Deadly volcano that's one of the most dangerous on Earth - but scientists can't predict when it will erupt because it's in the middle of a war zone.

Mount Nyiragongo is one of the most dangerous volcanoes in the world - and scientists say it is only a matter of time before it makes the city below a modern day Pompeii.

But they don't know when since, located as it is in the war-torn eastern edge of the Democratic Republic of Congo, the two mile high cauldron of lava is also one of the least well understood.  At the base of Nyiragongo sprawls Goma, a city of an estimated one million people, numbers swelling by the day as villagers from the countryside seek refuge from rebel and government forces.

'Goma,' he told National Geographic magazine, 'is the most dangerous city in the world.'

History suggests he may be right. In 2002 350,000 fled after the volcano shot more than 15million cubic yards of lava into downtown Goma, destroying 14,000 homes and burying buildings to the top of the first floor.

In 1977 lava raced down the mountain at more than 60 miles an hour, the fastest ever observed. Several hundred people died, even though the flow had hardened before it reached the main part of the city.

But both eruptions were mere grumbles compared with the devastation seismologists believe it is ready to unleash.

Nyiragongo has an intricate plumbing system, widespread as the roots of a tree. The recent eruptions hadn't been classic, spouting-out-the-top types, so-called Plinian eruptions, but rather fissure eruptions, like bursting pipes.

In 2002 after the initial seam opened, pressure blew open vents systemwide, shooting out fountains of molten rock, including in the very center of Goma itself.

These images, taken by Carsten Peter, are in the April 2011 issue of National Geographic magazine, available in newsagents now.

Deadly: Mount Nyiragongo is one of the most deadly volcanos on Earth but has barely been studied because of its dangerous location

Photographer Carsten Peter tests the thermal suit that Sims used to get close to the lava lake.

Exploration: A member of the expedition walks on the caldera's cooled lava floor, turned red by the reflected glow of the lake

Twice in recent years Nyiragongo's eruptions have hit the city, destroying homes and sending residents fleeing. But now, seismologists believe, the risk is not just near the city, but directly beneath it.

For the past 20 years the region has suffered nearly constant warfare, including a spillover from the genocide in neighbouring Rwanda.

A fragile, often broken peace is maintained by 20,000 United Nations troops, one of the largest peace-keeping missions in the world.

Aerial view of Mount Nyiragongo, an active volcano in the Virunga Mountains in Virunga National Park.