A CHANGING OUTLET GLACIER
During the so-called Little Ice Age, Hoffellsjökull formed as an outlet for ice flowing from the main body of Vatnajökull. The new tongue of ice advanced over the vegetated plain, blocking the lower mouths of gorges in the Hoffellsfjöll and Núpar mountains. Since drainage from these gorges was dammed behind the ice, the lagoons Gjávatn and Múlavatn appeared. These soon began to drain through annual jökulhlaups, which is the internationally used Icelandic word for glacial floods. In more recent times, Hoffellsjökull began to retreat, removing the ice dams in front of the gorges, so that both lagoons had disappeared by 1985. However, you can still see clear signs of earlier lagoon surface levels where Gjávatn used to be, with water up to 60 m deep.
Another change is that the Austurfljót glacial river stopped flowing in the autumn of 2008. It had carried melt water southeast from the main tongue of Hoffellsjökull to meet the Suðurfljót river below the farm of Svínafell, where they together formed the river named Hornafjarðarfljót. Since 2008, all water running from Hoffellsjökull flows from an ice tongue extending out of it to the west. Because the main tongue of the outlet glacier has not retreated as far as the western tongue, melt water can escape sooner from under it.
Hoffellsjökull was largest around 1890, but for the next 50 years it still reached all the way to the moraine ridge which envelops the lake in front of the glacier. During some of that time, lorries were driven up onto this ridge and filled with ice which they transported to the town of Höfn. The ice was used for chilling fish, both in boats and on shore. Due to climate changes, Hoffellsjökull has retreated a considerable distance. A big, deep lagoon is rapidly developing in the depression left behind, and will in future probably become a large lake.
Hoffellsjökull outlet glacier was the scene of extensive glaciological studies in the early part of the 20th century. Also, Hoffellsjökull served researchers as a route of access onto the main Vatnajökull icecap. One of the most famous expeditions was directed by the Icelandic meteorologist Jón Eyþórsson and the Swedish glaciologist Hans Ahlmann in 1936. Two geography students who accompanied them later became well known: Carl Mannerfelt in Swedish business and Sigurður Þórarinsson in Icelandic geological research.
Hoffellsjökull outlet glacier cuts through a central volcano which is named after Geitafell mountain and was active 5-6 million years ago. Mostly consisting of tholeite basalt but also to some extent of hyaloclastite and rhyolite deposits, the total thickness of the strata from this volcano is estimated as 2,700 m. There are indications of a high peak that may have been covered by glacier even before the Ice Age. Although ice has eroded this volcano, signs of a huge caldera appear on the slopes of both Hoffellsfjöll, east of this valley, and Viðborðsfjall to the west.
Over time, uplifting and erosion have made rock visible today which originally formed deep below the surface. The Geitafellsbjörg cliffs, east of Hoffellsjökull, represent a magma intrusion, mostly consisting of gabbro. The softer rock surrounding the magma intrusion has been eroded away by the glacier, and rivers have washed the eroded material towards the sea. Near the downstream end of Geitafellsbjörg, at Geitafellstangi, gabbro has been quarried and used in Reykjavík as cladding for the Central Bank of Iceland.
In December 1910, the Hoffell farmer, Guðmundur Jónsson, was looking for sheep in Hoffellsdalur valley when he found a large number of Iceland spar fragments in a gorge on Hoffellsfjall mountain. Together with the Reykjavík merchant Björn Guðmundsson, Guðmundur Jónsson started mining and exporting these crystals to countries like Denmark and Germany, where it was manufactured into microscopes and other optical instruments. Another use was in buildings in Reykjavík, where it can still be viewed in the domed ceiling just inside the entrance of the main building of the University of Iceland, as well as in the altar of the university chapel.
The farmer discovered the crystals in a gorge that was later named Námugil, with the first four letters in the name meaning "mine". Because the mine was at an elevation of about 500 m, the material was brought down by cable. The largest crystal from the mine weighed over 150 kg. Since production in the mine ceased in 1940, a rockslide has covered its entrance, so that the mine is hardly visible nowadays.
FLORA AND FAUNA
The mountainous area east of Hoffellsjökull is the habitat of several rare plants. Silver saxifrage, Saxifraga paniculata, and green spleenwort, Asplenium viride, grow in the cliffs, while the lichens Bryoria fuscescens, Bryoria simplicior, Hypogymnia tubulos, Vulpicida pinastria and Platismatia glauca inhabit the birch woods and shrubby areas.
Practical information for visiting the Hoffell area