Front variation measurements provide information on the advance or retreat of the glacier tongue. In the field, front variation is typically observed once a year (towards the end of the melt period) by repeat measurements of the distance between prominent landmarks (e.g., rocks or cairns) and the glacier front using tapes, laser rangefinders, or global positioning systems.
At multi-year intervals, front variation can also be measured from aerial and satellite images or reconstructed from moraine positions or historical sources. Front variations are measured in the horizontal plane using the measurement unit meter [m] with positive and negative values indicating glacier advance and retreat, respectively.
Cumulative front variations show the glacier reaction to the meteorological conditions of past years, decades or even centuries.

Figure 1. Repeat image from the same location in front of the tongue of Morteratsch Glacier in 1985 (top), and 2021 (bottom). Image: Jürg Alean, swisseduc.ch, https://www.swisseduc.ch/glaciers/morteratsch/2021/index-de.html?id=0.

Figure 2. Tongue location and changes in length of the Morteratsch Glacier since 1880. The measured retreat is cumulated over the years and plotted as a curve in the graph as a cumulative change in length. Source: SCNAT Wissen, https://naturwissenschaften.ch/snow-glaciers-permafrost-explained/glaciers/length_variation.