Superior Shoal

Superior Shoal's four geologic ridges. Contour interval: 20 feet.

The Superior Shoal is a geologic shoal of approximately 20 square miles (52 km²) located 50 miles (80 km) north of Copper Harbor, Michigan in the middle of Lake Superior whose highest point lies only 21 feet (6.4 m) below the lake's surface.^[1] The shoal is a hump of Keweenawan basaltic lava flows with ophitic interiors and amygdaloidal tops in an otherwise deep part of the lake, and though fishermen had known of its existence for generations it was only officially charted in 1929.^[2]:193 It has been theorized that the World War I French minesweepers Inkerman and Cerisoles, which disappeared during their maiden voyage on Lake Superior in mid-November 1918, may have run aground on this shoal^[2]:192 and some have theorized that it may have been to blame for the November 10, 1975 sinking of the SS Edmund Fitzgerald,^[3] and the November 21, 1902 disappearance of the SS Bannockburn, the "Flying Dutchman of the Great Lakes", as well. It is one of the known off-shore spawning and foraging habitats for the juvenile lean lake trout.^[4]

Geology

The shoal consists of four geologic ridges: the north ridge, the central ridge, the halfway ridge, and the south ridge. The north ridge is a subtle but distinct rise across the northern portion of the shoal; the central ridge consists of a few high peaks in the eastern-center of the shoal; the halfway ridge is the largest ridge and stretches in an arc from east to west across the entire feature; the south ridge is made up of two associated basalt rises on the southern edge of the formation. The Isle Royale Fault creates a gorge between the north ridge and the other three ridges.^[5]

A different shoal with the same name is located just off Delf Island in Georgian Bay east of Lake Huron in Ontario.^[6]

Coordinates: 48°4′N 87°5′W / 48.067°N 87.083°W

References

1. Marshall, James R. (2005). Shipwrecks of Lake Superior. Lake Superior Port Cities. p. 48. ISBN 978-0-942235-67-8.
2. Bourrie, Mark (2005). Many a midnight ship: true stories of Great Lakes shipwrecks. University of Michigan. ISBN 978-0-472-03136-8.
3. Stonehouse, Frederick (2006) [1977]. The Wreck of the Edmund Fitzgerald (6th ed.). Gwinn, Michigan: Avery Color Studios. ISBN 1-892384-33-7.
4. Horns, William H. (2003). Fish-community objectives for Lake Superior. p. 35.
5. Manson, Matthew; Halls, Henry C. (1991), "An investigation of Superior Shoal, central Lake Superior, with a manned submersible", Canadian Journal of Earth Sciences 28: 145–150, doi:10.1139/e91-013
6. United States (1921). Great Lakes pilot: including north channel, Lake Michigan, and Lake Superior. Lake St. Clair, St. Clair River, Lake Huron, Georgian Bay, Volume 1 (Second ed.). Hydrographic Office, US Navy. p. 249.