Sand cone
Sand cones , sometimes also called glacier, ice or melting cones , are a phenomenon on the surface of some glaciers . Often the structures made of ice and covered with a layer of sand have a circular cross-section and, depending on the stage of development, have a pronounced tip. The cones in the Alps reach a height of 1 to 5 m, rarely up to 10 m. There have been reports from Iceland of sand cones up to 30 m high.
Emergence
A prerequisite for the formation of a sand cone is first of all the presence of a glacier mill , which is partially filled with sand (stage A). This was typically brought in by surface glacier meltwater.
As the ice melts or evaporates in summer, the surface of the glacier sinks. The sand at the top of the glacier mill slides sideways and forms a pile (stage B).
The sand pile has a shielding and insulating effect against sunlight. As a result, the ice under the pile of sand melts more slowly than around it, so that the surface of the ice around the pile of sand sinks faster than under the pile itself (stage C).
If the ice cylinder under the sand heap continues to grow due to the subsidence of its surroundings, the insulating effect of the sand is missing on its sides. When it begins to melt from its upper edges, its shape changes into a truncated cone (stage D), the side surfaces of which are covered by sliding sand.
This process continues until the truncated cone has become a cone (stage E). This stage is stable longer because the sand re-insulates the ice cone against melting. The steepness of the surface of the cone is typically 40 °, the thickness of the sand cover 1–30 cm, more rarely 100 cm and more.
Typically, a cone of sand forms and disappears over the course of a summer. However, larger ones can survive two to three summers.
literature
- Alfred Güller: About «sand cones» on Central Switzerland and Valais glaciers . ( rero.ch [PDF; 5.0 MB ]).
- Gerhart Wagner, Jakob Saurer: Sand cone on glacier ice . 2006 ( wagnerger.ch [PDF; 138 kB ]).