By Marc Hequet
Along the Minnesota River and its tributaries waterfalls are common, but many are little known. Long ago, a deluge created dozens of lovely plunges in a long, broad river valley in southern Minnesota.
How many falls? The Minnesota Geological Survey says it doesn't have a count. But a geographer named Bob Douglas makes a hobby of discovering, or rediscovering, the falls.
"These falls were known to folks long before I found them," he says. "I'm just documenting them a bit."
The Gustavus Adolphus College professor is a Santa Claus–lookalike—indeed he is a veteran Santa, who needs no fake beard or tummy pillow. Outgoing and affable, ever pushing his spectacles back up his nose, Douglas speaks in a tone that is deliberate, but his conversation is never dull. As a geographer, he starts his search with U.S. Geological Survey topographical maps, with a scale of 1:100,000, to the more detailed 1:24,000. Where maps show abrupt change in elevation, fast-dropping streams might meet outcrops of hard Jordan sandstone. There Douglas may find waterfalls.
Some sandstone crumbles in your hands. Not Jordan sandstone, which is common in south-central Minnesota but often buried beneath many feet of Oneota dolomite. Jordan sandstone was deposited long ago in a shallow inland sea stirred by tides and currents. After 500 million years, the cold caress of glacial runoff wore through the softer dolomite, exposing Jordan sandstone.
Where Douglas's maps show a steep stream descent, he seeks permission to go onto the property. If he gets the go-ahead, he works his way upstream. When he discovers a waterfall, first he shoots photos. Then he climbs with a sturdy student, usually a geography major, along as spotter.
At the top, Douglas drops a rope knotted at 1-foot lengths to measure the falls' height. To check its width, he carefully wades across the stream, heel to toe. Each step is 1 foot, he says.
On his first visit, Douglas writes a physical description, including township, range, section, global-positioning coordinates, and road directions.
As Douglas knows, all of the falls in the Minnesota River valley owe their existence to a prehistoric disaster. Glacial River Warren burst onto the landscape about 10,000 years ago and carved a valley 350 miles long, 5 miles wide, and as much as 200 feet deep.
The stage for this disaster was set at the end of the last ice age. During the thaw a vast inland sea formed. Known as Glacial Lake Agassiz, its vast waters crashed against cold beaches in what now is Minnesota, the Dakotas, Manitoba, Ontario, and Saskatchewan. At its maximum, Lake Agassiz had four times the surface area of Lake Superior. Its southernmost point lay against a glacial moraine on the north-south continental divide near today's Browns Valley.
One day, rising glacial meltwater topped that natural dam. The torrent gouged a channel across southern Minnesota, likely in a matter of days. This incision event, as geologists call it, was probably brief, says Carrie Jennings, senior scientist at the Minnesota Geological Survey. The first inundation of Glacial River Warren might have taken just a week, with more torrents in subsequent centuries.
Streams in the drainage then dropped to the lower level of River Warren's excavation, says Jennings, some "in one big step"—creating waterfalls. That means all the falls in the Minnesota River drainage are approximately the same age.
Waterfalls can be cryptic. You can look right at one and not know it. Because some streams are dry part of the year, the falls temporarily disappear. Or the falls might be almost invisible because of high water. Once, during a period of low water, in dense woods five feet from the bank of the Minnesota River, Douglas found a spring-fed falls gurgling into the river near a boat landing in Ottawa. In high water, he might never have noticed the falls. Douglas and his wife, Judy, have found 30 falls along the Minnesota River and its tributaries, and he thinks he can find more. In the works is a plan to canoe the Blue Earth River, which joins the Minnesota at Mankato.
Douglas has knocked on doors and talked his way onto private property to see waterfalls. For example, one tumbles in the yard of a Kasota home; another is on a horse ranch near North Mankato.
A few falls are on public land. Best known is Minneopa, a glittering double falls five miles west of Mankato in the state park of that same name. At about 25 feet, Minneopa is the widest falls in this area. Most others are about 10 feet wide.
The highest falls is Minnemishinona at 42 feet, compared with 39 feet for the better-known Minneopa. West of North Mankato in a Nicollet County park, Minnemishinona Falls is a top local draw, though it is often just a dribble on the water-weary Jordan sandstone, which shows hues of grey, blue, and brown.
"Waterfalls for me are beauty," Douglas says. "They evoke a sense of solitude. They never stay the same."
Waterfalls keep moving, grinding away the hard capstone over which they plunge, pushing upstream. Come back in 1,000 years, or in 100 years—or in one year—and the falls could be very different.
Falls relentlessly erode the bedrock over which they flow. Sometimes the rock collapses in chunks that would barely fit in a pickup bed. Douglas says he recently found a boulder that eroded and fell to the bottom of the 15-foot-high Kasota private falls. In this way, waterfalls tend to "migrate" upstream. So enjoy the cascades. They won't last. After taking photos and measurements, Douglas has one last step in his discovery of a falls.
"I sit down," he says, "to admire it."