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Soldiers are helping firefighters search for missing people after Sunday's horrific volcanic eruption in Guatemala, when torrents of superheated rock, ash and mud destroyed villages.

The official death toll from the destruction at the Fuego volcano has risen to 69, the authorities say.

Thousands of people are being housed in temporary shelters.

Volcanologists report the eruption, which sent ash up to 10km (33,000ft) into the sky, is now over.

The eruption also generated pyroclastic flows - fast-moving mixtures of very hot gas and volcanic matter - descending down the slopes, engulfing communities such as El Rodeo and San Miguel Los Lotes.

Why did Fuego's pyroclastic flow kill so many?

Fuego's lethal eruption took the form of a pyroclastic flow, the same searing cloud of debris that cooked and choked the city of Pompeii after Mount Vesuvius exploded in 79 AD.

On its surface, a pyroclastic flow looks like a falling cloud of ash. But if you could peer into the cloud, you would find a really hot and fast-moving storm of solid rock, said Janine Krippner, a volcanologist at Concord University who studies pyroclastic flows.

"It's not really like anything else on Earth," Krippner said. People are familiar with avalanches of rock or landslides, but pyroclastic flows move much more quickly, traveling more than 50 miles per hour. The upper part of the pyroclastic flow resembles a grainy sandstorm, but it is filled with hot gases, whose temperatures range from 400 to 1,300 degrees Fahrenheit.

"The bottom [of this cloud] is a jumble of chaotic [lava] rocks. It's large boulders that are breaking up into smaller pieces," Krippner said. "They can knock trees down like matchsticks and destroy houses. They can send cars flying. They're incredibly dangerous.".....

"When you reach the surface with magma, there is a lot less pressure because there's a lot less rock, so the gas comes out," Krippner said. "During a violent eruption, that gas expands rapidly, forming bubbles in the magma. That then explodes, blowing the magma apart like shaking a bottle of coke and then opening the top."

But instead of foam, Fuego released sprays of solid rock.

Krippner said Fuego's latest eruption produced a larger-than-average pyroclastic flow, given it spread more than 10 kilometers downslope of the volcano crater. This may explain why it took so many by surprise.

© CNN
Residents flee El Rodeo village after the Fuego volcano erupted.

    

How exceptional was the eruption?

Fuego is one of Latin America's most active volcanoes. A major eruption devastated nearby farms in 1974, but no deaths were recorded.

Another eruption in February this year sent ash 1.7km (1.1 mile) into the sky.

Sunday's event was on a much greater scale.

This eruption is Guatemala's deadliest such event since 1902, when an eruption of the Santa Maria volcano killed thousands of people.

The death toll from the ongoing eruption of Guatemala's Fuego volcano (Volcano of Fire) climbed to 75 people on Tuesday. The bodies were recovered by search and rescue teams, Guatemala's National Institute of Forensic Studies confirmed, saying that only 23 have been identified so far. It is feared that the number of victims can rise substantially since 192 people still remain unaccounted for.

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