Formation of the ice cap

Vatnajökull is not a remnant of the Weichselian/Wisconsinan ice sheet that covered Iceland entirely during the Last Glacial Maximum around 18,000 years ago. The sedi­mentary record from lake Lagarfljót northeast of the ice cap, receiving meltwater from the Eyjabakkajökull outlet glacier, sheds light on the Holocene development of Vatnajökull. By about 9000 years ago, no glacial sediments can be detected and during the warmest period of the Holocene (5000–8000 years ago), the large Weichselian ice sheet had disappeared and probably only small glaciers remained on the highest mountains. The return of glacial meltwater to lake Lagarfljót (signifying the return of Eyjabakkajökull) is dated to ca. 4500 years ago. This is in accordance with other data from Iceland, indicating cooler summers from ca. 5000 years ago and expanding glaciers in the highlands. Tree logs found in the forefields of Fláajökull and Skaftafellsjökull are dated to about 2000 years ago, demonstrating that the corresponding valleys were ice-free at that time.

Vatnajökull began to take on its modern form when glaciers from mountain ranges at elevations between 1200 and 2000 m coalesced. According to numerical models, this stage was reached 1000–1500 years ago. By the time of the settlement (around 874 AD), the glaciers had coalesced into a continu­ous ice cap. The step-wise cooling in the latter part of the Holocene culminated in the Little Ice Age (LIA), a period of cooler and more variable climate from ca. 1450 to 1900 AD that affected most of the northern hemisphere. However, the outlet glaciers of southeast Vatnajökull did not reach the lowlands until the 17th and 18th centuries. By the end of the 19th century, the ice cap had reached its maximum Holocene size. Soon thereafter, the outlet glaciers started receding, marking the end of the LIA in Iceland.

 

Probable formation of Vatnajökull ice cap according to numerical models. About 3000–4000 years ago there were ice caps only on the highest mountains. These glaciers expanded and later merged to form one ice cap. Source: Modified after Björnsson (2017).

Probable formation of Vatnajökull ice cap according to numerical models. About 3000–4000 years ago there were ice caps only on the highest mountains. These glaciers expanded and later merged to form one ice cap. Source: Modified after Björnsson (2017).

 

Tree logs found in front of Skaftafellsjökull in 2007. Photo: Hrafnhildur Hannesdóttir.

Tree logs found in front of Skaftafellsjökull in 2007. Photo: Hrafnhildur Hannesdóttir.