Volcanoes I (Junior Cert Geography): Revision Notes

Volcanoes I

Volcanoes

A volcano is a mountain that forms when molten rock (magma) from beneath the Earth's surface erupts through a vent.

Formation of a Volcano:

• Magma is stored underground in a magma chamber.
• Pressure builds up in the magma chamber, forcing the magma to move upwards.
• The magma reaches the surface through a narrow opening called a vent.
• When magma exits the vent, it is called lava.
• The lava cools and hardens around the vent, forming a cone-shaped mountain.

Main Features of a Volcano:

• Magma Chamber: Underground area where magma is stored.
• Vent: The channel through which magma travels to reach the surface.
• Lava: Magma that has erupted onto the Earth's surface.
• Crater: A bowl-shaped opening at the top of a volcano, formed by past eruptions.
• Lava Flow: The spread of lava as it flows out of the vent.
• Ash and Cinder Cloud: A mixture of volcanic ash, dust, and gases ejected during an eruption

Life Cycle of a Volcano

Volcanoes can be classified based on their eruption activity:

• Active: A volcano that erupts regularly.
  • Example: Mount Etna, Sicily.
• Dormant: A volcano that hasn't erupted for a long time but could erupt again in the future.
  • Example: Mount St. Helens, USA, which erupted after being quiet for 120 years.
• Extinct: A volcano that hasn't erupted in recorded history and is not expected to erupt again.
  • Example: Slemish Mountain, County Antrim.

Pacific Ring of Fire

The Pacific Ring of Fire is a horseshoe-shaped zone around the edges of the Pacific Ocean, where many of the world's tectonic plates meet.

• This area is known for its high level of volcanic and earthquake activity.
• The Ring of Fire includes some of the most active volcanoes and frequent earthquakes in the world.
• Examples of Volcanoes in the Ring of Fire: Mount St. Helens (USA), Mount Fuji (Japan), and Mount Pinatubo (Philippines).

Mid-Ocean Ridges

A mid-ocean ridge is an underwater mountain range that forms due to volcanic activity at constructive plate boundaries.

• Formation:
  • Two tectonic plates move apart, due to convection currents, which creates a fissure (crack) in the Earth's crust.
  • Magma rises up through the fissure and emerges on the ocean floor.
  • When the magma contacts seawater, it cools and solidifies, forming new oceanic crust.
  • Over time, multiple eruptions cause the ocean floor to rise and form a ridge of volcanic mountains.
• Mid-Atlantic Ridge:
  • The Mid-Atlantic Ridge is a major example of a mid-ocean ridge, running through the Atlantic Ocean.
  • It formed due to the separation of the North American and Eurasian Plates.
  • In some places, like Iceland, the ridge is so high that it reaches above the ocean surface, forming volcanic islands.