Tindfjallajökull (, alternatively Tindafjallajökull) is a glacier in the south of Iceland whose name is also given to the underlying stratovolcano. Tindfjöll (, "peak mountains") is a ridge that extends to the south of the glacier and is an alternative name for the volcano. The name of the glacier in Icelandic means "Tindfjöll glacier".

Geography

Its highest peak is Ýmir at 1462 m, which takes its name from the giant Ýmir of Norse mythology. The peak Ýma is about 500 m to its east. The Thórólfsfell (Þórólfsfel) tuya at 595 m is on the southern flanks of Tindfjallajökull, about 8 km south of the glacier. Its eastern slopes abut the Þórsmörk ignimbrite. The western flank has a prominence near Austurdalur and the eastern flank that of Vestriöxl at 1002 m. About 2 km to the north of Ýma is the peak of Sindri at 1272 m. Ásgrindur at 1299 m is a similar distance north of Ýmir.

Volcano

The central volcano is 15 to 20 km in diameter with a 5 by wide caldera and has erupted rocks of basaltic to rhyolitic composition. The most recent eruption is suspected to have been in the Holocene, and the prior mountain building eruptions must have been before 55,000 years ago. There are eight tuyas in the volcanic system. The largest, the asymmetric Thórólfsfell tuya with its area of about 8 km2 and prominence of about 450 m is the type tuya for tuya's where there is no evidence for the presence of a large and long-lived meltwater lake under the ice cover, as meltwater was able to drain away between its formative eruptions. In the 1980's it was postulated that the Þórsmörk ignimbrite originated from the volcano but it originated from Torfajökull to the north. Sultarfell is a pale coloured rhyolitic hill in the fissure swarm north-east of Tindfjallajökull. There is a hot spring in Hitagil to the south-east so some geothermal activity remains.

Glacier

It is capped by a glacier that has been mapped to a maximum in the 1890's of about 22.6 km2 in area, but which by 2019 had had a 45% decrease in area. In 1945 to 1946 it was mapped to an area of 16.8 km2, in 2000 15 km2 and 2019 12.4 km2. The only current outlet glacier with a moraine is unnamed down the Eystri Botná valley but between 1994 and 2006 had surge glacier characteristics before regressing again. Part of the glacier to the north has now separated into three with one glacier being called Blesárjökull. A small glacier on the eastern slopes of Ýma called Ýmujökull has disappeared. The rivers that flow from the glacier are Hvítmaga to the north-east, Gilsá to the south, Þórólfsá to the south-west, Valá to the north-west and Blesá to the north. Hvítmaga, Gilsá and Þórólfsá drain into Markarfljót while Valá and Blesá drain into Eystri Rangá.