Minnehaha Falls

After leaving the Science Museum Wednesday, we decided to stop at Minnehaha Falls.  Sarah doesn't think she's ever been there and it's been a couple of years for the boys.  Plus, it was 83 or 84 degrees out - we had set a high temperature record that day.

The first views of the falls.  It's been a dry spring, with very little snow melt, not what the falls would typically look like in April.  Pictures were tough with the sun in the western sky, right behind the falls.

Ice lingers in the gorge with the little direct sunlight.  People were still walking back behind the ice.  Minnehaha Falls is formed as the creek falls over the Platteville Limestone and excavates the soft, St. Peter Sandstone underneath.  The limestone is undercut and occasionally large chunks of limestone breaks off and the falls migrate up stream.  But between the limestone and sandstone is a small layer of shale (essentially impermeable clay).

If you look closely, most of the ice starts to form at approximately the same level or layer.  Groundwater soaks through the soil, glacial material and limestone until it hits the shale, the water then moves horizontally along the shale until falling out into the gorge.  In the winter, it's obviously cold enough for the water to freeze.  You can see these frozen springs at sites all throughout Minneapolis & St. Paul during the winter, anywhere this combination of bedrock is exposed.

It was a pretty nice day for us (even though I felt sicker and sicker as the day went on - I ended up staying home from school the next day...).