In February 2013 I headed for Ahualulco’s famous Piedras Bola with a measuring tape in hand, hoping to find a certain stone ball which University of Guadalajara researchers claimed had a diameter of 3.02 meters.
The closest I came to that was a ball measuring 2.86 meters in diameter. Then, in this newspaper, I challenged anyone in the world to find a bigger naturally formed stone ball, called a megaspherulite in geological terms.
In four years I haven’t received a single reply, although I must admit the Reporter may not have a lot of readers in places like Costa Rica or New Zealand – among the few other places in the world where really big megaspherulites have been found.
Now, I am happy to report that what I had been hoping might be a world record has been broken once again by a Piedra Bola from the Ahualulco area.
This story begins with a casual remark by ornithologist Julio Álvarez: “Not all the Piedras Bola are up on the cerro above Ahualulco – there are a few on ranch land belonging to my family ... and they can be reached with no hiking at all.”
This comment resulted in a visit, along with Julio and geologist Chris Lloyd, to a place called El Potrero El Limón. As promised, the first stone ball lay only 99 meters from where Chris parked his truck, hardly a hike, but the four and a half kilometers of brecha from the highway to this spot is so rough and bumpy, I can’t see tourists thronging to visit this place for some time to come.
What might be the biggest natural ball in the world lies half buried in an arroyo which probably turns into a muddy stream during the rainy season. We couldn’t measure its circumference because its widest point is underground, but we could measure the diameter of what protrudes from the earth, which turned out to be 3.9 meters.
After this exciting discovery, we wandered about with Julio, who showed us another dozen stone balls, none as big as the first. Some of these rocks have been split in two, allowing Chris to get a good look at their structure. What he saw convinced him that the origin of these giant balls is still very much in question, even though geologist Robert L. Smith proposed theories back in 1968, when National Geographic Magazine featured the Piedras Bola on their cover. His and other explanations had suggested that the balls were formed by various mechanisms resulting in crystallization around a point deep inside a pyroclastic flow. Now, having looked at several sections of broken Piedras Bola, Lloyd says, “The texture of these great stone balls simply doesn’t support the crystallization theory. There are no radiating or concentric textures … there’s no texture at all – it’s just massive lapilli tuff.”