Lake Superior is the northernmost and westernmost of North America’s Great Lakes. It is the largest freshwater lake globally by surface area, spanning over 31,700 square miles. This vast expanse defines the border between the Canadian province of Ontario and the U.S. states of Minnesota, Wisconsin, and Michigan. Quantifying the volume of Lake Superior is necessary to grasp the scale of this massive hydrological feature.
Quantifying Lake Superior’s Volume
The volume of water in Lake Superior is primarily measured by multiplying its surface area by its average depth. Hydrologists estimate the lake contains approximately 2,900 cubic miles of water, or about 12,100 cubic kilometers.
The total volume is estimated to be close to 3 quadrillion U.S. gallons. This staggering number positions Lake Superior as the third-largest freshwater lake globally by volume, surpassed only by Lake Baikal and Lake Tanganyika. The average depth is 483 feet, with a maximum recorded depth of 1,332 feet.
The lake holds a volume of water greater than all the other Great Lakes combined. This significant contribution to the entire system is based on bathymetric surveys that map the lake’s deep basin.
Making Sense of the Scale
To conceptualize a volume of 3 quadrillion gallons, it is helpful to use comparisons that translate the number into a more tangible experience. The water in Lake Superior is so vast that it could theoretically cover the entire landmass of North and South America with a uniform layer one foot deep.
The volume is equivalent to holding the water of all the other Great Lakes—Michigan, Huron, Erie, and Ontario—with enough left over to fill three additional Lake Eries. This means the amount of water in one lake is greater than the combined total of the four lakes downstream from it.
The time it takes for the water to be fully replaced, known as the retention time, also demonstrates the scale of the basin. A single drop of water entering Lake Superior is estimated to remain in the lake for an average of 191 years before exiting into the St. Marys River. This exceptionally long flushing time has implications for any contaminants introduced into the system, as they would persist for nearly two centuries. The slow turnover rate emphasizes the deep and massive nature of the Lake Superior basin.
The Global Importance of This Freshwater Reserve
The massive volume of Lake Superior establishes it as a globally significant freshwater resource. It holds approximately 10% of the world’s liquid surface fresh water, excluding glaciers and ice caps. This makes the lake a major reservoir for a commodity that is increasingly strained worldwide.
The lake’s cold, clear, and deep waters support a unique ecology. It is classified as an oligotrophic system with relatively low nutrient levels, fed by over 300 streams and rivers. This diverse ecosystem includes over 80 species of fish. The biological health of this water body is tied to its volume and long retention time, which helps maintain its clarity and low temperatures.
Beyond its ecological role, the vast water mass significantly influences the regional climate, a phenomenon known as the lake effect. The water releases heat slowly in the fall and winter, resulting in increased snowfall on the downwind shores. Conversely, cooler water temperatures in the spring and summer temper the air along the shoreline, creating a milder environment than inland areas.