Page:Quarterly Journal of the Geological Society of London, vol. 33.djvu/194

156 156 AMUND HELLAND ON THE FJORDS, LAKES,

the sea, or that the part under water is about six sevenths of the whole mass.

The heights of several bergs were measured. Of all those at the mouth of Jakobshavn, three exceeded 83 metres, the loftiest being 121 metres (according to several measurements with a theodolite), the highest which I have ever seen. I estimate the quantity of ice above the sea to have been 3,000,000 cubic metres, aud the whole mass of the berg 21,000,000 cubic metres. The depth of Jakobshavn Fjord, where the Greenlanders fish for halibut, is, judging from the length of their lines, about 390 metres. From these numbers we will endeavour to estimate the quantity of ice discharged through the Jakobshavn Fjord. According to some measurements, the height of the glacier above the sea, where it " calves," is about 40 metres. Here, then, its whole thickness must be at least seven times the above height ; for if it were floating, and so less thick, there would be no " calving : " hence the thickness of the glacier must be here at least 280 metres. Its mean rate of motion is 14*25 metres a day. The breadth of the fjord is 4500 metres ; its sides slope at angles of 20°, so its transverse section is a little more than 1,000,000 square metres. Hence the quantity of ice passing through this daily in summer is about 16,000,000 cubic metres. In like manner we find that the quantity of ice discharged by the Torsukatak glacier is 6,300,000 cubic metres a day. 16,000,000 cubic metres of ice represent what we may call a large berg ; so we see that the daily discharge through the fjord of Jakobshavn, notwithstanding the considerable velocity of the glacier, is only equal to one large berg a day. This may, perhaps, surprise any one who has seen on a summer's day the bergs passing in great numbers out of the Jakobshavn Fjord ; but it must be remembered that all the bergs produced during the long winter have to be removed during the short space of summer. True, indeed, the rate of flow of the glacier is probably diminished in winter, so that the quantity discharged on a summer's day does not enable us directly to calculate that of the whole year. If the rate of flow continued uniform, the Jakobs- havn glacier would discharge annually 5,800,000,000 cubic metres ; the Torsukatak glacier 2,300,000,000 cubic metres. It is not, how- ever, probable that the quantity actually produced would be so little as half of the above, for this would require the glacier to be motionless during the three winter months. So we may estimate the quantity of ice annually discharged from the Jakobshavn Fjord to be between 2,900,000,000 and 5,800,000,000 cubic metres, and that from the Torsukatak Fjord between 1,150,000,000 and 2,600,000,000 cubic metres. Calculating in like way the discharge of the smaller fjords, as, for example, Alangordlek, we find that it hardly produces one hundredth part of that from Jakobshavn.

Large as are the quantities of ice thus yearly discharged from the fjords, they form but a small fraction of the rain- and snowfall of inner Greenland, the greater part of this passing away in rivers be- neath the glaciers. Dr. Rink*, who estimates the ice yearly dis-

3E.,i. B.
 * "Om Vandets Aflob fra det indre af Gronland," Naturhistorisk Tidsskrift,