Slap Boka / Boka Waterfall EarthCache

(SI) Slap Boka ima izvir sredi navpicnih sten kaninskega pogorja. Je najmogocnejsi in najvecji slovenski slap!

PRED ZACETKOM:
Opis tega Geološkega zaklada je dolg. Prosimo, preberite ga in si zapisite naloge za vpis se pred obiskom zaklada!

NALOGE ZA VPIS OBISKA
1. Oglejte si kamnine okrog koordinat Geološkega zaklada, na razglediscu. Kaksne kamnine vidite? Obrazlozite odgovor.
2. S koordinat zaklada si oglejte strme in navpicne skalne stene, ki obdajajo sotesko Boke. Kateri del sten je najbolj razpokan in prispeva najvec drobirja, ki polni dno soteske? Napisite, kje se ta del sten nahaja. Zakaj mislite, da je temu tako?
3. Zelo bomo veseli, ce kaksno zanimivo fotografijo z mesta zaklada prilozite svojemu vpisu (logu) obiska.

POMEMBNO!
- Preden vpisete obisk zaklada, posljite odgovore preko GC profila ali neposredno na e-naslov vane.si.geo@gmail.com. Takoj potem lahko vpisete obisk zaklada na spletu – ne potrebujete dodatnega dovoljenja. Ce ste fotografirali, prosimo, prilozite kaksno fotografijo.
- Vpisi brez ustrezne spremljajoce e-poste, ki vsebuje pravilne odgovore, bodo najprej trajno kodirani, kasneje izbrisani!
- Vpisi, ki vsebujejo odgovor bodo izbrisani!

Ob obisku tega zaklada lahko obiscete se dva tradicionalna v blizini:
- Boka Waterfall (SLO), GCPXZZ in
- Path to Boka view, GC2NMB2, manj kot 200 m od Geološkega zaklada.

(ENG) Boka waterfall has a source in the midst of the Kanin massif vertical cliffs. It is the most magnificent and largest Slovenian waterfall!

BEFORE THE BEGINNING:
This EarthCache has a long description! Please, read it and write down logging tasks before visiting the EarthCache site!

LOGGING TASKS
1. Look at the rocks around the EarthCache coordinates at the viewpoint. What kind of rocks are they? How can you tell?
2. From the EarthCache take a look at the vertical cliffs surrounding the Boka river gorge. Which part of the cliffs is fractured the most and is contributing the most of the rock debris which fills the gorge bottom? Describe the position of this part of the cliff. Why do you think this particular part of the cliffs is more damaged than the rest?
3. We would be glad if you added interesting photos from the EarthCache location to your log.

IMPORTANT!
- Send answers through GC profile or directly to e-mail vane.si.geo@gmail.com
before logging. After that you can log - you don't need additional permission to log. Please, upload photos if you have taken them.
- Logs without an accompanying e-mail containing correct answers will be encrypted and later deleted!
- Logs containing the answer will be deleted!

While visiting this EarthCache, you can also visit two traditional caches in the neighbourhood:
- Boka Waterfall (SLO), GCPXZZ, and
- Path to Boka view, GC2NMB2, less than 200 m from EarthCache.

(ENG) KANIN MASSIF
The area surrounding Kanin massif is a part of the Dinarides, which may be divided into the Southern Alps, the Inner Dinarides, and the Outer Dinarides. The Southern Alps are composed of smaller tectonic units, which include the Krn (or Julian) nappe.

The Kanin massif above the Bovec Basin belongs to the western Julian Alps, which are divided from the eastern Julian Alps by the Mojstrovka fault. Tectonic movements from south-southeast to north-northwest have continued since the Miocene epoch and have caused the raising of the massif as well as the deepening of the syncline (Bovec Basin).
The oldest rocks in the Bovec Basin are from the Triassic period when the area of today’s Julian Alps and Kamnik-Savinja Alps was submerged by a shallow sea where limestone precipitated and later partly dolomitized.
Today, the uppermost part of the Kanin anticline is formed of Upper Triassic Dachstein limestone, up to 1,200 meters thick. This limestone is characterized by up to two meters thick strata and Megalodon fossils.

