Chapter 34 - Iceland: glacial landforms and raised shorelines from the Bølling–Allerød interstadial

Abstract

Following the warming of Northern Hemisphere climate, northward migration of the Polar Front, and rising eustatic sea level prior to the Bølling–Allerød (B-A) interstadial, the shelf-based part of the Iceland Ice Sheet (IIS) collapsed. The ice sheet margin retreated rapidly and was positioned just inside the present coastline in South-west and North-east Iceland around 14.6cal ka BP. An equilibrium between the rates of eustatic sea level rise and crustal rebound maintained high relative sea level for nearly 400 years, allowing the formation of marine limit shorelines, which now occur at altitudes between 60 and 150m a.s.l. Lava flows of inferred Bølling–Allerød age suggest ice-free areas the Northern Volcanic Zone (NVZ) and Reykjanes Peninsula, and exposure ages of table mountains within the NVZ imply enhanced volcanic activity under a rapidly thinning ice sheet during this period. Numerical modelling experiments suggest that the IIS margin had retreated far into the western and north-eastern highlands during the middle to late B-A. The well-preserved Fossvogur sedimentary sequence in Reykjavík indicates climate deterioration during late B-A with tidewater glacier expansion and subsequent oscillations mainly during Younger Dryas (YD). In many parts of Iceland, potential B-A deposits may have been overridden or covered by subsequent YD and Early Holocene (Preboreal) advances.