Bohinjsko jezero / Lake Bohinj EarthCache

(SI) Sprehod skozi vas, ki stoji na vrhu čelnega ledeniškega nasipa in čez fosilne jezerske terase.

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. Koliksne so velikost, prostornina in teza FUZINARSKEGA KAMNA? To je najvecjegi balvana celnega ledeniskega nasipa, ki se nahaja na tocki FUZIN. Tudi ce tega, neobvezega dela poti niste obiskali, lahko odgovorite s pomocjo vrednosti A in B, ki ste ju zapisali med sprehodom pri Bundrovem kamnu (tocka EARTHC).
1a. Ocenite ali izracunajte priblizno velikost Fuzinarskega kamna: dolzina 2,5*A, sirina 1,8*A, visina 2,5*B.
1b. Izracunajte prostornino. Ta vec kot 10 kratno presega prostornino Bundrovega kamna!
1c. Priblizno izracuanjte težo Fuzinarskega kamna. Ne bodite preseneceni nad izjemno veliko stevilko. S tem rezultatom boste dobili obcutek, kaj vse je potovalo z ledenikom!

2. Neobvezna naloga: Na poti od obrezja Bohinjskega jezera (tocka 7TRAIL) do Stare Fuzine (tocka TRAIL6) se sprehajate preko jez, ki razmejujejo fosilne jezerske terase. izmerite razdaljo od tocke TRAIL7 do razmejitve med prvo in drugo teraso. Izmerite se razdaljo od tocke TRAIL7 do razmejitve med drugo in tretjo teraso.

3. Zelo bomo veseli, ce kaksno zanimivo fotografijo z mesta zaklada prilozite svojemu vpisu (logu) obiska. Zanimiva bi bila tudi fotografija katerega od drugih balvanov v Stari Fuzini – veliko jih lezi ob hisah, sredi vrtov ali celo sluzijo namesto opornega zidu.

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!

(ENG) A walk through village, built on top of glacier's terminal moraine, and across fossil lake-bed terraces.

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. Size, volume and weight of FUZINARSKI KAMEN! That is the largest boulder of terminal moraine, positioned at waypoint FUZIN. Since this is at not obligatory part of the trail, you can answer with the help of dimensions A and B of Bundr stone, which you have written down at waypoint EARTHC.
1a. Estimate or calculate approximate size of Fuzinarski kamen: length is 2.5*A, width is 1.8*A, height is 2.5*B.
1b. Calculate volume. It is more than 10 times the volume of Bundr stone!
1c. Calculate approximate weight of Fuzinarski kamen. Don’t let large number surprise you! This result gives you some insight about what glacier could transport.

2. Additional, not obligatory task: on your walk from lake shore back to Stara Fuzina measure a distance from waypoint TRAIL7 to slope which is dividing first and second fossil terrace (counting from the lake shore). Measure the distance from waypoint TRAIL7 to divison between second and third terrace too.

3. We would be glad if you added interesting photos from the EarthCache location to your log. Photos of some other boulders would be welcome too. There are many in Stara Fuzina, some resting at house walls, other in the middle of vegetable gardens, some are used as supporting walls…

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 an 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!

(ENG) LAKE BOHINJ
... is a beautiful alpine lake with astonishing surroundings. With 3.19 square km surface, 11.35 km circumference and 92.5 million cubic metres volume, it is the largest permanent lake in Slovenia. It is positioned in the glacial valley between Mount Vogel on the south and Mount Prsivec on north, altitude of the lake surface is 526 m. Valley is of tectonic-glacial origin, since the lake depression has been tectonically formed, and later reshaped by Bohinj glacier. Surroundings of the lake have been shaped by glacier too: terminal moraines on the east side of the lake, at village Stara Fuzina, are most obvious; there are ground moraines on the southern lake shore.
Bohinj glacier, the cause for our EarthCache, has been large. Its beginning has been at heart of mountains, above Lake Bohinj valley. In the coldest period glacier has extended along Sava Bohinjka all the way to Begunje and south of Radovljica. It has also spilled over valley edges, across Sorica alpine meadow to Baca, over Rovtarica to the edge of Selce valley and across Pokljuka to Mrzli studenec.

