Fph iii. Full interglacial (Substages late II – III)
The continued infilling of floodplain depressions and channels caused a decrease in channelised flow routes. The periodic and increased flooding encouraged by this restriction of streams to relatively few channels, resulted in widespread vertical accretion across virtually all the floodplain surfaces. This typical stable meandering or anastomosing river behaviour appears to have occurred throughout lowland Britain during interglacial periods. Its consequences are that flowing channels remain relatively fixed in the positions inherited from the previous late-glacial, though the inset channels were not necessarily in contact with the sediments of that time. Streams were not always restricted to single-thread flow channels but probably included complexes of shallow channels separated by vegetated islands or banks (cf. Holocene analogues ). The floodplain areas beyond the channels continued to accumulate marsh or peat-like sediment, with surface wetness augmented by spring activity at slope-foot localities. These extensive overbank areas locally provided a dense, wet woodland complex, as well as drier areas, both of which were colonised by diverse communities of plants and animals. The latter included humans in the later Pleistocene, e.g. Hoxnian (=Holsteinian) Stage. Soils developed on the drier surfaces above the water table, as at Swanscombe, Kent. Areas were also cleared by large vertebrates, as discussed above.
The shift from forests dominated by deciduous broad-leaved trees to mixed deciduous-coniferous forest during this period appears to have had little detectable effect on sedimentary sequences. There is some evidence increased inorganic input of this in the preserved sequences resulting from the slightly more open nature of the forests. However, organic sedimentation, with a fine inorganic component, seems to have continued at some sites. In this period during the Holocene, major valley alluviation was driven by forest clearance by Neolithic humans, a feature previously absent.