Consequences of retreating glaciers

Sea level rise

Icelandic glaciers contain 3500 km3 of ice, which if melted would raise global sea level by 1 cm. To put this into context, the Greenland Ice Sheet has in recent years lost twice the amount of ice annually that the SE outlet glaciers of Vatnajökull lost in total since ca. 1890. Meltwater from glaciers in Antarctica and Greenland is the main cause of global sea level rise, which currently amounts to 3–4 mm per year on average. Thermal expansion due to warming of the ocean also contributes to sea-level rise and accounts for approximately half of the rise during the past century.

Global sea level rise. Source: Björnsson et al. (2018).

Global sea level rise. Source: Björnsson et al. (2018).

 

Rock avalanches

A number of landslides and rock avalanches have fallen on glaciers in southeast Iceland during the last decade, including onto the Morsárjökull and Svínafellsjökull glaciers. Undercutting of the mountain slope by glacial erosion and the retreat of the glacier are the main contributing factors for the rock avalanches, along with thawing permafrost and weaknesses in the bedrock. Landslides falling into glacial lakes may cause tsunamis and river floods and thus pose hazard to people.

 

View towards Morsárdalur, Morsárjökull and Skaftafellsjökull, with Skaftafellsheiði, Kristínartindar and Skarðatindur between the outlet glaciers. Breiðamerkurjökull in the background. A large rock avalanche fell on Morsárjökull in March 2007, one of the largest in Iceland for decades. Photo: Snævarr Guðmundsson, 13th of september 2014.

View towards Morsárdalur, Morsárjökull and Skaftafellsjökull, with Skaftafellsheiði, Kristínartindar and Skarðatindur between the outlet glaciers. Breiðamerkurjökull in the background. A large rock avalanche fell on Morsárjökull in March 2007, one of the largest in Iceland for decades. Photo: Snævarr Guðmundsson, 13th of september 2014.

 

Crustal uplift

As Vatnajökull ice cap thins and retreats, the underlying crust rebounds at an accelerating rate. The rate of uplift is highest closest to the glacier margin where the greatest mass loss takes place. Measurements indicate an uplift rate of 40 mm per year at Jökulheimar at the western margin of the ice cap, compared with 12 mm per year at Höfn in Hornafjörður to the southeast of the glacier. The future of shipping through the inlet of Hornafjörður bay is uncertain due to the uplift in this area. However, rising sea level due to warming climate and melting glaciers counteracts the crustal uplift to some degree.

 

Crustal uplift in Iceland 2004–2016. Source: Valsson (2017).

Crustal uplift in Iceland 20042016. Source: Valsson (2017).

 

Increased volcanic activity

The removal of surface ice load as the glaciers retreat can lead to enhanced magma generation and volcanic activity, and this may already be happening in the subglacial volcanic systems of Vatnajökull. Model calculations simulating the effect of the glacier changes in 1890–2010 indicate that magma generation has increased by 100–135%, which corresponds to an addition of 0.2 km3/year of magma beneath Iceland. Should 25% of this magma reach the surface, it would be equivalent to the 2010 Eyjafjallajökull summit eruption every seventh year.

 

Tourism

As the outlet glaciers continue to retreat, access for guided glacier walks becomes increasingly difficult at some locations – as well for the volunteers of the Iceland Glaciological Society who measure the retreat! On the other hand, increased opportunities for boat tours on the glacial lakes may arise. Ice caves are becoming popular tourist attraction in winter. Meltwater runs at the base of the glacier and creates tunnels into the ice. Increased air temperature in the spring weakens the walls and the ceilings of the ice caves and they may collapse. Flash floods along the caves during summer can also be dangerous. With increasing number of glacial tours in the vicinity of Vatnajökull, there are also increasing opportunities to educate travellers and communicate information about climate change and retreating glaciers.

 

One of the ice caves of Breiðamerkurjökull glacier. Photo: Þorvarður Árnason.

One of the ice caves of Breiðamerkurjökull glacier. Photo: Þorvarður Árnason.

 

Glaciers and biota

Glaciers not only sculpture the land, they also influence the biota. Advancing glaciers ruin vegetated land and destroy habitats of many species. When the glaciers retreat and thin, new land emerges in front of them and on nunataks (mountain tops extending through the ice). Ecological succession and community building start, as the first organisms colonise the newly deglaciated areas. Few so-called pioneer species colonise the land closest to the glacier, but, farther away, the number of species increases, and the ecosystems become more complex. Thus, deglaciated areas, not least nunataks, provide a unique opportunity to follow the process of succession and evolution of an ecosystem.

The largest nunataks on Vatnajökull, Esjufjöll mountains in Breiðamerkurjökull, reach up to 1600 m above sea level and have presumably been ice-free since the end of last glacial period. Their untouched ecosystems, which have never been cultivated or grazed, provide a unique opportunity to study the impact of warming climate on biological communities. Studies there, and on several more recent and smaller nunataks in Breiðamerkurjökull, show that both the number of plant species and the altitude of continuous vegetation increase with warming climate. The nunataks differ both in size and age. As noted above, the oldest parts of Esjufjöll have presumably been ice-free for ca. 10.000 years. Another nunatak, Kárasker, appeared in 1935, while the youngest one in a series of five small ones appeared as recently as 2016. Recent studies show that the composition on these “biological islands” in the glacier, depends on several factors including the size of the nunataks, age and their distance from the nearest source of life, i.e. the glacier edge.  Hence the nunataks provide an excellent model to test various theoretical models in ecology related to species colonisation and community development.

Results show e.g. that primary succession on new lava fields, versus that in front of receding glaciers and on nunataks, may differ significantly. Pioneer species on lava fields are commonly mosses and lichens. However, in front of Skaftafellsjökull, flowering plants are among the first settlers and on nunataks in southeast Vatnajökull, invertebrates form a community before the arrival of plants. These invertebrate food webs are made of detrivores such as mites and collembolas feeding on bacteria and organic matter, with spiders as the main predators. The microorganisms and most of the early pioneer invertebrates are wind-borne, i.e. carried by wind onto the nunataks.

 

Birch on Skeiðarársandur. Photo: Bjarni Diðrik Sigurðsson.

Birch on Skeiðarársandur. Photo: Bjarni Diðrik Sigurðsson.