Evolution of spit system in Lake Mossoe, Denmark
Soee, N.E. 1, Odgaard, B.V. 1, Kroon, A. 2, Kristiansen, S.M. 1
1 Department of Geoscience, Aarhus University, Denmark, (nes@geo.au.dk). 2 Department
of Geosciences and Natural Ressource Management, University of Copenhagen, Denmark
A complex spit system at the eastern end of Lake Mossoe, Denmark, has been investigated in
order to record past lake levels and wind regimes. The lake formed after the last glaciation in
an east-west elongated depression created by ice. Present lake is 9 km long (aspect ratio 5:1),
mean depth is 9 m and max depth is 22 m. Prominently westerly winds in Denmark have
promoted spits to evolve in the eastern part during the Holocene.
A Digital Elevation Model (LiDAR), boreholes and excavations were used to observe the
morphology of the spit system. A chronology of spit formations were established by OSL
datings.
Present eastern shoreline of Lake Mossoe is formed by a connection of two spits, which has
cut off an eastern basin. One spit prograded from the northern shoreline towards SE and was
active by 4.2 ka. The other and youngest spit prograded from the southern shoreline towards
NNW and reached the proximity of the first spit by 1.94 ka. Subsequently, further supply of
sediment has build-up the present barrier shoreline. Lake-bottom erosion, observed from
seismic profiles, constitutes a part of the sediment source to the northern spit. The main
sediment source of the southern spit is an erosional cliff situated 500m westward on the
southern shoreline.
The isolated basin east of the barrier shoreline is subsequently filled with sediments and is
now a drained meadow. Two remnant spits are observed by LiDAR in the meadow, which
both are formed around bluffs on the former southern shoreline. Both spits have their
proximal part in the south and distal part in the north. The smallest and most eastern of the
two spits is the oldest and stopped prograding shortly after 10.2 ka. The younger remnant spit
is c. 400 m long and is situated parallel and close to the spit forming the present eastern
shoreline. The tip of the remnant spit is dated to 2.08 ka. Thus, the spit has probably been
active in the distal part, while the youngest spit was prograding on the western side of its
more proximal part.
Activation of each spit in the system is thought to be controlled by wind and lake level
changes. Storms induced erosion on bluffs and generated alongshore wave-induced currents
transporting sediment towards the location. Refraction of waves curved the shoreline and
transported the sediment towards the distal part of the spits. Lowering of the lake level during
the Holocene is an explanation for the shifting of spit formation in a westward direction.