoes:3 Main Types of Volcanoes:

• Scoria Cone

• Shield Volcano

• Stratovolcano

ScaoriaScaoria• Also called cinder cones.• They are the most common volcano, smallest (height is

usually less then 300 meters)• Composed of ejected basaltic tephra. The tephra

usually contains gas bubbles which gives it a cindery appearance.

• Most cinder cones are symmetrical with straight sides and a very large summit craters.

Shield VolcanoShield Volcano

• These volcanoes are broadly shaped with a width usually around 100 kilometers.

• Its height is usually 1/20th of its width.• Their shape is caused by the extrusion of

basalt lava that spreads over the summit area.• These volcanoes are generated from Hawaiian

eruptions. (They are usually calm eruptions with a steady flow of lava coming out of them.)

StratovolcanoStratovolcano

• Is also called composite cones. • These volcanoes are the ones that many people

recognize.• They are also the most deadly of the volcano types. • The bottom of the volcanoes are not as dangerous as

the tops of stratovolcanos.• Due to lateral blast, some volcanoes contain several

eruptive centers, or a caldera.• Typically, stratovolcanos form convergent plate

margins. (One plate lowers down beneath an adjacent plate in the subduction zone.)

Active VolcanoesActive Volcanoes

• Active volcanoes are ones that have erupted recently or one that volcanologists believe might erupt soon. They are kept at very close watch to ensure the safety of the people and animals in the area.

Dormant VolcanoesDormant Volcanoes

• Also known as sleeping volcanoes, these have been quiet for quite some time but still show signs of erupting.

• A volcano becomes dormant when the vent is blocked by hardened lava, called a plug, or if the magma seeps back under the Earth’s crust.

• A volcano could be dormant for hundreds of years and then suddenly erupt again, usually being very violent.

• The eruption is so violent because the pressure underneath the plug builds up, so the plug gives away and a large eruption occurs. Then the volcano is classified as active again.

Extinct VolcanoesExtinct Volcanoes

• An extinct volcano is one that has not erupted for thousands of years.

• Sometimes it is hard to tell if a volcano is dormant or extinct, so they will be listed as dormant until volcanologists are sure there will be no more eruptions

• Example: Mount Vesuvius in Italy

Famous VolcanoesFamous Volcanoes

• The first recorded Volcano was Mount Etna in Sicily, Italy in 475 B.C. It has erupted 250 times since then. The latest eruption was in 1979 when a new crater opened without warning and erupted.

• Mount Vesuvius in Italy is an extinct volcano, known mostly for it’s destruction. It erupted on August 24, 79 A.D. and 2,000 people died when they were buried under ash and mud. There was no liquid lava, only volcanic ash and volcanic bombs.It has been dormant since 1944 but volcanologists think that it may become active again.

Mt. Vesuvius Erupting

Famous Volcanoes (cont.)Famous Volcanoes (cont.)• In 1902 Mount Pelee on an island off Martinique a volcano

erupted without disaster. It was an old volcano with a crater filled with water.

• The Mexican volcano, Paricutin formed in a cornfield without notice and erupted in 1852 and has been dormant since.

• On May 18, 1980 Mount St. Helens on the coast of Washington erupted for the first time in 120 years. The eruption was as strong as 30,000

• atomic bombs. When it exploded, • a huge area was ripped out from • it’s sides and left a large crater. • The eruption lasted 9 hours. Due • to Volcanologists prediction, many • people had left their homes, • although sixty people were killed.

Mt. St. Helen’s

Famous Volcanoes (cont.) Famous Volcanoes (cont.)

• Mount Fuji is the highest and most sacred mountain in Japan. It is a dormant volcano and last erupted in 1707.

• The largest volcano in the world is in Mauna Loa, Hawaii. It is 30,000 feet above the ocean floor and is 60 miles wide at the base. It has erupted 40 times in the last 150 years.

• The tallest volcanoes are in Chile, South America. • Volcanoes that are always erupting: Stomboli in Italy,

Yasur in the Pacific Ocean, and Erta’Ale in Africa.• Furnace Peak in the Indian Ocean is the volcano that

has erupted the most times in the 20th century, it has erupted 80 times since 1900.

Bibliography Bibliography

• http://www.geology.sdsu.edu/how_volcanoes_work/

• http://www.learner.org/exhibits/volcanoes/• http://www.sciencenet.org.uk/database/earth/

earthscience/g00178d.html• http://www.minerals.co.nz/html/main_topics/

resources_for_schools/volcanoes/volcanoes_world_famous.html

• http://www.groton.k12.ct.us/WWW/fsr/student/Spring02/Volcano/famous_volcanoes.htm

• http://www.famousvolcanoes.netfirms.com/