Climate change and slope stability in Iceland

Over the last decades climate has warmed up worldwide and changes have occurred in the general weather patterns. Where the increase in temperature has rapidly been gathering pace in the last decade. These changes have also been observed in Iceland. From 1980 to 2015 the average temperature increase has been 0,47°C per decade and the average precipitation has increased from 1500 mm/year to around 1600-1700 mm/year. The increased temperature changes have also resulted in more frequent thawing periods and rainfall events during winter months, especially in the lowlands.

Mass movements, including rock falls, rock avalanches, debris flows and debris slides, are common geomorphological processes in Iceland and thus present a significant and direct threat to many towns, villages, and farmhouses. Weather conditions, e.g. precipitation and temperature variations, and earthquake activity are the most common triggering factors for such activity in Iceland. During the last decades several, somewhat unusual, mass movements events have occurred in the island. These events have been unusual both regarding their size, increased frequency, their triggering factors and not at least the timing within the year they have occurred.

One of the most visible consequence of temperature rise in Iceland is the fast retreat and thinning of outlet glaciers and formation of proglacial lakes. The frequency of mass movements on outlet glaciers have increased considerably from the turn of the century compared to the last 4 decades of the 20^th century. New discoveries of unstable slopes above outlet glaciers have also increased considerably from 2000.

In recent years, there has been an increasing interest worldwide in the influence of climate warming and possible decline of mountain permafrost on the occurrence of mass wasting phenomena. The rising frequency of rapid mass movements, such as debris flows, debris slides, rock falls and rock avalanches, in mountainous areas have been linked with mountain permafrost degradation. Several mass movements, which can be connected to thawing of mountain permafrost, have occurred in central N and NW parts of the island during the last decade.

Majority of landslides in Iceland in the past century have either occurred in relations with low-pressures systems that pass-through Iceland from August to November, bringing in high winds with heavy rainfall, or during spring snowmelt in May and June. But in the past two decades snowmelt and thawing periods are becoming more frequent and longer during wintertime resulting in higher frequency of slope failures during that time of year. Over the past 20 years’ large landslides events (> 300.000 m³) have become more frequent compared to the second half of the 20^th century. 

Climate change certainly seems to be affecting slope stability in Iceland and is an increasing risk. Especially slopes close to retreating glaciers and those affected by thawing of mountain permafrost. Changes in temperature and precipitation patterns in late fall and during winter months are causing slope failures that were not as common in the past.