Bluff Country Reader / STPNS
August 07, 2006


Researcher delves into Spring Valley Caverns in Fillmore County

By Bluff Country Reader staff

SPRING VALLEY, Minnesota (STPNS) -- Sushmita Dasgupta, a researcher from the University of Minnesota, is completing her doctoral study in geochemistry with information gathered from Spring Valley Caverns in Fillmore County.

Born in the city of Kolkata, India, Dasgupta obtained her bachelor's and master's degrees in geology from Jadavpur University in Kolkata.

She commented, “I love chemistry and traveling, so I decided to study geochemistry, which would let me enjoy both. I joined the Ph.D. program in the Department of Geology and Geophysics at the University of Minnesota in fall 2001. I work with Larry Edwards, my advisor, Calvin Alexander, another professor in the department, and John Ackerman of Spring Valley Caverns.”

One reason Spring Valley Caverns were chosen to use in her studies is because Ackerman has always allowed scientists access to do research in these caves.

Sushmita Dasgupta, a researcher from the University of Minnesota, gathered information as she works toward her doctorate degree in Spring Valley Caverns, which is part of the Cave Preserve in Fillmore County.
Photo by Mary Whalen

The type of research that has been done and will be done in Fillmore County is extensive. Some of the projects include using dye tracing to establish underground water flows and sampling underground water to determine its purity, which includes identifying any outside properties, such as chemicals.

Other research includes speloethem (formations) dating to determine when they began growing, analyzing speleothems to determine climatic history and to provide a picture of historic plant life in Fillmore County.

There will also be work done in bat research and soil sampling to date chronological development of what is now referred to as Fillmore County. Work will also be done in soil sampling to search for drugs that will cure cancer and other human illness.

Fossil studies and radon studies have been done and scientists from around the United States have used an array of machines on the property to determine if they are capable of detecting underground voids, or in other words, caves and caverns.

Ackerman stated, “Although I enjoy assisting the scientists, my real thrill is discovering unknown cave systems. In fact, most of the scientists and researchers encourage me to make such discoveries so they can advance their research.”

One reason scientists are thrilled with Ackerman's willingness to open the discoveries of the Cave Preserve to them is because uncommercialized caves allow researchers an environment free of contaminates. This is important because interaction with the outside is limited and formations are relatively unaltered.

The need for this “natural lab” environment is crucial to the research Dasgupta is undertaking on speleothems. Commonly called cave deposits, they are formed when rainwater, which mixes with carbon dioxide in the soil, becomes acidic, dissolving the limestone when passing through it. Rainwater then carries the dissolved limestone with it into the cave below. In the cave the water is no longer able to carry the limestone in a dissolved state, hence it is deposited, forming underground structures.

There are many types of speleothems, but for her work Dasgupta is interested in stalagmites, the long cylindrical column-like forms that grow up from the cave floor.

“High resolution studies of Spring Valley stalagmite records and comparison with other global records can give us information about past atmospheric circulation patterns,” she explained.

These structures form by deposition of calcium carbonate on the cave floor from cave drip waters. When these deposits form in the cave they incorporate information not only about the ambient temperature of the cave but also the type of vegetation growing above the cave. Furthermore, these stalagmites can be dated very precisely by radioactive dating methods involving uranium and thorium.

Although one speleothem from the Spring Valley Caverns was recently dated to more than 100,000 years before present, Dasgupta is working with three stalagmites of different ages.

The oldest stalagmite in her present studies ranges in age from 8,500 years to the present. All the stalagmites were dated in the radioactive dating laboratory in the Department of Geology & Geophysics at the University of Minnesota.

Besides the radioactive dating technique, Dasgupta also employed band counting method to obtain ages of the stalagmites. The latter method is only employed if annual banding is present in a stalagmite, and in all her samples these bands are present. These bands are fluorescent bands, which are imaged with a microscope. The combined application of these two dating methods gave researchers precise ages of the stalagmites.

As mentioned before, cave deposits can store climatic information in them. There are chemical species called isotopes, which can vary in ratio due to a change in the depositional conditions. Dasgupta has been working with oxygen and carbon isotopes. These isotopes were analyzed at the stable isotope laboratory in the Department of Geology & Geophysics at the University of Minnesota.

Changes in the ratio of carbon isotopes reflect changes in vegetation above the cave, and changes in oxygen isotopic composition in the Spring Valley Caverns mean changes in temperature.

It was found that both the oxygen and carbon isotopes have varied significantly in the past. The oxygen isotopes reflect that the area around Spring Valley was warmest from 6,000 to 5,000 years ago. The temperatures have started declining from about 2,400 years back, which means the area is experiencing a colder period compared to 8,000 years ago.

The carbon record matches with the oxygen record and shows scientists that plants conducive to drier conditions dominated during warmer periods. Recording this information seems to prove that since cool season plants are more common now, a definite temperature change has occurred.

Work is still in progress regarding analyzes on cave flooding in the area and this will be able to tell scientists about extreme rainfall events in Spring Valley.

"Studying past climate can help us understand the climate system better and help in the prediction of future climate changes," said Dasgupta.

She is grateful to have the opportunity to do research in Fillmore County and encourages others to venture into these caverns.

Ackerman welcomes interested parties to contact him through his Web site:

Although he has no interest to commercialize his discoveries, Ackerman is driven by a desire to discover, protect and to perpetually preserve the caverns for future generations.

He explained, “I consider myself a temporary steward of the caves and as such feel that no single person can 'own' such phenomenal underground treasures.”

However, by his “legal ownership” of the Spring Valley Caverns, many are given an opportunity to explore a world beneath the surface that would not exist without his dedicated work.

The Minnesota Speleological Survey, the University of Minnesota, and the Quarry Hill Nature Center in Rochester have regular access to the caves. Boy Scouts and Girl Scouts and many college and high school outing groups also visit the caves.

Ackerman keeps very busy. He is married and has three children. He is the owner of Ackerman's Furniture Service in the Twin Cities. This business, restoring furniture, employs 15 highly skilled individuals and is known as one of the top furniture restoration facilities in the United States.

His main hobby involves his lifelong love of caves and he is excited to have found cave number 30 just recently, which is located high up along the Deer Creek bluff face on his 500-acre Spring Valley Cave Preserve.

An interesting point to ponder is that when Ackerman purchased his first parcel of land, there was only one large cave on it, which had been sealed for more than 30 years. Even then he had no interest in commercializing it.

“The day that I removed the rusty gate from the cave opening is the day that I allowed scientific researchers in. I consider myself a spoke in a wheel. In other words, a participant in a circle which includes conservationists, researchers and scientists, all of whom are interested in studying and preserving our subsurface environment,” he said.

Dasgupta is one among many who appreciate Ackerman's dedication and willingness to allow research to the extent he has.

“Stalagmites forming deep underground in limestone caves have great potential to reveal past climate changes. Comparison of this temperature record with past climatic records from other regions, such as the North Atlantic region, shows how the climate of southern Minnesota was linked to the global climate system. And this aspect is important for studies that model future climate changes,” concluded Dasgupta.

On a personal note, when Dasgupta is not doing research, she works for a voluntary organization called Vibha, which is dedicated toward helping underprivileged children in India and the United States. To contact Sushmita Dasgupta, e-mail her at

Article by Mary Whalen
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