May 30, 2022 – Hutchinson, Kansas
In addition to the Cosmosphere, a world-class space science museum, the city of Hutchinson, Kansas, features another prominent attraction: the only salt mine in the country that’s open to the public. Have I got your attention yet? Read on!
Formerly known as the Kansas Underground Salt Museum, Strataca is owned by the Hutchinson Salt Company, which began operations in 1923 as the Carey Salt Company. Nancy and I visited Strataca in late May 2022.
The salt extracted from the mine is not the type that you’ll find in your kitchen salt shaker. There are a number of impurities in the mineral, which makes it ideal for managing icy roads and for feeding livestock.
Strataca’s story begins, as do all of the good ones, in the late part of the Paleozoic Era, known as the Permian Period, about 275 million years ago. Kansas, along with much of the rest of present-day North America, was covered by a vast inland sea. The waters eventually receded, leaving behind an immense deposit of salt that, over tens of millions of years, was covered with layers of shale and other sediments like sand, gypsum, and silt. That 275-million-year-old deposit of salt is now 650 feet below the Kansas prairie.
The museum has been at this location on the east side of Hutchinson since 1986. Of the 15 salt mines in the United States, Strataca (née the Kansas Underground Salt Museum; the name was changed in 2013) is the only one that is open for visitor tours. I’m trying to remember to take pictures of the exteriors of the museums we see; it seems that the American flags are flying at half-mast more often than not. We visited Strataca on Memorial Day.
A double-deck elevator takes two sets of up to 15 people each on a four-minute trip 650 feet down into the bowels of the earth. (It’s not really the bowels of the earth; the top crust of the earth, which makes up about 1% of the radius of our planet, has an average thickness of nine to 12 miles. In other words, the 650-foot elevator ride takes visitors down about 1% of 1% of the earth’s radius. Still, the elevator ride is pretty neat!)
Excavating the shaft for this visitor elevator was no mean feat. In addition to penetrating hundreds of feet of sedimentary rocks, the shaft also had to descend through part of the Ogallala Aquifer – one of the world’s largest natural underground reservoirs. The aquifer is about 130 feet thick at the site of the museum. To construct the shaft, engineers used liquid nitrogen to freeze the area of the aquifer immediately surrounding the planned shaft, then excavated the ice and replaced it with a concrete liner. The process was completed in 15-foot increments, and took just over a year between March 2004 and March 2005.
Upon exiting the elevator, visitors enter a large chamber filled with interesting exhibits that tell the wondrous story of sodium chloride (NaCl). As you can see, every visitor has to wear a hard hat. I jostled my way to get a blue one. The temperature in the mine year-round is 68 degrees Fahrenheit, with a relative humidity of 45%.
Let’s go back topside for a moment. This map, located in the museum’s visitor center, shows the extent of the mine (in yellow) with the rest of the city of Hutchinson to the west (left). The 1.5-square-mile mine is immense; if each of the excavated areas was lined up in a straight line, the chamber would extend for 150 miles. Pillars of solid rock salt, 40 feet square, are left to separate each chamber and support the upper level of salt.
Okay, back down
into the bowels of the earth 650 feet below the surface. Here’s a closeup of the salt deposit. As you can see, it’s quite different from the Morton’s that’s in your kitchen cabinet. The sodium chloride is mixed with a number of other minerals, including shale and sulfur compounds, which is why it’s primarily used to de-ice roadways.
The year 2023 will mark a century of mining by the Hutchinson Salt Company (formerly Carey Salt). It mines in the room and pillar process. This involves excavating, with the use of explosives, large chambers alternating with square pillars, measuring 40 square feet, that support the upper level of the mine. The process results in something of a checkerboard pattern, if it could be viewed from above. The mine’s chambers are very large, ranging from 2,500 to 15,000 square feet in size, with ceiling heights of 11 to 17 feet. The room and pillar method differs from traditional precious metal mining, in which miners follow the vein of gold or silver ore, for instance (unless it’s more cost-efficient to simply take an entire mountain apart, which seems to be happening more often).
Strataca has retained a lot of Carey Salt’s equipment from the early days of the mine (I’m guessing partly because it would cost time and money to return them to the surface, but it’s still fun to see the specialized equipment). The machinery is fairly well-preserved, considering the relatively high humidity; the salt can’t be good for metal parts, though. This machine was used to cut long slits at the bottom of a salt wall; when explosives in the wall were detonated, the slit ensured that the salt fragments fell forward into the chamber.
The excavation takes place in much the same way today, but using modernized equipment. The rock salt fragments are transported via conveyors to crushers, then taken to the surface using large buckets on a hoist. When operating at capacity, the skip, or mine elevator, can carry four tons of salt to the surface every three minutes. The skip is also used to transport miners into and out of the operation. Miners formerly used a rail system to move about the operation underground, but have since started using old junk cars that have been modified to run on bio-diesel fuel. Developed almost entirely from old cooking oil, the burning of bio-diesel doesn’t leave particles suspended in the environment. There are many instances of several generations of Hutchinson families being employed by the mine.
This was an interesting exhibit; it’s essentially a waste dump site. Early in the mine’s history, employees would leave their empty food packaging underground because it was more cost-effective to use the skip to transport either rock salt or miners. The salty environment, well away from the sun’s ultraviolet rays, has preserved the trash remarkably well; a lot of the sandwich wrappers and empty drink cups look like they were tossed aside last week instead of in the 1950s.
Nancy and I went on a couple of different guided tram rides through the mine. We got to see chambers that were excavated decades ago, using earlier mining methods. The mining company has placed a number of environmental sensors throughout the operation, which provide early detection of any possible shifting of the rock salt walls. The Mine Safety and Health Administration, which oversees operations in U.S. mines, considers this salt mine one of the safest in the world.
Nancy really enjoys being underground. I mean, really. She’d been looking forward to visiting the Hutchinson salt mine for a number of years, and we both had a great time. Luckily for us, our underground adventures were only beginning – we’d be able to descend into
the bowels of the earth natural caves at two U.S. national parks in the months to come. Multiple times at each cave, even!
A salt mine might seem like something of a “so what?” kind of experience. But it’s the salt that comes from this mine, and others like it, that keep our roads safe to drive in wet and freezing weather. We’re glad we went, and, combined with the Cosmosphere, Strataca makes an excellent reason to visit Hutchinson.