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Lake depression filled with ice	...	Lake depression today

	...		...
Bohinj glacier full extent	...	Glacier retreating	...	Last glaciation

[Figure 1] The Bohinj glacier, clippings from animation "The Bohinj Glacier"

Glacier has been pushed to movement by relentless pressure of ever new material mounting at its source – ice which has formed in larger quantities than could be melted through summer. Glacier’s sliding speed has been varying from some tens to some hunreds of meters annually. Process, which has been slow but very long-lasting, has formed typical U-shaped valleys. Some are very well visible in Bohinj. In the Sava Bohinjka valley glacier has been several hundreds metres thick, data show thicknes of 800 m! At this height water from surface of glacier seeped into limestone hillsides of Jelovica and formed karst caves. We can admire rare calcite crystals there today. Glacier dammed Radovna river and caused forming of Bled Vintgar. It has also carved out depression of Lake Bled.
Lake Bohinj formed in the emptied depression of last glaciation, behind extensive moraines at village Stara Fuzina, which have been left behind glacier. We know that has been done by glacier, since there is a significant difference between glacial and river deposits. Glacial deposits tend to be unsorted, and with a high degree of angularity, though some rocks may show flattening and striation if they were entrained in the base of the glacier. Moraine material is ranging in size from silt-sized glacial flour to large boulders. This debris may have been plucked off a valley floor as a glacier advanced or it may have fallen off the valley walls as a result of frost wedging or landslide. Fluvial, that is river deposits, tend to be moderately rounded, rather than angular and tend to be well sorted as larger sediment will be deposited first, finest last as the current slackens.
Lake Bohinj is still existing today only because it is placed at the upper-most part of the Sava Bohinjka valley, which's karstic hinterland prevented extensive filling with the gravel. Lake water level has been about 18 m higher than today after the end of last glaciation, and lake extended to nowdays Stara Fuzina.
Lake Bohinj is about 4.3 km long and up to 1.2 km wide today. Lake depression, which steeply declines, is unparsed and without shallows, abrasion terrace is barely indicated. Carbonate silt and clay are predominant among lake sediments. Only one tenth of lake is less than 10 m deep, and 80% is deeper than 20 m, 20% more than 40 m even. Maximum depth of 45 m is in eastern part of lake, in the middle of “Fuzinarski zaliv” (Ironworkers gulf). Easter part is deeper than western, which is slowly filled by river Savica.

[Image 2] Lake Bohinj with marked depth, clipping from monutaineering map Bohinj

TRAIL AND EARTHCACHE
If you stayed in Bohinj for several days, you could really explore beautiful surroundings of the lake. Even if you have one day only, take your time and walk around the lake. It is worth to do it.
EarthCache takes you to a shorter walk: through Stara Fuzina (translated: Old ironworks) village and across meadows between village and eastern lake shore. It will take you one to two hours, depending of the variant you decide for. Starting point is at parking area, near grocery store in Stara Fuzina (waypoint PARKNG). Parking is free of charge (for now) but time-limited. Is should be good enough for a short hike.

1. Since there is a problem with direct access this is a temporary advice to reach EarthCache point.
From parking area walk to Waypoint TRAIL1, continue to crossrods at waypoint TRAIL5, follow road to waypoint TRAIL3, turn right to the narrow paved road which leads you South-East in the direction of EarthCache. At the end of the paved road you are standing just in front of the large boulder. Take a look at enclosed photo.

[Figure 3] End of paved road, in front of large boulder; (Bundr stone)

2. This large boulder at the crest of moraine clearly indicates that the mound has not been made by liquid water, but has been pushed and left here by a large glacier tongue. Estimate the size of this boulder. Write down your estimation as A=length or width (both dimensions are approximately equal), B=height. You will need this data for solving logging task.
You don’t need to be very skillful to climb to the top of boulder too. But even from the foot of rock you have a good view across the village, towards Upper Bohinj valley (Zgornja dolina). You can clearly see U-shape of the Upper valley. River Mostnica is quite some meters beneath you, between steep slope of moraine and rest of the village. Looking towards north-west, along the crest of moraine, you can see many smaller boulders protruding from grassy ground. You can return to your car the same way you came to Bundr stone.

