varve analysis

Method of archaeological dating using annual varve (glacial deposit) thickness patterns formed in lakes near the edge of a glacier's retreat. A hot summer results in a thick varve, owing to a greater meltwater rate and discharge of gravel and clay, whereas a cold summer results in a thin one. By analysis of thickness patterns and cross-linking to adjacent regions, a chronology has been developed back to the end of the last Ice Age.

The method was pioneered by the Swedish geologist Gerard de Geer, who first noted the regular patterns of glacial deposits in lakes in 1878. He tracked and dated the complete 3,600-year glacial retreat in southern Scandinavia. This sequence was then tied to river estuary varves (caused by rhythmic annual flooding) spanning about 7,500 years up to AD 700.

Varve analysis and pollen analysis can be used together to date the first appearance of plant or tree species. The appearance of the alder tree Alnus glutinosa in Sweden, in approximately 6850 BC, has been identified by the occurrence of pollen in the varve structure.