Fjallsjökull glacier

An outlet of Öræfajökull

Fjallsjökull is an outlet glacier of Vatnajökull, flowing from the southern part of the Öræfajökull volcanic system. It occupies a valley between Breiðamerkurfjall and Ærfjall before reaching the low ground of Breiðamerkursandur.

Approximately five kilometres above the present terminus, the glacier crosses a sequence of bedrock steps. These changes in gradient produce icefalls, crevasses and the broken surface visible from the lagoon.

The glacier is temperate, meaning that much of its ice is at or close to its melting point. Meltwater, movement and calving continually reshape the lower tongue. The visible front is therefore not a fixed wall but the temporary edge of a moving body of ice.

Fjallsjökull was once connected with neighbouring outlet glaciers. It separated from Breiðamerkurjökull to the north by 1945 and from Hrútárjökull to the south by 2010 as the ice retreated into separate valleys.

The surrounding ridges make the glacier appear close and concentrated. This distinguishes Fjallsjökull from broader glacier tongues whose scale is more difficult to understand from ground level.

The formation of Fjallsárlón

Fjallsárlón formed as Fjallsjökull retreated from the low ground in front of its present terminus. Small proglacial lakes began appearing here around 1936, and one developed into the lagoon seen today.

In 1945, the lagoon covered approximately 0.5 square kilometres. By 2018, its surface area had expanded to about 3.7 square kilometres. The increase represents newly exposed land and water where glacier ice previously occupied the valley.

The lagoon has also become considerably deeper. Measurements recorded a maximum depth of about 45 metres in 1951, increasing to 119 metres by 2016.

Icebergs calve from the glacier front and drift across Fjallsárlón. Their number, size and location vary continuously with temperature, wind, water movement and activity at the terminus. Some remain near the glacier, while others cross the lagoon or become stranded in shallow water.

Unlike Jökulsárlón, Fjallsárlón does not connect directly with the sea. Its outlet, Fjallsá, flows for approximately eight kilometres across Breiðamerkursandur before reaching the Atlantic.

A glacier in rapid retreat

Fjallsjökull reached its greatest historical extent during the eighteenth and nineteenth centuries. Between approximately 1890 and 2010, it lost about 23 per cent of its surface area and around 35 per cent of its volume.

The retreat has exposed the basin now occupied by Fjallsárlón. It has also brought the glacier front into increasingly deep water. Deeper water encourages melting at the terminus and allows larger sections of ice to break away, which can accelerate further retreat.

Research published in 2025 used sonar measurements of Fjallsárlón together with surveys of the bedrock beneath the glacier to examine how the lagoon may develop. If recent retreat rates continue, the lagoon is expected to expand into two deep basins beneath the present glacier.

The study estimates that Fjallsárlón could eventually more than double its current surface area and triple its volume, reaching a maximum depth of approximately 210 metres. The exact timing depends on future climate and glacier behaviour, but the projections place the largest extent within roughly the next one to two centuries.

The lagoon is therefore not merely scenery in front of the glacier. It is the visible result of retreat and an active influence on how Fjallsjökull continues to change.

Walking around Fjallsárlón

Fjallsárlón is accessible throughout the year from Route 1. The paved access road from the highway is slightly more than 500 metres long and ends at the main parking area.

A marked circular route begins near the visitor facilities. The path descends towards the lagoon and reaches viewpoints overlooking Hrútárjökull, Ærfjall, Fjallsjökull, Breiðamerkurfjall and Fjallsárlón.

The complete loop is approximately 1.5 kilometres and has an estimated walking time of 45 minutes. The national park classifies it as challenging, so visitors should not assume that its short distance makes every section effortless.

The path follows part of the lagoon before climbing onto higher ground and returning along a section of the former main road. These changes in elevation provide different relationships between the foreground, floating ice and the glacier.

Most visitors should allow around one hour. This provides time for the loop, the principal viewpoints and waiting for temporary changes in light or the position of ice on the lagoon.

The glacier front and lagoon edge are dynamic environments. Visitors should remain on marked routes, respect any temporary closures or ranger instructions and avoid approaching unstable ice.

Viewing the glacier and entering it

Fjallsjökull can be viewed safely from the marked paths around Fjallsárlón, but stepping onto the glacier is an entirely different activity.

A glacier surface may conceal crevasses, meltwater channels and unstable snow bridges. The ice moves, fractures and changes through the season. A route that appears straightforward from a distance cannot be judged safely by an inexperienced visitor.

Anyone entering Fjallsjökull should do so as part of a properly organised glacier tour with a qualified guide and appropriate equipment. Guided access depends on the season, weather and the condition of the glacier.

Visitors do not need to walk on the ice to understand Fjallsjökull. The view across the lagoon reveals the glacier’s structure particularly well: the descending icefalls, darker bands of sediment, fractured terminus and icebergs separating from the front.

Keeping those two experiences distinct is important. Fjallsárlón is an accessible viewpoint; Fjallsjökull itself is moving glacier terrain.

• Fjallsjökull flows from the southern part of Öræfajökull beneath the Vatnajökull ice cap.
• Breiðamerkurfjall borders the glacier to the north and Ærfjall to the south.
• Fjallsjökull was once connected with both Breiðamerkurjökull and Hrútárjökull.
• Small lakes began forming in front of the retreating glacier around 1936.
• Fjallsárlón expanded from approximately 0.5 square kilometres in 1945 to about 3.7 square kilometres in 2018.
• The maximum measured depth increased from about 45 metres in 1951 to 119 metres in 2016.
• Fjallsjökull lost approximately 23 per cent of its surface area and 35 per cent of its volume between about 1890 and 2010.
• Research indicates that the lagoon may eventually reach a maximum depth of approximately 210 metres.
• The marked Fjallsárlón loop is approximately 1.5 kilometres and takes about 45 minutes.
• Fjallsá carries water from the lagoon across Breiðamerkursandur to the Atlantic Ocean.