Summary of Findings Additional Research


Marshes of Long Point, Ontario. (Photo by Glenn Elert, 1998)
Summary of Findings

While Great Lakes barrier systems look very much like oceanic barrier systems, in some cases their origins and the controls on their barrier systems are not as similar as their landforms make them appear. Here are some of the main comparisons this site has covered:

  1. Longshore drift. Regardless of location this is the dominant process that forms and nourishes both oceanic and lacustrine barrier landforms.
  2. Sediment supply. Both systems have a wide range of possible inputs, including input from rivers, reworking of the coastal platform, erosion of bluffs and headlands, nourishment from backshore dunes, deltaic deposits, glacial deposits, artificial nourishment, runoff from human-developed land, and biogenic material. In oceanic systems, river input and the reworking of the coastal platform create the largest barrier systems, while in the Great Lakes, bluff erosion of glacial sediments feeds the largest lacustrine systems.
  3. Coastal Platform. Both oceanic and lacustrine barrier systems require a shallow and flat shelf on which to build. In oceanic systems, the continental shelf most commonly provides the foundation, while in the Great Lakes, the platform can be provided by wave-cut glacial sediment or the deposition of river sediment.
  4. Influence of Glaciers. While glacial activity can provide sediment to and affect the formation of barrier systems, its role in oceanic environments is minor compared to that of Great Lakes systems. In the Great Lakes, they are responsible for most of the sediment (whether through coastal bluff erosion or eroded from the surrounding land and delivered through streams and rivers), for raising lake-levels due to glacial meltwater which cut platforms that serve as foundations, the deposition of debris and glaciolacustrine sediment that creates the substrate of the wave-cut platforms, and for the continued fluctuation of lake levels from isostatic rebound.
  5. Wind and Waves. In both systems, winds create waves which cause longshore drift, and erode, rework and transport sediment. In oceanic systems, wind a nd waves are extremely important as they shape the available sediment into the familiar barrier landforms.. Lakes, however, are more likely to be fetch-limited, which will also limit wave heights.
  6. Aeolian processes. Winds can also transport sand from the beach back into the dunes, removing it from the beach system. Additionally, Crowe, Coakley and Ptacek (1998) make mention of the fact that in the Great Lakes, the predominant winds blow directly onshore in many locations, increasing wind erosion, compared to the Atlantic coastline, whose predominant winds are not blowing east into coast.
  7. Landform Frequency and Size. In the Great Lakes, barrier systems tend to be smaller than oceanic systems, both in the size of the landforms and the overall extent and complexity. There are also no large barrier island complexes. There could be many explanations for this, including (1) like the Pacific coast, the coastal platforms are small compared to continental shelves, especially those of the Atlantic coast and its large systems of barrier islands; (2) there are no large rivers with extensive drainage basins, like the Mississippi River, that provide enormous amounts of sediment; and (3) the colder climate of the Great Lakes prevents high erosion rates year-round.

To summarize, both oceanic and lacustrine barrier systems require a stable and shallow coastal platform on which to initially build, adequate available sediment and an appropriate processes to supply the sediment (consequently shaping the sediment into a barrier landform). While longshore drift is the dominant process for both oceanic and lacustrine systems, during their initial stages, they have relatively different influences. In oceanic systems, wave- and tidal-action, the existence of any number of sediment inputs, and the presence of an existing continental shelf combine to allow the formation of a barrier system. In the lacustrine barrier systems of the Great Lakes, their development depends on the historical presence of glaciers to carve a platform and deposit the necessary sediment, and then the waves to shape it onto a barrier landform.


Additional Research

By closely examining three Great Lakes barrier systems, some relationships between oceanic and lacustrine barrier systems were discovered, and more questions arose. Here are some examples of the questions that further research could answer:

  1. It's clear that the glaciers were responsible for the formation of the coastal platform in Lake Erie, which gave rise to numerous barrier systems around the lake. Was a similar platform created in any of the other Great Lakes, and was it as successful in creating barrier systems?
  2. On the southern shore of Lake Ontario, the lack of sand prevents the development of any large barrier landforms. Are there locations that have the right conditions for barrier system development, but have no barrier landforms? If so, why did they not form there?


To understand the full breadth of Great Lakes barrier environments, more locations should be more closely examined.

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A COMPARISON OF OCEANIC BARRIER SYSTEMS AND GREAT LAKES BARRIER SYSTEMS
Copyright 2004, Jennifer Bruce