Dachstein limestone lies on a 1,000-meter package of Norian and Rhaetian Main Dolomite. The dolomite outcrops along faults in the Krnica Valley, and in normal superposition in the Moznica and Reklanica valleys form the lower part of a steep mountain wall (Jurkovsek 1987). Since its formation, the Kanin massif anticline has been dissected into numerous tectonic blocks that have moved along right-lateral strike-slip faults.

Depending on the degree of fracturing that appears in the rock along the faults, we can distinguish crushed, broken, and fissured zones. Crushed zones are impermeable and vulnerable to mechanical erosion. In dolomite, these zones are wider and filled with fine-grained breccia (millonite) compared to those in the limestone where coarser-grained breccia usually forms. Areas of millonite are usually impermeable and form hydrological barriers. Broken zones are highly porous, very permeable, and hydrologically important in dolomites. Since the rock is usually broken into various large blocks, water flows easily around, along, or through these zones. Fissured zones are very permeable as well, and the most important karst conduits usually form in them (Car and Janez 1992, Car and Pisljar 1993). This way karst springs may respond to precipitation in just a few hours (Gams 1974: 40).

KARST SPRINGS AND FAMOUS DEEP CAVES
The great thickness of the Dachstein limestone strata has influenced the development of the karst and the nature and position of the karst springs. The geological structure of the Kanin massif causes springs to occur on its flanks, mainly in the Bovec Basin (Bocic, Boka, Susec-Mala Boka, Zvika, Vodica, Glijun, Kladenki, Srnica) and to the north (Moznica, Goriuda). Only a few periodic springs are located higher on the slopes of the mountains. Water is forced to the surface due to the water table in the Quaternary sediments or by impermeable rock layers.
The rapid tectonic rise of the Julian Alps in the Quaternary period encouraged the rapid and deep carving of valleys. The adaptation of the karst system is usually slower than the changes that require it, and limestone karst massifs may be karstified some dozens of meters above the present water table due to the deepening of the valleys or the tectonic rising of mountains. This is the reason numerous karst springs and former spring caves can be found high above valley bottoms.
We can also observe a duality in the formation of caves of the Kanin massif: More or less vertical shafts developed in the upper part (which is above the water-table and only periodically filled with water). Those came into existence through percolating rainwater and water from melting snow flowing from the edge of a glacier or by water percolating through tectonically predisposed fissures under the glacier. At the contact with the water-table level, a zone of more or less horizontal passages and water outflow from the karst massif developed. In many cases, horizontal passages follow the lithological contact between Main dolomite and Dachstein limestone.
The Kanin massif is famous for its numerous and very deep vertical shafts. The deepest cave researched so far is Cehi II (1500 m), and the world’s longest vertical section (643 m) in a cave was discovered in 1996 in the Vrtiglavica cave. More than eight hundred karst caves and shafts have already been discovered in the Kanin massif, of which eleven are more than five hundred meters deep. One of the most internationally known cave systems Mala Boka – BC4 Polska jama, has one entrance at the height of 1730 m and the other, a visible crack in the mountain slope east of Boka waterfall, at a height of 433 m.

BOKA, THE MOST MAGNIFICENT OF SLOVENIAN WATERFALLS
The results of water tracing investigations show that an estimated average of 5.5 m3 per second of water flows from about fifty square kilometres of the Kanin massif under normal water conditions. About 85% of the discharge is received by the river Soca.
The western part of the massif is drained toward Boka, while its central and eastern parts drain toward Glijun. The Glijun spring typically has a discharge of around 1m3 per sec., but this can oscillate between a minimum of 0.15 to a maximum of 15m3 per sec. The Boka spring has an average discharge of 0.2m3 per sec. with a maximum flow that may reach as high as 50 m3 per sec. during periods of heavy precipitation (the exact flow has not yet been measured, some estimates reach as high as 100 m3 per second!) but may also dry up completely in the prolonged drought.

