A New Advance of the Moreno Glacier

Since the reconnaissance of Nichols and Miller, the Moreno Glacier has again dammed the Canal de los Témpanos. We were informed of this fact by an eye-witness on Ianding at Lago Argentino. It happened at the end of September 1951. When flying back two months later, the pilots of the L.A.N. told us that the waters had risen 9 m. behind the ice dam. According to HeimReference Heim ² and the above-mentioned authors, the damming of the Canal de los Témpanos in the twentieth century, that is since the settlement of this region, has occurred during:

• January 1917

• January to December 1935

• July 1939 to 17 February 1940

• Beginning of 1941 to 21 March 1942

• April to December 1948

• End of September 1951 and still persisting in February 1952.

It may be noted that, while the destruction of the dam occurs on the return of warm weather, the obstruction happens at every period of the year. Yet the wastage of the glacier is due principally to melting by the tepid water of the immense lake, and consequently seems to be related to the season. But really we know nothing about the temperature of the lakes of Argentino and Viedma throughout the year, although this may be of great interest.

The upper layers are exceptionally warm; at 1 km. from the front of the Viedma GlacierFootnote * in a bay crowded by floating blocks of ice and small icebergs (Fig. 1, p. 173), the temperature of the water was about 12° C. and the ice melted quickly, allowing the crystals, which were of hazel nut size and surprisingly uniform, to be seen. The greatest part of the lakes of Argentino and Viedma lie inside the barren Pampa, where the relative dryness and great purity of the air allow a high degree of insolation. Therefore, the cold melt water certainly flows to the bottom without mixing.

Fig. 1

The Viedma Glacier

Retreating Glaciers

Fig. 2, p. 171, taken from the U.S. Air Force Charts, ³ shows the south Patagonian ice field. It will be seen that the retreating Ameghino, Mayo and Upsala Glaciers are fed from snow fields through narrow passes. The firn line is about 1200 m. in this watershed.

Fig. 2.

The South Patagonian Ice Field. The stippled areas are the parts of glaciers lying below the firm line

The Ameghino Glacier issues from the snow field of the Moreno Glacier to the south through a narrow defile 18 km. from its end. The Mayo Glacier has two narrow passes at 9 and 12 km. from its snout. (If it continues to retreat it will uncover a hitherto dammed fjord which is still unexplored, and whose lower end is only 8 km. from an unexplored fjord in the Pacific Ocean.) The Upsala Glacier is fed by the Altiplano Italia, a flat ice field of an altitude of 2100 m., perhaps also by the Bertacchi Glacier, and three other narrow parallel glaciers at distances of respectively 11, 17, 25 and 30 km. from the snout. It is also probably fed through a pass 35 km. distant.

These conditions can entail a lag of twenty to fifty years between the variations of these glaciers and that of the Moreno Glacier with its simple shape. This, possibly, is the reason why they are still retreating while the Moreno advances.

The Viedma Glacier

This glacier is similar to the Moreno in its dimensions and its “orthodox” configuration ; it is essentially alpine in type, although immensely larger than the average Alpine glacier. It has diminished since the beginning of the century, its small right arm having disappeared (as reported by a local inhabitant, A. Madsen, to A. Heim). But a photograph from De AgostiniReference Agostini ⁴ taken in December 1930, when compared with Fig. 1, shows that the front has been stationary or has even advanced during the last 20 years. Rocks are no longer seen under the southern part of the front, the whole breadth of the glacier reaching to Lago Viedma.

Some new local phenomenon would perhaps have counteracted this advance. Observing still confidential A.A.F. photographs of 1945, Professor Carlos Keller of the University of Chile, found a volcanic crater of 7.7 km.² which was giving forth smoke in the accumulation area of the Viedma Glacier at the foot of the Mariano Moreno range. By kind permission of the Argentine Government we were enabled to fly over Monte Fitz Roy when returning, and I distinctly saw the crater of ashes among the ice, on a level with the glacier. It in no way resembled a nunatak, but was without any sign of volcanic activity. At the firn line there was an irregular brown marking which could not be explained by any moraine deposit, and is perhaps the evidence of a relatively recent eruption of ashes.

