For Dionisio Pulido and his family, Feb. 20, 1943 began as an average day of clearing and burning shrubbery from their cornfields near the village of Parícutin, Mexico to prepare for the spring sowing.

Later that afternoon, as Pulido moved to a different field to continue his work, he stumbled upon a small hill that had suddenly appeared. Atop the hill was a shallow crack, six feet wide and 150 feet long.

A number of small tremors had been felt over the previous few days, so Pulido was puzzled but not particularly concerned. He returned to the task of clearing brush.

Then a sound like thunder rolled through the earth. Pulido spun around to see that the hill had lurched upward to a height of more than six feet and was belching gray ash into the air.