Boka waterfall is fed by river Boka, which springs at the ledge in the middle of vertical cliffs. Water boils from deep green pools in the midst of large rock blocks. A marked mountain trail leads to this source, but nothing more has been known about the water channel inside the mountain until cave-divers researched a part of it in 1975.
The first underwater chamber opens about 7 m under the spring surface, and is almost completely closed by large stone blocks, and remains of one or more rockfalls. The water channel continues vertically downwards for a few more meters before opening into the large oval cave carved into the rock, about 10 m wide and 8 m high. This water cave is directed only slightly downwards to the lowest point, about 25 m under the source and 50 m inside the mountain. After this point, the cave turns upwards and reaches the surface at the end of the 102 m-long underwater siphon. Researchers have followed the water course further and found about 30 m long lake, strong rapids, and a passage in three levels.

There is a lot of sediment in the dry, upper passage, and even many stalactites, a real rarity in the Alpine caves! So, it is clear, that most inner-researched parts of the water channel are carved in limestone. Only the last underground part of the water channel with the siphon is carved through the dolomite. Just before the Boka source, water direction changes from horizontal to vertical when it reaches the vertical fault and finds its way upwards to the source pool.
From the source, river Boka flows over the top of a very compact block of dolomite to the edge of the cliff. Water is spread almost 30 m wide at the top of the cliff and rushes down in the beautiful waterfall! After about 106 m of undisturbed free-fall water meets a 33 m high, steep rocky section - the second part of the waterfall. So, altogether, the Boka waterfall is almost 140 m high! It is magnificent at the time of average water level, mighty at the time of thawing snow, and awesome and unforgettable after heavy rain!
Valley under the waterfall has been formed in the tectonically crushed, highly fractured zone, parallel to the fault. Water erosion has been unstoppable in removing broken stone and carving an ever deeper gorge. In times of high waters, the waterfall is still providing enough energy to deepen the gorge even more. So, Boka is a rarity among Slovenian waterfalls, because its height is still growing!

EARTHCACHE AND ACCESS
EarthCache coordinates are set at the viewpoint, at the edge of the mountain pasture which offers a unique view of the waterfall and the short source river which feeds it - from above, across the gorge! The final viewpoint is positioned at a higher altitude than the waterfall source.

There are two trails leading to the EarthCache, both are quite accurately shown on Open Street Map, you also have all needed Waypoints enclosed. Trail 1 starts on the right bank of the river, at the end of the road bridge across the Boka river. This trail is well maintained only to the first viewpoint then it gradually gets worse: the last section, above the viewpoint near GCPXZZ tradi, the steep trail is covered with loose gravel!

We recommend Trail 2 to families. It starts in the village Žaga (park your car at waypoint PARKN3). It is less steep and in good condition. Additional waypoints will help you to find the beginning of trail and take the correct direction at each branching of the trail. This trail will take you too high to search for traditional geocache tradi GCPXZZ, but close enough to the upper tradi, GC2NMB2, hidden at the lower border of mountain pasture.
Both trails are marked with red stripes and red circles, usually painted on rocks or trees. Walking sticks are highly recommended, especially for Trail 1. Even thou you only have to ascend about 420 m, good, sturdy shoes are the best option.

Note: You use trails at your own risk. Use only trails you are fit and equipped to. Be safe and enjoy!

REFERENCES
1. Blaz Komac, The karst springs of the Kanin massif, Anton Melik Geographical Institute ZRC SAZU, Acta geographica No. 41, 2001.
2. Anton Ramovs, Slapovi v Sloveniji (Waterfalls in Slovenia), Slovenska matica, Ljubljana, 1983.
3. Uros Herlec, Geotrip ‘02 in Sloveniji [text Uros Herlec, Branka Hlad, Marko Simić ; ilustration Marko Kocevar, Darja Trtnik Medved; photography Marko Simić ... et al.]. Ljubljana: Ministry for the environment, Agency RS for the environment, 2005.
4. Kras na Kaninskih podih (Karst at Kanin), Franci Gabrovsek & Bojan Otonicar, Institut za raziskovanje krasa ZRC SAZU, Postojna, 3. slovenski geoloski kongres - Bovec, 16.-18. september 2010.
5. Photos in figure 4: A – D, from websites, authors named in the caption of figure 4.

