Using the data in Table 1, calculate the mean annual rate of glacier retreat for the selected glaciers in the Southern Andes between 2010 and 2020.
Show your working. Give your answer to one decimal place.
| Glacier | Average annual retreat rate (metres per year) |
|---|---|
| Upsala | 41.8 |
| Viedma | 37.5 |
| Grey | 32.4 |
| O'Higgins | 28.1 |
| Tyndall | 24.6 |
| Serrano | 19.3 |
| Dickson | 16.2 |
| Balmaceda | 11.8 |