Geoscience Reference
In-Depth Information
Table 3.1
The parameters of the investigated stalagmite in Elata Cave (after Paskaleva et al.
2008
)
H
(cm)
D
Average
cm
Measured natural
frequency, f
0
Hz
Elastic
modul, E
GPa
Density
gr/cm
3
Tensile
failure stress
MPa
Theoretical natural
frequency, f
0
Hz
a
g
cm/s
2
Elata Cave
237
11.3
17.8
7.49
2.5 ± 0.08
1.62 ± 0.42
4.88
325.9
Fig. 3.20
Map and
longitudinal profile of
Razhishka Cave (after Beron
et al.
2006
)
gallery developed along a fracture with meridional
direction (Fig.
3.20
). The cave ends with a giant
breakdown on the contact area with a transverse
crack. In 1979, students at the University of Mining
and Geology, M. Georgiev and Z. Andonov, carried
out geophysical electrical profiling on the plateau
surface above the cave to seek an extension. The
measurement shows the presence of a large cave
gallery after the collapse (Zlatkova
1987
). Numerous
attempts
During field study conducted in September 2003,
in
Razhishka
Cave
were
identified
the
following
indicators of seismotectonic activity:
(A) Fallen stalagmites covered with a thick layer
of calcite deposits. They are distributed in the inner
parts of the cave at 100-280 m distance from the
entrance. The fallen stalagmites have length up to 1 m
and diameter up to 30 cm;
(B) Massive stalagmite with height of 230 cm and
diameter of 80 cm, cut by an open subhorizontal
crack. The crack is filled with calcite deposits. The
upper part of the stalagmite is at horizontal dis-
placement of 7 cm. (direction 222) and rotated to the
base (Fig.
3.21
);
(C) Massive inclined stalagmite with height of
3.5 m, cut by a crack. The inclined stalagmite is
supported by its neighboring stalagmite formed near
the wall of the cave gallery. Thick speleothem
deposits cover the tops of the two stalagmites and
form anomalous double stalactone (Fig.
3.22
);
(D) Dislocated passage well visible on the ceiling of
the cave due to vertical fault movement to the direction
10. The dislocation is clearly traced on a horizontal
distance of about 15 m, between 50 and 70 m from the
entrance of the cave. The height of the cave ceiling in
this part is about 4.5 m but then increases sharply and
tracking the dislocation is difficult (Fig.
3.23
).
by
cavers
to
find
prolongation
after
the
breakdown have been unsuccessful till now.
From geomorphological point of view, Razhishka
Cave along with other caves of the Lakatnik karst
basin is an emblematic example of leveled karst. The
vertical cave system Razhishka Cave (the oldest
upper fossil dry level)—Temnata Dupka Cave (active
water cave with length of more then 6,000 m)—karst
spring Jitolyub (water cave with sump) demonstrate
the stages in the development of the karst process and
its relation to the tectonic development of Vratsa
Mountain and incising of Iskar River during the
Quaternary. The vertical range of the system is
approximately 220 m. Using geomorphological cor-
relation between the relative height of the cave hyp-
sometric levels and the river terraces of Iskar River, it
can be assumed that the Razhishka Cave was formed
at the beginning of the Lower Pleistocene.