(SI) KANINSKO POGORJE
Obmocje Kanina in okolice pripada Dinaridom, ki jih lahko razdelimo na Juzne Alpe, Notrenje Dinaride in Zunanje Dinaride.

Kaninsko pogorje nad Bovsko kotlino spada k Zahodnim Julijskim Alpam, ki jih od Vzhodnih Julijskih Alp locuje Mostrovski prelom. Tektonsko pogojeni premiki se od juga-jugovzhoda proti severu-severozahodu nadaljujejo ze vse od Miocena in so povzrocili dvig Kanina, kot tudi poglobitev Bovske kotline.
Najstarejse kamnine Bovske kotline so iz triasa, ko je bilo obmocje danasnjih Julijskih Alp, Kamniskih in Savinjskih Alp pod gladino plitvega morja, kjer je iz usedlin nastajal apnenec in se kasneje z dolomitizacijo delno pretvoril v dolomit.
Najvisji del Kaninskega pogorja je zgrajen iz zgornjetriasnega dachsteinskega apnenca debeline do 1200 m. Ta apnenec ima znacilne en do dva metra debele sloje in fosile megalodontidnih skoljk.

Dachsteinski apnenec lezi na 1000 metrskem paketu norisko-retijskega (glavnega) dolomita. Dolomit izdanja vzdolz prelomov v dolini Krnice, v normalno lezecih plasteh v Moznici in Reklanici pa tvori spodnji del strme gorske stene. Po nastanku Kaninskega pogorja jebilo to razkosano na stevilne bloke, ki so zamaknili vzdolz desno zmicnih prelomov.

V odvisnosti od stopnje razpokanosti kamnine, ki jo opazujemo vzdolz prelomov, lahko razlikujemo med zdrobljeno, razlomljeno in razpokano cono. Zdrobljene cone so za vodo neprepustne in obcutljive na mehansko erozijo. V dolomitu so te cone sirse in zapolnjene z drobnobrecasto kamnino (milonitom), v apnencu pa z breco. Razlomljene cone so zelo porozne, zelo prepustne za vodo in hidrolosko pomembne v dolomitu. Ker je kamnina obicajno prelomljena v razlicno velike bloke, jih voda zlahka zaobide, tece vzdolz ali skozi te cone. Tudi razpokane cone so prav tako zelo prepustne za vodo, obicajno v njih nastanejo najpomembnejsi kraski vodonosniki. Preko teh vodnih poti lahko kraski izviri ze v nekaj urah reagirajo na padavine.