NOT OBLIGATORY PART OF TRAIL
LARGEST BOULDER:
Althou this is not obligatory, we urge you to continue exploration. Instead of returning back to car, step over fence at waypoint TRAIL3, and continue north-westwards ascending across pasture, towards waypoint FUZIN. After only 100 m from the road, at the edge of pasture, you will see a huge boulder, standing at the side of slope. This one has a name too: Fuzinarski kamen (Ironworks stone). It’s western, overhanging side, has been used for local mountain-rescue-team trainings some time ago. Looking at this boulder it is hard to imagine that it has hitchhiked to get here. And it has been even larger at the time – many large and small pieces have broken away since.
If the pasture is used by catle at the time you are there, please ask locals for permission to cross it. Otherwise there are no problems for access.

FOSSILE LAKE-BED TERRACES:
1. Waypoint TRAIL5: Turn towards West at the crossroads and follow road straight towards lake.

2. Waypoint TRAIL6: Follow right gravel road, which leads you straight towards Lake Bohinj. Take a rest at the lake shore and enjoy great views across the lake.

3. For returing to Stara Fuzina go first to waypoint TRAIL7. Turn away from lake there and follow gravel road towards east. Road brings you to the village at waypoint TRAIL6. You have less than 300 m to parking area. On your way from lake shore to village, you cross three fossil lake-bed terraces. Terraces have been formed by gradual retreating of lake to today’s extent. It happened because water slowly carved new outflow through moraine at Ribcev Laz, where short river Jezernica flows out of the lake (after just some tens of meters it is joined by river Mostnica and together they form Sava Bohinjka). The joungest terrace, the one closest to the lake, is devided from the second by steep, several meters heigh slope. Next dividing slope is already less pronounced and almost leveled at some stretches. Third division, between third and fourth terrace is already at the village edge and noticeable at some parts, elsewhere is not visible and probably leveled with the help of human hands too.

Described trails (except pasture near waypoint FUZIN) are public and freely accessible. Locals will gladly help with information.

[Figure 4] Clear divison between fossile lake-bed terraces

Photo: vane_si
References:
- The Bohinj Glacier, animation, Narodni muzej Slovenje; screenplay: Milos Bavec, Timotej Knific; expert advisor for geomorphology and glaciology: Milos Bavec; geomorphology consultant. Jurij Kunaver; paleozoology consultant: Vida Pohar; photographer: Joze Hanc;
- Dedi.si; Matija Zorn (Geografski institut Antona Melika, Znanstvenoraziskovalni center Slovenske akademije znanosti in umetnosti);Slovenian only;

[Figure 5] Lake Bohinj

(SI) BOHINJSKO JEZERO
Bohinjsko jezero je s povrsino 3,19 km2, obsegom 11,35 km in 92,5 milijoni m3 vode najvecje stalno naravno jezero v Sloveniji. Lezi v ledeniski dolini med Voglom na jugu in Prsivcem na severu, njegova gladina pa ima nadmorsko visino 526 m. Je tektonsko-ledeniskega nastanka, saj je jezerska kotanja tektonsko zasnovana, preoblikoval pa jo je Bohinjski ledenik. Ledenisko je preoblikovana tudi okolica jezera: celne morene ali ledeniski nasipi so najbolj opazne vzhodno od jezerske obale pri Stari Fuzini, na juznem obrezju pa so talne morene.
Bohinjski ledenik, krivec za nas EarthCache, je bil mogocen. Njegov zacetek, redisce, je bilo v osrcju gora nad danasnjim Bohinjskim jezerom. Najdlje je segal vzdolz celotne Save Bohinjke in naprej po ravnini do Begunj, njegov jezik pa je bil juzno od Radovljice. Poleg tega je na robovih segal cez Sorisko planino do Sorice in naprej do Bace, cez Rovtarico na obrobje Selske doline in cez Pokljuko do Mrzlega studenca.

