Friday, September 07, 2007

Note on Glacier-Recession, By T. V. Hodgson.

I would ask, what right have we to accept so readily the assumption that the temperature-conditions are becoming less severe, and that therefore the ice-cap is receding? It appears to me that the evidence is very weak at the best.
To begin with the Barrier, the amount of recession is small compared to its enormous area. It is greatest on the eastern side, where we have absolutely no knowledge whatever as to the source of supply. As compared to the mountains of the west, King Edward VII Land, from the little that has been seen of it, is low-lying country, and if such should ultimately prove to be the case it may also prove to be the larger feeding-ground.

Only in one spot has the rate of movement of the Barrier been measured. It was a rather crude measurement on a sledge journey near Minna Bluff, and is probably only local; it works out roughly at about a quarter of a mile a year. There is no evidence whatever as to the seasonal fluctuations of this ice-sheet: a series of mild or of severe seasons seems to me to be amply sufficient to account for the difference in the position of its northern face. The icebergs met with by the “Discovery” were for the most part very small, and I think I am right in saying that none of them were over three miles long.

As to glaciers, many of them do not come down to sea-level, but end abruptly, frequently at some considerable distance from it, and it is very much open to question if they have ever been anywhere near sea-level.

These facts have been interpreted as proof positive that the glaciation of the region is receding, it being regarded as certain that in no very far distant period in such a climate all these glaciers did come down to sea-level, and that those that do so now were formerly of far greater extent. This, I think, is far too hasty a conclusion, especially when we consider that McMurdo Sound has never previously been visited by man, and very little is known of the entire region from the point of view of its physiographical conditions. Some of the so-called glaciers, like that in McMurdo Sound described in the present paper, the Drygalski ice-sheet, and probably others, require more detailed examination before any really definite and satisfactory opinion can be pronounced.

Within forty miles of our winter quarters were no less than three active volcanoes, one smoking vigorously, the other two quiescent, and in such a volcanic district it is only fair to ask what would be the probable effect of—(1) volcanic eruption, (2) earthquake.

First with regard to volcanic eruption. For how long would the trace of such an occurrence be perceptible except by actual and close examination of the ground? Apparently not more than a few weeks. Lava-flows certainly might be conspicuous for a much longer period; but their age and finer characters are not to be detected at distances measured by the mile. Ashes and other volcanic ejecta might cover large areas, and under some conditions, such as seen in the Brown Island rubble-mass, would absorb the sun's heat and quickly effect considerable changes in the subjacent snow and ice. Under other conditions the snow might speedily and effectively hide all traces of any eruption as visible from a distance.

In the matter of earthquakes, their effect might be far more serious, and at the same time even less conspicuous. It is by no means inconceivable that the land in the vicinity of McMurdo Sound has undergone some change of level quite recently from a geological point of view. How could it be recognized on a first visit? Further, what would be the effect of a “good average” earthquake on the sea ice in such a region? It would certainly mean considerable rupture, with probably a serious effect on the adjacent shores. From such a sheet at the Great Ice Barrier it is quite reasonable to suppose that a single earthquake of any magnitude would make such a difference to that sheet as would take many years to replace.

Statement of a denier

0 Comments:

Post a Comment

Links to this post:

Create a Link

<< Home


Web Counters