As scientists in a report from the Vesuvius Observatory put it, the initial collapse of the volcanic cloud “billowed through the evacuated town of Herculaneum” at 500°C (about 930°F). Other scientists describe it in much more violent terms than “billow,” especially when the cloud reached the drop-off at the shore.

Several years ago now, I went to a lecture at South Street Seaport where a volcanologist and archaeologist described the passage of the pyroclastic cloud surging through the narrow streets so dramatically, before sending the audience back out into the narrow, cobblestone-paved streets of lower Manhattan, that I’ve had the vision for these panels in my mind ever since.