Mauna Loa eruption: What's happening inside the world's biggest volcano?
- Published
Watch: Spectacular scenes as Hawaii volcano erupts
Mauna Loa - the world's largest active volcano - is erupting for the first time since 1984.
Lava is flowing down the side of the volcano at a temperature of 1,000C, but experts say this does not yet pose a big threat to local inhabitants.
How big is Mauna Loa?
Mauna Loa, which means "long mountain" in Hawaiian, is the largest active volcano in the world.
It covers 2,035 sq miles (5,271 sq km), and is one of a chain of five volcanoes which form Hawaii's Big Island.
This one volcano alone comprises half of the whole island.
Mauna Loa's summit is 13,680ft (4,170m) above sea level, but its base is on the sea floor. From there to the summit is 30,085ft (9,170m), making it taller than Mount Everest.
Why is Mauna Loa erupting?
Plumes of super-heated material called magma have been welling up underneath Mauna Loa and neighbouring volcanoes from a "hotspot" deep within the Earth.
"No one knows exactly why this hotspot exists," says Dr Carmen Solana, a volcanologist at Portsmouth University, "but it may be caused by the decay of radioactive material within the Earth's mantle.
"These plumes of magma formed the whole of the Hawaiian Islands."
When Mauna Loa erupted, says Dr Solana, magma first welled up in the caldera - the bowl-shaped pit at the summit of the volcano. Called Mokuaweoweo, it covers an area of six sq miles (15 sq km) and is 600 ft (180m) deep.
Magma then comes out in fountains from "rifts", or fissures in the rock, on the side of the volcano. Some of these fountains are 40m high.
It flows down the mountainside as liquid lava, which has a temperature of 1,000C.
Lava is also propelled into the air, some of which stretches into thin strands of glass called Pele's hair.
"Pele was the name of the goddess who was said to live on Hawaii, and the shards are wispy and browny-gold in colour," says Dr Solana.
Why is Mauna Loa's eruption important?
Mauna Loa has erupted 33 times since 1843, the date of the first recorded eruption. On average, that it is one eruption every five and a half years.
However, the last eruption was almost 40 years ago.
"There have been some signs of magma welling up over the past 10 years," says Andrew Hooper, a professor of geophysics at Leeds University in the UK, "but there has been no eruption until now."
The current eruption on Mauna Loa is giving a new generation of scientists the chance to study how the volcano works, says Professor Hooper.
A satellite image of lava flowing down the slopes of Mauna Loa
"It will be interesting for us to see where the magma is stored inside Mauna Loa - where it stays in between welling up from the Earth's mantle and coming out from the volcano's surface," he says.
Is Mauna Loa's eruption dangerous?
Unlike many volcanoes, Mauna Loa usually does not produce really explosive eruptions, in which plumes of ash and gas shoot high into the air.
Instead, the lava flows at a fairly slow pace down the volcano's side.
"The lava flows are not life threatening," says Professor Hooper, "because you can get out of the way of them."
"Also, the lava is not going west down the volcano towards the closest towns, but to the north-east. It would have to travel quite a long way in that direction before doing serious damage to property."
However, local people may be more at risk from the gases which Mauna Loa is emitting.
"Volcanic gases, including sulphur dioxide... react with moisture in the air to produce 'vog', which is volcanic fog," says Dr Solana.
"This could cause a problem to people downwind. It could irritate the eyes, and cause breathing problems for some people."
The local health authorities say that air quality is still good, external, but warn that it could get worse.
If it does, local residents are advised to avoid outdoor activities and to stay indoors with doors and windows shut.