Long-term Terminus Behavior
Fig. 15. Map showing locations of glacier termini monitored with SAR
Fig. 16. Terminal position changes on west side of South Patagonian Icefield
Fig. 17. Terminal position changes on east side of South Patagonian IcefieldSeasonal Terminus Behavior
Fig. 18. Seasonal changes in termini of Greve and Pio XI glaciers
We have used NASA SIR-C/X-SAR scenes in combination with ERS-1 and ERS-2 SAR data to map the terminus positions of 23 outlet glaciers of the South Patagonian Icefield (SPI) from July, 1992 through January 1997.
| NO. | Name | Change (m) | Time Period |
| 1 | LUCIA | -600 | 11/92 - 1/97 |
| 2 | PASCUA | 0 | 11/92 - 1/97 |
| 3 | ORIENTAL | 0 | 7/92 - 1/97 |
| 4 | BRAVO/RIVERA | 0 | 7/92 - 1/97 |
| 5 | O'HIGGINS (*) | 0 | 7/92 - 1/97 |
| 6 | CHICO | 0 | 7/92 - 1/97 |
| 7 | VIEDMA | 0 | 1/93 - 10/94 |
| 8 | UPSALA | -1200 | 1/93 - 10/95 |
| 9 | SPEGAZZINI | 0 | 10/94 - 10/95 |
| 10 | MAYO | 0 | 4/94 - 10/95 |
| 11 | AMEGHINO | 0 | 4/94 - 10/95 |
| 12 | MORENO (*) | 0 | 4/94 - 10/95 |
| NO. | Name | Change (m) | Time Period |
| 13 | JORGE MONTT | -2600 | 1/93 - 1/97 |
| 14a | OFHIDRO (N. ARM) | 0 | 7/92 - 1/97 |
| 14b | OFHIDRO (S. ARM) | -1400 | 7/92 - 1/97 |
| 15a | BERNARDO(N. ARM) | 0 (thinning) | 7/92 - 1/97 |
| 15b | BERNARDO(S. ARM) | 0 (thinning) | 7/92 - 1/97 |
| 16a | TEMPANO (N. ARM) | 0 (thinning) | 7/92 - 1/97 |
| 16c | TEMPANO (S. ARM) | 0 | 7/92 - 1/97 |
| 17 | OCCIDENTAL | 0 (thinning) | 7/92 - 1/97 |
| 18 | GREVE (*) | -1800 | 7/92 - 1/97 |
| 19a | PIO XI (N ARM) (*) | 0 | 7/92 - 1/97 |
| 19b | PIO XI (S ARM) (*) | -850 m | 7/92 - 1/97 |
| 20 | HPS 10 | 0 | 7/92 - 1/97 |
| 21 | HPS 12 | -1200 | 7/92 - 1/97 |
| 22 | HPS 13 | 0 | 7/92 - 1/97 |
| 23 | PENGUIN | 0 | 7/92 - 1/97 |
(*) Indicates interannual oscillations +/-
Of the 23 glaciers for which we have SAR coverage, many showed no change between 1992 and 1997, seven showed obvious retreat (of up to 1 km on Upsala Glacier), and four showed oscillating behavior of both advance and retreat during that time (for example, Greve Glacier.). These results are summarized in Figs. 16 and 17
Figure 16. The magnitude of changes in the terminal positions of nine of the major calving outlet glaciers from the west side of the South Patagoninan Icefields between 1992-1997.
Figure. 17. The magnitude of changes in the terminal positions of nine of the major outlet glaciers from the east side of the South Patagoninan Icefield between 1992-1997.
The data for Figs. 16 and 17 for behavior prior to 1992 are taken from the following: Aniya et al. (1992); Mercer (1968; 1970); Naruse et al. (1995); Warren and Sugden (1993); Warren (1994); Warren and Rivera (1994); and Warren et al. (1995).
Many of the glaciers draining the South Patagonian Icefield have been retreating throughout this century. There are a few exceptions, notably Pio XI Glacier and Moreno Glacier which have been advancing. We have combined our observations from the 1990s with air photos taken in the 1975 and previously published information on the 20th century position of these glaciers to extend the long term time series of terminus changes to the present.
One of the important questions raised in this study is how much of the recent change seen in these glaciers is an indication of global warming and climatic change and how much is controlled by local factors such as calving dynamics. Many glaciers in this area have undergone rapid retreat during the second half of this century from an advanced unstable position and no longer show retreat since they have reached a stable position again at a new pinning point (for example O'Higgins Glacier.) Some other glaciers seem to still be in rapid retreat, and have not yet reached a stable position (for example Upsala and Jorge Montt Glaciers.)
The closely repeated coverage in time by SIR-C/X-SAR and ERS-1 and ERS-2 imagers has shown a sequence of scenes that suggest there may be an important seasonal control on the terminus behavior some of the calving Patagonian outlet glaciers. Two calving glaciers, Greve Glacier and the north arm of Pio XI Glacier, both show a series of synchronous advances and retreats over the period of SAR coverage.
Figure 18. Seasonal behavior of Greve and Pio XI glaciers, western side of South Patagonian Icefield. Both glaciers calve into the same proglacial lake, Lago Greve, which was formed when a stream was blocked due to the advance of Pio XI earlier this century.
One hypothesis is that lower water levels (both in the lake and under the glacier) during the austral winter allows the center section of the glacier terminus to advance further into the lake. Then, throughout the spring and summer this advanced position becomes unstable as the glacier melting increases and contributes to a rising lake water level, and the terminus calves back to a more stable position.
Understanding the non-climatic controls on the behavior of calving glaciers is an important problem if we want to use the historic and contemporary record of change of calving glaciers as indicators of climate change. And this problem is especially important in Patagonia where almost all of the outlet glaciers are (or were until recently) actively calving into fiords or freshwater lakes.