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Lake depression filled with ice	...	Lake depression today

[Image 1] Bohinjski ledenik

Vztrajni pritisk vedno novega materiala je ledenik silil k drsenju, ki je imelo razlicno hitrost, od nekaj deset do nekaj sto metrov na leto. Pocasen, a casovno zelo dolg proces je povzrocil nastanek znacilnih U-dolin, lepo vidnih v Bohinju. V dolini Save Bohinjke, v Soteski, je dosegel debelino vec sto metrov, podatki kazejo na celih 800 m! Na tej visini je voda s povrsja ledenika ponikala v apnencasto pobocje in povzrocila nastanek kraskih jam na Jelovici, kjer danes lahko obcudujemo redke kristale kalcita. Zajezil je dolinsko Radovno in povzrocil nastanek soteske Vintgar. Izdolbel je kotanjo Blejskega jezera.
Bohinjsko jezero je nastalo v izpraznjeni celni kotanji zadnje poledenitve, za obseznimi ledeniskimi nasipi, ki jih je pri Stari Fuzini zapustil bohinjski ledenik. Vemo, da je to delo ledenika, ker se ledeniski nasipi ali groblje precej razlikujejo od recnih naplavin. Material v ledeniskih grobljah po velikosti ni razvrscen. Kamni so v glavnem ostrejsih robov, ceprav so lahko nekateri splosceni in nabrazdani, tako oblikovani med dnom lednika in skalno podlago. Grobljo sestavlja mesan material, vse od kamene moke do velikih kamnitih balvanov. Ta material je bil iztrgan z dolinskega dna ko je cezenj napredoval ledenik ali pa se je zrusil s pobocij ob strani doline, kot posledica zmrzlinskega preperevanja ali podorov. Precej drugace je z recnimi naplavinami. Te vsebujejo zmerno zaobljen material in so pretezno jasno sortirane, ker se ob zmanjsevanju moci vodnega toka tezji material usede prej kot drobnejsi.
Bohinjsko jezero se je lahko ohranilo, ker lezi povsem v zgornjem delu doline Save Bohinjke, kjer zaradi kraskega zaledja ni prislo do obseznejsega nasipanja proda. Ob koncu zadnje poledenitve je bil vodostaj jezera visji za priblizno 18 m in jezero je segalo do zdajsnje Stare Fuzine.
Bohinjsko jezero danes meri v dolzino okrog 4,3 km in sirino do 1,2 km. Jezerska kotanja, ki se strmo spusca, je nerazclenjena in brez plitvin; abrazijska terasa je komaj nakazana. Med jezerskimi sedimenti prevladujeta karbonatni melj in glina. Le desetina jezera je plitvejsa od 10 m in kar 80 % ga je globljega od 20 m, 20 % celo od 40 m. Najvecja globina 45 m, je v vzhodnem delu jezera, sredi Fuzinarskega zaliva. Vzhodni del jezera je za okrog 10 m globlji od zahodnega dela. Zahodni del jezerske kotanje zasipava vodotok Savica.

[slika 2] Bohinjski jezero – z oznacenimi globinami

POT IN GEOLOŠKI ZAKLAD
Ce se vam ne mudi, priporocamo sprehod po poti okoli Bohinjskega jezera. Mnoge care cudovite okolice jezera pa vam bo priblizalo le vecdnevno raziskovanje.
Geološki zaklad vas popelje na krajsi sprehod: po Stari Fuzini ter preko travnikov med vasjo in vzhodnim obrezjem jezera. Za izhodisce lahko uporabite parkirni prostor v Stari Fuzini v blizini trgovine (waypoint PARKNG). Parkiranje je (zaenkrat) brezplacno, a casovno omejeno. Bo pa povsem zadoscalo za kratek izlet.

1. Ker je direktni dostop problematicen, je tu zacasen nasvet za dostop do Geološkega zaklada.
Od parkirnega prostora pojdite do tocke TRAIL1, nadaljujte do krizisca na tocki TRAIL5, sledite cesti do tocke TRAIL3, zavijte desno na ozjo asfaltirano cesto, ki vas popelje jugovzhodno, v smeri Zemeljskega zaklada. Na koncu asfalta stojite tik pred velikim balvanom. Poglejte spodnjo sliko.

