Appearance of De Geer moraines in southern and western Finland — Implications for reconstructing glacier retreat dynamics

•Timely and comprehensive update of the De Geer moraines distribution in southern and central Finland•Classification of De Geer moraine appearances according to their maturity and regularity•LiDAR DEM investigations revealed that De Geer moraines are more widespread in Finland than previously presented.•A clear relationship exists between proglacial water depth and De Geer moraine interdistance.•Interdistances of mature and regularly-spaced De Geer ridges reflect the rate of deglaciation.

LiDAR digital elevation models (DEMs) from southern and western Finland were investigated to map and discriminate features of De Geer moraines, sparser and more scattered end moraines, and larger end moraine features (i.e., ice-marginal complexes). The results indicate that the occurrence and distribution of De Geer moraines and scattered end moraine ridges in Finland are more widespread than previously suggested. This is probably attributed to the ease of detecting and mapping these features with high-resolution DEMs, indicating the efficiency of LiDAR applications in geological and geomorphological studies. The variable appearance and distribution of moraine ridges in Finland support previous interpretations that no single model is likely to be appropriate for the genesis of De Geer moraines at all localities and for all types of end moraines. De Geer moraine appearances and interdistances probably result from a combination of the general rapidity of ice-margin recession during deglaciation, the proglacial water depth in which they were formed, and local glacier dynamics related to climate and terrain topography. The correlation between the varved clay-based rate of deglaciation and interdistances of distinct and regularly spaced De Geer moraine ridges indicates that the rate of deglaciation is probably involved in the De Geer ridge-forming process, but more thorough comparisons are needed to understand the extent to which De Geer interdistances represent an annual rate of ice-margin decay and the rapidity of regional deglaciation.

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