A varve is simply defined as: an annual sediment layer. Where we see varves today, mostly in lake (lacustrine) deposits, but also in some marine environments, there are seasonal or annual variations in deposition responsible for contrasting layers within one year. Unlike many other environments, preservation and recognition of annual structures in glacial lakes is nearly guaranteed because the activity of organisms (burrowing) is generally very low and does not significantly disturb layers after they form. Thus, varves formed in glacial lakes, or glacial varves, are distinctive features of glacial lacustrine environments. It should be noted that in many places, especially on the internet, varves are frequently defined as a type of glacial lake sediment. This definition stems from the fact that varves are common in glacial lake environments, but this definition overlooks the most important aspect of all varves. Varves are defined as annual sediment layers and they can occur in many different environments. According to De Geer (1940) the term “varve” in English is derived from the Swedish term “varv”, (“hvarf” in its older spelling), for the cyclic clay deposits underlying the land surface of eastern Sweden.
Varve archetype is a light / dark coloured couplet deposited in a glacial lake. The photo below is a typical varve exposure.
This photo is of a typical varve exposure, but is not the one in the park.
The varves in this earthcache were deposited in a glacial lake more than 25,000 years ago (Reference: http://www.gac-cs.ca/publications/VancouverGeology.pdf - Page 85). The darker horizons may have been deposited in winter and the lighter, sandy layers could reflect rapid deposition in spring or summer. The glacial lake was in Capilano Canyon and may have been from a lake on the edge of the ice, or may have been from a lake in the canyon.
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1. Estimate the thickness of the thinnest varve and the thickest varve in the outcrop.
2. Estimate the number of varves in the exposure, there are many more but not exposed.