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II.—Contributions to the Study of Volcanos

Published online by Cambridge University Press:  01 May 2009

John W. Judd
John W. Judd
Affiliation:
On the Origin of Lake Balaton in Hungary.
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Extract

In our last chapter we referred to the frequency of the occurrence of lakes in districts which contain volcanos that are still active or have only recently become extinct. In connexion with this subject, we must also call attention to the interesting circumstance that, wherever the geologist finds evidence of the former action of subaerial volcanos, there he almost invariably detects proofs also, that numerous lakes have been formed and successively filled up with sediments. Very strikingly is this fact illustrated among the great series of volcanic rocks, which, during a great portion of the Tertiary period, were being erupted in Central and Southern Europe; and which form an almost complete girdle surrounding, but lying at a considerable distance from, the great central masses of the Alps. We have in these districts the most unmistakable palæontological evidence that the periods of violent volcanic activity were also characterized by the repeated formation and filling up of lake-basins.

Type
Original Articles
Information
Geological Magazine , Volume 3 , Issue 1 , January 1876 , pp. 5 - 15
Copyright
Copyright © Cambridge University Press 1876

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References

page 5 note 1 See Geol. Mag. 1875, Decade II. Vol. II. p. 349.Google Scholar

page 5 note 2 It has been suggested to me by my friend Mr. Scrope that this fact of the very constant connexion between volcanic action and the formation of lake-basins would be brought out very clearly and impressively by an estimate of the number of lakes which at present exist in the Auvergne, together with those which have in very recent times been filled up with alluvium. The large map of that part of the Auvergne included within the Department of the Puy de Dôme, prepared by the Abbé Le Coq, lends itself admirably to such a purpose, and I have obtained from it the following results. The area of the Department of the Puy de Dôme is only a little greater than that of the English county of Lincoln, yet its surface is studded over with the relies of no less than 276 lakes and lakelets. These may be classified as follows:

In this estimate I have included only the smaller examples of lakes of very recent date. The exact limits of the larger ones formed in the great river-valleys of the district it is now very difficult to define; and the patches of lacustrine sediment, filling innumerable depressions both of large and small size, of older date, are greatly obscured by later formed volcanic products or have been to a very great extent removed by denudation. I need only add that, as Le Coq well shows, the district of the Auvergne could never have been the seat of powerful glacial erosion, although the perpetual snow which may have clad the higher parts of the district during the Glacial Period may have contributed to the preservation, though not to the formation, of the lakes in question, in the manner pointed out in this paper.

page 9 note 1 There is still some doubt remaining as to the dimensions of the Victoria Nyanza. If Mr. Stanley's map represents the true positions of points on its shores, then the lake would certainly be larger than Lake Superior. If, however, Captain Speke's determinations of positions be accepted as the more accurate, as Mr. Ravenstein advocates, then the African lake would be about one sixth smaller than the American.

page 12 note 1 Mr. Scrope has called my attention to the interesting circumstance that in both the Scandinavian and North American regions, which exhibit such a vast number of lakes, we have unmistakable proofs that considerable movements of the surface of the land have been going on in comparatively recent times.

page 14 note 1 “The Great Ice Age,” page 289.