The Gorner Glacier (Gornergletscher) is a valley glacier found on the Monte Rosa massif close to Zermatt in the canton of Valais, Switzerland. It is about 14 km long and 1 to 1.5 km wide. The entire glacial area of the glacier related to Gorner Glacier is 68 km², which makes it the second largest glacial system in the Alps after the Aletsch Glacier system. Numerous smaller glaciers connect with the Gorner Glacier. Its tribunaries are (clockwise on this map ): Gornergletscher (after which the whole system is named), Grenzgletscher, Zwillingsgletscher, Schwärzegletscher, Breithorngletscher and Theodulgletscher (although this one is actually disconnected now); also Monte Rosa Glacier used to be connected. The main tribunary is Grenzgletscher.
An interesting feature of this glacier is Gornersee, an ice marginal lake at the confluence area of Gorner- and Grenzgletscher. This lake fills every year and drains in summer, usually as a Glacial lake outburst flood. This is one of few glacial lakes in the Alps exhibiting this kind of behaviour.
It is the source of the Gornera river which flows down through Zermatt itself. However most of its water gets captured by a water catchment station of the Grande Dixence hydroelectric power company. This water then ends up in the Lac des Dix, the main reservoir of Grande Dixence.