SLOPE MORPHOLOGY OF ICELANDIC FUGLAÞÚFUR

Fuglaþúfur are unique Icelandic hills with apex tussock growth enhanced by fertilization from bird feces. These features are found all along the Icelandic coast but their frequency drops off with increasing distance from the ocean. Fuglaþúfur stabilize and armor hill tops, strongly influencing hillslope evolution. The goal of this investigation was to identify patterns and scales of fuglaþúfur on different substrates and to evaluate their role in insulating slopes from freeze/thaw erosional processes, controlling slope stability. Fuglaþúfur were grouped topographically into three broad categories: glacial moraines, coastal sand dunes, and old lava flows. Size and shape of the fuglaþúfur were recorded by surveying topographic profiles and vegetation thickness. To evaluate insulating characteristics, soil temperature was measured with custom-built thermistor arrays. Thermistors have an accuracy of 0.1 degrees C and were mounted in 1” ID PVC tubes using a parallel, 3-wire half-bridge configuration. Thermistors were mounted on wooden dowels and inserted into 1” diameter PVC tubing. The arrays were secured in place with expanding insulating foam and sealed with epoxy. The probes were placed in holes drilled in the fuglaþúfur apex and in the unprotected, south-facing slope. Holes were backfilled after emplacement, connected to Campbell Scientific dataloggers, and recorded for four days.

Fuglaþúfur vary significantly with age and substrate. Tussocks on older geomorphic surfaces have distinct densely-packed, thick vegetation with a tall conical shape and a small depression in the center at the top. The second type of fuglaþúfur is found on unsorted sediments of glacial moraines that date to the Little Ice Age maximum, which makes them less than 150 years old. Here they tend to have a much thinner, broader vegetated apex and are more closely-spaced than those on older surfaces. The third type of fuglaþúfur develops on ephemeral features such as well-sorted sand dunes found commonly on strandplains. These tussocks are usually the longest, widest and thickest. Time series data of temperature fluctuations clearly show that fuglaþúfur have an insulating effect on freeze/thaw cycles.