Having gone to undergraduate school at North Dakota State University in Fargo in the mid-1990s, one became aware of a distinct transitional zone as you headed east towards the Twin Cities.  A short drive across the Minnesota border, you could see what was the shoreline traces that marked a clear shift of geology and with some study, begin to piece together the story of the past millenia, involving a glacier, a lake, and the reason the Red River flows to the north.

A recent Ghosts of Minnesota post “A Minnesota beach where there is no water”  by Troy Larson, reminded me of this place and the influence the immense glacial Lake Agassiz on the landscape of the upper sections of the Plains, a lake formed at the end of the last ice age, some 8,000 to 14,000 years ago.

A map of the territory by Warren Upham, from the earth 19th Century shows the extent of the Lake, and as mentioned by Larson, “Today, Lake Agassiz is believed to have been even larger than what is represented on this map.”

Larson gives some context:

“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.”

A close up shows the area around the North Dakota-Minnesota border, bisected by the Red River (of the North).

The post covers some photos of the area near Fertile, Minnesota, home of the Sandhill Recreation Area and nearby Agassiz Dunes Natural Area, and as explained in the Ghosts of Minnesota post by Larson: “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.”  With places like a dune called “Death Valley” named due to the instability of the shifting sands, this is an atypical plains landscape.

image – Ghosts of Minnesota

image – Ghosts of Minnesota

While there are plenty of lakes in Minnesota (yes, well over 10,000) the sort of expansive lake left traces of a more significant water body, as mentioned by Larson:

“The sand feels just like beach sand. It’s a soft, fine grain sand that shifts beneath your feet when you walk on it.” 

image – Ghosts of Minnesota

A more expansive map from a recent CBC article that covered a new book by Bill Redekop (@billredekop) entitled “Lake Agassiz: The Rise and Demise of the World’s Greatest Lake” exploring the hidden mystery of the lake.  “For millennia, the evidence of its existence remained hidden in plain sight, but slowly details of the landscape began to merge in the minds of people passing through the province.” The modern map (via the CBC article) shows a more expansive Lake Agassiz, and the extent:

As Redekop explains, the investigation of the hidden connects the modern to the historical.  He summarized the feeling after writing the book:

“”Now I have two landscapes: the one that I see and the one that I imagine, that I know was there 10,000 years ago.”

The deep time of geology, as mentioned here in the post on Seattle area, leaves many traces and clues to .  Beaches without lakes, valleys without creeks, all connect us to a historical past that shapes our present and future.

Header image of Lake Agassiz dunes – via Ghosts of Minnesota