How Volcanoes Are Formed

Magma rises through cracks or weaknesses in the Earth's crust.

Pressure builds up inside the Earth.

When this pressure is released, as a result of plate movement for example, magma explodes to the surface causing a volcanic eruption.

The lava from the eruption cools to form new crust.

Over time, after several eruptions, the rock builds up and a volcano forms.


-Resembles a warriors shield 

-Can vary in size- some shield volcanoes can be a few km, whereas some can have a diameter of up to 95 km

-In Hawaii, some have an altitude of 8000 meters above sea floor

which is 12000 above their base.

-Some of the largest Volcanoes on this planet are actually shield volcanoes

-For example, the Mauna Loa, located on Big Island in Hawaii, is the biggest of this type.


  • A shield volcano forms during a lava flow of melted material, usually those that flow from the summit itself. The most common type of shield volcano is those that have formed over a long- term eruption- however some, due to their low- angle slopes have been formed from the collection of lava from multiple eruptions. Because of the variety of how shield volcanoes are formed, they come in many different shapes and sizes. The ones in Iceland, for example, are small in size and symmetrical. However the ones in Hawaii, such as the Mauna Loa, are much larger and broad. The shield volcanoes in the Galapagos Islands differ from both of these, having flat tops and steep middle slopes.

Examples of Shield Volcanoes

Mauna Loa- 4170m asl

Mauna Kea- 4205m asl

Kilauea- 1277m asl

Fernandina- 1476m asl

Rangitoto- 260 m asl

Belknap- 2096m asl

Newberry- 2435m asl

Composite Volcanoes

  • Also known as stratovolcanoes
  • Conical volcano built up by layers of hardened lava and volcanic ash
  • Known for violent and explosive eruptions
  • Lava can continuously flow up to 15km 


  • Constructed from multiple eruptions, sometimes recurring over hundreds of thousands of years, sometimes over a few hundred.
  • Composite cones can grow to such heights that their slopes become unstable and become vulnerable to collapse from the pull of gravity. Famous examples of composite cones are Mayon Volcano Philippines, Mount Fuji in Japan, and Mount Rainier, Washington, U.S.A. 
  •  Some composite volcanoes attain 2000 to 3000 meters in height above their bases. Most composite volcanoes occur in chains and are separated by several tens of kilometres. There are many  composite volcano chains on earth, especially  around the Pacific rim, known as the "Rim of Fire".

Examples Of Stratovolcanoes

  • Mount Cameroon- Cameroon
  • Mount Nyiragongo- Congo
  • Borawli- Ethopia
  • Mount Kenya- Kenya
  • Ol Doinyo Lengai- Tanzania
  • Mount Kilimanjaro- Tanzania
  • Mount Meru-Tanzania
  • Mount Boucherie- North America
  • Mount Bona- Alaska

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by joshmarshallgm


Public - 4/13/16, 8:04 PM