Vegetation plays a key role in preventing remobilisation of tephra and aeolian activity following tephra fall. Volcanic eruptions are frequent in Iceland, with an eruption occurring every two years. Several volcanic systems known for producing large explosive eruptions currently show signs of increased activity. The 2010 eruption of Eyjafjallajökull and the 2011 Grímsvötn eruption have brought to attention the consequences of tephra fall for ecosystems and human health. Furthermore, remobilisation of tephra has presented a problem in the wake of the eruptions. The Hekla 4 tephra (c. 4200 cal. yr BP) is one of the most extensive Icelandic Holocene tephra layers and the eruption produced an estimated ~9 km3 of tephra. To examine the vegetation changes brought on by the tephra fall sediment cores were taken from two lakes in northwest Iceland. Vegetation reconstructions before and after the tephra fall were made based on pollen data.
Results/Conclusions
The vegetation reconstructions provide an insight into the responses of two vegetation communities to tephra deposition (>8 cm) during a period of cooling climate; a stable birch woodland and an open birch woodland under stress. Changes are recorded in the pollen assemblage of the woodland after the tephra fall, the most significant change is the temporary disappearance of herb pollen, indicating that the understory vegetation in the woodland was buried by the tephra. However, birch (Betula pubescens) trees were not severely affected and the woodland recovered within several decades. In contrast, in the open woodland that was already at its ecological limit the tephra represents a major boundary between vegetation communities. A decrease in Betula pollen and increase in Vaccinium-type, Empetrum nigrum and Cyperaceae pollen indicates that the vegetation community shifted to dwarf shrub heath in response to the tephra fall and cooling climate.