Guatemala’s Volcan de Fuego (“fire volcano”) has undergone a complex, violent eruption process over the last few days, resulting in the deaths of at least 25 people, and injuring hundreds more. Three of those that perished were children in what amounts to be the most explosive eruption to take place at the site in more than four decades, and the second eruption this year.

Much of the media’s attention is being paid to an 8-kilometer (5-mile) lava flow that’s reported to have emerged from the ash column-topped edifice, which infiltrated Rodeo village.

The existence of this lava flow is difficult to verify, though. Instead, it appears that it's the pyroclastic density currents (PDCs) are doing the majority of the damage, with reports already coming in of charred, collapsed remains of people. The lava flow appears to be a colloquial reference to these PDCs that's since been misreported.

In one particularly jarring piece of footage, someone films a PDC as it rushes down a valley. Only at the last minute does the cameraperson begin to flee after realizing just how quickly it’s approaching. So what exactly is happening here?

PDCs refer to hot mixtures of ash, gas, lava blebs, and debris that emerge from explosive volcanic activity. They form through a variety of means: when the ash column generated by the eruption becomes denser than the air around it – through cooling or loss of momentum perhaps – and falls down to Earth, for example. The “boiling over” of an eruptive vent, or the collapse of lava domes – viscous masses of lava extruded from a vent – can also do the trick.

When PDCs form, they rush down the slopes of the normally steep side of the stratovolcano they emerge from. The United States Geological Survey (USGS) explains that speeds vary, but 80 kilometers (50 miles) per hour is a good average, meaning you can never outrun them. Internally, they can reach temperatures of between 200°C and 700°C (390-1,300°F).

There is a variety of PDCs. Flows are the most common, but surges also exist when the gas-to-debris ratio is a lot higher. Either way, it’s the PDCs that you’re seeing in plenty of the footage. Getting swept up in one is 100 percent lethal: you’ll either die of extreme heat shock and organ failure, or asphyxiation.

“Pyroclastic flows are not like rivers of lava at all,” Dr Janine Krippner, a volcanologist at Concord University, told IFLScience. For one thing, “pyroclastic flows are much faster and they can engulf valleys rapidly.”

As explained by the USGS, you might also be killed by flying debris. Containing “rock fragments ranging in size from ash to boulders,” they add that “even relatively small flows that move less than 5 km (3 mi) from a volcano can destroy buildings, forests, and farmland.”

Unconsolidated ash, if saturated by rain, can turn into a fast-moving, concrete-like mudflow named a “lahar”, which can sometimes be more deadly than the eruption itself. “Now that this loose pyroclastic material has been deposited on and near the volcano,” the risk of lahar formation is real, Krippner added. 

Elsewhere, volcanic ash is raining down, including on the capital, Guatemala City, located 40 kilometers (25 miles) away from the volcano.

“It is important to remain calm because the Fuego volcano erupts throughout the year,” said David de Leon, spokesman for the National Disaster Prevention Authority, per Reuters.

There are a few other things worth noting here. As tends to happen in these situations, lots of over-hyped reports and footage claiming to be from the eruption in question are being circulated. Do not believe everything you see at face value: check with trusted sources and volcanologists. Real people’s lives hang on the spread of information, whether it’s correct or false.

If anything, this latest eruption reminds us that somewhere in the world, there are nearly two-dozen volcanoes erupting at any given moment. Kilauea and Fuego – two entirely unrelated events, by the way – just happen to be threatening people’s lives.