Geoscience Reference
In-Depth Information
of the past have not been summarized on a regional scale, especially by a com-
parison with glacial evidence from adjacent mountain massifs. That is why the
Institute of Geography participated in two terrain studies in 2007 and 2008, ded-
icated to a research of former glaciations in Rila. The first fieldwork was initiated
and organized by the Geosciences Institute - University of Tubingen, Germany,
and led by Prof. Joachim Kuhlemann. For 9 days all main valleys of Rila moun-
tain were searched and moraine features were described and mapped. Samples were
also taken for cosmogenic nuclide dating ( 10 Be) to estimate absolute age of glacial
deposits. Although some preliminary results were already published (Kuhlemann
et al., 2008 ), acquiring of data from this study is still going on. Results obtained by
now indicate that the deposition of the lowest terminal moraine in Rila mountain
(that above Beli Iskar village at 1,150 m a. s. l.) was undoubtedly during the period
of the Last glacial maximum (Last Glacial Maximum, LGM - 23,000-19,000 years
BP) (a sample taken from the first of the four ridges up the valley). The main con-
clusion from this study is that most landforms from the relict glacial complex are
quite new with the oldest moraine features dating from Late Würmian (LGM) and
newest probably from the cold phases during the Holocene. No glacial accumulative
landforms were registered from earlier glacials (e.g. Riss or Mindel) as some of the
previous authors suggested, although there are geomorphic traces of previous glacial
stages, such as parallel trough valley trimlines and some old cirque shoulders.
Analysis of the positions of LGM terminal moraines and of the configuration
of trimlines in the analyzed river (for which aerial photographs were also studied)
showed that the Equilibrium line altitude (ELA) of Rila glaciers during their maxi-
mum spread (LGM) had been lying at 2,150-2,250 m a. s. l., with a gradual rise from
NW to SE. Considering a temperature lapse rate of -0.6 C/100 m alt., this should
mean that average temperatures during the coldest phase of the LGM were about
6 C lower than at present. Compared to the Alps and the mountains of the west-
ern and central Mediterranean the LGM Equilibrium line in Rila was situated much
higher, and differences between N and S aspects were quite small. These results
suggest a considerable smaller moisture supply in Rila mountain during the LGM
and support the hypothesis of a compensatory warm advection from the south in
the eastern Mediterranean as a response to the cold northerly advections in Western
Europe for this period (Fig. 12.4 ).
To study the newest traces of glaciation, a fieldwork was held in summer 2008.
Its task was to research the morphology of the bottom of Ledeno ezero - the highest
lake in Rila, situated at 2,709 m a. s. l. On the created detail bathymetry map (second
after the one made by the Austrian team of S. Leutelt-Kipke, 1932 ) a well-outlined
crescent-shaped ridge can be identified underwater in the shallow SW part of the
lake (Fig. 12.5 ). The crest rises up to 2 m from the shallow part of lake bottom,
its highest point lying 2.1 m under the water level. Geomorphic indications, mete-
orology records and historical sources give advantages to the hypothesis that this
ridge represents a relatively young moraine feature, formed probably by a peren-
nial snow patch (microglacier) during the Little Ice Age (LIA). Today there are no
perennial snow patches in Rila, and some small spots of last winter snow may sur-
vive the summer only in years colder than average, but historical sources say that
Search WWH ::




Custom Search