Description Development Sediment Budget Lake Levels Other System Controls


Long Island in Apostle Islands, Wis. (Photo by Louis Maher, 1966)
Description

Added to the Apostle Islands National Lakeshore in 1986, Long Island is located on the northwest tip of the Chequamegon Point barrier spit. Accessible only by boat, it is a popular recreation site for hiking, swimming, and picnicking. It is also thought to be a nesting ground for the endangered piper plover. Throughout its history, Long Island has gone through periods of disconnection (usually due to storm washover) and reconnection with the Chequamegon Point spit. Long Island is 6.4 km long, and varies in width from 75 to 380 meters. It is the only Apostle Island without a bedrock core (Bona, 1990).


Location map of Long Island, Chequamegon Bay, Bad River and Kakagon River. (Bona, 1990)
(click to enlarge)
Development

Most of the Apostle Islands are remnants of interfluves (northeast-flowing streams that have cut valleys into the sandstone which were later flooded by melting glaciers), but Long Island's origins are very similar to that of an oceanic barrier island. Long Island looks like a recurved barrier spit protruding into Chequamegon Bay, however, due to its stability and long life, it is generally considered to be a barrier island (Nuhfer and Dalles, 1987).

Long Island's origins begin with the submergence of the Chequemegon Bay platform by rising lake levels around 1,500 years ago. Oak Point Bar, a barrier island just south of Long Island, built on a high point on the bedrock shelf of the bay.

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Bathymetry of Chequamegon Bay. (Bona, 1994)
(click to enlarge)

From the Bad River sediment transported west through longshore drift, a spit developed where the shoreline orientation changed dramatically, and built out to join with Oak Point Bar. Once they united, the abrupt changes in sediment supply and longshore drift encouraged the development of a second island, Long Island, in front of the Oak Point Bar (Bona, 1990). Additionally, a shift in the Kakagon River outlet from Chequamegon Bay to Lake Superior provided additional sediment and encouraged the growth of the Chequamegon Point spit (Nuhfer and Dalles, 1987). The Chequmegon spit eventually prograded out to connect with Long Island, further enhancing the effects of longshore drift along the system (Bona, 1990).


Development of Long Island. (Bona, 1990)
(click to enlarge)
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Sediment Budget

Today, dominant northwest longshore drift of from the Bad and Kakagon Rivers continues to feed Long Island and Chequamegon Point. The sediment is predominantly sand with small amounts of gravel, probably of glacial origin. While there is one area of erosion about 3 km from its lakeward tip, Long Island is prograding at a rate of 1.1 meters per year, and a series of east-west beach ridges and bog-filled swales are relics of previous shoreline locations. Over the last 200 years, Long Island has experienced periods of detachment to Chequamegon Point, but it eventually reestablishes its connection to the mainland. It is currently joined with Chequamegon Point (Bona, 1990).


Breach between Long Island and Chequamegon Point. (Photo by Louis Maher, 1966)
(click to enlarge)
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Lake Levels

Overall, the Great Lakes are seeing a rise in lake levels of 0.2 meters per century, but local factors can influence the amount of rise that is actually happening (Nuhfer and Dalles, 1987).

  1. Seasonal variations. Lake levels can fluctuation up to 1 meter, depending on the time of year (Bona, 1990).
  2. Isostatic rebound. Lake Superior is experiencing continued uplift from the pressure the weight of the glaciers, however, the north shore is rising more quickly, and the tilt of the basin is causing a relative drop on the southern shore. The rate of drop at Long Island is estimated to be about a fall of 20 cm per century (Bona, 1990).
  3. Seiches. Lake Superior may not experience tidal influences, but it does see seiches as large as 30 cm (Bona, 1990).

Fortunately, Long Island is not currently suffering from the changes in lake levels. While most of the spits and beaches on the Apostle Islands are drowning and eroding due to lake-level rise, Long Island enjoys continued sediment input and growth. However, as with any barrier system, even the smallest change can disrupt the equilibrium and cause instability.

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Other System Controls
  1. Winds. While winds can come from any direction, the predominant direction is from the northeast, across the longest possible fetch of 400 km. This wind pattern encourages the western direction of drift. On the western tip of Long Island, the channel traffic can also send waves from the west and northwest, affecting whatever wind waves exist during that time (Bona, 1990).
  2. Human intervention. With the construction of the first lighthouse in 1858 and the eventual settlement and recreational use of Long Island and Chequamegon Point spit, humans were bound to have an impact (Nuhfer and Dalles, 1987). Fires, logging, clearing, and construction are all concerns. Additionally, some also believe that farming and construction in the drainage basins of the Bad and Kakagon Rivers may be contributing increased sediment into the rivers which help feed Long Island and Chequmegon Bay spit (Bona, 1990).
  3. Ice. Since Chequmegon Bay is relatively shallow, it accumulates a great amount of ice, which typically lasts from November to April. The ice insulates the bayside from winter and springs storms, and it pushes sediment up onto the beaches (Bona, 1990).
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A COMPARISON OF OCEANIC BARRIER SYSTEMS AND GREAT LAKES BARRIER SYSTEMS
Copyright 2004, Jennifer Bruce