The Physics
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Pressure at the Deepest Point in the Great Lakes

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Bibliographic Entry Result
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Strahler, Arthur. The Earth Sciences. New York: Harper&Row, 1963: 731. "Elevations and depths of the Great Lakes are shown by a profile in figure 41.6. Superior has the greatest depth, 1330 ft (370m); Michigan, Huron, and Ontario are of moderate depths, 800 to 900 ft (240 to 275 m); while by comparison Erie is very shallow, 200 ft (60 m)" 3.7 MPa
The World Book Encyclopedia. Chicago: World Book Company, 1996: Page 346. [Diagram] Lake Superior 1,330 ft (405 m) Depth 4.1 MPa
Minnesota Pollution Control Agency. Lake Superior Basin Information Document 1997. Minnesota: 1997: 24. "Lake Superior (Figure 4) is the largest, deepest and coldest of all the Great Lakes. At 31,700 square miles (The Great Lakes, 1995), Lake Superior is the largest freshwater lake in the world by area. By volume, it is the third largest with a total of 2,900 cubic miles (The Great Lakes, 1995). The hydraulic residence time for Lake Superior is 173 years (Quinn, 1992) and its maximum depth is 1,332 feet deep (The gReat Lakes, 1995)." 4.1 MPa
Encyclopedia Britannica. London: William Benton, 1971: 774. "Lake Superior at the head of the system stands at an average altitude of 600 ft above mean sea level and is 1, 333 ft deep.[406]" 4.1 MPa
Encyclopedia Britannica. London: William Benton, 2002: 445. "Lake Superior … is the second largest lake in the world (after the Caspian Sea) and the largest and deepest of the Great Lakes (mean depth 487 feet [148 m]). It lies at an elevation of 600 feet (183 m) above sea level and discharges into Lake Huron through the St. Mary's River." 1.55 MPa (at mean depth)

The Great Lakes -- Lakes Superior, Michigan, Huron, Erie and Ontario -- are the largest group of fresh water lakes in the world. Lake Michigan is the only lake out of the five that lies entirely within the United States. The other four are between the United States and Canada, forming part of the boundary that separates the two countries.

About 250,000 years ago a vast continental glacier moved across the land that is now the Great Lakes region. The glacier dug out deep depressions in the soft rocks and displaced large quantities of earth and rock. The glaciers withdrew about 11,000 to 15,000 years ago. The rocks and earth blocked the natural drainage of the depressions. The glaciers melted, water gradually filled in the depressions and the Great Lakes were formed.

The Great lakes have a massive area of 244,780 km2. Lake Superior is the largest of the five lakes with an area of 82,414 km2. Lake Superior is also the deepest with an approximate maximum depth of 405 m.

Pressure is defined as the force on a unit surface area. In the SI system, the unit of pressure is the pascal (Pa), which is equal to the force of one newton over an area of one squared meter. In a fluid at rest the pressure at any certain point is the same in all directions. Pressure increases uniformly with depth in a fluid. This concept is expressed in the formula P = ρgh, where P is the pressure in pascals, ρ [rho] is the density of the fluid in kg/m3, g is the acceleration due to gravity in m/s2, and h is the depth of the liquid in meters.

To find the gauge pressure at the deepest point of the Great Lakes the pressure formula P = [rho]gh can be used. To find the absolute pressure the pressure at the surface is added. The pressure at the surface is equal to 100,000 Pa. The density of water is equal to 1,000 kg/m3. The acceleration due to gravity on earth is equal to 9.81 m/s2. The approximate depth of Lake Superior, the deepest lake of the Great Lakes, is 405 m.

For example:

P = [rho]gh + 100,000 Pa
P = (1000 kg/m3)(9.81 m/s2)(405m) + 100,000 Pa
P = 4,073,050 Pa or 4.1 MPa

Sheena Grant -- 2003