INVESTIGATION POSSIBILITIES OF EOLIAN DEPOSITS AND PROCESSES ON
THE TERRITORY OF LITHUANIA USING LARGE SCALE VERTICAL AERIAL
PHOTOGRAPHY
B. KARMAZA
Lithuanian Institute of Geology, LT-2600 Vilnius , st. T. Ševčenkos 13, Lithuania
e-mail: bkarmaza@geologin.lt
On the grounds of works based on field and
laboratory deciphering of aerial photographs, it is
possible to confirm with certainty that eolian
deposits are efficiently and well deciphered
everywhere, independently in spite of their position
in different landscapes. These landscapes form
a specific photographic picture in vertical aerial
photographs. Such deposits are also traced well
during aerial visual observations.
The tone and pattern of a photographic record,
types and forms of relief, topsoil and vegetation
cover, indications of economic assimilation of a
territory are the main signs for deciphering eolian
deposits and processes as well as their character and
intensity.
The tone of an vertical aerial photographic
picture of eolian sands varies from white to darkgrey on aerial photographs. The plots of eolian
sands absolutely devoid of vegetation cover have
a dazzling-white photo tone on aerial photographs
because of a uniform lithologic composition, deeper
occurrence of groundwater level and high reflecting
ability. In places covered by herbaceous vegetation
the tone of aerial picture is grey. The aerial pattern
of sand is even, and in plots covered with trees it is
dotted.
Morphological expressiveness is one of the main
distinctive peculiarities of eolian deposits for their
deciphering. Dunes and hillocks are distinguished
by characteristic forms of relief distinctly observed
with a stereoscope both on open plots and those
covered with wood. On vertical aerial photographs
it is possible to trace a whole complex of eolian
relief: deflation plane, hillocky eolian relief, weakly
developed dunes and hillocky-depressional surface
of sand deflation.
In woodlands, the elementary forms of eolian
relief are identified by a characteristic density
of trees.
Alongside relief forms, the major sign for
deciphering and simultaneously the sign indicating
the intensity of eolian processes is vegetation. The
role of vegetation consists not only in its ability to
consolidate the surficial part of sand mass by roots
and to prevent the development of deflation
processes, but also in decreasing the wind velocity
at Earth’s surface and in contributing to a partial
discharge of wind-driven sand flow. According to
the degree of vegetation development, eolian sands
are usually subdivided into unconsolidated, weakly
consolidated, semi-consolidated and consolidated.
On unconsolidated and weakly consolidated sands
wood vegetation is usually absent or is found in
solitary forms. As the vegetation cover develops,
the sands are enriched in humus which in its turn
contributes an increase of vegetation cover. As
a result, on semi-consolidated and consolidated
sands a considerable number of different
herbaceous plants, bushes and trees which are
distinctly fixed on aerial photos begin to grow.
Trees and bushes form a dotted pattern on aerial
photos, and their density may be evaluated rather
from vertical aerial photographs. Herbaceous plants
do not form a dotted pattern, however, they have an
influence on the tone of aerial photo picture (the
denser the herbaceous cover, the darker the tone
of an aerial photo). Thus, by the tone and pattern
of vertical aerial photo it is possible to judge almost
with certainty about the degree of sand
consolidation. Unconsolidated sands are presented
on vertical aerial photographs by almost white tone,
a dotted pattern is absent; weakly consolidated
sands are depicted by a grey, dark-grey tone,
the dotted pattern is expressed very weakly; semiconsolidated sands form a dotted pattern and
consolidated sands give a dark-grey tone; the dotted
pattern is practically absent.
The main characteristics of eolian sands are
their weak consolidation by vegetation and
looseness. These features bead to the formation
of eroded parts in forest roads, distinctly visible on
aerial photos. Sand is very good reflector, thus on
vertical aerial photographs the intervals of eroded
roads are surrounded by a peculiar dazzling-white
halo; a road-bed stretching across the deflated sands
(across the halo) is hardly seen. The other, no less
important indication of the roads crossing the eolian
deposits is their decreased linearity compared with
roads built on a firmer ground. These roads are
meandering,
they
twist,
pass
round
the unconsolidated plots. The absence of arable
land is characteristic of the areas of eolian sand
development.
All the enumerated features allow a rather
reliably determination and mapping of eolian
deposits and processes by aerial photographs. From
the orientation of eolian relief forms on vertical
aerial photos, it is possible to judge about
the direction of prevailing winds. The direction and
velocity of sand displacement are determined most
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precisely by comparative deciphering of materials
of repeated vertical aerial photographs.
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