ROCKWALL RETREAT AND SEDIMENT PRODUCTION IN FLYSCH
BADLANDS (SW SLOVENIA)
Matija ZORN
Anton Melik Geographical Institute, Scientific Research Centre of the Slovenian
Academy of Sciences and Arts
Gosposka ulica 13, SI-1000 Ljubljana, Slovenia
matija.zorn@zrc-sazu.si
Steep bare rocky slopes are a morphogenetic particularity of the flysch part of the
Istrian Peninsula in SW Slovenia and NW Croatia. On them, microrelief forms are
of a short life cycle, since erosion processes are fast.
Measurement of sediment production of flysch rocks from steep slopes was
made using four »half-open« experimental plots (bounded on top and open on
the sides) from 1.8 to 4.5 m2 in size. Measurements were done in the Dragonja
river basin (SW Slovenia), which belongs to the submediterranean climate
region.
The sediment production of flysch rocks on average amounts to around 89 kg/m 2
annually, which means that the rock walls are retreating at a rate of 3.5 cm to
almost 5 cm per year (Zorn 2008; Zorn and Mikoš 2008). The erosion plots were
situated in the lower part of a flysch rock face that was chosen as a suitably
characteristic example of flysch rock faces in Istria due to its relatively rapidly
alternating flysch sequences (sequential thicknesses from a few centimeters to
as much as 15 centimeters), great brokenness of the rock, and dominance of
claystone over sandstone. Measured and calculated was also annual sediment
supply from this badlans to the fluvial system; annual sediment supply amounts
up to 12%.
The badlands presented not only flysch rock faces with inclinations from 70 o to
90o but also eroded slopes with erosion rills and gullies with inclinations from 40 o
to 60o. For measuring the movement of material along erosion gullies, a dam was
built in one of the gullies. From a contributing surface area of 0.1 hectares,
twenty tons of material was captured behind the dam in fourteen months (Zorn
2008).
All measurements were conducted weekly. Calculated were monthly and
seasonal averages, as well as linear statistical links between the studied erosion
processes and weather conditions.
References:
Zorn, M. 2008: Erosion processes in Slovene Istria. Geografija Slovenije 18.
Ljubljana. (in Slovene)
Zorn, M., Mikoš, M. 2008: Rockwall retreat on badlands in Slovene Istria.
Geologija 51 (1), pp. 107–118. (in Slovene)