Short Essay About Volcanoes

A volcano is a mountain with a hole where lava (hot, liquid rock) comes from a magma chamber under the ground.[1]

Most volcanoes have a volcanic crater at the top. When a volcano is active, materials come out of it. The materials include lava, steam, gaseous sulfur compounds, ash and broken rock pieces.

When there is enough pressure, the volcano erupts. Some volcanic eruptions blow off the top of the volcano. The magma comes out, sometimes quickly and sometimes slowly. Some eruptions come out at a side instead of the top.

Volcanoes are found on planets other than Earth. An example is Olympus Mons on Mars.

Volcanologists are scientists who study volcanoes using methods from geology, chemistry, geography, mineralogy, physics and sociology.

Types of volcanoes

The lava and pyroclastic material (clouds of ash, lava fragments and vapor) that comes out from volcanoes can make many different kinds of land shapes. There are two basic kinds of volcanoes.

Shield volcanoes

These volcanoes are formed by fluid low-silicamafic lava.

Shield volcanoes are built out of layers of lava from continual eruptions (without explosions). Because the lava is so fluid, it spreads out, often over a wide area. Shield volcanoes do not grow to a great height, and the layers of lava spread out to give the volcano gently sloping sides. Shield volcanoes can produce huge areas of basalt, which is usually what lava is when cooled.

The base of the volcano increases in size over successive eruptions where solidified lava spreads out and accumulates. Some of the world's largest volcanoes are shield volcanoes.

Even though their sides are not very steep, shield volcanoes can be huge. Mauna Kea in Hawaii is the biggest mountain on Earth if it is measured from its base on the floor of the sea.[2]


A stratovolcano, also known as a composite volcano,[3] is a tall, conical volcano. It is built up of many layers of hardened lava, tephra, pumice, and volcanic ash.

Unlike shield volcanoes, stratovolcanoes have a steep profile and periodic eruptions. The lava that flows from stratovolcanoes cools and hardens before spreading far. It is sticky, that is, it has high viscosity. The magma forming this lava is often felsic, with high-to-intermediate levels of silica, and less mafic magma. Big felsic lava flows are uncommon, but have travelled as far as 15 km (9.3 mi).[2][4]

Two famous stratovolcanoes are Japan's Mount Fuji, and Vesuvius. Both have big bases and steep sides that get steeper and steeper as it goes near the top. Vesuvius is famous for its destruction of the towns Pompeii and Herculaneum in 79 AD, killing thousands.


Main article: Caldera

A caldera is a basin-like feature formed by collapse of land after a volcanic eruption. This happens after a huge stratovolcano blows its top off. The base of the crater then sinks, leaving a caldera where the top of the volcano was before. Krakatoa, best known for its catastrophic eruption in 1883, is much smaller now.[2]

How volcanoes are formed

There are two main processes.

Volcanoes are made when two tectonic plates come together. When these two plates meet, one of them (usually the oceanic plate) goes under the continental plate. This is the process of subduction. Afterwards, it melts and makes magma (inside the magma chamber), and the pressure builds up until the magma bursts through the Earth's crust.

The second way is when a tectonic plate moves over a hot spot in the Earth's crust. The hot spot works its way through the crust until it breaks through. The caldera of Yellowstone Park was formed in that way; so were the Hawaiian Islands.


A traditional way to classify or identify volcanoes is by its pattern of eruptions. Those volcanoes which may erupt again at any time are called active. Those that are now quiet called dormant (inactive). Those volcanoes which have not erupted in historical times are called extinct.


Main article: List of active volcanos

An active volcano is currently erupting, or it has erupted in the last 10,000 years. An example of an active volcano is Mount St. Helens in the United States (US).[5]


A dormant volcano is "sleeping," but it could awaken in the future. Mount Rainier in the United States is considered dormant.[5]


Main article: List of extinct volcanos

An extinct volcano has not erupted in the past 10,000 years.[5]Edinburgh Castle in Scotland is located on top of an extinct volcano.[6]

Some volcanoes

  • Kilauea (Hawaii, USA)
  • Krakatoa (Rakata, Indonesia)
  • Mauna Loa (Hawaii, USA)
  • Mauna Kea (Hawaii, USA)
  • Mount Ashitaka (Japan)
  • Mount Baker (Washington, USA)
  • Mount Edziza (British Columbia, Canada)
  • Mount Etna (Sicily, Italy)
  • Mount Erebus (Ross Island, Antarctica)
  • Mount Hood (Oregon, USA)
  • Mount Fuji (Honshu, Japan)
  • Mount Rainier (Washington, USA)
  • Mount Ruapehu (North Island, New Zealand)
  • Mount Shasta (California, USA)
  • Mount St. Helens (Washington, USA)
  • Novarupta (Alaska, USA)
  • Olympus Mons (Mars (planet))
  • Popocatépetl (Mexico-Puebla state line, Mexico)
  • Surtsey (Surtsey island, Iceland)
  • Santorini (Santorini island, Greece)
  • Tambora (Sumbawa, Indonesia)
  • Teide (Tenerife, Canary Islands, Spain)
  • Vesuvius (Gulf of Naples, Italy)
  • Yellowstone Caldera (Wyoming, USA)

Largest volcano on Earth

The Earth's largest volcano has been discovered.[7][8] It is 2km below the sea on an underwater plateau known as the Shatsky Rise. This is about 1,600km east of Japan. The previous record-holder, Mauna Loa in Hawaii, is still the largest volcano on land.

