The Great Lakes experience significant wave action, often challenging the common perception of a typical lake. Their sheer size—collectively the largest group of freshwater lakes on Earth—gives them many characteristics of oceans, leading to their frequent description as “inland seas.” This expansive surface area allows for the generation of large and powerful waves, particularly during strong weather events. Waves on the Great Lakes are a fundamental part of the freshwater ecosystem, influencing everything from coastal geology to maritime safety.
How Waves Form on Inland Seas
Wave generation on the Great Lakes is a process of energy transfer from the atmosphere to the water’s surface, driven primarily by wind. As wind blows over the water, it creates friction, which initially forms small ripples known as capillary waves. The wind “grips” these ripples, allowing more energy to be transferred and causing the waves to grow in size and speed.
The size of these wind-driven waves depends on three main factors: wind speed, wind duration, and the distance the wind travels over the water without obstruction, called the “fetch.” The Great Lakes, especially Lake Superior, have long fetches—distances that can exceed 350 miles—which permits waves to accumulate substantial energy. Strong storm systems, particularly during the fall, can sustain high winds over these long distances for hours, generating waves that can reach heights of 20 feet or more.
What Limits Wave Height and Power
Great Lakes waves do not achieve the sustained height or raw power of deep-ocean waves. The primary limiting factor is the finite size of the lakes, which restricts the maximum available fetch compared to the thousands of miles of open ocean. This limitation caps the amount of energy transferred from the wind to the water surface.
Another constraint is the relatively shallow average depth of the lakes compared to the ocean basins. As waves approach the shore, the lake bottom causes friction, slowing the base of the wave and forcing the crest to rise and break sooner. This shallow-water effect limits energy accumulation and prevents the formation of the massive, long-period swells characteristic of the deep ocean. The gravitational influence of the moon and sun produces only minuscule tides (less than two inches), meaning predictable tidal energy is absent.
Unique Wave Phenomena
The enclosed nature of the Great Lakes basin leads to unique water movements that go beyond standard wind-driven waves.
Seiches
The most notable is the seiche (pronounced “saysh”), a standing wave oscillation that causes the entire body of water to slosh back and forth. Seiches are typically caused by sudden shifts in atmospheric pressure or strong winds that rapidly push water to one end of the lake. When the force subsides, the water rebounds, starting an oscillation that can last for hours or even days.
The period between the high and low water levels during a seiche can range from four to seven hours, often mistaken for a normal tide cycle. These events can cause rapid water level changes of several feet; Lake Erie is particularly susceptible due to its shallow depth and east-west orientation.
Rogue Waves and Meteotsunamis
In addition to seiches, the Great Lakes can occasionally produce rogue waves or meteotsunamis. A meteotsunami is a large, single- or few-wave event caused by fast-moving severe weather systems like squall lines. These progressive waves can be highly destructive, sweeping people off piers and causing localized flooding.
Navigating Great Lakes Wave Hazards
The wave dynamics of the Great Lakes present several specific hazards for both mariners and coastal communities. For navigation, the lake-generated waves are often steeper and closer together than ocean swells, creating an unpredictable “chop” that is difficult for small vessels to manage. Furthermore, storm systems can generate waves very rapidly, giving mariners little time to seek safe harbor.
Along the shorelines, wave energy is a major factor in coastal erosion, especially during periods of high lake levels or severe storms. The wave action, combined with storm surges, can undercut bluffs and damage coastal infrastructure. In the winter and spring, powerful waves and wind can drive massive sheets of lake ice onto the shore, a process called “ice shove,” which can destroy structures and reshape the coastline. Rip currents, narrow channels of water moving rapidly away from the shore, are also a significant risk on Great Lakes beaches.