Lakeshore Landforms

View of several small islands off the shore of Isle Royale National Park, Michigan

The designated lakeshores in the national park system have shorelines and are, therefore, considered coastal and are managed accordingly. Nevertheless, because even the largest lakes are very small compared to oceans, some distinct differences exist, geomorphically speaking. Many lakeshores have much smaller waves and currents than occur in ocean basins. Furthermore, lakes are naturally short-lived: they tend to fill with sediments and to be emptied by streams downcutting their edges. Thus, some lake waves and currents have insufficient time for creating large landforms. Also, lake tides, where they do exist, are generally too slight to provide waves and currents with a wide vertical range to work in (Wyckoff 1999).

Although astronomical lake tides (those caused by Moon–Sun gravitational attraction) are relatively insignificant, other movements of lake water can be substantial. In the event known as a seiche, wind pushes water up against one shore and the water then flows back to the opposite shore, like water in a washtub being rocked. Seiches can be important in the transportation of sediments. Investigators have measured seiches in Lake Erie up to 8 feet (2.4 m) in height. Seiches also can be produced by earthquakes, sudden changes in atmospheric pressure, heavy rains, surges in glacial meltwater from nearby mountains, and variations in water density (Wyckoff 1999).

Waves on large bodies of water such as the Great Lakes shape shores of loose material, building sand barriers (including spits), as well as beaches with scarps, berms, and beach ridges. Storm waves can attack weak bedrock that fringes lakeshores, undercutting these rock formations and creating cliffs. In cold regions in winter, expanding lake ice pushes sand and rock fragments up the beach, creating ridges. Waves on the largest lakes, such as Lake Bonneville during the pluvial period, have cut terraces on adjacent highland slopes (Wyckoff 1999).

Lakeshores also exhibit rill marks, swash marks, and ripple marks. On the landward side of beaches, enough sand may be deposited for dunes to form; for example, the spectacular Indiana Dunes at the southeastern edge of Lake Michigan formed of glacial drift.

Littoral Caves

The headlands on rocky lakeshores are exposed to intense wave, wind, and storm action. Eventually littoral caves may form in less resistant, easily erodible bedrock located on promontories. Also see Sea and Littoral Caves as part of NPS—Caves and Karst.

Lakeshores in Parks

• Sleeping Bear Dunes National Lakeshore, Michigan—[Geodiversity Atlas] [Park Home]
• Indiana Dunes National Park, Indiana—[Geodiversity Atlas] [Park Home]
• Isle Royale National Park, Michigan—[Geodiversity Atlas] [Park Home]
• Apostle Islands National Lakeshore, Wisconsin [Geodiversity Atlas] [Park Home]

Related Links

• NPS—Beaches and Coastal Landforms
• NPS—Caves and Karst, Littoral Caves
• NPS—Coastal Geology
• NPS—Geology
• NPS—Oceans