Munich is situated in the Northern Alpine Foreland. The northern part of this sandy plateau includes a highly fertile flint area which is no longer affected by the folding processes found in the Alps, while the southern part is covered with morainic hills. Between these are fields of fluvio-glacial out-wash, such as around Munich. Wherever these deposits get thinner, the ground water can permeate the gravel surface and flood the area, leading to marshes as in the north of Munich.