Volcanoes have been in the news a lot recently, one volcano in particular located in Iceland at the Eyjafjallajökull glacier, which brought Europe's air travel to a halt.  But what is a volcano?  I'm going to try and explain them, but don't forget I'm not a volcanologist.  Volcanology is the study of volcanoes.

The first thing you have to understand is the structure of the earth, there are three layers:-

1. The Crust: The crust is the outer layer of Earth. It is made up of plates about 18 miles thick, these plates sometimes move. It is the bit we live on.
2. The Mantle: The second layer is called the mantle. It is about 1,800 miles thick.
3. The Core: The inner layer is called the core.

Between the Earth's crust and the mantle is a substance called magma which is made of rock and gases.  When plates on the surface collide, one plate slides on top of the other, the one beneath is pushed down.  Magma is squeezed up between the plates.

A volcano is a landform that can take many shapes, but we usually envisage the classic cone shape, a kind of mountain that opens downward into a pool of molten rock (magma) below the surface of the earth.  As pressure builds up it needs to escape somewhere, so it forces its way up “fissures” which are narrow cracks in the earth's crust, so the volcano acts like a giant safety valve.  Gases, rock and magma erupt through the opening and spill over or fill the air with lava fragments and ash.  These eruptions can cause lateral blasts, lava flows, hot ash flows, mudslides, avalanches, falling ash and floods. Volcanic eruptions have been known to knock down entire forests. An erupting volcano can trigger tsunamis, flashfloods, arthquakes, mudflows and rockfalls.

Once the magma erupts through the surface of the earth we call it lava:  Flowing lava ranges from 1,300° to 2,200° F (700° to 1,200° C) in temperature and glows red hot to white hot as it flows.

Volcanic ash, which caused all the recent problems in Europe, is made of pulverized rock, and can be harsh, acidic, gritty, glassy and smelly. The ash can cause damage to the lungs of older people, babies, people with respiratory problems and livestock.

More than 80 percent of the earth's surface is volcanic in origin and gaseous emissions from volcanoes formed the earth's atmosphere. Now there are around 1510 'active' volcanoes in the world, 80 or more volcanoes are under the oceans.   To be considered active a volcano has to have erupted in the last 10,000 years, and have a reasonable chance of erupting in the future.

There are no live volcanoes in the UK, but there are extinct ones, for example Arthur's (Archers) sat in Edinburgh the capital of Scotland is an extinct volcano.  In fact Edinburgh is situated on top of a series of extinct volcanoes.

In the U.S.A volcanoes are found mainly in Hawaii, Alaska, California, Oregon and Washington. The greatest chance of eruptions near areas where many people live is in Hawaii and Alaska. The danger area around a volcano covers about a 20-mile radius. In May 18, 1980, Mount St. Helens erupted in Washington state. It killed 58 people and caused more than $1 billion in property damage.  Rock debris from a lateral blast of Mount St. Helens travelled at around 250 miles per hour.

Some volcanoes are neither alive or extinct, they are dormant.  The May 18, 1980 eruption of Mount St. Helens in the Cascade Range of Washington State happened after more than 100 years of dormancy. When the volcano erupted, it took the lives of 58 people and caused $1.2 billion in damage.

The 1992 eruption of Mount Pinatubo in the Philippines Islands caused 342 deaths and more than 250,000 people had to be evacuated.

Myths and Legends

There are many myths and legends surrounding volcanoes.

The name itself "volcano" has its origin from the name of Vulcan, the god of fire in Roman mythology.

The Legend of Pele

The Native Hawaiians know all about volcanoes. This isn't surprising as Mauna Loa, in Hawaii, is probably the biggest volcano in the world: It rises off of the seafloor to 13,000 feet above sea level or about 29,000 feet above the seafloor.  According to legend, volcanic eruptions were caused by Pele, the beautiful but tempestuous Goddess of Volcanoes. Pele had frequent moments of anger, which brought about eruptions. She was both honoured and feared. She could cause earthquakes by stamping her feet or volcanic eruptions and fiery lava by digging with her Pa'oa, her magic stick.

Pele had a long and bitter argument with her older sister, Namakaokahai. The fight ended by forming the Hawaiian Islands.

First, Pele used her magic stick on Kauai, but she was attacked by her older sister and left for dead. Pele recovered and fled to Oahu, where she dug several "fire pits," including the crater Diamond Head, in Honolulu. After that, Pele left her mark on the island of Molokai before traveling further southeast to Maui and creating the Haleakala Volcano. By then, Namakaokahai, Pele's older sister, realized she was still alive and she went to Maui to do battle. After a terrific fight, Namakaokahai again believed that she had killed her younger sister. But Pele was still alive and she was busy working at the Mauna Loa Volcano, on the big island of Hawaii. Finally, Namakaokahai realized that she could never crush her sister's indomitable spirit and she gave up the struggle. Pele dug her final and eternal fire pit, the Halemaumau Crater, at the summit of the Kilauea Volcano. She is said to live there to this day.

You can read more myths here.

Test your vocabulary with this crossword.