EPISODE:
ALPINE DRIFTING
"Others have referred to the deluge,—a convenient agent in which they find a simple solution of every difficult problem exhibited by alluvial phenomena" (Lyell 1833, p.148)
Charles Lyell (1797-1875) first suggested in 1833 (p.149) that earthquakes might shake rocks onto glaciers and also dam glacial meltwater lakes; ice-bergs calving off the glaciers would thus carry massive stones and if the dam gave way they would float these down valley. In 1835 (p. 424) Lyell was openly critical of the mechanism suggested by von Buch following the Val des Bagnes disaster, stating that water could not transport the stones, but ice-bergs could: "Ice, as has been often suggested, may have contributed its aid to the transfer of such blocks; for some of the masses are so enormous, that not even a flood like that in the valley of Bagnes, in 1818, can be supposed to have conveyed them to considerable distances by the power of water alone . . . [Alternatively,] on the bursting of the temporary barrier, the whole mass of waters, together with huge rocks buoyed up by ice, would descend with tremendous violence into the lower country."
Moraine ridge-dammed lake in front of the
Steigletscher (Stein Glacier) in the Bernese Alps. The huge moraine dates from
1860, the maximum of the Little Ice Age. In addition to ice fall and
moraine-dammed lakes, there are examples of landslide-dammed lakes in the Alps:
see
http://www.swisseduc.ch/glaciers/alps/index-en.html
(GoogleEarth snapshot)
QUESTIONS
Icebergs had been seen to transport massive rocks in the open ocean. How might one refute Lyell's hypothesis with some simple calculations?
REFERENCES
Lyell, C. 1833 Principles of geology, volume 3 (John Murray, London)
http://www.google.com/books?id=zqkJAAAAIAAJ&pg=PR3
1835 edition: http://books.google.com/books?id=oaIBAAAAYAAJ&pg=PA5#v