What is a push moraine?
A push moraine is a ridge formed when an advancing ice sheet bulldozed existing layers of sand, gravel and loam in front of it and pushed them up into hills. The Dutch term is stuwwal. The Dutch push moraines date from the Saalian, the penultimate glaciation, around 150,000 years ago, when the north of the country lay under an ice sheet several hundred metres thick. At the ice margin the layers were thrust up and tilted, disturbing their original order, and boulder clay was pushed along too.
Well-known examples are the Veluwe, the Utrechtse Heuvelrug (the most westerly), the ridge at Nijmegen and the Montferland. The islands of Texel and former Wieringen also owe their higher cores to push moraines.
Application
- Expect sand, but test it. The ground is usually load-bearing sand and gravel, so shallow foundations are often possible. Because the layers are tilted, there may be local lenses of loam or boulder clay. A site investigation removes the guesswork.
- Allow for a deep water table. Groundwater is often deep, which suits basements. A loam layer can still trap rainwater and create a perched water table.
- Plan for slopes. On sloping plots, think about excavation, retaining walls and surface water, so run-off does not reach your walls or your neighbour’s.
- Check restrictions on boreholes. Push moraines are often important for drinking water abstraction. In groundwater protection zones, boreholes and ground source heat systems may be restricted or banned; check with the relevant authority first.
- Use infiltration. Sandy ground drains well, so a soakaway often works here, provided there is no loam layer beneath it.
Common mistake: assuming the whole plot is uniform sand because the house stands on a push moraine. The pushing is exactly what makes layers change over short distances.
Related terms
- Boulder clay
- Groundwater level
- Cone penetration test
- Perched water table
- Ground source energy
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