As school children, most of us learned about the last ice age, in the Pleistocene Epoch, during which the Laurentide Ice Sheet covered more than half of North America. Between 13,000 and 8,500 years ago, the ice sheet went through multiple melt phases in which the ice sheet created a giant glacial lake–Lake Agassiz, named for Swiss-American Geologist Louis Agassiz, one of the first to postulate about our past ice ages.
Lake Agassiz was a massive body of fresh water in the middle of North America, larger than all of the Great Lakes combined. As the ice sheet retreated, ice dams held back the meltwater to create glacial Lake Agassiz. As the lake drained, sometimes slowly, other times in sudden, catastrophic outflows, the lake shrank and changed, leaving behind a table-flat landscape with some of the richest farmland in the world, and even sandy beaches from it’s ever-shifting shoreline. To the geologically educated, the signs of Lake Agassiz are everywhere, but even to those like myself, without a geologic eye, there are places where you can see the remains of this monster lake. In late May of 2017, I visited one of those places, outside Fertile, Minnesota. It’s a Minnesota beach where there is no water.
Not having ever been to this fascinating place, I initially had some trouble finding my way in. There’s a separate attraction, the Agassiz Dunes Natural Area, a wildlife observation preserve, just to the south, but there is a tract of privately owned land that separates it from the actual dunes I had come to see. After some searching, I discovered the Agassiz Dunes are accessible via a series of horse and snowmobile trails just west of the golf course on the southwest edge of Fertile.
Above: Standing at the top of the dune on the north edge of the site, looking south. Interestingly, if you turn around and look north, the view from this spot looks down into a ravine that looks much more typical of Minnesota (below). These dunes were formed as the ice sheet retreated and the weather became dry and hot. In wetter times, foliage appears and covers the dunes, and in dry periods, the growth retreats and the sand becomes more visible.
The sand feels just like beach sand. It’s a soft, fine grain sand that shifts beneath your feet when you walk on it.
There were deer tracks in the sand in a number of places, but this area is owned by the city of Fertile and there is no hunting allowed.
Above: The sign once bore the name of this particular dune. “Death Valley,” an active, unstable dune.
Above: Looking north. The path to the left leads to the Death Valley dune.
As I stood looking at the scene shown above, it occurred to me that when you grow up in a place, you just get used to certain things and don’t give much thought to them. Like, why there are businesses dedicated to sand and gravel all over the area, or why places are named the way they are, like the Sandhill River or the Sandhill River Golf Course. It’s because, like, ten thousand years ago, Lake Agassiz left all this sand behind. Duh.
Walk a quarter mile in another direction, and you wouldn’t know you’re in a geologically unique area… it just looks like Minnesota.
About a half-mile to the south is the Agassiz Dunes Natural area. There’s a small parking area just off the road where you can get out and enjoy nature, watch birds, etc…
Above: The tire tracks from my vehicle show how sandy the soil is.
What do you know about Glacial Lake Agassiz and the Agassiz Dunes? Please leave a comment below.
Photos by Troy Larson, copyright © 2017 Sonic Tremor Media