Underneath the modern town of Ercolano near Naples and its much more widely known counterpart, Pompeii, lies the Roman town of Herculaneum. Like Pompeii, Herculaneum was also buried by the eruption of Vesuvius in AD79, but unlike her sister city, buried under tons of falling rock and ash, this roman town was buried under 17m of mud in an instant when it found itself in the path of the volcanoes pyroclastic flow. This lead to a level of preservation unseen anywhere else.
If you are unsure what 17 meters looks like the image in the image on the left we are looking along the old harbour front on the left and the green in the moat would have been the beach and the Mediterranean the big “wall” on the right of the image is the layer laid down by the AD79 eruption.
Accounts of the events point to this being primarily laid down by the first of the six pyroclastic flows that occurred during the eruption. This boiling mass of gasses and rocks was so hot that when it hit the hundreds who were hiding in what are now assumed to be the boathouses along the beach were killed instantly and moments later the flow buried the town.