A mold from Pompeii -- it looks as if this person was praying at the time of death. (istockphoto.com/snem)

Do you know what a pyroclastic surge is? It’s when the boiling column of ash spewing out of a volcano drops and rebounds sideways off the slopes of the volcano like a really scary basketball. And by really scary basketball, I mean a poisonous cloud of debris so scorching hot that it vaporizes your clothes and, more unfortunately, your skin. You’re dead in an instant.

At least that’s what happened to the folks who were hanging out in boathouses on the beach facing Herculaneum in A.D. 79. You’ve probably heard of the massive Mount Vesuvius volcanic eruption that avalanched the wealthy coastal towns of Herculaneum and Pompeii. But did you know that the surge was 932 degrees Fahrenheit and that it boiled beachgoers’ brain tissue? (For more details, read National Geographic, emphasis on “graphic.”)

The cool thing (if you want to call it that) about being vaporized by a pyroclastic surge is that your wet tissues (like your skin and your blood) mix with the ash, and this creates a protective barrier for your bones. So, centuries later, when an archeologist finally happens upon your skeleton, it’s intact and in the same position you were in when the surge hit. For example, researchers who excavated the Herculaneum boathouses can tell that the people died instantly simply by reading their posture.

And that’s what gets everybody about the Mount Vesuvius eruption: the people’s posture. It’s rare that one thing kills so many people at once. And it’s even rarer when each person’s dying moment is preserved like a paw print in sidewalk cement. People who lived in Pompeii weren’t vaporized instantly like the Herculaneum beachgoers. Instead, they suffocated when Mount Vesuvius’s hot ash and poisonous gases deluged their community. The ash that mounted on people’s bodies after they’d died eventually got wet and dried as casts. So even after their clothes, skin and tissues decomposed, detailed imprints of their bodies were hardened into the ash.

And body language speaks louder than words, right? Archeologists pumped plaster into the cavities where the bodies had been, and when those molds dried, they could see these people’s facial expressions. They could tell that a dog tethered by a chain had pulled that chain taut in its struggle to climb out of the mounting ash.

There’s only one firsthand account of the Mount Vesuvius eruption — from a guy named Pliny the Younger who survived the ordeal and wrote: “I admit that I derived some poor consolation in my mortal lot from the belief that the whole world was dying with me and I with it.” So I guess at least there was that.