| In temperate glaciers, snow repeatedly freezes and thaws, changing into granular ice called firn. |
| Melt and percolation through the weak firn layer bring most of the freeboard volume to the melting point. |
| Under the pressure of the layers of ice and snow above it, this granular ice fuses into denser and denser firn. |
| Conversely, an unusually light winter snowfall causes older firn and ice of lower albedo to be exposed earlier in the summer, producing increased melt and runoff. |
| Changes in the Earth's surface albedo are a useful indicator of firn pack loss and glacier retreat. |
| The more glacier ice that is exposed as the snow and firn disappear, the lower the albedo, and the faster the glacier loses mass. |
