Types of Volcanoes
This page provides an overview of various volcano types and their characteristics, which is essential for understanding tectonic hazards in A-level geography.
Shield Volcanoes are formed from basaltic rock and have gently sloping cones due to less viscous lava. They are typically found in hot spots and above double oceanic plate boundaries, with gentle and predictable eruptions.
Vocabulary: Basaltic rock - A type of igneous rock formed from cooled lava, typically dark in color and low in silica content.
Cinder Cone Volcanoes are the most common type, characterized by symmetrical cones that may occur as single or secondary cones. They are formed by airborne fragments of lava ejected from the vent, building up layers.
Calderas are formed when gases build up under a blocked vent, resulting in internal eruptions that create huge craters at the summit. They are found on destructive plate boundaries and cause very explosive and unpredictable eruptions.
Example: The Yellowstone Caldera in Wyoming, USA, is one of the largest known calderas in the world.
Acid/Dome Cone Volcanoes have steep sides and form from very viscous lava. They are often found on continental crusts and cause explosive and unpredictable eruptions. The rock type associated with these volcanoes is Rhyolitic.
Composite Volcanoes are the most common on land and are found on destructive plate boundaries. They cause explosive and unpredictable eruptions.
Highlight: Understanding the different types of volcanoes is crucial for revising A-level geography and comprehending the theory of plate tectonics.
The page also mentions volcanic hotspots, which are caused by a concentration of radioactive elements inside the mantle. A plume of magma rises from these hotspots to eat into the plate above, creating an active volcano where lava breaks through.
Volcanic hazards are also discussed, including:
- Ash Clouds: Small pieces of pulverized rock and gas shot into the atmosphere.
- Volcanic Gases: Sulphur dioxide, water vapor, and carbon dioxide emitted from volcanoes.
- Lahars: Volcanic mudflows that usually run down valleys on volcanoes.
- Pyroclastic Flows: Fast-moving currents of super-heated gas and ash, reaching temperatures of 1000°C and traveling at speeds up to 450 mph.
- Volcanic Bombs: Thick viscous lava fragments ejected from the mouth of a volcano.
Definition: Pyroclastic flow - A dense, fast-moving flow of solidified lava pieces, volcanic ash, and hot gases that occurs during certain volcanic eruptions.