[slika 3] Konec asfalta pred Bundrovim kamnom

2. Tocka EARTHC (koordinate Geološkega zaklada): Na vrhu celnega nasipa je obticala velika skala, ki so ji domacini nadeli celo ime – Bundrov kamen. Ta veliki balvan zelo jasno kaze, da nasipa sredi doline ni ustvarila tekoca voda, temvec ga je narinil in odlozil velik ledeni jezik ledenika. Priblizno ocenite velikost balvana. Podatke si zapisite kot vrednosti A=dolzina ali sirina (obe sta priblizno enaki), B=visina. Potrebovali jih boste pri resitvi naloge za vpis Zemeljskega zakladae.
Z malo spretnosti se lahko povzpnete tudi na vrh Bundrovega kamna, a ze od vznozja je zelo lep razgled cez vas ter navzgor po Zgornji bohinjski dolini, ki vam kaze svoj znacilni U-prerez. Mostnica se pretaka precej metrov pod vami, med strmim celnim pobocjem ledeniskega nasipa in preostalim delom vasi. Pogled v severozahodno smer razkrije veliko manjsih balvanov, ki raztreseni molijo iz travnatih tal. Od Bundrovega kamna se k avtu vrnete po isti poti po kateri ste prisli.

NEOBVEZNI DEL POTI
NAJVECJI BALVAN:
Ceprav to za vpis zaklada ni potrebno, svetujemo, da nadaljujete z raziskovanjem. Namesto, da bi se vrnili k avtu, pri tocki TRAIL3, prestopite ograjo in se preko pasnika odpravite po bregu navzgor, se naprej v smeri severozahoda, proti tocki FUZIN. Na robu pasnika ze po dobrih 100 m zagledate ogromen, ob brezini stojec balvan, ki so ga poimenovali Fuzinarski kamen. Na njegovi zahodni, previsni steni, so se nekdaj celo urili domaci gorski resevalci. Kar tezko si je predstavljati, da se je ta velika gmota nekoc kot z avtostopom pripeljala na ledeniku. Se celo vecja je bila, saj so se kasneje od nje odlomili mnogi vecji in manjsi kosi.
Ce se na travniku pase zivina, za dovoljenje za prehod vprasajte domacine. Sicer za dostop ni ovir.

FOSILNE JEZERSKE TERASE:
1. Tocka TRAIL5: Na kriziscu zavijte proti zahodu in po cesti naravnost proti jezeru.

2. Tocka TRAIL6: Drzite se desne makadamske ceste, ki vas popelje naravnost k Bohinjskemu jezeru. Ob obrezju si privoscite pocitek in se nauzijte cudovitih pogledov preko jezera.

3. Za vrnitev proti Stari Fuzini se ob jezeru odpravite do tocke TRAIL7, od koder zavijete stran od jezera, po makadamski cesti naravnost proti vzhodu. Pot vas pripelje nazaj v vas na tocki TRAIL6 od koder je do parkiranega avta slabih 300m. Na poti od jezerskega obrezja do vasi boste preckali tri fosine jezerske terase, ki so nastajale ob postopnem umikanju jezera na danasnji nivo. Voda si je namrec skozi ledeniske nasipe postopno preglodala odtok pri Ribcevem Lazu, kjer se danes odteka kot Jezernica. Najmlajso - spodnjo teraso, ki je najblize jezeru, od naslednje deli vec metrov visoka in zelo ocitna jeza. Naslednja jeza je ze precej manj izrazita in se na posameznih mestih povsem izgubi. Tretji visinski preskok je ze na obrobju Stare Fuzine, viden le se na posameznih mestih in neizrazit, verjeto zravnan tudi s pomocjo cloveskih rok.

Navedene poti (razen pasnika pri tocki FUZIN) so javne in prosto dostopne. Domacini vam bodo radi pomagali z informacijami in pri usmerjanju.

[Image 4] Izrazita razmejitev fosilnih jezerskih teras

Foto: vane_si
Viri:
- Bohinjski ledenik, animacija, Narodni muzej Slovenje; scenarij: Milos Bavec, Timotej Knific; strokovni sodelavec za geomorfologijo in glaciologijo: Milos Bavec; svetovalec za geomorfologijo. Jurij Kunaver; svetovalka za paleozoologijo: Vida Pohar; fotograf: Joze Hanc;
- Dedi.si; Matija Zorn (Geografski institut Antona Melika, Znanstvenoraziskovalni center Slovenske akademije znanosti in umetnosti);
- www.gea-on.net; besedilo »Bohinjski ledenik«: Jurij Dobravec in Majda Kozjek;

[Image 5] Bohinjsko jezero