KRASKI IZVIRI IN SVETOVNO ZNANA GLOBOKA BREZNA
Velika debelina dachsteinskega apnenca je narekovala razvoj krasa ter naravo in razporeditev kraskih izvirov. Geoloska sestava Kaninskega pogorja pogojuje nastanek izvirov na pobocjih. Najvec jih je v Bovski kotlini (Bocic, Boka, Susec-Mala Boka, Zvika, Vodica, Glijun, Kladenki, Srnica) in na severu (Moznica, Goriuda). Le nekaj obcasnih izvirov lezi visje na pobocjih gorovja. Vodo na plan prisili visina podtalnice v kvartarnih nanosih ali pa za vodo neprepustne plasti kamnin.
Hiter dvig Julijskih Alp v Kvartarju je vzpodbudil hitro in globoko dolbljenje dolin. Prilagoditev kraskega sistema je obicajno pocasnejsa od geografskih sprememb, ki jo zahtevajo. Zato je kraski masiv lahko zakrasel samo do globine vec deset metrov nad sedanjim nivojem podtalnice. To je tudi razlog, da so stevilni kraski izviri ali suhe jame bivsih izvirov tudi visoko nad dnom dolin.
Opazna je tudi dvojnost v nastanku jam na Kaninskem pogorju. Bolj ali manj navpicna brezna so nastala v zgornjem delu (ki je nad ravnino stalne vode in z vodo le obcasno zapolnjen). Brezna so nastala zaradi pronicanja padavinske vode, sneznice, odtoka vode z roba ledenika ali vode pronicajoce skozi tektonsko nastale razpoke pod ledenikom. Na stiku z gladino podtalnice je nastalo obmocje bolj ali manj vodoravnih rovov. V tem obmocju je nastal tudi odtok vode iz kraskega masiva. V mnogih primerih vodoravni rovi sledijo stiku med norisko-retijskim dolomitom in dachsteinskim apnencem.
Kanisko pogorje je znano po stevilnih in tudi zelo globokih navpicnih breznih. Najgloblja jama doslej je Cehi II (1500 m), najdaljsi nabpicni odsek (643 m) na svetu, je bil odkrit leta 1996 v breznu Vrtiglavica. Doslej je bilo na Kaninskem pogorju najdenih ze vec kot 800 kraskih jam in brezen, od tega je 11 globljih od 500 m. Eden svetovno najbolj znanih jamskih sistemov Mala Boka – BC4 Polska jama, ima en vhod na visini 1730 m in drugi, jasno viden kot razpoka v pobocju vzhodno od slapa Boka, na visini 433 m.

BOKA, NAJMOGOCNEJSI SLOVENSKI SLAP
Rezultati hidroloskih raziskav kazejo, da je v normalnih vodnih pogojih povprecen odtok vode, s povrsine okrog 50 kvadratnih kilometrov Kaninskega pogorja, 5,5 kubicnih metrov na sekundo. Okrog 85% od tega prejme reka Soca.
Zahodni del pogorja se odvodnjava proti Boki, osrednji in vzhodni del pa proti Glijunu. Izvir Glijun ima srednji pretok 1 m3/s, vendar ta niha med 0,15 in 15 m3/s. Izvir Boke ima srednji pretok 0,2 m3/s, najvecji celo 50 m3 v obdoblju mocnih padavin (tocen maksimum ni bil merjen, nekatere ocene sezejo tudi do 100 m3/s!), a lahko celo povsem presahne v daljsih susnih obdobjih.

Slap Boka napaja recica Boka, ki izvira na polici sredi navpicnih sten. Voda vre iz globokih zelenih tolmunov med velikimi skalnimi bloki. Iz doline k izviru vodi oznacena planinska pot, vendar dolgo ni bilo nic znanega o vodnem rovu, iz katerega priteka Boka. Leta 1975 pa so del vodne poti raziskali jamski potapljaci.
Prva podvodna dvorana se odpre priblizno 7 m pod gladino izvira in je skoraj povsem zaprta z velikimi skalnimi bloki, ostanki enega ali vec skalnih podorov. Vodni rov se nadaljuje navpicno navzdol se nekaj metrov in potem odpre v veliko ovalno jamo izdolbeno v skalo. Jama je priblizno 10 m siroka in 8 m visoka. Vodni rov je usmerjen skoraj vodoravno, z manjsim padcem proti toku do najnizje tocke, priblizno 25 m pod gladino izvira in 50 m v notranjosti gore. Tam se rov obrne navzgor, podvodni sifon pa se konca po 102 metrih, ko rov ponovno doseze gladino vode. Od tam so raziskovalci preplavali 30 m dolgo jezero ter sledili jami cez mocne brzice v rov, ki poteka v treh etazah.

