Geoscience Reference
In-Depth Information
entrances are situated on the left bank of the deep
Kastrakli Gorge and are difficult to access. It is easier
to enter the cave from the upper, small, vertical
entrance that is on the edge of a 20 m cliff. After
penetration through a 25 m narrow passage, one can
reach the main gallery of the cave where the stalag-
mites to be studied are located.
The cave is developed by Proterozoic marbles of
the Dobrostan Marble Formation. The total length is
635 m with a denivelation of 35 m. The cave consists
of one large northwest/southeast gallery with height
of up to 12 m and width of 8-10 m in some places
(Fig.
3.60
). Typical formations are rich speleothems
of different types: stalactites, stalagmites, draperies,
flowstones, and sinter lakes (gurs).
Eminova Cave was discovered by Sofia cavers
S. Petkov and Ts. Ostromski in 1992. After digging
the 25 m narrow passage near the entrance, in the
same year it was explored and surveyed by Ts.
Ostromski, S. Petkov, M. Zlatkova, Z. Iliev, G.
Raichev, and others. The cave is rarely visited and is
well protected from negative human impact.
During a visit by the Hungaro-Bulgarian team in
2007 (Dr. K. Gribovszki, T. Czifra, Dr. G. Surányi,
Dr. K. Kostov, and G. Nikolov) it was found a suit-
able thin stalagmite with 117 cm height and 5.1 cm
maximal diameter for in situ measurement
(Fig.
3.61
). The results are presented in Table
3.4
.
The peak ground acceleration that can break the
studied stalagmite is in the range of 6.0-10.5 m/s
2
.
Unfortunately, the very thin stalagmites in Eminova
and Snezhanka caves are not suitable for sampling for
U-series dating. On the base of conducted research,
we can suppose that the measured speleothems have
not been exited by high horizontal acceleration in the
last millennium.
Fig. 3.61
Dr. Katalin Gribovszki measuring the natural fre-
quency of the stalagmite in Eminova Cave (photo G. Suranyi)
As a result of the field measurements in Snezhanka
Cave and the theoretical calculations, the investigated
stalagmites were not excited by horizontal accelera-
tion higher than 9.2 m/s
2
in the last few thousand
years (Gribovszki et al.
2009
).
3.3.2.5 Eminova Cave
Eminova Cave is located in the southern part of the
Western Rhodopes Mountains about 5 km northeast
of the village of Borino, Smolyan District. The two
Table 3.4
The parameters of the studied stalagmites in Eminova Cave (Paskaleva et al.
2008
)
H
(cm)
a
g
(m/s
2
)
D
Average
(D
Min
- D
Max
)
(cm)
Measured
natural
frequency
f
0
(Hz)
Theoretical
natural
frequency
fo(Hz)
Elastic
modul, E
(GPa)
Density
(g/cm
3
)
Tensile
failure stress
(MPa)
1
2
3
4
5
6
7
8
9
Eminova
Cave
117
4.2
3.0-5.1
17.5
5.7
3.735
2.14 ± 0.25
3.83 ± 0.81
6.0-10.5
