During the destruction of the Roman city Pompeii in 79AD, the neighboring city of Herculaneum was destroyed by lava, but by superheated ash. This ash was over 500 degrees Celcius and coated everything in a superfine coat of carbon. Rather than destroying the city, it supercooked buildings, food, leather, and people into nearly perfectly preserved charcoal covered forms.
The clouds that engulfed the city traveled at 65mph, and so most people of the town died.
Source: The Destruction of Herculaneum: Vesuvius Claimed More Than One Victim