PATTERNS AND RATES OF QUATERNARY CRUSTAL MOVEMENTS IN THE UNITED KINGDOM: COASTAL EVIDENCE

A wide range of former marine/shoreline features are present around the British coastline from which regional crustal movements can be evaluated. Interpretations based upon Late Quaternary (last 15,000 years) features/deposits has allowed detailed assessments of patterns and rates of crustal movement to be made which have been compared with tide gauge records. In general the Holocene marine evidence indicates that northern Britain is rising (0.5-1mm/yr) in response to glacial unloading whilst south-eastern Britain is sinking (1-2mm/yr).

Marine features associated with former interglacial periods (Stages 5e, 7, 9/11and 13) are also present however their interpretation is difficult, since their age and association with sea level at the time of formation are often poorly constrained. It seems likely that at least some of the sites may have been influenced by glacio-isostatic movements. The evidence suggests that long-term subsidence has prevailed in the southern North Sea at a rate of 0.05-0.1 mm/yr. The shoreline evidence however also suggests that rates of subsidence may have been 3-5 times faster in the early Quaternary. There is also some limited evidence of uplift of some parts of the United Kingdom, however this may have been localised and of limited duration. Certainly few of the Stage 5e raised marine deposits in western and southern Britain appear to have been displaced. In contrast features/deposits in eastern England appear to have undergone limited subsidence.

The long term crustal movements clearly suggest rates of movement considerably lower than that proposed by the Holocene data. This implies that the rates of movement derived from Holocene data have been influenced by glacio-isostatic movements and thus are not representative of longer the term crustal movements.