A violent earthquake rocked the coastal Roman city of Pompeii. Miles below the surface, on a bed of liquid fire, the shelf of the Mediterranean Sea collided with the European continent. Sea water followed and formed a steamy, sulphorous gas. Solid rock melted into the liquid fire to become magma. Both the magma and the gas, expanding with tremendous heat and pressure, rose toward the surface and filled a vast chamber that had formed there eons before.

From this chamber, a vent reached up within a volcano that the Romans called Vesuvius, though they thought it nothing more than a peaceful mountain. The occasional Greek or Roman scientist who climbed the steep slopes to the flat summit typically reported nothing of interest. The crater lay hidden, filled to the rim where ancient rock had collapsed, eroded, and given birth to green life over centuries of sleep.

Now, with the collision below the surface, the volcano awoke. The mass of the mountain and the ancient surface material barely suppressed the magma and gas pushing up from below. If the earthquake had been stronger, perhaps more of the debris would have shifted and cleared the vent, allowing the magma and gas to break through.

But the collision ran its course, and the vent remained sealed. The Romans who survived the earthquake mourned their dead, cleaned up the wreckage, and went about their lives, completely unaware that their peaceful mountain was a lethal volcano, and that the volcano was preparing to erupt.