CIRCLEVILLE, Piute County — Farmers in southern Utah are scratching their heads and trying to figure out what caused an unusual phenomenon in an irrigation pond.
Earlier this week, Gary Dalton of Circleville discovered a mysterious crater that suddenly appeared under the water.
"The sun was just right," Dalton said, "so I saw this blasted thing that no one had ever seen."
He noticed it after most of the water was drained from the pond for irrigation. Just beneath the surface he saw concentric circles in the pond bottom with a diameter of about 25 feet. The outer ring is a circular depression filled with algae. An inner circle looks as though something erupted from beneath, forming what looks startlingly like a small volcanic crater.
"My heck, I guess that's Martian art," Dalton said. "I don't know."
Experts from the Utah Geological Survey took a look and were initially baffled.
"Well, yeah, we've got several theories," said veteran geologist Bill Lund as he examined the pond. "Most of them have gone up in smoke."
Most of the theories were disposed of almost immediately. Some had speculated that the feature was caused by a natural spring, pushing up from under the pond after being supercharged by recent rains. But Lund said that theory was quickly disproved by aerial photos that were taken before the pond was excavated 2 ½ years ago.
"This was an alfalfa field and there was no spring here," Lund said. "It's not a spring."
Another theory was that a buried pipeline had been punctured during construction of the pond. But Lund said there is no pipeline.
Another possibility is that there was a burp of methane gas from decaying organic material under the pond. Lund strongly doubts that theory because the local geology isn't the type that sometimes causes such events.
"If we were in coal country," Lund said, "I'd be thinking about that a little harder but, you know, we're not."
Earthquakes sometimes will cause similar features in sand or mud, due to liquefaction of soils. But Lund ruled that out because there have been no earthquakes in the Circleville area powerful enough to trigger liquefaction.
When Dalton's son Michael was asked what his own pet theory is, he said the obvious: "I have no idea." Another son joked that it was either a volcanic eruption or a Martian landing.
During the geologists' visit, Dalton and his sons maneuvered a platform-lift over the crater to get a closer look.
Although the Daltons saw a fiery meteor in the sky a few weeks ago, Lund has essentially ruled that out as the cause; the sighting took place long before the crater appeared. Also, no one in nearby Circleville reported hearing any loud booms.
"We don't think it's an impact crater," Lund said. "We don't think anything hit there."
Hovering over the crater in the lift, the curious farmers and geologists lowered a tape measure into the crater. The central depression is about 7 inches deep. They were able to push the handle of a pitchfork another 13 inches or so straight down in the soft center.
"Obviously something came up and created this ring," Lund said. "But then it collapsed back on itself and closed off the vent. Whatever the vent was is closed."
From those observations, a leading theory emerged: a geologic condition called collapsible soils. The pond has been drained and refilled more than a dozen times in the last two years. The theory is that the repeated loading of weight on the soil eventually led some of the soil under the pond to collapse, creating a small eruption.
"As it collapsed and compacted," Lund said, "it forced some air and some water up and created this thing. It looks like a one-off thing. It just happened one time. That's it."
That remains the most likely explanation, even though Lund said he has never seen such a phenomenon take place under water.
"I mean there are still some unanswered questions here," Lund said. "That's for sure."
That's probably just as well with the Dalton family. They can still savor some of the mystery while refilling their pond and getting back to the business of growing crops.