Description:
<p>Lava tongues pouring from the 1973 eruption of the volcano Eldfell on the island of Heimaey off South Iceland built up a delta platform into the sea, threatening to close the entrance of the most important fishing harbour of Iceland. A new coastline was formed along the southeast side of Heimaey, but a narrow passage to the harbour was preserved when the eruption stopped. Changes in pebble shape over a 15 year period have been monitored on fresh beaches accumulating along the lava delta as a result of high energy cliff erosion. Rapid coastline changes and northeasterly sediment transport along the beaches and shoreface are reported. The beach material reached certain shape characteristics within a few months of coastal processes after the eruption. These characteristics have not changed significantly with time, indicating frequent flushing of beach material out of the beach profiles into deeper water, probably during storms. The beaches are then maintained by continuing cliff erosion on adjacent reaches. The considerable water depth at the lava margin (over 50 m) and subsidence of the lava (and its coastline, leading to some transgression) due to thermal contraction may be among factors in delaying the development of a stable coastline. It is suggested that any sudden development of the pebble shape parameters on the beaches may be taken as an indicator of coastline stabilization and an increased risk of sediment transport towards the harbour entrance.</p>