Tuesday, January 29, 2013

Frozen Minnehaha Falls




A week ago, a colleague of mine visited Minnehaha Falls and took the picture above to show me.  The bedrock of the Minnehaha Falls area consists of the resistant Platteville Limestone, the Glenwood Shale and the St. Peter Sandstone.  As water falls over the more resistant limestone, it erodes the weakly cemented St. Peter Sandstone at the base of the 53-foot waterfall.

What's interesting to me in the picture isn't how the water has slowly frozen in the waterfall through the course of a Minnesota winter, it's all of the other frozen water to the right and left of Minnehaha Falls.  In between the limestone and sandstone is the Glenwood Shale.  As water soaks downward through the upper layers of soil it comes to this impermeable layer of shale and flows laterally until eventually reaching the eroded valley carved by Minnehaha Creek.  At this point the water cools to the point of freezing, forming a ring of large icicles.

On September 29, 2012, I took a gigapan of Minnehaha Falls (with a very low amount of water).  For a full size version of the gigapan, please click here.

For a more detailed post on the Minnehaha Falls, please click here.