The death toll from a volcanic eruption in Guatemala continues to rise as family members desperately search for missing loved ones who could be buried in a thick blanket of ash.
The Volcan del Fuego erupted Sunday, hurling ash 4,500 metres above sea level and sending a river of lava and rocks — also known as pyroclastic flow — down the sides of the volcano and engulfing nearby towns.
WATCH BELOW: Father and son drive toward ash cloud to help others after volcanic eruption in Guatemala
Pyroclastic flows are much faster and more deadly than lava, meaning residents who are in the vicinity may not stand a chance of surviving.
“Pyroclastic flows can come out of the volcano at up to 150 kilometres an hour. If it’s coming out, you can’t outrun them. Even in a car … you cannot outdrive them,” Brian Cousens, an associate professor at the University of Carleton’s department of Earth sciences, said.
“A lot of people were caught staring at this … mesmerized by the eruption and didn’t know what the danger was until it started moving downslope — and then it’s too late,” he added.
As of Tuesday, the death toll from the volcano reached 69, with only a fraction of the victims identified.
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Why are are pyroclastic flows so deadly?
Pyroclastic flows are volcanic gas, hot lava blocks, blobs of magma (pumice) and ash, that moves at a very high speed down volcanic slopes.
The flows move fast and “destroy everything in their path,” according to the U.S. Geological Survey (USGS). This is because they have rock fragments ranging in size from ash to boulders that can reach speeds of up to 80 km/h.
“The extreme temperatures of rocks and gas inside pyroclastic flows, generally between 200 C and 700 C, can ignite fires and melt snow and ice,” the USGS said on its website.
WATCH: Hiker captures eruption of Guatemala’s Fuego Volcano on camera
Cousens said because of the rapid speed and high temperature, nothing survives in its path.
“It can knock down trees and buildings. Not much that will stop it,” he said.
The most infamous example of the power of pyroclastic flow was the eruption of Mount Vesuvius in AD 79. That’s when a pyroclastic flow from the volcano buried the Roman cities of Pompeii and Herculaneum.
Pyroclastic flow is also how 30,000 people died in the eruption of Mount Pelee in 1902.
How is it different than Hawaii’s Kilauea volcano?
“Lava flows at a few metres per minute, so you can watch it come. And people in Hawaii had plenty of time to pack and leave,” he said.
WATCH: Eyewitness captures Guatemalan volcano on the morning of eruption
— With files from Reuters