A daliebult is a small round or oval mound in a peat or lowland-bog area, formed when soft peat material was pushed up through the frozen top layer. It is a geomorphological phenomenon dating from the last ice age and the period after it, and is related to the daliegat (its opposite: a depression or pit).
How does a daliebult form?
During and after the last ice age (the Weichselian, c. 115,000-11,700 years ago) the soil in north-western Europe was partly permanently frozen (permafrost). In certain situations the following process occurred:
- The top layer froze hard
- Wet peat or soft clay below was under pressure
- At a weak spot the soft material was pushed upward
- After thawing, a small mound remained in the landscape
In effect, a daliebult is a frozen ‘bubble’ of squeezed-up material. The phenomenon is most common in lowland bogs and stream valleys.
Occurrence
Daliebulten are found across the lowlands of the Netherlands, north Germany and parts of the United Kingdom:
- Drenthe and the Frisian peat country
- De Wieden and Weerribben
- Vechtdal and Hunzedal
- Comparable mounds occur in Cumbrian and Scottish bogs
The mounds are usually only a few decimetres to one metre high and a few metres across. Centuries of farming have often levelled them, but in nature reserves they remain visible.
Significance for construction
Daliebulten have no direct effect on construction itself, but they matter in two situations:
- Archaeological value — daliebulten are often rich in archaeological evidence because early settlers used the dry mounds in an otherwise wet landscape
- Foundation advice — under or beside a daliebult the soil stratification can differ; site investigation is especially important there
Difference from other peat features
- Daliegat — a depression, where peat has been washed away or has subsided
- Pingo scar — a round depression with a rim, formed by a collapsed ice hill from the ice age
Related terms
- Daliegat
- Pingo scar
- Peat
- Soil investigation
- Geological terms
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