It is known that the North German Plain was formed during the
Pleistocene era as a result of the various
glacial advances of terrestrial
Scandinavian ice sheets as well as by
periglacial geomorphologic processes. The terrain may be considered as part of the Old or Young Drift (
Alt- or
Jungmoräne), depending on whether or not it was formed by the ice sheets of the last glacial period, the
Weichselian Ice Age. The surface relief varies from level to undulating. The lowest points are low moorlands and old marshland on the edge of the ridge of dry land in the west of Schleswig-Holstein (the Wilster Marsh is below sea level) and in the northwest of Lower Saxony (Freepsum, below sea level). The highest points may be referred to as Vistula and Hall glaciation terminal moraines (depending on the ice age which formed them) – e.g., on the
Fläming Heath above sea level) and the
Helpt Hills ). Following the ice ages, rain-fed,
raised bogs originated in western and northern Lower Saxony during warm periods of high precipitation (as influenced by Medieval Warm Period). These bogs were formerly widespread but much of this terrain has now been drained or otherwise superseded. The coastal areas consist of Holocene lake and river marshes and lagoons connected to Pleistocene Old and Young Drift terrain in various stages of formation and weathering. After or during the retreat of the glaciers,
wind-borne sand often formed dunes, which were later fixed by vegetation. Human intervention caused the emergence of open heath such as the
Lüneburg Heath, and measures such as deforestation and the so-called
Plaggenhieb (removal of the topsoil for use as fertilizer elsewhere) caused a wide impoverishment of the soil (
Podsol). The most fertile soils are the young marshes (
Auen-Vegen) and the Börde areas (Hildesheim Börde, Magdeburg Börde, with their fertile, loess soils). High-level bog peat can be found in the poorest soils, e.g. in the
Teufelsmoor. In the loess areas of the lowland are found the oldest settlement locations in Germany (
Linear Pottery culture). The northeastern part of the plain (Young Drift) is geomorphologically distinct and contains a multitude of lakes (e.g. the Mueritz lake in the
Mecklenburg Lake Plateau) which are vestiges of the last ice age. The retreating glaciers left this landscape behind around 16,000 to 13,000 years ago. In comparison, the dry plains of northwestern Germany (Lower Saxony, western Schleswig-Holstein, and the Bochum area of North Rhine Westphalia) are more heavily weathered and levelled (
Old Drift) as the last large scale glaciations here occurred at least 130,000 years ago. The region is drained by rivers that flow northwards into the
North Sea or the
Baltic and tributaries to the
Rhine river that flows West. The Rhine,
Ems,
Weser,
Elbe and
Havel are the most important rivers which drain the North German Lowlands into the North Sea and created woods in their flood plains and folds, e.g. the
Spreewald ("Spree Forest"). Only a small area of the North German Plain falls within the catchment area of the
Oder and
Neiße rivers which drain into the Baltic. ==Climate and vegetation==