In favourable geological and geomorphological settings of the NW Iberian Range glacial lakes accumulate and preserved fine laminated sediments (varves, rhythmites, graded layers). Their occurrence seem to be dependent on various interacting environmental factors, such as basin and catchment morphometry, catchtment´s rocks and soils types and climate conditions. Image analysis of Backscattered Scanning Electron microscope Images (BSEI) of thin sections provides high-resolution digital documentation related to the number, texture, structure and composition of laminated sediments at annual and subannual scale. A careful construction of a fine-scale physical/textural properties of annually laminated lake sediments were emphasized in the present study. Nine kinds of detrital rhythmites are identified that can be grouped in two main types: i) Single rhythmites with two laminae. A single annual unit is composed of two layers (laminae) that can be distinguished on the basis of their thickness, composition and texture. ii) Multiple rhythmites with more than two laminae. In detail, these individual layers are representing certain seasons or even shortterm events whitin seasons (e.g. nival melt, spring floods, summer glacial melt, autumn storms, etc.). Detrital rhythmites are present in both sedimentary lacustrine records since their glacial origin (31360 y. Cal BP in the Hornillo lake and 20420 y. Cal BP in the Grande lake) to the beginning of the Holocene.