The 310,000 sq km (119,000 sq mi) volcano, Tamu Massif, is comparable in size to Mars' vast Olympus Mons volcano, which is the largest in the Solar System. It was formed about 145 million years ago when massive lava flows erupted from the centre of the volcano to form a broad, shield-like feature. That suggests the volcano produced a flood basalt eruption.

The Tamu Massif extends some 30 km (18 miles) into the Earth's crust. The researchers doubted the submerged volcano's peak ever rose above sea level during its lifetime and say it is unlikely to erupt again.

"The bottom line is that we think that Tamu Massif was built in a short (geologically speaking) time of one to several million years and it has been extinct since," co-author William Sager, of the University of Houston told the AFP news agency.
"There were lots of oceanic plateaus (that) erupted during the Cretaceous period (145-65 million years ago) but we don't see them since. Scientists would like to know why... The biggest oceanic plateau is Ontong Java plateau, near the equator in the Pacific, east of the Solomon Islands. It is much bigger than Tamu – it's the size of France".[7]

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Wikimedia Commons has media related to Volcano.
Mount Fuji, an active stratovolcano in Japan that last erupted in 1707–08
Parts of a volcano:
1. Large magma chamber
2. Bedrock
3. Conduit (pipe)
4. Base
5. Sill
6. Branch pipe
7. Layers of ash emitted by the volcano
8. Flank
9. Layers of lava emitted by the volcano
10. Throat
11. Parasitic cone
12. Lava flow
13. Vent
14. Crater
15. Ash cloud
Edinburgh Castle on the site of an extinct volcano, c. 1581

A volcano is an opening, in the planet’s surface which allows hot, molten rock, ash and gases to escape from below the surface.

The name, “volcano” originates from the name Vulcan, a god of fire in Roman mythology. Volcanoes are like giant safety valves that release the pressure that builds up inside the Earth. The Hawaii islands were formed by 5 volcanoes.

Classified by the extent of their activity volcanoes are of four types. An ‘active’ volcano is one that erupts regularly. There are about 500 known active volcanoes on Earth, not counting those that lie beneath the sea.

A ‘dormant’ volcano is one that has not erupted for many years, although there is still some activity deep inside it. An ‘extinct’ volcano is one which has ceased to be active.

A volcanic eruption occurs when hot rocks and lava burst from a volcano; and geysers and springs are actually just volcanoes that throw boiling water high in the air. They are caused by volcanic heat warming trapped ground water.

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The liquid rocks inside a volcano are called magma and when it flows out it is called as lava. Fresh lava has temperatures from 700 degrees C to 1200’C and glows red-hot to white hot as it flows. The most dangerous volcanic eruption recorded is the eruption of Mount St. Helens in Washington.

The tallest volcano in the world is the Ojos del Salado, a volcano in Chile. The world’s largest volcano is the Muano Loa in Hawaii.

Volcanoes are generally concentrated on the edge of continents, along the island chain, or beneath the sea forming long mountain ranges. A major part of the world’s active volcanoes above sea level encircle the Pacific Ocean forming the “Ring of Fire.”

Volcanoes can have serious affects on the lands and people around them when they erupt. The destruction they leave in their wake accounts for the total annihilation of the surrounding landscape. Around 2, 00,000 people have lost their lives to volcanic eruptions in the past five hundred years.

Buildings are destroyed, people are rendered homeless, people are killed, plant and animal life are both destroyed and the poisonous gases that emanate from the volcanoes can cause death and diseases like pneumonia in the people who survive it.

However not everything associated with the volcanoes is negative. The crust of the earth exists due to
the large volumes of magma that did not erupt but instead cooled below the surface. It results in rich soil which is good for cultivation.

The volcanic ash that blows out of the volcano increases soil fertility by adding nutrients to the soil. Ground water heated by magma can be tapped for geothermal energy. Most of the metallic minerals like copper, gold, silver, lead and zinc are mined from the magmas found deep within the roots of extinct volcanoes.

With the increasing studies done by scientists on volcanoes it is becoming possible to gauge the activity level of a volcano. With this information although it might not be possible to prevent the erupting of a volcano at least the massive destruction of lives can be avoided by getting people evacuated in time.

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