The Mysterious Island

A view upstream along my creek.  The "mysterious" island is on the right bank

Picking up on a theme of a current family adventure film, but without bees the size of rhinoceroses...

Ever since I came to my preserve, I've been fascinated by a fairly sizable island (2-3 acres) in my creek.  The smaller streams in the Mid-Atlantic don't have islands; the valleys are too deeply incised into our metamorphic and sedimentary bedrock to form islands.  These streams are straightforward down cutters.  So, how to explain this rocky, wooded island? 

I've also been concerned that I am "losing" the forest on the island.  The trees at the edge are being undercut by the current...

...and flooding from severe storms washes over the center of the island and topples trees and removes topsoil.  Surely, this landscape isn't long for this world.

I've worried and puzzled over this situation for years.  I had some suspicion that it was related to the long-breached colonial mill dam located just downstream from the lower tip of the island but couldn't put the puzzle together fully.

Then, in 2008, a seminal paper appeared in the journal Science.  The two authors posited that all of the streambeds in the Mid-Atlantic had been significantly modified through the construction of colonial water powered mill dams.  Now that the dams had either breached naturally or had been removed purposefully, the streams were regaining their natural channels and were quickly washing away the "legacy sediments" that had accumulated behind the mill dams.  Furthermore, the urbanization of these same watersheds generates rapid and excessive runoff, so legacy sediment removal was progressing even faster than it would if the watersheds had returned to more natural conditions after the milling operations ceased.  Exactly the explanation I had sought for the disappearance of my island.

I'm still distressed that the forest, with some remarkably large American beech, oaks, and tuliptrees is washing away, but this really only represents a return to more natural conditions in the streambed.  Of course, try to tell that to the aquatic invertebrates that are smothered by the eroding sediments after each storm.

A view downstream at the head of the island where the creek divides

Ruins of the stone foundation of a water powered mill located just upstream of the island