What is a volcano?
A volcano is a conical hill or mountain formed by material from the mantle being forced through an opening or vent in the Earth's crust.
What are the main features of a volcano?
What are active, dormant and extinct volcanoes?
Volcanoes are found in three states - extinct, dormant and active.
- An extinct volcano will never erupt again.
- A dormant volcano has not erupted in 2000 years.
- An active volcano has erupted recently and is likely to erupt again
What are the different types of volcano?
There are a number of different types of volcanoes. The way they are formed depends on a number of factors e.g. the fluidity of the lava (how runny it is) and the temperature of the lava.
Composite
Composite volcanoes, sometimes known as strato volcanoes, are steep sided cones formed from layers of ash and lava flows. Composite volcanoes can rise over 8000 feet. Examples of composite volcanoes include Mount Fuji (Japan), Mount St Helens (USA) and Mount Pinatubo (Philippines).
A simple cross section through a composite volcano
When composite volcanoes erupt they are explosive and pose a threat to nearby life and property.
Shield
Shield volcanoes have gently sloping sides and are formed from layers of lava. Eruptions are typically non-explosive. Shield volcanoes produce fast flowing fluid lava that can flow for many miles. Examples of shield volcanoes include the Hawaiian volcanoes. Although these eruptions destroy property, death or injury to humans rarely occurs.
Dome (Acid Lava Cones)
Acid lava is much thicker than lava which flows from shield volcanoes. Dome volcanoes have much steeper sides than shield volcanoes. This is because the lava is thick and sticky. It cannot flow very far before It cools and hardens. An example is Puy de Dome in the Auvergne region of France which last erupted over 1 million years ago.
Where are volcanoes located?
Volcanoes are found along destructive (subducting) plate boundaries, constructive (divergent) plate boundaries and at hot spots in the earth's surface.
What is the Ring of Fire?
The 'Ring of Fire'is a volcanic chain surrounding the Pacific Ocean. It is formed along a destructive (subducting) plate boundary.
The Earth's Ring of Fire
What are lahars and pyroclastic flows?
The most destructive aspect of volcanoes are lahars and pyroclastic flows. Lahars are volcanic mudflows created when water (from rain or melt water from glaciers) and ash mix. This deadly combination can have devastating results on the surrounding area. When lahars settle they can be metres thick and as hard as cement. Lahars can occur long after a volcanic eruption. Pyroclastic flows are avalanches containing hot volcanic gases, ash and volcanic bombs. On steep volcanoes pyroclastic flows can reach speeds of over 100 miles per hour.
Why do people live close to volcanoes?
- Volcanoes have a wide range of effects on humans. These can be problematic or beneficial. It is usually the destructive nature of volcanoes which is more widely documented. However, many people rely on volcanoes for their everyday survival. Today, many millions of people live close to volcanoes for this very reason.
- People live close to volcanoes because Geothermal energy can be harnessed by using the steam from underground which has been heated by the Earth's magma. This steam is used to drive turbines in geothermal power stations to produce electricity for domestic and industrial use. Countries such as Iceland and New Zealand use this method of generating electricity.
- Volcanoes attract millions of visitors around the world every year. Apart from the volcano itself, hot springs and geysers can also bring in the tourists. This creates many jobs for people in the tourism industry. This includes work in hotels, restaurants and gift shops. Often locals are also employed as tour guides.
- Lava from deep within the earth contains minerals which can be mined once the lava has cooled. These include gold, silver, diamonds, copper and zinc, depending on their mineral composition. Often, mining towns develop around volcanoes.
- Volcanic areas often contain some of the most mineral rich soils in the world. This is ideal for farming. Lava and material from pyroclastic flows are weathered to form nutrient rich soil which can be cultivated to produce healthy crops and rich harvests.
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