Nova geomorfološka dognanja na Triglavu

Abstract

In our study of the traces of the mechanical mouldering that can be
found in the Julian Alps we have limited ourselves to a broad peneplain
that encircles the Triglav Mountain at a height of 2300—2500 m. All this area
which consists of Triassic limestones is situated just below the snowline and
thus it lies above the line with the compact vegetation. We have become
interested in the problem here discussed after it had been established that
the peneplain has a cover of fine scree of varying thickness which is known
to be a product of the mechanical mouldering of the bedrock. Particularly
large quantities of this fine scree have been found on the broad plateau Za
planja, west of the peack of the Triglav Mountain, while on the other hand
it appears in comparatively small quantities on the karstified more or less
level surfaces (podi), in the notheast of Triglav ; in this latter area it occurs
in somewhat larger quantities only around the hut Staniceva koca and on
Kredarica.
In our investigation of these differences we have come to the conclusion
that it is necessary to take into consideration the slight diferences that can
be observed in the composition of the limestone. At the same time we have
also found that the climatic conditions, above all the lenght of the period
when a certain area is usually covered with snow, are also a decisive
factor.
The plateaus situated to the west of the Triglav Mountain are widely
open to the south and its winds which blow off from these plateaus large
quantities of snow: for this reason the snow melts here faster and so the
floor is here exposed during a longer period to the mechanical mouldering.
I he snow, however, remains much longer on the karstified more or less
level surfaces in the area northeast of the Triglav Mountain. These surfaces are somewhat inclined towards the north. They are closed towards the
south and southeast by a ridge which extends from Triglav towards the east
over Kredarica and Rež. These surfaces are covered by quantities of snow
that are larger than is the average here as this has been established by
observers who workin the new meteorological station at Kredarica. Here
the snow remains much longer and for this reason the bedrock here is less
exposed to the process of mechanical mouldering; here the chemical decomposition of the limestone is the prevalent process. During the former centuries when the snowline extended much lower into the valley than it
does nowadays these areas were even longer covered by snow. This fact is
proved both by oral and written reports, and particularly by the large
number of pictures. There are many elements which seem to indicate the
very great importance of these colder periods for the emergence of the
present differences in the state of mouldering of the high plateaus around
the Triglav Mountain.
During the subsequent investigations our attention has been called to
the consequences the mechanical mouldering of the bedrock has on the
morphology of the area. This problem became most clearly evident on the
plateau west of the Trigla v Mountain, especially in the limestones which
show a higher degree of dolomitization; here we can find particularly large
quantities of fine scree. The decayed find scree represents an important
obstacle to an efflux of water into the Karstic floor; here the water can
therefore flow over the surface in spite of the porosity of the limestone.
This leads to a retransportation of the fine scree and finally to its accumulation. In this way the Karstic pot-holes become filled up with this fine scree and conditions develop which make even longer flows of water over
the surface possible. Yet in spite of all these depositions we could also
observe characteristic traces of erosion, particularly in the places between
the individual Karstic pot-holes and in the area where the peneplain bends
downwards towards the lower levels. This the process of deposition is
simultaneously accompanied by of the erosion.
Moreover, the frequent freezing and melting of the ground has also its
share in the transportation and assortement of the material. This is proved
by the well developed circular rings of scree, the polygonal nets, and by the
traces of solifluction. We shall leave, however, the details regarding the
genesis of these forms and the different types of solifluction to one of our
later studies.
In our study of the material that had been deposited by the glacier on
the peneplain around the Triglav Mountain it has been established that an
equally old Holocene fine scree which can be found in the large talus slopes
that occur on the western side of the Trigla v Mountain had also been accumulated in beautiful moraines on its northeastern side, in the area of the present day glacier and in the coomb valley of Planika and the neighbouring coomb valley between the Lower Triglav and Kredarica. The debris are therefore of the Holocene age. Because of the small quantities of the
fine scree in these coomb valleys the idea has been proposed that these
moraines had been deposited in a period closer to the present age than to
the last glacial epoch and that they could perhaps be compared with the
already know n and hisorically identifiable moraines that can be found
below the Triglav Glacier.
On the basis of the differences that can be observed in the way how
the debris of the moraines that occur below the Triglav Glacier are covered
with algae we could divide these moraine depositions into three large
groups: in the oldest moraines (I), the rocks are already nearly completely
covered with algae. The scree has therefore a dark gray, nearly black colour.
In the younger depositions (II), the algae can be found in considerably
smaller quantities on the scree; neither are the rocks from these moraines
any longer completely covered with the same. In the oldest moraines any longer completely covered with the same. In the oldest moraines (I), the
mono-, bi-, and tricellular forms are prevalent, while in the younger
moraines we can only fin d the mono- and bicellular forms. In the third
group of depositions (III) no algae whatever can be found on the moraine
scree.
The oldest moraine depositions (I) have comparatively very large dimensions. In spite of this they were vocered during the second phase (II)
by a new front moraine, while at the two sides the glacier only leaned on
the older lateral moraines; the depositions of this second phase are therefore particularl y impressing. They can be clearly distinguished from the older moraines by the fact that they are considerably less overgrown. They
have a very light colour, similar to that of the rock y walls below the
Kredarica and above the Trigla v Glacier which were still covered by snow
and ice even during the sixties on the XIXth
century. The moraine depositions of the third phase, however, are in comparison with those of the
two older phases quite insignificant and point to a contemporary considerable recess of the glacier.
If we take into consideration the way how these debris are grown over,
the morphologic and stratigraphic peculiarities of the moraine depositions,
as well as the paintings and photos of the glacier and the topographic maps
of the same we come to the conclusion that the second phase had apparently been developed about the year 1850. The depositions of the third phase can in all probaility be placed into the period about the year 1920;
those of the first phase go persumably back into the XVIII th or even into
the XVII th century. Of the same age are probably also the moraines that
can be found in the large coomb valleys on the southern and southeastern
sides of the Trigla v Mountain. The regular observations of the Triglav Glacier have been started
i n 1946. The results of the first eight years of these observations (1946—1954)
have been collected at the Institute of Geography of the Slovene Academy
of Arts and Sciences by Drago Meze; they were published i n 1955 in Geografski Zbornik. For this reason we cover in our present report the last eight years only, the period between 1954 and 1962 for which no report has
yet been published. During this period, too, the glacier continued to recede
without any interruption. The largest recession has taken place above the
so-called Glava where a recession of 28,40 m was observed during the
years 1954—1959 alone. Simultaneously, the thickness of the glacier has
also been considerably decreased. The recession of the Trigla v Glacier was
rather constant, wit h the onl y exception of the year 1958 when there was
a particularl y significant recession.
Finall y we can also mention the fact that during all the last eight
years the snow did not so completely disappear fro m the glacier as it did
in 1954 when there was almost no snow even in the upper border area of
the glacier, immediately under the rock y wall. Particularl y large quantities
of snow were preserved on the glacier down to the end of the meltin g
period during the last three years (1960—1962). Since the year 1959 it has
been observed that the quantity of the snow has constantly been increasing.