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What are these potholes?

Presque Isle River is the largest river in the Porcupine Mountains, draining over 300 square miles of forest land in the Upper Michigan and Northern Wisconsin. The amber colored water of the river, and the persistent foam beneath the waterfalls, are largely the result of tannins and other water-soluble plant compounds that wash into the river as it journeys to meet Lake Superior. The finely terraced rock over which the river flows is called the Nonesuch Shale.

It is composed of sand and clay particles that were deposited in a shallow lake that covered this area almost a billion years ago. The round potholes in the riverbed form an eddy current continually swirls pebbles and sand grains in a circular path. Over time, the scouring action of these materials wear away the softer shale, forming the large smooth-sided potholes that can be seen here.

What's the story here?

Having seen couple other bigger waterfalls earlier in the day and not having seen any of these rock formations previously (due to Spring snow melts and overflows), I almost did not shoot this picture. Returning from Presque Isle to the main land on a delicate suspension bridge - delicate because it shakes if wind blows; it shakes if people walk around the bridge, let alone on it; and it shakes when you breath normally while standing still on it - these rock formations caught my attention, thanks mainly due to the lower levels of water.

I held my breath for about a minute and 20 seconds - first 50 seconds or so to minimize the bridge-shake and last 30 to get a couple pretty crisp 10 seconds exposures (5 seconds after each shot to account for Long Exposure Noise Reduction). Thankfully, no one was around the bridge to induce camera shake. Little did I know the Yoga & Pranayama I learnt over 20 years ago halfway across the globe would come in handy in photography!

At the end of it all, it was very very satisfying and yes, a minute & 20 seconds - often a minuscule amount of time in our daily standards - did feel like eternity. I am glad that the elements - natural as well as man-made - cooperated with me and like a friend of mine later pointed out, the (photo) gods were smiling at me for those 80 seconds!

In a 10 mile neighborhood ...

  1. Manabezho Falls
  2. Raging Rainbow Falls

Archive ID
Focal Length
Shutter Speed
Exp Bias
Light Value
HF Distance
Focus Distance
Depth of Field
Field of View
2007-07-14 19:56:41 -0400
46.70843 N, -89.97286 E, 825 ft
AF-S DX Zoom-Nikkor 18-70mm f/3.5-4.5G IF-ED
35.0 mm (35 mm equivalent: 52.0 mm)
10 second(s)
2.09 m
10.00 m
inf (1.73 m - inf)
38.1 deg (6.90 m)