Geology and Genesis
Coastal plain
The formation of the western coastal flat of Belgium started about
10,000 years ago, at the beginning of the Holocene. The sea level
was rising as the ice sheets started to melt in a warming climate.
Sand and clay sediments were laid down on the lower parts of the
land. With a rising sea level also the ground water level rose
and peat swamps formed, which in turn were inundated and marine
sediments were laid down on the peat. The first 4000 years of
the Holocene the coast formed a tidal mud flat with fresh water
swamps inland. Between 5300 and 4700 years BP the coastal plain
was sedimented to a height, that in the largest part of the coastal
plain peat was formed and around 4200 years BP a large peat cushion
was formed. The formation of this large peat cushion suggests
that the coastline was (semi-) closed and the fossil dunes of
Ghyvelde-Adinkerke are assumed to be a remnant of this coastline.
Fossil dunes
From 3300 years BP the marine influence increased and several
inundation-phases took place (Dunkirk transgressions) alternated
by regression periods. Dunkirk 0 transgression started 1300 BC
and is also called the pre-Roman transgression. This transgression
did not really affect the Belgian coast landscape but at De Panne
the old dunes were formed. A new dune belt formed 3,5 km before
the coast and between this dune belt and the dunes of Ghyvelde-Adinkerke
a tidal area was present. The old dunes from De Panne are partly
eroded and from the 11th century were covered by the Younger Dunes.
During the Dunkirk I transgression parts of the old sea-defence
dunes were eroded but there was little influence on the Old Dunes
of De Panne. The Dunkirk II transgression had a large influence
on the Old Dunes, large parts were eroded and only several islands
survived in the surroundings of De Panne. After the erosion, sedimentation
took place, the channels were filled with sandy sediments and
the peat was covered with clayey material. During a second regression
period, called the ‘Karolingische’ regression (8th-11th century
AD), the build-up of the Younger dunes started and the coastal
plain was closed off from the sea. The Dunkirk III transgression
took place in the 11th and 12th century AD and the coastal plain
was inundated again, but this transgression had little effect
on the Westhoek dunes.
Young dunes
The formation of the Younger Dunes took place in several phases.
The first phase is called the ‘mobile dune phase’ (9th-10th century
AD). Large sand drifts from the dry beach started this phase.
A larger storm frequency during the Middle Ages caused stronger
coastal erosion, which caused a larger sand supply to feed the
sand drifts. The mobile dunes moved land inwards and a zone of
500 to
800 m wide was covered under the dune sand. When the mobile dunes
had passed, a flat to slightly undulating dune area emerged of
about 6-7 m high, which was stabilised by vegetation. The second
phase was the ‘parabolic dune phase’ in which parabolic dunes
formed under the influence of the vegetation, behind the mobile
dunes. The stabilising effect of the vegetation was strengthened
by the ground water level rise, which was the result of the broadening
of the dune area. At the beginning of the 16th century the movement
of the mobile parabolic dunes ceased, the current dune fringe
is probably the result of afforestation of the dune front, to
stop the polders from being covered under the drift sand. In later
phases the influence of people became even more important. Because
of overexploitation, overgrazing, collecting firewood etc. the
dunes became mobile again. Overexploitation is probably also the
cause of the present 120 ha mobile dune complex in the Westhoek
state nature reserve.
