The cross section look like this. A slight bit larger.
Within 100 miles of the Kensington rune stone site 300 of these three sided holes have been found.
These holes range fron a few inches to over a foot deep.
To me these holes could be Viking moring stone holes, but if they are, then there were a lot more Viking in the mid-west than we ever thought.
Here are six way I can think of to add water to the midwest.
This is still going on today.
300 million were killed in the 1700 and 1800. That number of beaver would dam up a lot of water.
All the rivers and lakes in the midwest freeze each winter to a depth of a few feet still today.
When she described the sea of reeds and the clacking sound they made. Reeds grow where it is wet.
The saga description of the flow out of Hudson bay 1000 years ago make it sound like it had three times the flow it has today. That makes me suspect the Hudson bay of 1000 years ago reached south all the way to the north south contintinal devide.
Makes me suspect a connection between the holes and the Vikings.
As with the 12,000-BP barrier across the Bering Strait, establishment archeologists have erected another barrier which researchers cross at their peril. This time, the line is drawn at L'Anse aux Meadows, in Newfoundland, where a Viking presence has been officially acknowledged. Any Viking innuendoes south of this point in North America are verboten.