The total area of this small glacier is about 19 kmē.  It is located just north of the so-called Fljotshlid County and is named after many peaks protruding through the firn.  The highest peaks are Ymir (1,462 m) and Yma.  A few of them are worthy challenges for mountaineers and during late winter and spring skiers frequent the area and stay in the three huts up there.  Under the ice cover of the eastern part the mountain structure is mainly rhyolite and under the northeast part is a cinder cone called Sindri.  It and several other similar craters suggest volcanic activity of this small central volcano during the early part of Holocene.  Traces of high temperature activity and the outlines of a caldera also support the theory about the existence of an active central volcano, which was mostly active during the latter part of the Ice Age.

In the slopes of this small mountain massif and the Thorsmork Area a thick layer of ignimbrite suggest a tremendous pyroclastic eruption about 250 thousand years ago.  Similar eruptions took place on the island Caribbean island Martinique in 1902, killing about 30,000 people, in 1980, when St Helens exploded, and in 1883, when the Indonesian island Krakatau exploded and caused the death of about 40,000 people.