Corrie Glaciers Around Monte Fitz Roy

This mountain, 3441 m. high according to my calculations, is a fantastic tower of granodiorite, which rises from 1300 to 2000 m. over corrie glaciers flowing east—west, at the margin of the Patagonian ice field the “Hielo Continental”. The region was explored by De Agostini in 1931 and 1936, and numerous photographs are published in his book.Reference Agostini ⁴

All these glaciers end in a lake, formed by a barren moraine, except the small ones on steep slopes which cannot reach the bottom of the valley. This has often been considered a sign of very recent glacial retreat. (In the French Alps the only example is, I believe, the lake formed at the end of the Glacier des Bossons during recent years.) Now we must consider that, first, owing to the very strong and persistent west winds which produce important aeolian erosion, vegetation settles with great difficulty on barren mountains unless there is the screening effect of a forest. Secondly, these lakes are almost on the level with large neighbouring, horizontal valleys, so that fluvial erosion must be small and they cannot be drained off very quickly. The date of 1780–1880 advanced by Nichols and Miller after studying the Ameghino Glacier seems more credible than a more recent date.

At the south of Monte Fitz Roy flows the Grande Glacier (sometimes called the Fitz Roy Glacier although it does not come from the Fitz Roy). This ends in Lago Torre, from which flows the Fitz Roy River. The southern side ends at a rocky cliff 50 m. above the waters of the lake, while the north side is lower and afloat. The photographs of De Agostini in 1931, and of Heim in 1946, show no variation between these two dates. The glacier has not retreated 200 m. and decreased in height by 30 m. during these years as stated by Heim.

Between 1946 and 1952 the floating part of the glacier has retreated a little, but the level of the lake has been lowered from 12 to 15 m. by the erosion of the morainic dam by the river. The five or six rocky eminences forming part of the same cliff between the conic of the Grande Glacier and the valley have remained unchanged since 1931.

A similar lowering of the lake could perhaps explain the recession of the Rio Blanco Glacier between 1932 (first photograph of De Agostini) and the present day. In De Agostini’s photograph the glacier flowed over a cliff on the south side and plunged into the lake, covering a third of it without breaking up into seracs. To-day it only reaches the top of the cliff, from which seracs fall every two hours with terrific noise, forming four avalanche cones. From these cones blocks of white ice and firn laden with rock debris extend, more or less united, to form a little ice pack rather than a true re-formed glacier (Fig. 3, p. 173).

Fig. 3.

Laguna Sucia and the Rio Blanco Glacier

On 16 December 1913, as local inhabitants told De Agostini, a huge flood of water, earth and rocks washed down the Rio Blanco valley. An accumulation of rocks, still visible although invaded by vegetation, proves that it was caused by the destruction of a great dam in front of the Rio Blanco GIacier. We can assume that the glacier has been retreating since then, and has not yet reached its new equilibrium.

The next corrie glacier to the north, Piedras Blancas Glacier, so named for its white granodioritic frontal moraine, and Marconi Glacier, have the same extension as in 1936. The same can be said of the Gorra Blanca Glacier, which is not a corrie glacier but an outflow of the “Hielo Continental” through a broad pass between Cerro Gorra Blanca and Cordón Marconi.

Conclusion

There is then no proof of a general recession of south Patagonian glaciers during the last twenty years as in Europe. The known examples can be explained by local orographie factors. I think that hitherto authors have been influenced by the important and undeniable recession of glaciers in the Andes near Santiago and Mendoza, and the consequent production of many important “stone rivers,” but the climatic conditions of Pantagonia are quite different, and no extrapolation through 2000 km. can supply the missing records.

A pilot who has flown over Patagonia for the last twenty years has assured the writer that the climate has become less cold but wetter and cloudier during that time. With the invasion of settlers and sheep there were many huge fires which destroyed an important part of the primeval woods. This may make for dryness, but the influence of the relatively near and almost unknown Antarctic Continent should prevail.