Transcript What is a Volcano? - ric0003livingstoneprimaryschool

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no longer active and no longer likely to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.
Common types of eruptions
1. Plinian Eruptions:
Plinian eruptions cause a rapid pyroclastic flow which covers up anything in it’s
flow path. Magma, full of gas, erupts sending gas, ash and cinders up to 45 km
into 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 since
1983.
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 found
in the Mediterranean Sea. Little amounts of thick lava, steam and gas are
frequently ejected high in the air.
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 Guinea
Photograph by Olivier Grunewald
Mount Merapi, Indonesia
Photograph by John Stanmeyer
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 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,"
Mexico
This 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
Mount Bromo, Indonesia
Photograph by John Stanmeyer
Karymsky, Russia
Photograph by Klaus Nigge
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 list
Volcano 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 Geographic
Web address: http://environment.nationalgeographic.com/environment/natural-disasters/volcano-profile/
Encyclopedia Britannica 2006
Web address: http://media-2.web.britannica.com/eb-media/48/4948-004-9AC9A872.jpg
Oxford Reference Online
Web Address: http://www.oxfordreference.com/media/images/volcanoes1.jpg
U.S. Department of the Interior, U.S. Geological Survey, Cascades Volcano Observatory
Web Address: http://vulcan.wr.usgs.gov/Imgs/Gif/PlateTectonics/Maps/map_plate_tectonics_world.gif