ABSTRACT
The subsurface of London is often assumed to be relatively simple, with Late Cretaceous and Palaeogene strata sitting within and forming a synclinal structure (the London Basin). The surface has been modified by mostly fluvial processes during the Quaternary.
More recently, a picture of more complex conditions has begun to be developed, largely driven by the need for deeper foundations, groundwater control and tunnelling. One group of significant features are referred to as ‘drift-filled hollows’ (DFH). These are commonly closed depressions in the surface of the bedrock (typically the London Clay Formation), that are infilled by later deposits. Adjacent and underlying strata is sometimes disturbed
A new database shows that DFH are more widespread than previously thought, but also highlights issues in how they are classified. It also raises questions about the validity of the ‘simple’ geological model of London and highlights the danger of using assumptions when planning development, and for reconstructing past events.
