During the Pleistocene (also known as ice age), pronounced climatic fluctuations occurred that resulted in at least eight cycles of glacials and interglacials. In glacial periods the earth experienced severe cooling and the advance of glaciers over the land up to the 40th parallel in some places. Hence, glaciers periodically covered vast areas of the continents and at maximum glacial extent roughly 30 % of the earth’s surface was covered by ice sheets 1500 m to 3000 m thick. Since large volumes of water were tied up in these continental ice sheets, global sea levels could temporarily drop 100 m or more. During subsequent interglacial periods the global sea level again rose due to ice retreat and melting. The Holocene is the present interglacial.
Pleistocene inheritance is found in coastal systems in the form of rocks formed by glaciers (Sect. 2.4) and by sediments deposited in the Pleistocene. During interglacial times in the Pleistocene drowned coastlines were common; the sea-level rise allowed temporary marine incursions and hence sediment deposits into areas that are now far from the sea. Because of the repeated glacial and interglacial periods, those sediments deposited during the Pleistocene are generally well-compacted by the ice cover. Buildings in the Netherlands are often built on piles touching the hard Pleistocene substrate. Many present-day morphological features are Holocene in age. They are shaped by erosion and deposition on the one hand and sea-level changes on the other hand (Sect. 2.5). The sediments are either loose alluvial sediments supplied by rivers during the Holocene (from around 12 thousand years ago) or older (Pleistocene). Marine processes may rework these older deposits and feed the coastal system again from the sea.