VOLCANIC eruptions are devastating, life threatening events, yet somehow beautiful. As magma wells to the surface and is propelled into the air, a spectacular show of raw power ensues.

The eruption of Mount Kilauea on the island of Hawaii has prompted a state of emergency in the vicinity. The Hawaiian Islands are positioned above a hotspot under the earth’s crust.

The hotspot is a plume of molten mantle rock that has risen from the depths to lie just underneath the earth’s crust.

The islands form as new molten rock is pushed through the crust into the sea, producing new land.

The Pacific Ocean floor is a gigantic crustal plate moving, slowly but surely, northwest. As the plate moves, the hotspot creates and leaves behind a chain of islands.

The first formed was Kauai, followed by Ohau, then Maui, finally Hawaii, the biggest and newest island. Different types of volcanoes eject different types of rock and this explains different shapes of volcanoes.

The classic cone shape, like Mount Vesuvius in Italy, produces a thick, viscous lava that moves slowly and sticks to the sides of the mountain being formed giving rise to the cone shape.

In Hawaii the lava is thinner, less viscous and produces volcanoes that have a more shield-like shape as the lava travels further, consuming everything in its path. As magma surges through the crust, gasses dissolved under pressure are released.

When magma mixes with cold ground water, it can be explosive, creating spectacular displays of hot lava shooting into the air.

Globs of hot lava, known as lava bombs, can be thrown many miles from the volcano’s crater and it was one of these that hit an unnamed man sitting on his balcony near Mount Kilauea, shattering his lower leg, the only reported human casualty so far.

When lava flows from the volcano crater or rises through fissures in existing rocks it begins to cool, forming a crust. The Hawaiians have interesting names for different types of lava.

Slow flowing lava that flows and folds over itself can produce rope like textures which the locals call “pahoehoe” (pronounced pa-ho-e-ho-e) literally “rope like”. Another has a blocky sharp surface and is called ‘aa’ (pronounced ah-ah).

It’s said it got its name from the pain you experience walking barefooted or in sandals on the surface of the cold solidified lava with razor sharp edges.

When hot lava meets a cold sea, the dissolved gasses form poisonous clouds of acidic gas, mixed with microscopic glass-like fragments of rock. This lava haze, or laze is deadly and can kill in seconds.

Volcanoes aren’t unknown in the UK, but all of ours are extinct. There’s no expectation or reasonable mechanism for the volcano ever to erupt again.

This differs from a dormant volcano, where there has been no evidence of an eruption within the past 10,000 years. Mount Snowdon, the highest mountain in Wales, is an extinct volcano, which was formed after an eruption 450 million years ago.

In Edinburgh, Arthur’s seat is evidence of a massive volcanic eruption 335 million years ago.

Volcanoes have taken take on a mythical status in human history with stories of the anger of “gods” being the cause of eruptions leading to stories of people, usually virgins, being thrown into the crater to appease them.

This is more Hollywood fiction than fact, but human and animal sacrifice to the “gods” who control volcanoes cannot be ruled out.

Our understanding of volcanoes and how they work increases year on year, but like earthquakes they’re a lot harder to predict than the weather.

Some volcanoes do provide warnings of impending eruptions from bulges in the sides of the mountains (as happened with Mt St Helens in 1980) to earthquakes and the venting of gasses, lava and clouds of hot pulverized ash.

Volcanoes produce natural minerals that make soil rich – tempting farmers to plant their crops on the hillsides and to set up villages, towns, even cities and of course there have been historic eruptions that devastated yet preserved communities, such as the hot ash that engulfed Pompeii and Herculaneum in Italy.

The Island of Santorini in the Aegean Sea (which many believe was the site of the Island of Atlantis) saw one of the most devastating eruptions ever recorded.

The fallout spread over 60 miles from the centre, annihilated the population and its infrastructure and sent tsunami waves to Crete and many other islands. Another eruption in 1883 killed an estimated 36,000 people. When the Indonesian island of Krakatoa erupted, it caused the single loudest noise ever recorded on earth.

By James Williams