Geology Reference
In-Depth Information
small sand- or silt-sized intraclasts, which after
redeposition may constitute important component
of other tufa facies or build independently intraclast
tufa deposits (sensu Pedley 1990).
relatively high SI
calc.
value. However, the SI
calc.
reached higher values in summer 2003, when the
rate of growth was slightly slower. Hence, the dis-
cussed phenomenon is hard to envisage. One poss-
ible explanation is the specific winter hydrological
condition in the Slovak Karst area. Although the
H
´
j site is characterized by continental climate,
with maximum concentration of rains in spring
and summer, evapotranspiration causes that the
water flow in stream may be higher in cold season
(
ˇ
erm
´
k 1994).
The lower growth rate of tufa at the H
´
j dam site
in summer 2003 was caused by periodical emersion
of the tablet during reduced flow conditions in
summer 2003. Water flew only through the spillway
in the tufa dam, leaving the rest of the crest, where
the tablets were placed, emerged (Fig. 3g).
The seasonal tufa growth rate and SI
calc.
changes
are generally covariant at the Karw
´
w site. The
SI
calc.
calculated for the station just upstream of
the studied points reached maximal value of 0.94
in June 2003, which is consistent with maximum
growth rate of tufa in summer 2003. The SI
calc.
trend is generally similar at the Z
´
zriv
´
site
with the maximum value in late June. It is seemingly
contradictory to the tufa growth rate, which implies
the maximal growth in autumn 2002. However,
in the spring of 2003 the seasonally exposed tablet
experienced significant period of corrosion followed
by precipitation, which is documented by newly
formed tufa deposited on corroded surface of the
limestone tablet. Moreover, the water level in the
rivulet feeding the tablet between June and
October 2003 fall drastically, which resulted in
drying up of the limestone tablet (Fig. 6b). Thus,
the growth rate obtained for the period June -
October 2003 is significantly underestimated.
To sum up, the only one general rule detected
during the experiment was the response of tufa
depositing streams to exceptional weather con-
ditions in summer 2003. Central Europe experi-
enced prolonged drought and hot weather (Sch¨r
& Jendritzky 2004). This resulted in the elevated
SI
calc.
values in all studied streams, regardless of
the type of water supplying the tufa and in the
episode of more efficient tufa growth. This is not
valid for the points where tablets were emerged
after the fall of water level, that is for the Z
´
zriv
´
site and the H
´
j upper waterfall and dam points.
Seasonality of tufa growth
The seasonality of tufa growth can manifest itself in
two ways. The first is seasonally varying rate of
growth recorded as varying mass of tufa deposited
in different seasons, the second is seasonal alterna-
tion of tufa textures. The experiments described
here shed some light on both manifestations of
seasonality.
Seasonal mass increment. The comparison of the
tufa amount which grew during particular seasons
in particular study sites lead to the conclusion that
there is no one common trend in tufa growth rate
(Table 3, Figs 7, 8). At the Z´zriv´ and Karw ´w
study sites the greatest mass increment was recorded
in the summer of 2003. At two points of the H´j site
more tufa grew during the winter of 2002 - 2003,
while in the third point tufa grown in summer
2003 slightly prevails. At all points studied at
the L ´ˇky site, overwhelmingly dominates the tufa
increment from the summer 2003. This points
to the importance of local factors, specific for par-
ticular
sites,
which
effectively
govern
the
tufa
growth rate.
At the L ´ˇky E point tufa grew at a relatively low
rate - only 6.77 mg/cm
2
/day - between August -
November 2002, while between June - October
2003 the growth rate was as high as 10.71 mg/
cm
2
/day. At other points at L ´ˇky waterfall the
trend is similar regardless the tablet type
(Table 3). Changing water chemistry can fully
account for the above difference. The SI
calc.
value
for the water feeding the studied points in summer
2003 reached 1.27, the highest value ever recorded
for this point. The elevated SI
calc.
is associated
with elevated TDS value. It is adequately explained
by the changing ratio of deep and shallow contri-
bution to stream water that feeds the L ´ˇky water-
fall. The change was probably due to a weather
anomaly; the summer 2003 was exceptionally dry
and hot in central Europe, with the amount of rain-
fall lower than average (Sch¨r & Jendritzky 2004).
Hence, the proportion of deep water increased, alter-
ing the chemistry of feeding water, and stimulating
vigorous growth of tufa.
At the H´j site, the rate of tufa growth at both
studied points in the lower segment of the stream
was highest in the winter season 2002 - 2003. This
was independent of SI
calc.
values calculated for
November 2002 and March 2003, which are slightly
lower than those for the summer season. The vigor-
ous tufa growth in the winter season coincides with a
Seasonal textural sequence. The textures of growing
tufa, as was shown above are controlled by closely
interrelated factors like temperature, irradiance, bio-
logical activity and hydrology: especially intensity
of a water flow. All these factors change in the
course of a year. One could thus expect a similar
sequence of tufa textures in a one-year increment
in all the studied sites, reflecting the periodical
Search WWH ::
Custom Search