Richard W. Ojakangas
Autor de Roadside Geology of Minnesota
Sobre El Autor
Obras de Richard W. Ojakangas
Etiquetado
Conocimiento común
- Género
- male
- Nacionalidad
- USA
- Lugar de nacimiento
- Warba, Minnesota, USA
- Lugares de residencia
- Duluth, Minnesota, USA
- Educación
- Stanford University (PhD|1964)
University of Minnesota, Duluth (BS) - Ocupaciones
- professor emeritus
geologist - Relaciones
- Ojakangas, Beatrice A. (wife)
Ojakangas, Gregory (son) - Organizaciones
- University of Minnesota, Duluth
Miembros
Reseñas
Estadísticas
- Obras
- 6
- Miembros
- 82
- Popularidad
- #220,761
- Valoración
- 3.9
- Reseñas
- 3
- ISBNs
- 9
The glacial geology can be better appreciated from topographic views. The ultraflat land in the northwest corner of the state is Lake Agassiz lakebed, and Red Lakes and Lake of the Woods are remnants (as are Lake Winnipeg, Lake Winnipegosis, Lake Manitoba, Cedar Lake in Manitoba and Lac la Ronge in Saskatchewan). At various times Lake Agassiz drained to the Arctic Ocean, Hudson Bay, the Atlantic, and the Gulf of Mexico; this last drainage route left the wide swath of flat terrain extending diagonally across the southern half of the state and now occupied by the Minnesota River, a classic example of an “underfit” stream – much smaller than its valley suggests (it was Glacial River Warren in the Pleistocene). Minnesota still has three drainage basins (to the Arctic Ocean via the Red River of the North, the Atlantic via the Great Lakes, and the Gulf of Mexico via the Mississippi) the triple point where the three connect is, again, pretty subtle. For this part of the state author Richard Ojakangas includes various historical tidbits to fill out the text; even so three quarters of the state take up only one quarter of the book.
There is, of course, a satisfactory amount of “real” geology in the northeast corner of the state, where the last glaciation conveniently scraped everything down to bedrock and didn’t leave a lot of ground moraine and outwash when it melted back. What’s there is pretty interesting indeed, including what were for a while the oldest known rocks in North American (since passed up by some in Wyoming and Ontario); surface traces of the Mid-Continent Rift; some nice Proterozoic greenstone belts documenting the very beginnings of continental drift; a Proterozoic suture zone; the Iron Range, and the Gunflint Chert where the first Proterozoic bacterial fossils were discovered (although the actual first discovery was made from Gunflint Chert outcrops in Ontario). Since major highways are sparse, the book provides a lot of get-out-and-walk investigations in this area, including mine tours and hikes along the Superior lakeshore.
Given the limitations of dealing with a state where much of the geology is Pleistocene, this is pretty well done. There are a lot of illustrations (sadly, many of the glacial geology pictures are of fresh roadcuts noted as “since grassed over”). I was a little disappointed in the lack of large scale geological background; it would have been nice to see some continental reconstructions from the Proterozoic illustrating how the continental collisions and rifting were supposed to work back then. To be fair, though, that issue is still unresolved so it might have been overly speculative for Ojakangas, and his reconstructions of Pleistocene glaciation episodes are well presented and very instructive. There’s an “Additional Reading” section which isn’t really a bibliography but is instead just what it says; additional reading for the layman geologist. I definitely want to do some more research on Glacial Lake Agassiz but will search for some more technical works.… (más)