Water

Measurement of the speed

The measurement of the speed at which a glacier is moving was certainly one of the first operations carried out by the first glaciologists in the 19th century, along with the observation of the front variations. In order to measure the speed at which the ice is moving, it is necessary to determine a fixed point on the glacier, easy to recognize thanks to some particular feature (e.g. a large boulder on the surface), or else marking it with one or more stakes, and constantly taking measurements (a number of times a year for a number of consecutive years) of the glacier movement vis-à-vis a fixed observation point outside the glacier. Today, the use of aerial photographs and satellite images, together with use of particular instruments such as GPS, make this operation much easier, rapid and precise than in the past when operators had to take measurements directly on the glacier, often having to face a number of difficulties in reaching the measurement points. By means of more complex observations, made by aligning masses or glacier sinkhole systems, it has been possible to identify different areas moving at different speeds in the glacier. The speed at which glaciers move varies greatly in different glacier structures. The speed can vary during the year (usually slowing down in winter) and also from one year to another.