I'm hoping to push through the December 1957 issue of the IGY Bulletin before I start some holiday travel later this week. I know, not the best time to go traveling, but planning was made before Omicron came along, and everyone in the party is fully vaccinated and boosted. So crossing my fingers (and being as careful as I can) on this one.
First, some back ground on ocean ridges, the theme of this article. The bathymetric mapping of the sea floor took off in the late 1800s, first with soundings by lowering weighted lines to the sea bottom, then by sonar in the 1920s, and then by multibeam and sidescan sonar in the 1960s. Bruce Heezen and Marie Tharp's Physiographic Map of the North Atlantic in 1957, the year of the IGY, was the first map that enabled the general public to visualize what the ocean floor really looked like. Twenty years later they produced the first complete world map of the ocean floors.
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| Heezen and Tarp map of the sea floor, 1977 (Lamont-Doherty Earth Observatory) |
Marie Tharp's contributions were downplayed early in her career due to the sexism prevalent in the Earth sciences. Belatedly, Tharp became recognized for her accomplishments. Twenty years further on, in 1997, the Library of Congress named her as one of the four greatest cartographers of the 20th century.
The diagram below illustrates major features of the sea floor. There is no scale in this schematic illustration, but the Mid-Atlantic Ridge system rises about 3 km above the ocean floor, and is 1000-1500 km wide.
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| Major features of the sea floor (University of Puerto Rico) |
Understanding the origin of the mid-ocean ridges became key to the theory of sea-floor spreading in the early 1960s, which in turn became incorporated into the theory of plate tectonics later that decade.
The IGY Bulletin article starts with:
On August 12, 1957, geophysicists on IGY Drifting Station A, in the Arctic Ocean, reported that the ice floe on which the station is established had floated over a submarine ridge, or mountain range, rising more than 5000 feet above the ocean floor.
The ridge was inferred from a series of 13 seismic depth soundings (yielding shorter echo times from the elevated ridge for the seismic waves) and gravity measurements (higher values due to rock in the ridge displacing lower density ocean water). The fact that the ridge feature could be observed over several days of drifting suggested that it was fairly extensive.
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| From the IGY Bulletin article |
The article stated that the topographic extent of the discovered feature (shown by the series of dots left of center in the above figure) was uncertain, but it seemed to parallel a previously known feature, the Lomonosov Ridge (discovered in 1948, and now the focus of an important geopolitical dispute).
By comparing with the contemporary map of the Arctic sea floor below, and as also stated in this article, the feature discovered in 1957 was what is now recognized as Alpha Ridge.
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| Arctic Ocean seafloor features map. Note the orientation is not the same as for the preceding map. |
The Bulletin article continues by discussing the implications of sea floor bathymetry for better understanding water circulation in the Arctic Ocean.
In prepping for this post, I bought the only stamp I could find showing a mid-ocean ridge, from Ascension island. It has its own listings in the Scott catalogs, but is part of the British Crown Colony of St. Helena. As the map on the stamp shows, Ascension as well as St. Helena are on the Mid-Atlantic Ridge system. The stamp was issued in 1980 to commemorate the sesquicentennial of the founding of The Royal Geographic Society.
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| Ascension stamp, Scott #268 (not my stamp, which has yet to arrive) |
I visited three islands of the beautiful Azores chain in 2016, and had a great time. All these islands, also on the Mid-Atlantic Ridge system, are largely volcanic, and I visited several great volcanic spots.
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| Sete Cidades volcano crater lakes, island of São Miguel, Azores |
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