Part 16

Stake 1 2 3 4 5 6 7 8 9 10 Inches 8 10 14 16 16 16 18 17 15 14

234. Thus the winter motion of the Mer de Glace near the Montanvert is, in round numbers, half the summer motion.

235. As in summer, the eastern side of the glacier at this place moved quicker than the western.

§ 34. Motion of the Grindelwald and Aletsch Glaciers.

236. As regards the question of motion, to no other glacier have we devoted ourselves with such thoroughness as to the Mer de Glace; we are, however, able to add a few measurements of other celebrated glaciers. Rear the village of Grindelwald in the Bernese Oberland, there are two great ice-streams called respectively the Upper and the Lower Grindelwald glaciers, the second of which is frequently visited by travellers in the Alps. Across it on August 6, 1860, a series of twelve stakes was fixed by Mr. Vaughan Hawkins and myself. Measured on the 8th and reduced to its daily rate, the motion of these stakes was as follows:--

MOTION OF LOWER GRINDELWALD GLACIER.

Stake 1 2 3 4 5 6 7 8 9 10 11 12 Inches 18 19 20 21 21 21 22 20 19 18 17 14

237. The theodolite was here planted a little below the footway leading to the higher glacier region, and at about a mile above the end of the glacier. The measurement was rendered difficult by crevasses.

238. The largest glacier in Switzerland is the Great Aletsch, to which further reference shall subsequently be made. Across it on August 14, 1860, a series of thirty-four stakes was planted by Mr. Hawkins and me. Measured on the 16th and reduced to their daily rate, the velocities were found to be as follows:--

MOTION OF GREAT ALETSCH GLACIER.

East Stake 1 2 3 4 5 6 7 8 9 10 11 12 Inches 2 3 4 6 8 11 13 14 16 17 17 19 Stake 13 14 15 16 17 18 19 20 21 22 23 Inches 19 18 18 17 19 19 19 19 17 17 15 Stake 24 25 26 27 28 29 30 31 32 33 34 Inches 16 17 17 17 17 17 17 17 16 12 12 West

239. The maximum motion here is nineteen inches a day. Probably the eastern side of the glacier is shallow, the retardation of the bed making the motion of the eastern stakes inconsiderable. The width of the glacier here is 9,030 links, or about a mile and a furlong. The theodolite was planted high among the rocks on the western flank of the mountain, about half a mile above the Märgelin See.

§ 35. Motion of Morteratsch Glacier.

240. Far to the east of the Oberland and in that interesting part of Switzerland known as the Ober Engadin, stands a noble group of mountains, less in height than those of the Oberland, but still of commanding elevation. The group derives its name from its most dominant peak, the Piz Bernina. To reach the place we travel by railway from Basel to Zürich, and from Zürich to Chur (French Coire), whence we pass by diligence over either the Albula pass or the Julier pass to the village of Pontresina. Here we are in the immediate neighbourhood of the Bernina mountains.

241. From Pontresina we may walk or drive along a good coach road over the Bernina pass into Italy. At about an hour above the village you would look from the road into the heart of the mountains, the line of vision passing through a valley, in which is couched a glacier of considerable size. Along its back you would trace a medial moraine, and you could hardly fail to notice how the moraine, from a mere narrow streak at first, widens gradually as it descends, until finally it quite covers the lower end of the glacier. Nor is this an effect of perspective; for were you to stand upon the mountain slopes which nourish the glacier, you would see thence also the widening of the streak of rubbish, though the perspective here would tend to narrow the moraine as it retreats downwards.

242. The ice-stream here referred to is the Morteratsch glacier, the end of which is a short hour's walk from the village of Pontresina. We have now to determine its rate of motion and to account for the widening of its medial moraine.

243. In the summer of 1864 Mr. Hirst and myself set out three lines of stakes across the glacier. The first line crossed the ice high up; the second a good distance lower down, and the third lower still. Even the third line, however, was at a considerable distance above the actual snout of the glacier. The daily motion of these three lines was as follows:--

First Line.

Stake 1 2 3 4 5 6 7 8 9 10 11 Inches 8 12 13 13 14 13 12 12 10 7 5

Second Line.

Stake 1 2 3 4 5 6 7 8 9 10 11 Inches 1 4 6 8 10 11 11 11 11 11 11

Third Line.

Stake 1 2 3 4 5 6 7 8 9 10 11 Inches 1 2 4 5 6 6 7 7 5 5 4

244. Compare these lines together. You notice the velocity of the first is greater than that of the second, and the velocity of the second greater than that of the third.

245. The lines were permitted to move down wards for 100 hours, at the end of which time the spaces passed over by the points of swiftest motion of the three lines were as follows:

Maximum Motion in 100 Hours.

First line 56 inches. Second line 45 " Third line 30 "

246. Here then is a demonstration that the upper portions of the Morteratsch glacier are advancing on the lower ones. In 1871 the motion of a point on the middle of the glacier near its snout was found to be less than two inches a day!