Tephrochronology and Late Holocene Soil Erosion in South Iceland

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The scale of soil erosion in Iceland since the Norse Settlement is generally well-known, but the detailed patterns of change are less clear. Through the application and refinement of tephrochronological frameworks, established by the late Professor Sigurður Pórarinsson and Guðrún Larsen, it has been possible to study in some detail the pattern of aeolian sediment accumulation around Eyjafjallajökull, and infer a pattern of soil erosion on a local scale. Later pre-historic rates of sediment accumulation seem to have been comparatively uniform in the zone between ca 500m above sea level (a.s.l.) and the sandur edge, but historic rates vary with altitude. In the early historic period, dramatic increases in upland sediment accumulation rates imply the early onset of acute local soil erosion in natural grasslands. These high rates decline through time, presumably as slopes stabilise at bedrock or gravel surfaces. At lower elevations inferred onsets and peaks of severe local soil erosion occur progressively later, indicating that a zone of severe instability moved slowly downhill, reaching low lying areas during the last two centuries. The timing and location of these changes reinforces the view that they are primarily anthropogenic. Settlement in the area has always tended to be restricted to the coastal strip and the lower slopes rising from major floodplains. Extensive early denudation in the uplands may have been an important contributory factor in the early abandonment of Landnám farm sites in the Pórsmörk area. Although later abandonments appear to be ultimately the result of social and cultural factors, some may have also been encouraged by the effects of anthropogenic soil erosion.