Moominmama and The Rocks of Lake Superior

 

Wherein Moominmama visits the Apostle Islands and Pictured Rocks National Lakeshore to see how erosion shapes the sandstone in interesting ways...

Water turns out to be one of the most artistic forces of erosion on earth, and the sandstone formations along Lake Superior are a fine example. 

The best way to see the formations are by boat, which means Moominmama was back on the water, recovering today from a six-hour journey in a sea kayak. As tired as I am, it was great fun to travel under arches and into caves carved by the water into these ancient sedimentary deposits. 

Photographs can make it hard to show scale, so I invite you to look closely at the lower right area of this photo. Barely visible is the kayak of our leader, Colin, inside this colorful cave at Pictured Rocks. The cave also extends further back than it appears.

This national park gets its name from what looks like paint along the cliff faces, which is the result of minerals leaching through the sandstone. Iron stains red, maganese stains black, copper stains blue-green and limonite, white. 

You can see these colors in the cave, but more typically along the exposed cliffs faces like this, where you might think someone dumped cans of paint over the cliff's edge.

These are some of the same colors I saw on cliff faces in the Utah canyons, and it turns out many of the same forces coloring and shaping the Lake Superior shoreline were at work millions of years ago in Utah, when the sandstone there was shaped by an inland sea.

Take for example this arch, Lover's Leap, which I had a chance to kayak underneath!

The feature is a function not only of wave action but also variations in the density or strength of the sandstone layers and the cycles of freeze and thaw that loosen sections of rock over time, dropping them into the water below. The only difference in Utah is that the water isn't below anymore!

There are also many small caves and tiny rows of holes in areas where weaker rock was eroded away before the the harder layers. And like many areas in Utah, a harder layer of rock with more limestone protects sections, allowing the softer sandstone below to wear away beneath. Here's another arch photo taken while I was in the Apostle Islands (as was the photo at the very top.)

The other major difference is the impact of glaciers because none of the Great Lakes would be here if the ice hadn't carved them, compressed them and shoved sand and rock to new locations over the underlying bedrock. Lake Superior is, of course, the largest at more than 350 miles long and 160 miles wide.

The largest freshwater lake in the world by surface area, Superior's waters and wind have all the force of a sea. The kayaks used here are "sea kayaks" for good reason. What started out as a calm surface when we launched kicked up much heavier waves by the afternoon. And this was a quiet day! I'd hate to be out there in a storm.

In years past, ships that brought supplies, or transported the products of loggers and miners, confronted this weather and sunk at regular intervals. Underwater hazards like sand bars and narrow channels near islands brought down hundreds of boats over the years. That's one of the reasons Lake Superior has so many lighthouses. 

Today, the warning lights are all high-powered, high-efficiency lights run off solar. The lighthouses, the ones preserved, serve only as tourist attractions. The lighthouse keepers and their carefully tended fires and old fresnel lenses are long gone.

But the remaining lighthouse are still very picturesque! And Moominmama has signed up for a trip on a glassbottom boat to see some of the lighthouses and shipwrecks tomorrow. More on that in next week's blog post, when I also hope to touch on the Ojibwe or Anishenaabe heritage in this part of the Great Lakes.