Spodnji del troetaznega rova je stalno pod vodo, srednji del ima aktiven pretok, zgornji pa je suh. V zgornjem rovu je veliko zanimivih usedlin in tudi stevilni kapniki, ki so v alpskih jamah prava redkost. Tu je jasno videti, da vecji del vodnih rovov poteka v apnencu. Le zadnji del pred izvirom, to je podvodni del s sifonom, je izdolben skozi dolomit. Tik pred izvirom vodni rov doseze navpicen prelom, ki vodo usmeri naravnost navzgor v izvirni tolmun.
Recica Boka od izvira tece povrh zelo kompaktnega sklada dolomita do roba stene. Na rou stene se voda razporedi skoraj 30 m siroko in zgrmi navzdol v cudovitem slapu! Po priblizno 106 m neoviranega padca voda doseze 33 m visoko strmo skalno stopnjo – spodnji del slapa, po kateri zdrsi do dna doline. Skupna visina slapa Boka je torej skoraj 140 m! Cudovit je v casu srednjega pretoka, mogocen v casu topljenja snega ter naravnost sapo jemajoc in nepozaben po obilnih padavinah!
Dolina pod slapom poteka vzdolz preloma. Nastala je v obmocju mocno razpokane prelomne cone s tektonsko zdrobljenimi kamninami. Vodna erozija je neustavljivo odnasala zdrobljene kose kamnine in dolbla vse globljo sotesko. V casu visokih voda ima slap se vedno dovolj moci za dodatno poglabljanje soteske. Slap Boka je tako eden od redkih med slovenskimi slapovi, ker se njegova visina se vedno povecuje!

GEOLOŠKI ZAKLAD IN DOSTOP
Koordinate Geološkega zaklada so postavljene na razgledno tocčko, na robu planine od koder se odpira edinstven pogled na slap in kratko rečico, ki polni slap – od zgoraj, čez sotesko! Razgledišče je namreč višje od ustja slapa.

K zakladu vodita dve poti, ki sta precej točno označeni na Open Street Map, našemu opisu pa so priložene tudi vse potrebne točke poti (waypoints). Pot 1 (Trail 1) se prične ob cestnem mostu, na desnem bregu rečice Boka. Pot je dobro vzdrževana le do novega lesenega razgledišča z informacijskimi tablami (točka 13), potem je postopoma vse slabša: zadnji odsek, nad razglediščem pri tradicionalnem zakladu GCPXZZ ima nekaj strmih delov, ki so zaradi kamnitega drobirja kar precej zoprni in težje prehodni.

Družinam in manj veščim priporočamo Pot 2 (Trail 2) . Prične se v vasi Žaga, avto pustite na točki PARKN3. Pot je manj strma od prve in v dobrem stanju. Pot je sicer kar dobro označena, a točke poti vam bodo pomagale najti začetek in prave odcepe na stezi. Pot 2 vas bo popeljala previsoko za iskanje tradicionalnega zaklada GCPXZZ, a še vedno povsem blizu drugega, GC2NMB2, ki leži na spodnjem robu planine.
Obe poti sta markirani z rdečimi krogi in črtami, običajno po skalah in drevju. Zelo priporočamo pohodne palice, še posebej za Pot 1! Tudi na ustrezno hribovsko obutev ne pozabite, čeprav je vzpona vsega skupaj približno 420 m.

Opomba: Poti uporabljate na lastno odgovornost! Hodite le po poteh za katere ste ustrezno pripravljeni! Zelimo vam varno pot in veliko uzitkov!

VIRI:
1. Blaz Komac, Kraski izviri pod kaninskim pogorjem, Geografski institut Antona Melika ZRC SAZU, Geografski zbornik st. 41, 2001.
2. Anton Ramovs, Slapovi v Sloveniji, Slovenska matica, Ljubljana, 1983.
3. Uros Herlec, Geotrip ‘02 v Sloveniji [tekst Uros Herlec, Branka Hlad, Marko Simić ; lustracije Marko Kocevar, Darja Trtnik Medved ;fotografije Marko Simić ... et al.]. - Ljubljana : Ministrstvo za okolje in prostor, Agencija RS za okolje, 2005.
4. Kras na Kaninskih podih, Franci Gabrovsek & Bojan Otonicar, Institut za raziskovanje krasa ZRC SAZU, Postojna, 3. slovenski geoloski kongres - Bovec, 16.-18. september 2010.
5. Fotografije na sliki 4 – s spletnih strani, avtorji so navedeni v pojasnilu pod sliko 4.