Proglacial River Research Articles

Rates and causes of proglacial river terrace formation in southeast Iceland: an application of lichenometric dating techniques

The immediate proglacial areas of most of the Oraefajökull outlet glaciers in southeast Iceland are characterized by well‐developed river terraces, formed by the recent downcutting of the major meltwater streams. This paper examines the rates and causes of dissection in two contrasting cases, using lichenometric dating to establish the ages of individual terraces. An age–size curve for the aggregated Rhizocarpon sub‐genus is developed from lichen measurements on dated recessional moraines, and is compared with similar curves obtained by previous workers. Levelling profiles of the terraces are then used in conjunction with the lichenometric dates to determine mean rates of net erosion between each dated surface, and to study the associated variations in channel slope. The results obtained for the Svinafellsá show that the timing and rates of downcutting have been closely related to frontal movements of the Svinafellsjökull glacier. The Kotá terraces, however, may have been formed independently of glacier fluctuations, and are thought to represent stages in the gradual recovery of the stream from the aggradational effects of the 1727 jökulhlaup.