How much water is there in Lake Superior?

Lake Superior contains an astounding 2,900 cubic miles of water, making it the largest freshwater lake in the world by surface area. With a surface area of 31,700 square miles, Lake Superior could cover the entire states of South Carolina or Maine. Here’s a quick rundown of some key facts about the immense amount of water in Lake Superior:

Lake Superior Fast Facts

  • Total water volume: 2,900 cubic miles
  • Deepest point: 1,333 feet
  • Average depth: 483 feet
  • Water residence time: 191 years (the time it takes for the lake’s water to be completely replaced)
  • Shoreline length: 2,726 miles
  • Surface area: 31,700 square miles

Visualizing the Volume of Water

It’s hard to wrap your head around just how much water 2,900 cubic miles is. Here are some comparisons to help conceptualize it:

  • It’s enough water to cover all of North and South America under a depth of 1 foot.
  • It’s more than 3 quadrillion (3,000,000,000,000,000) gallons.
  • It’s over 350 billion (350,000,000,000) Olympic-sized swimming pools.

Another way to comprehend the vastness is to think about drinking it all. If you drank 8 ounces of Lake Superior water every day, it would sustain you for over 2 million years!

Depth and Shape

Lake Superior’s average depth is 483 feet, deeper than the average depth of Lake Michigan (279 ft) and Lake Huron (195 ft). But Superior’s most striking depth is at its deepest point of 1,333 feet, well over a quarter mile down. This max depth is second only to Lake Baikal in Russia, the world’s deepest lake.

The bottom terrain of Lake Superior ranges from shallow sandy regions to deep pits and trenches. The steep drop-offs and deep waters are due to the lake’s formation – it lies in a depression carved out by ancient glaciers. Lake Superior’s irregular shape also comes from this glacial history, with its “bays and inlets sculpted by the scouring action of glacial ice sheets” (EPA).

Water Supply and Output

The primary source of water for Lake Superior is precipitation falling directly onto its surface. The lake’s vast watershed, draining over 81,000 square miles in the U.S. and Canada, also feeds water through rivers and streams. The largest tributary is the Nipigon River, supplying about 5% of the lake’s total water.

There are only two outlets for water to leave Lake Superior – the St. Marys River and the evaporation off its surface. The St. Marys River flows eastward and connects the lake to Lake Huron, part of the Great Lakes system. Evaporation accounts for about 39% of total water loss each year.

Water Input Source Volume Per Year
Precipitation onto lake surface 91 km3
Surface runoff from watershed 114 km3
Total Input 205 km3
Water Output Volume Per Year
Evaporation 80 km3
Outflow through St. Marys River 125 km3
Total Output 205 km3

Water Residence Time

Water residence time refers to how long water stays in a particular lake or reservoir before flowing out or evaporating. For Lake Superior, the residence time is about 191 years – meaning it would take around two centuries to completely refresh all the water in the lake.

This lengthy time results from the large volume of water compared to the relatively small rates of evaporation and outflow. Lake Superior has by far the longest residence time of the Great Lakes. For comparison, Lake Erie only has a residence time of 2.6 years!

Water Quality

Lake Superior maintains exceptionally clean and clear water quality due to its cold temperatures, large volume, and lack of urbanization along its shoreline. It holds about 10% of the surface freshwater in the world, but only 1% of the nutrient inputs. This makes Superior an oligotrophic lake, meaning its nutrient and algae content are low.

However, threats in recent decades include:

  • Toxic pollutants like mercury and PCBs
  • Invasive species disrupting the ecosystem
  • Increased surface water temperatures
  • Shoreline development and habitat loss

Ensuring the long-term health of Lake Superior requires vigilant monitoring, sustainable use of resources, control of invasive species, and low-impact development along its shores.

Significance

The tremendous volume of clear, fresh water in Lake Superior is one of the most valuable resources in North America. The lake moderates climate, provides drinking water, enables shipping and transportation, offers recreation opportunities, and supports livelihoods. It holds 10% of the world’s surface freshwater supply, serving multiple states, provinces, tribal nations, and an international border region.

Understanding Lake Superior’s immense scale, yet fragile nature, fosters appreciation and advocacy for protecting its waters. Quantifying the lake’s 2,900 cubic miles of water is just the beginning of comprehending its global significance.

Conclusion

Lake Superior stands out for many superlatives – largest by surface area, second deepest, and most voluminous of the Great Lakes. Its 2,900 cubic miles of water seem almost unfathomable. That’s enough to flood all of North and South America in 1 foot of water! And at its deepest point, you could stack two and a half Sears Towers on top of each other before reaching the bottom. Lake Superior’s vast scale and pristine waters make it one of the most valuable freshwater resources on Earth. But it also faces environmental threats that require vigilance. Understanding the immensity of Lake Superior creates appreciation for the critical need to protect its waters now and for future generations.

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