Lake Champlain does not experience true, measurable gravitational tides. The daily rise and fall of water levels observed in oceans are driven by astronomical forces, which do not produce a significant effect on this relatively small, enclosed body of water. Any natural water level fluctuations noticed on Lake Champlain are instead caused by atmospheric and weather-related forces.
Understanding the Mechanics of Oceanic Tides
Oceanic tides are a direct consequence of the gravitational forces exerted primarily by the Moon and, secondarily, the Sun. The Moon’s gravity is not uniform across the Earth’s vast diameter; this difference in gravitational pull is known as differential gravity and generates the tides.
On the side of Earth facing the Moon, water is pulled toward the Moon more strongly than the solid Earth, creating a bulge. On the opposite side, the solid Earth is pulled more strongly than the distant water, leaving the water behind to form a second, opposing bulge. The Earth rotates underneath these two gravitational bulges, which remain aligned with the Moon.
As any point on the globe passes through the center of a bulge, it experiences a high tide, and passing between the bulges results in a low tide. This celestial geometry and the fluid nature of the world’s oceans allow for the twice-daily, predictable rhythm of the astronomical tide.
Scale Matters: Why Lake Size Nullifies Gravitational Tides
For differential gravitational force to create a noticeable tidal bulge, the body of water must be vast enough to show a significant difference in distance between its near and far sides relative to the Moon. Lake Champlain is too geographically constrained and its mass too small for this differential pull to register a measurable effect. The tidal force is inversely proportional to the cube of the distance, meaning the force difference across a short distance is negligible.
Lake Champlain is an enclosed, rigid basin, which prevents the large-scale movement of water required to form astronomical bulges. The predicted astronomical tide on a body of water the size of Lake Champlain would be on the order of a fraction of an inch. This minuscule gravitational influence is completely masked by other environmental factors and overwhelmed by far more powerful local forces.
Seiches: The Real Driver of Lake Champlain’s Water Movement
The water level fluctuations noticed on Lake Champlain are due to a phenomenon called a seiche, which is a standing wave oscillation in an enclosed body of water. Seiches are meteorological events, not astronomical ones, and are caused by local weather conditions.
The primary triggers for a seiche are sudden changes in barometric pressure or sustained, strong winds blowing across the lake surface. Strong winds push water toward one end of the long, narrow basin, causing the water level to pile up at that end while simultaneously dropping at the opposite end.
When the wind subsides, the piled-up water rushes back across the lake to restore equilibrium, creating a sloshing motion that can continue for hours. During strong events, the difference in water level between the north and south ends can vary by as much as one to one and a half feet. These oscillations cause water levels to appear to rise and fall over hours or days, an effect often mistaken for a true tide.