The Unteraar glacier is the third largest glacier in the World Heritage site and one of the largest ice streams of the Alps. The ice stream is fed by three firn areas. The smaller Strahlegg, Finsteraar and Lauteraar glaciers meet and unite to the Unteraar glacier, which flows into the Lake Grimsel. The combined valley glacier has currently a total surface area of 24,4 km2 and is 12,3 km long. The glacier tongue is compared to other glaciers in the Alps very heavily covered with debris. The steep cliffs surrounding the glacier are the reason, since rock falls often drop down on the ice. The Unteraar glacier can be considered as the "cradle of the glaciology": already in the 19th century renowned scientists made their fieldwork here and began to contribute first evidences to the theories regarding the Ice Ages and glacial advances.