Cover sand (Dutch: dekzand, German: Decksand) is fine, aeolian (wind-deposited) sand that was laid down during the last ice age — the Weichselian glaciation, roughly 116,000–11,700 years ago — as a thin blanket over large parts of north-west Europe. In the Netherlands and northern Germany it forms a continuous mantle over the higher sand grounds of regions such as Drenthe, the Veluwe, Brabant and the North German Plain.
How cover sand was formed
During the last ice age, north-west Europe was a cold, almost vegetation-free steppe. Strong winds blew fine sand out of dry river beds and the exposed North Sea floor onto the land. This sand settled into a layer ranging from a few decimetres to several metres thick. Where shrubs and tussocks slowed the wind, elongated rises formed: cover-sand ridges.
Properties
Cover sand has several characteristic properties that make it recognisable to archaeologists, geologists and soil scientists:
- Grain size — mostly very fine to fine sand (105–210 µm)
- Sorting — very well sorted, with little gravel or loam
- Colour — beige-yellow to light brown, sometimes with thin loam bands
- Permeability — well draining
- Fertility — naturally poor, leaches quickly
Cover-sand ridges
A cover-sand ridge is a natural elevation of a few metres formed by wind action. These ridges were preferred settlement locations in prehistory and the Middle Ages because they were higher and drier than the surrounding stream valleys. Many Dutch *esdorpen* (heath villages) and German *Esch* settlements were built on cover-sand ridges, often with characteristic *esch* fields adjacent to them.
Significance for construction
Cover sand is a favourable foundation soil for buildings and earthworks:
- Bearing capacity — when well compacted, cover sand has adequate bearing capacity
- Dewatering — its good permeability means well-point dewatering is often required
- Foundations — usually allow shallow foundations (strip footing), provided they extend below the frost line
- Archaeology — building projects in cover-sand areas often require an archaeological assessment
Related terms
- Soil type
- Boulder clay
- Loess
- Soil investigation
- Frost line
- Strip foundation
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