Varve

Varve is a term used in geology to describe pairs of sediment layers that accumulate in a lake during a single year, typically in glaciolacustrine or other low-energy environments. In many temperate and polar lakes, a varve consists of a lighter-colored, coarser summer layer deposited during the ice-free part of the year, overlain by a darker, finer winter layer deposited under ice when energy is low and organic-rich material accumulates. The precise appearance and composition of the layers depend on local factors such as sediment supply, glacier melt, productivity, and chemistry.

Over time, a sequence of varves records a chronological stack that, when counted from the top down, yields a year-by-year chronology. Varve counting is used to reconstruct past climate, sedimentation rates, and hydrology in Quaternary lake sediments. While it provides high-resolution relative dating, varve chronologies are most robust when anchored by independent dating methods such as radiocarbon ages or tephra layers.

Limitations include disturbance by bioturbation, floods, volcanic ash falls, or hiatuses that disrupt annual laminations. In some lakes, annual layers are not clear or are interrupted by multi-year deposition events, complicating counting. Consequently, varve records require careful stratigraphic analysis and often corroboration with other dating techniques to produce reliable timelines.

Varves are most well known from high-latitude and high-altitude lakes with pronounced seasonal contrasts, though laminated lake sediments with annual-like layering occur in various quiet-water settings worldwide.