The Oberaletsch glacier with a surface of approximately 19 km2 is the second largest glacier in the Aletsch area and the third largest in the World Heritage site Swiss Alps Jungfrau-Aletsch. Since 1850, the left glacier tongue shrunk more than 1.5 km. The Oberaletsch glacier was divided during high extension periods at the Obfliejeregga in two glaciers: the left tongue pushed through the Oberaletsch gorge, filled it with ice and merged at the "Tälli" with the Great Aletsch glacier. At this confluence they reached earlier with the cattle across the ice from Üsseren to the Inner Aletschji. The right glacier tongue was wider and flatter and ended near the huts of the Üsseren Aletschji. Above the Oberaletsch gorge and in the Üsseren Aletschji witness high and sharply ridged moraine ramparts of the former expansion of the Oberaletsch glacier until mid-19th century.
The right glacier tongue melted after the last high expansion around 1850/60 within only 25 to 30 years to a small rest. At the same time also the glacier tongue in the gorge was separated from the Great Aletsch glacier. Since the start of the measurements in 1964, this tongue melted back by 300 m, since 1870 by as much as 1.500 m.