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There's science behind sticky gumbo soil

There's science behind sticky gumbo soil


Asked to pinpoint the Gumbo Capital of Montana, soil scientist James Bauder is stuck for a response.

But, if you ask him where you could stick a pin in a Montana map and have the highest probability of finding gumbo, he has a ready answer.

"I'd say it would probably be between the Yellowstone River and the Missouri River. I would be inclined to put it somewhere south and in the area of Fort Peck," said Bauder, who has been on the faculty at Montana State University in Bozeman for 28 years.

While Montana's slick gumbo mud has no designated capital, if you hit rain, gumbo isn't all that hard to find in Eastern Montana.

Ideal soil contains equal amounts of sand, silt and clay. Gumbo is pretty much all clay.

Houston black gumbo, a sticky, heavy clay soil, was one of the first soils specifically classified as gumbo by soil scientists, Bauder said.

Ordinary folks are less precise about their mud.

Some Eastern Montanans use the term gumbo and bentonite interchangeably. But bentonite is a specific slick, sticky form of clay with its own unique chemical makeup.

"A soil scientist could tell one from the other," Bauder said.

So could the folks who mine and market bentonite.

Gumbo is the common term for all kinds of sticky dirt, said Bob Stichman, the vice president of sales for Wyo-Ben. The company, with headquarters in Billings, processes sodium bentonite from Wyoming's Big Horn Basin using plants at Lovell, Greybull and Thermopolis, Wyo.

Surface soil is relatively young in geological terms, dating back several thousand years. Bentonite comes from volcanic ash that dates back 100 million years or more. The ash settled in a vast inland sea and underwent specific chemical changes.

Bentonite's commercial uses stem from its ability to glom onto water, absorbing enough water to expand 10 to 12 times its dry size. Water actually becomes attached to the bentonite crystals through an electrochemical reaction.

Commercially, bentonite is used in oil and gas drilling to bind water into a drilling mud. The mud cools the drill bit and carries cuttings out of the drilling hole. Bentonite is also used in pond liners, clumping cat litter, wine clarification and cosmetics.

"None of these applications would be appropriate for gumbo," Stichman said.

Bauder can't recall any commercial uses for gumbo.

"Nobody's ever called me up and said, 'I've got a truckload of gumbo, where can I sell it?' " Bauder said.

But, under the right conditions - like those in North Dakota's Red River Valley - gumbo makes very productive farming soil. The only hitch is that there's a very narrow window for working the soil.

"When the soil is wet, you don't want to be on it. And, when it's dry, it's like working concrete," Bauder said.

In dry years, gumbo trumps some other soils as prairie rangeland because of its ability to hold water.

What happens when water hits gumbo?

Bauder compares it to putting thousands of BB gun pellets configured in the shape of a bowling ball inside a wastebasket and then filling the basket with water. All the spaces between the BB's can hold water.

When rain hits gumbo's surface, the water essentially plugs up the pores on the soil's surface, increasing the time it takes for the water to flow through it.

Why does gumbo get sticky?

Basically, for the same reason adding water to flour creates a sticky dough, Bauder said. Adding water brings out the soil's adhesive properties. Also, soil, in general, has a negative electrical charge and wants to stick to things that are positively charged.

In the case of gumbo, the soil particles are flat, like sheets of paper that slip and slide when wet. When gumbo is wet, some of those particles stick to the surface of your tires or your boots. When the gumbo dries, the bonding force becomes even greater as it hardens on those surfaces.

Jack Horner, a world-class authority on dinosaurs and the curator of paleontology at the Museum of the Rockies has often run across gumbo during field work.

"If you're around Jordan and somebody says there's gumbo out there, they could be talking about mudstone with a lot of volcanic ash in it," he said. "If you're on the other side of the lake by Glasgow and stuck in gumbo, you're probably talking about marine sediments."

Near the landfill in Billings, Horner has run across black shale, a marine shale, as the underlying rock beneath gumbo mud. He associates the Huntley-Shepherd area's gumbo with Bearpaw shale.

When dinosaurs roamed the Earth, Eastern Montana was a very different place. But those dinosaurs definitely encountered mud.

A display at the Museum of the Rockies shows fossil prints from several juvenile brontosaurs and an illustration showing them stuck in mud clear up to their knees. The fossils were unearthed south of Billings in Carbon County, a muddy place that has yielded fossil prints of more than two dozen brontosaurs so far.

"Critters have been getting stuck in the mud around Billings for 150 million years," Horner said.

Then he chuckled, as if he saw some cosmic parable in the story.

The thing about gumbo, Horner said, is that you really can't describe to people what it's like, unless they've been stuck in it.

"You tell them it gets muddy, and they say they've seen mud.'

When you tell them they haven't seen mud like this, they just don't believe you.


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