What is a Volcano?

Beneath the land and water we see on the Earth’s surface lies the outer layers of the Earth’s crust which are broken into massive rock slabs called Plates.

Volcanoes are often found along the edges of these large plates. About 90 percent of all volcanoes exist within the ‘Ring of Fire’ which circles the edges of the Pacific Ocean.

There are about 1,900 volcanoes on Earth that are still considered active. Meaning that they are likely to explode again because they show some level of activity. Many other volcanoes however; lie dormant, showing no current signs of exploding but can become active again in the future. Others are considered extinct – no longer active and no longer likely to explode.

An aerial photograph of a volcano taken by the NASA Earth Observatory.

What is a volcanic eruption?A volcano erupts when hot melted rock (magma), gas and other debris is pushed up through the Earth’s crust.

Volcanoes are essentially vents on the Earths surface from which fiery power in the form of molten rock, debris, and gases can escape from deep within the earth’s core.

Just as when water boils, the magma from deep within the Earth’s core bubbles upwards to where it is held back by the Earth’s crust. In certain places it breaks through the faults in the crust, allowing the hot mass to reach the Earth’s surface and let the heat escape. When thick magma and large amounts of gas build up under the surface, eruptions can be explosive, expelling lava, rocks and ash into the air. Less gas and more viscous (thick flowing) magma usually mean a less dramatic eruption, often causing streams of lava to ooze from the vent.

Volcanoes are more common in some places than others. The mountain-like mounds that we associate with volcanoes are what remain after the material spewed during eruptions has collected and hardened around the vent. This can happen over a period of weeks or many millions of years. Sometimes, flashes of lightning add to the drama of an eruption. Although volcanic lightning is a common occurrence, researchers still do not what causes it. Some believe that static charges are formed by collisions of rock fragments, ash, and ice particles resulting in lightning.

A typical volcanic eruption

How does a volcano erupt?As magma rises,

gases expand and water

becomes steam.

This creates huge pressure.

When the pressure becomes

too great, a volcano erupts.

Eruptions can range from

gentle oozing, to violent explosions.

Different types of eruptions

There are 6

different types of

volcanic eruptions.

Icelandic, Hawaiian,

Valcanian, Plinian,

Pelean and

Strombolian.

1. Plinian Eruptions: Plinian eruptions cause a rapid pyroclastic flow which covers up anything in it’sflow path. Magma, full of gas, erupts sending gas, ash and cinders up to 45 kminto the air in an eruption plume. Ash can drift up to thousands of kilometers and the explosion can cause landslides, mudslides and floods.

2. Hawaiian Eruptions: Hawaiian volcanoes are low-pressure volcanoes. The lava that emerges is thick and slow-flowing. As an example, Mount Kilauea has been erupting since1983.

3. Strombolian Eruptions: Stromboli erupts every 15-30 minutes, shooting out lava blocks and gases.Strombolian eruptions are named after a volcanic island called Stromboli foundin the Mediterranean Sea. Little amounts of thick lava, steam and gas are frequently ejected high in the air.

Common types of eruptions

Volcanic ash

Volcanic ash is deadly. It is hard and

abrasive, like finely crushed glass.

After blasting into the air, it forms an

eruption plume, suffocating people

and animals. The ash, Poisonous gases

& mudslides following an Eruption can

have the greatest impact on people

and the landscape. After an eruption,

gases, ash and heavy smoke blend into

the air. So, when people breathe, they

are suffocated.

Well-known volcanoes

Tavurvur, Papua New GuineaPhotograph by Olivier Grunewald

Tolimán, one of three dormant volcanoes which surround Lake Atitlán in Guatemala. The lake is the deepest lake in Central America and formed 84,000 years old when a volcano exploded and created the caldera. There are more than 30 volcanoes in Guatemala. Only three are active. Photograph by Anne McCormack 

Mount Merapi, IndonesiaPhotograph by John Stanmeyer

Mount Etna, Italy Photograph by Geoff Mackley

White Island, New Zealand. Tourists can take a boat or helicopter to White Island and walk right into this volcano's crater. There are no plants, the air smells like rotten eggs, and bursts of steam from the ground sound like jet engines. What a vacation! Photograph by Paul Chesley 

Popocatepetl volcano, nicknamed "El Popo," MexicoThis volcano was was quiet for almost 70 years. Then, in 1993, it began to rumble, and it's been sending smoke and glowing rocks into the air ever since.Photograph by Sarah Leen 

Karymsky, Russia

Photograph by Klaus Nigge 

Mount Bromo, IndonesiaPhotograph by John Stanmeyer 

People in Indonesia often throw valuables into the volcano such as money, food, even live chickens in offering to the ‘spirits’ they believe live in the volcano. They believe these gifts will keep the spirits happy and keep the volcano from erupting.

Interesting Facts!• Lava erupts at temperatures of up to 1,200 degrees Celcius!

• There are volcanoes on other planets… The gigantic Olympus Mons on Mars is a massive 25km high and is a whopping 600km wide! How cool is that!?

• The Galapagos Islands formed when plates moved over hot spots!

• The main island of Hawaii, an active volcano, is taller than Mt. Everest, if you measure from the ocean floor

• There are 600 active volcanoes on the Earth today

More interesting facts…• The opening at the top of a volcano is called a caldera, from the

Spanish word meaning "pot"

• In 1935, the U.S. Air Force bombed a lava flow headed for the Hawaiian city of Hilo. The flow slowed and stopped, but nobody has been able to prove that the bombs were responsible

• There are no active volcanoes in Australia

• Ancient Hawaiians buried the dead in lava tubes

• Magma comes from the Greek word meaning "dough"

• Some volcanic ash can make soil very fertile and is good for vegetation however, too much can cause devastation to crops and plants

Reference listVolcano Ian Rohr, Blake Education, 2006

Earthquakes and Volcanoes Brian Knapp, Grolier Publishing Company, 2000

Eyewitness Volcano Dorling Kindserly Publishing Company, 1992, 1998

Volcanoes and Thermal Springs Peter J. Meijer, New Holland Publishers, 1998

National GeographicWeb address: http://environment.nationalgeographic.com/environment/natural-disasters/volcano-profile/

Encyclopedia Britannica 2006Web address: http://media-2.web.britannica.com/eb-media/48/4948-004-9AC9A872.jpg

Oxford Reference OnlineWeb Address: http://www.oxfordreference.com/media/images/volcanoes1.jpg

U.S. Department of the Interior, U.S. Geological Survey, Cascades Volcano ObservatoryWeb Address: http://vulcan.wr.usgs.gov/Imgs/Gif/PlateTectonics/Maps/map_plate_tectonics_world.gif