The dust and ash rings of a retreating glacier in Iceland
All of the glaciers in Iceland are retreating (except maybe Drangajökull). At their melting tongues, you can typically retrace their history through rings of dust or volcanic ash. They function like the growth rings in a tree. All of the glaciers will have some sorts of layers. These layers can be thick layers of volcanic ash after an eruption in a nearby glacier or simply annual dust. These lines will be extra black and often very thick. You can see a great example melting out of this ice berg on the Jökulsárlón lagoon. After the Eyjafjallajökull eruption in 2010, there is a layer of ash up to 10 meters thick. Since the eruption, it has snowed on top of the layer for two years, meaning that the layer is trapped under dozens of meters of snow and won’t be visible until it melts out at the edges.
I don’t think the layers in the photo above are the results of eruptions. That would be an awful lot of eruptions. These are most likely the result of annual dust storms. As this is a small glacier in a very dusty area (Kerlingarfjöll), it gets covered every summer by dust storms. You can see this year’s layer already covering the fresh snow in some patches. Then as it snows in the winter, the layer gets covered with several meters of snow, which eventually get compacted into a layer of ice. Dust layers close to each other indicate a year of little snow accumulation.
Photo by AxelSig.