ELLISON BAY

ELLISON BLUFF COUNTY PARK

This site is located high atop the dolomite bluffs that characterize the Green Bay side of the Door Peninsula.  Spectacular views of Green Bay and the bluffs of the peninsula to the southwest are promised to the visitor on a clear day. Here you can see massive dolomite cliffs up close.  This page discusses the structure of these formations and how groundwater flow is affected by the characteristic structures.

Typical of the western side of the Door Peninsula, the Ellison Bluff County Park area is characterized by steep dolomite bluffs, and the absence of till bluffs and sandy beaches.  Ellison Bluff rises about 180 feet above the water level of Green Bay.  None of the bluffs display the character of the shoreline any better than Ellison Bluff (Schneider, 1989).                                                        

The view from the second observation point is southwestward along the “anti-dip” slope of the Niagara Escarpment.  The full height of the escarpment is not visible, however, because the lower part is submerged beneath the water of Green Bay.  Water depth in the vicinity of Ellison Bay is about 100 feet, thus in some places the full height of the escarpment reaches as much as 300 feet (Schneider, 1989).

Some landforms visible from this vantage point are Chamber’s Island (the large island), Horseshoe Island, and the Strawberry Islands.  Across Green Bay and to the west and northwest is the Upper Peninsula of Michigan.  Both horizontal and vertical fractures in the dolomite cliffs seen here up close are the roots of the water contamination problem that is associated with carbonate terrains like those here on the Door Peninsula (Schneider, 1989).

The nature of the geology of the Door Peninsula causes problems for the inhabitants of the area.  A very thin soil (generally less than 1 m thick) cover overlies the intensely fractured and jointed dolomites (Stieglietz and Schuster, 1993).  The area is currently sparsely populated but population is on the rise.  There is no municipal water source, so buildings on the peninsula are required to use wells for water and individual septic tanks for waste disposal (Stieglietz and Schuster, 1993).  Soils are insufficiently thick for proper filtration to occur before the waste water returns to the groundwater system. Karst topography is another contributing problem to groundwater contamination as caves and sinkholes common in karst topography provide a direct conduit into the groundwater system (Sherrill, 1978).

 The two primary aquifer units on the Door Peninsula are the Mayville Dolomite of Silurian age and underlying sandstone units of Cambrian and Ordovician age (Stieglietz and Schuster, 1993).  In the Mayville Dolomite, water occurs primarily in fractures that are nearly vertical, and in larger horizontal bedding plane fractures.  This provides an intricate network of water flow channels that efficiently transport water from the surface to the groundwater reserves.  The fractures are enlarged by dissolution, which contributes to the efficiency of water flow within the aquifer.  Recharge of the Silurian aquifer occurs primarily through precipitation, which is greatest during the spring months by the combination of snowmelt and rainfall (Sherrill, 1978). 

Groundwater contamination is rapidly becoming a formidable problem due to the nature of the soil cover and the increasing population of the area. This problem is most severe at the end of the summer tourist season (Sherrill, 1978). Contamination of the groundwater system does not occur continuously throughout it, but primarily where fractured bedrock is near or at the surface.  Contaminants enter the groundwater system from human,  agricultural, industrial and municipal sources (Sherrill, 1978).   The most common contaminant is bacterial, both viral and pathogenic (Sherrill, 1978).  The fractured nature of this bedrock rapidly transmits the insufficiently treated water directly into the aquifer, resulting in contamination of the groundwater system (White, 1988).   

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Ellison Bay Overlook at Grand View Motel

Here you will be treated to a spectacular panoramic view of Ellison Bay and the dolomite bluffs of the western side of the Door Peninsula.  Evident here is the terracing of the bluffs due to the various levels of ancient glacial lakes during the Pleistocene period of geologic history.  Terraces on the bluffs are very visible from this vantage point.  The Grand View Motel is obviously named for the “grand view” that one can admire here.

Uplift of the Door Peninsula has been recorded and is easily visible from this location on the Peninsula.  We will view it here from the Grandview Motel parking lot.  Two geologic events contributed to the recording of the stair-stepped bluffs that can be seen from this vantage point. The first event was the isostatic rebound of the land surface as glaciers melted and retreated from over this area during the Pleistocene epoch of geologic history (Bradbury and Muldoon, 1993).  This uplift has also caused tilting of the land due to the different rates of rebound throughout the Great Lakes region. The southern end of the Lake Michigan basin is currently rebounding at a much slower rate than is the northern end, so drainage of the present-day Lake Michigan is toward the south (Bradbury and Muldoon, 1993). Second, as glaciers periodically advanced and retreated over this area, lake levels rose and fell in response to the varying rates and magnitudes of glacial melt water and discharge (Schneider, 1993).

These phases are also recorded in beach ridge complexes on the Peninsula, which are most clearly viewed from the air.  Beach ridges showing paleo-lake levels of Lake Michigan and glacial Lake Algonquin are visible with as much as 60 ft. of elevation change from current lake levels.  (Clark and Ehlers, 1993). Beach ridge complexes are well preserved on the Peninsula due to the continuous and slow uplift due to rebound as well as consistent and gradual decline in lake level (Clark and Ehlers, 1993).  Each parallel ridge represents a period where the uplift and lake level were in equilibrium. These still-stand stages are recorded by the formation of ridges that once were close to the shoreline (Dott, 1993).   

There is evidence of about eight shorelines recording lake levels from both glacial and post-glacial times (Niagara Escarpment Commission, 1999).  These shoreline deposits are identified by the presence of wave cut cliffs, sand and gravel beach deposits, rock terraces, and the stair-stepped topography of the shoreline.  The highest lake level is correlated to glacial Lake Algonquin, which was located in the Lake Michigan basin approximately 9,000 years ago, and currently stands 60 ft above the modern lake level (Schneider, 1993).