Researchers Say Mystery Of The Mima Mounds May Finally Be Solved

Brett Smith for redOrbit.com – Your Universe Online

The origins of Mima mounds, piles of dirt which can measure around 8 feet high, have baffled scientists for decades. Some have speculated they are Native American burial sites, but human remains have never been found inside the tiny hills.

Now, researchers have found gophers are most likely responsible for the earthen mounds, according to a report presented at the American Geophysical Union Fall Meeting in San Francisco on Monday.

The mounds were first discovered in 1841 in Washington State and have since been found all over the world.

“The big mystery surrounding Mima mounds is that, until now, nobody really knew how they formed,” report researcher Manny Gabet, of San Jose State University, told Rebecca Morelle of BBC News. “Over the past couple of hundred years, people thought they might be Native American burial mounds, or they were caused by earthquakes or glaciers. Some people even suggested extraterrestrials.”

Using computer simulations, Gabet and his colleagues found the structures were actually created by the burrowing actions of gophers. In areas prone to waterlogging, the gophers slowly move small amounts of earth up toward the surface in an attempt to stay dry, the researchers found. Over the course of centuries, the little hillocks slowly form.

“I developed ‘digital gophers’ and had them behave like they do in real life, and to my surprise Mima mounds just started to form in this virtual landscape,” Gabet said. “The (computer) model results look so similar to the mounds in every way – not just the dimensions, but also the way they are packed and how many you get per area.”

“It replicates the real-life situation almost perfectly,” he added.

A description of the report on the AGU website linked the mounds to the evolution of the subterranean mammals.

“Mima mounds are the largest structures built by non-human mammals, and may provide a rare example of an evolutionary coupling between landforms and the organisms that create them,” the description said.

However, gophers are only found in North America – meaning the origins of Mima mounds in other parts of the world are still shrouded in mystery. Gabet said other burrowing mammals, such as moles, could be responsible for the mounds found on other continents.

“Mima mounds in the US are infested by gophers,” he said. “A good place to start would be to dig into these mounds (in other countries) and see what kind of critters are living inside of them.”

The Mima mounds are thought to have been built by pocket gophers, which get their name from the large pouches found inside their cheeks. Weighing around 2 pounds as full-grown adults, pocket gophers use their cheek pouches to transport and hoard food in their burrows. A gopher often announces its presence with a mound of fresh dirt from which it has emerged. These mounds can appear in gardens or lawns, often to the chagrin of homeowners.

Pocket gophers are solitary outside of breeding season and have been known to aggressively maintain their territory. Occasionally, males and females will share the same burrow.