Ancient Lake Minnewaukan
Devils Lake owes its existence to a continental glacier that covered much of North America during the Pleistocene Epoch. Carving a basin as it advanced over the landscape, the glacier deposited excavated materials along its leading edges, leaving terminal moraines marking the farthest extent of glacial ice sheets. Near the end of the Pleistocene, roughly 11,000 years ago, the glacier began its retreat. As the glacier withdrew, glacial meltwaters poured into the basin, creating a vast proglacial lake dammed by morainal deposits. Native Americans called this lake Minnewaukan, meaning, among other possible interpretations, Bad Spirit Water. Recent flooding has perhaps given credence to a legend told by those Native Americans, claiming that the lake once overflowed and flooded the entire world.
Based on abandoned beaches, or strand lines, geologists estimate that the ancestral lake reached a maximum surface elevation of between 444 and 445 meters. At that elevation, the lake covered about 1,050 square kilometers, held about 5 million acre-feet of water and had a maximum depth of around 50 meters. A natural outlet called Tolna Coulee, which allowed water to flow out of the basin and prevented the lake from rising and expanding further, controlled the maximum elevation. How often the lake has overflowed is uncertain, but geologists believe it has happened at least twice over the past 4,000 years, most recently around 2,000 years ago.
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