Birch Creek Embayment

Steven Dutch, Professor Emeritus, Natural and Applied Sciences, University of Wisconsin - Green Bay

This puzzling gap in the Silurian Escarpment may mark either a Pleistocene landslide or more likely a small pre-Pleistocene valley. The north-south road running down the center of the map is County PP. Section 26 is bounded on the north by Shirley Road, on the east by Blake Road and on the south by School Road.
mbirchcr2.gif (6390 bytes) A simplified map of the embayment: named roads are in red and bedrock escarpments in purple. Unconsolidated deposits between 800 and 840 feet elevation are in light brown, between 840 and 900 feet in green. Moraines are shown in dark brown (above 920 feet south of the embayment and 940 north).

There appear to be two zones to the embayment. The upper zone, above about 840 feet (light green), is a very gently sloping bowl. The lower segment, below 840 feet, is more rugged.

Whatever this feature is, it was already formed by the late Pleistocene because moraines on the edge of the escarpment (dark brown) wrap around it.

The upper bowl appears to continue north as a flat surface below the escarpment. Note also that the apron of glacial deposits (green and light brown) is very broad north of the embayment and very narrow south of it.  Either the embayment was a source of sediment that was carried north or a source of water that eroded the deposits to the south.

The panorama below is taken from Shirley Road looking south and southwest across the embayment.

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Looking west along School Road from the crest of the escarpment at the southwestern edge of the embayment. The left turn in the distance is visible on the location maps above.

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Immediately south of the road are outcrops, showing that bedrock extends to the very edge of the embayment.

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Looking east along School Road across the very gentle upper bowl of the embayment.

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Looking south along Blake Road. School road crosses in the near distance. We see here the back slope of the raised lip of the embayment.

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A possible clue: boulders in the bed of Birch Creek just west of County PP.

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Created 24 May 2000, Last Update 24 May 2000