Caving in karst country

Underneath the rolling farmland in southeast Minnesota, there's a lot to be learned about soil conservation. If you're not afraid of getting stuck.

Headlamps illuminate a karst-country cave. Contributed photo by Photo by Martin Larsen

BYRON, Minn. — Underneath the rolling farmland in southeast Minnesota, there's a lot to be learned about soil conservation. If you're not afraid of getting stuck.

Living and working in Fillmore County, Shona Snater, soil health organizer for the Land Stewardship Project, said she'd heard stories of "cavers risking their lives and sanity to discover caverns and underground streams" to research the unusual karst geology.

The karst geography of southeastern Minnesota has features like caves, hollows and rolling hills that are formed mostly of limestone. This kind of topography makes water in the area more difficult to protect from contaminants, according to the Minnesota Pollution Control Agency.

"The rumors were verified," said Snater after meeting farmer and caver Martin Larsen, and learning about his caving experience during a LSP soil health learning session.

For the past year, Martin allowed Snater to tag along as they descended into caves that had not been cleaned or shaped for commercial tours. She said that her "fascinating initiation to caving" was at Holy Grail Cave near the Iowa border, which was discovered in 2008 after a storm collapsed the roof of a tall dome.


Snater documented some of her experiences with Larsen is a recent issue of the LSP newsletter.

Exploring a cave requires both physical and emotional strength, said Snater, and "experienced cavers develop a certain walk to navigate the muck-filled tunnels, cutting an edge into the mud with the side of the boot and balancing on the edge of the foot."

"We do not often encounter situations of complete darkness and quiet above ground, and it is unnatural for the body to be under 60 feet of limestone," said Snater. "A subconscious panic starts to creep into the body and eventually the mind, the longer you are literally encased in the crust of the earth."

Snater said her experiences caving were not as extreme as some of Larsen's -- "crawling through pitch-black passages that can be so tight a person has to strip off extra gear and shove it through a pinch point first, before wriggling through themselves."

"I've been stuck for over an hour," said Larsen.

Crawling, he said, makes it unlikely that a spelunker would get stuck so badly they could not get out. Getting badly stuck is more likely while moving vertically through a fissure, which is what he was doing when he got trapped.

"The deeper you go into the fissure, the tighter it gets, and gravity works against you," said Larsen. "It was very painful and physically demanding to move an inch, and I had about 20 feet to get out."

Larsen wears a few hats as a fifth-generation farmer near Byron, staff member with Olmsted County Soil and Water Conservation District and president of the Minnesota Caving Club. His passion in geology has led to him facilitating numerous karst studies, including groundwater dye tracing, spring monitoring and nitrate reduction analysis.


A farmer his whole life, Larson got into caving a little more than five years ago, when he said he was "looking for a new adventure."

He eventually connected with John Ackerman, who he calls "the most active caver in Minnesota." Ackerman is credited with discovering more than 50 caves in southeast Minnesota and for establishing the Minnesota Caving Club and Minnesota Cave Preserve.

Soil health connection

It didn't take long for Larsen to see the impact of activity on top of the ground to what's happening below.

As a conservationist and farmer, he was familiar with surface-level conservation and what it looked like.

"But I was surprised and intrigued at the way these sinkholes function underground and interact with the cave system," said Larsen.

Particularly, Larsen was surprised to see how quickly events on the surface can reach the caves.

"What we see in the water at the surface comes into the caves in a matter of seconds," said Larsen.

With soil health efforts gaining traction, including on his own farmland, Larsen said it has aligned for him to become the caving spokesperson for LSP.


"Soil health and better farming practices on the surface can help our aquifers, drinking water supply and our cave systems," said Larsen.

Farmers are able to watch soil move, said Larsen, but they can't watch nitrates move. An examination below the surface is required.

"Caving gives the unique opportunity to stand 60 to 120 feet below a crop and collect the water coming from the ceiling into the cave," said Larsen. "What happens on the land surface only takes time to move deeper and deeper."

Larsen said that plants grown in row formations are "inherently leaky crops," and they lack the capability to hold nitrates in the rooting zone.

Time and time again, said Larsen, corn and soybeans leach nearly twice the standard for nitrate in drinking water set by the U.S. Environmental Protection Agency.

Cover crops can reduce that by at least 30 percent and up to 60 percent, he said.

"So cover crops are one of the only lights at the nitrate tunnel, because they are proven to reduce nitrates below the rooting zone," said Larsen.

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