Varve

A varve is a sediment layer deposited in a lake over one year. Its seasonal layers can preserve a dated record of environmental change.

Seasonal sedimentation: The seasonal deposition of particles as changing weather and water conditions alter transport and settling. Seasonal shifts in runoff, biological activity, and lake mixing produce varve layers.
Varve chronology: A timeline built by counting and correlating annual sediment layers. Counting successive varves can establish an annual age sequence.
Lake sediment: Mineral and organic material that settles and accumulates on a lake bed. Varves are a time-structured form of lake sediment.
Rhythmite: A sedimentary sequence of repeated layers whose recurrence may or may not be annual. A rhythmite is not a varve unless its cycles represent one year.
Glacial lake: A lake formed or maintained by glacial processes, often receiving abundant meltwater sediment. Many classic varves form where glacial meltwater delivers sediment during summer.
Glacial Lake Agassiz: A vast proglacial lake that occupied central North America during the last deglaciation. Its deposits preserve varve sequences used to study deglacial history.
Sedimentation: The settling and accumulation of particles transported by water, wind, ice, or gravity. Annual layers arise when sedimentation changes predictably through the year.
Turbidite: A sediment deposit left by a turbidity current, commonly graded from coarse to fine particles. Turbidites record individual flows, unlike varves' recurring annual deposition.
Suspended sediment: Particles carried within water rather than resting on the bed. Seasonal inflows suspend and deliver the mineral particles that settle into varves.
Paleoclimatology: The study of past climates using natural records preserved in Earth materials. Varve thickness and composition can track past climate-driven changes in lakes.

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