Firn Spiegel 1 : Thin layer of clear ice on the surface which permits sunlight to pass through to cause melt in the subsurface layers. A highly-reflective, mirror-like surface
The American Avalanche Institute, Glossary of Terms, Wyoming, USA 2002. http://www.avalanche.org/moonstone/biblio%20&%20gl oss/GLOSSARY%20OF%20TERMS.htm, (ND/ Avalan/ Snowpack - Amer) {472}