Johan Christian Dahl, Eruption of the Volcano Vesuvius, 1821, oil on canvas, 98.3 x 137.5 cm, Statens Museum for Kunst, Copenhagen. Source
When Dahl was visiting Naples in 1821, Mount Vesuvius erupted. The artist was able to sketch the event from (very!) nearby, and he then used these drawings to create a series of oil paintings. This natural phenomenon would have greatly appealed to the Romanticists and their followers.