TIL about “pyroclastic flow.” Imagine the column of gases and ash and pumice pebbles spewing 32km into the air during the eruption of Vesuvius. The column is able to grow that tall because there’s so much upward force behind it, but eventually the sheer mass of the column overwhelms the upward force and it collapses in on itself and comes crashing down. Now, instead of that 400-degree miasma pushing skyward, 32km of hell is pushing down along the ground at 300mph, toward your town. The first victims of Vesuvius died when they took shelter indoors — 18 hours of raining pumice pebbles caved in the roofs of their homes. The other two thirds died when the pyroclastic flow spewed into town, enveloping them in an instant. Nature.