Fire, Ice, and Climate Change in Iceland

Fire and ice have consistently shaped Iceland’s history, so much so that red and white, the colors symbolizing these elements, make up two of the three colors on the island nation’s flag. In a new twist to the relationship between fire and ice in Iceland, a recent paper in Geology details the link between climate-driven changes in glacier volume and volcanic activity.

Photo of Eyjafjallajökull Volcano
Eyjafjallajökull, a volcano in Southern Iceland, erupting in 2010 (Source: Sverrir Thorolfsson/Creative Commons).

At the end of the last Ice Age, around 12,000 years ago, large scale glacial retreat across Iceland led to increased volcanism due to reductions in surface pressure. This impact of glacier retreat on volcanic activity has been supported by a number of previous research according to Charles B. Conner, an author of the study who spoke to GlacierHub. However, the link between smaller changes in glacial ice masses and their effects on volcanic eruptions is a less established phenomena, fueling the motivation for this latest research.

While climate-driven fluctuations in glacier size might not be the first thing that comes to mind when one imagines volcanoes, ice does impact fire. Throughout time, as glaciers retreat and advance, they exert varying pressure loads on the Earth’s crust and mantle, according to Conner. When a glacier retreats, magma production in the mantle and the crust’s magma storage capacity increase, the latter due to a reduction in surface pressure. Conversely, when a glacier advances, magma production in the mantle is suppressed and the crust’s magma storage capacity decreases, as a result of added surface pressure.

Maps of volcanic ash sample sites and Iceland Holecene volcanos and ice masses
Maps detailing Northern European volcanic ash sample sites and Iceland Holecene volcanos and ice masses, respectively (Source: Swindles et al.).

Iceland has many volcanoes due to its location atop the Mid-Atlantic Ridge, a massive crack in the Earth’s crust where magma from the mantle makes its way to the surface; 130 volcanoes to be exact. Thanks to Iceland’s northern latitude, many of these volcanoes are covered by glaciers, making the country an ideal place to examine possible links between the two. To study these linkages over a relatively short time scale, the authors of the study focused on the mid-Holocene period, a time period from roughly 7,000 to 5,000 years ago.

To determine changes in volcanic activity over time, they relied on two data sources: Icelandic volcano records and northern European volcanic ash deposits. One might think that when examining geological records, adjacent sources such as those taken near the study area would provide more insights than those taken thousands of miles away in Europe. However, local volcanic record analysis is often confounded by the burial or reworking of evidence by subsequent eruptions. By using European ash deposits as a proxy for direct evidence, they were able to circumvent possible complications. Examining both of these data sources, the study’s results point to a marked decline in the frequency of eruptions over a 1,000-year period, from 5,500 to 4,500 years ago.

Nonetheless, the drivers behind volcanic activity in Iceland are numerous and complex. One possible explanation for the decline could be a decrease in the rate of magma supplied to the Earth’s mantle, leading to the subsequent decrease in eruptions. However, the authors contend that a change in magma supplied is unlikely to be the cause of this particular decrease, as it occurred across multiple volcanic systems within the country. Rather, the authors point to an external factor, such as a change in glacial ice volume, as a more likely driver due to the simultaneous decline in volcanism.

But was there evidence to support a climatic change that would drive glacial advance during the mid-Holocene? As it turned out, yes. Paleoclimate records reviewed for the study showed conditions ripe for glacial advances across Iceland, lower temperatures and increased precipitation. Core samples taken from the Icelandic Shelf and the North Atlantic indicated oceanic cooling, while reduced productivity in records taken from lakes in Iceland show evidence of cooling over land. Concurrently, ice cores taken from Greenland suggest a deepening of the Icelandic low pressure system, usually associated with above normal precipitation and lower than normal temperatures in the North Atlantic.

Photo of Mýrdalsjökull glacier
Mýrdalsjökull glacier atop the volcano Katla in Southern Iceland (Source: Adam Russell/Creative Commons).

Next, to assess the impacts of this glacial advance on volcanic activity, the authors assayed the correlation between the Greenland ice core data, representing climate conditions, and the European ash deposits, representing eruptions. The correlation revealed a 600-year time lag between the climatic event and the successive decrease in volcanic activity. This lag incorporates both the varying response times across Icelandic glaciers to climate changes and the uncertainties that exist for new magma to reach the surface.

Chart showing Volcanic sample data, glacier data, and climate data
Chart outlining the study’s volcanic sample data, glacier data, and climate data for the mid-Holecene (Source: Swindles et al.).

While this study focused on past climate changes and their influences on glaciers and volcanoes, it has relevant implications for the changing climate of the present. As the Earth warms due to increased greenhouse gas emissions, glaciers around the world are melting. In Iceland, glaciers have lost an estimated 10 km3 per year since 1995. Given that deglaciation leads to increased volcanic activity, humans seem to be doing the job nature once did in regulating eruptions in Iceland.

Nobody alive today is likely to see increased volcanism in Iceland because of climate change given the time lag of 600 years between a climate event and a change in volcanic activity identified by this study. When asked about the possibility that human activity might impact this lag, Conner told GlacierHub that at this time it is not known if rapid climate change will lead to changes in the timing of resultant volcanic eruptions. Although, he said it is possible “that the rate of volcanic activity changes much more rapidly than it did during natural deglaciation in the past, but this is speculative.”


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