In some parts of the ancient resort community of Herculaneum, volcanic debris from the 79 A.D. eruption of Vesuvius accumulated to depths of over 50 feet; the entire mass of rock in this photo—from the floor of the tunnel to the level surface above—is hardened lava from the eruption that covered Herculaneum. As the volcanic debris dried into a form of tufa, it sealed in all kinds of organic material: food, leather and even papyrus scrolls.