Bled, Alpski biser / Bled, Alpine Pearl EarthCache
Bled, Alpski biser / Bled, Alpine Pearl
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Blejsko jezero leži na nadmorski višini 475 metrov, obkrožajo pa ga tri višje ležeče alpske planote visoke 1300 metrov: Pokljuka, Mežakla in Jelovica. V njegovi bližini tečejo kar tri reke, Sava Bohinjka, Sava Dolinka in Radovna. K sreči se nobena ne zliva v jezero, saj bi tako velik prodonosni vodotok zasul jezersko kotanjo. Površina jezera je 1,45 km², dolžina 2100 m in širina 1380 m. Okrog jezera vodi sprehajalna pot po kateri ga obhodite v eni uri. V poletnem času je jezero priljubljeno med kopalci, saj temperatura vode v juliju doseže 25°C. Voda v njem se izmenja v letu in pol. Največje ribe so somi, ki dosežejo velikost dveh metrov.
Današnja podoba Blejskega kota z morenskimi griči, skalnimi osamelci, rečnimi terasami, prodnimi nanosi, opuščenimi strugami in jezerom je posledica delovanja Bohinjskega ledenika in kasnejšega delovanja rečnih tokov. Bohinjski ledenik je naravno tektonsko udorino še poglobil in za čelnimi morenami blejskega kota je nastalo Blejsko jezero.
Najstarejši kamnini sta srednje permski apnenec in apnenčeva breča, ki ju najdemo na hribu Straža. Srednje triasni dolomit, ki spada med trde kamnine se nahaja na Osojnici in na otoku. Srednji triasni laporji pa sestavljajo zahodni del Gradu in širšo okolico Male Zake. Iz zadnje poledenitve najdemo obsežne morene na severu v območju Gorij, Zasipa in Bleda.
Bohinjski ledenik je po würmski poledenitvi, pred 15.000-20.000 leti z brušenjem in poglabljanjem okolice, odrivanjem in nalaganjem materiala, v Blejskem kotu ustvaril značilno ledeniško pokrajino. Reke so med ledenimi dobami vrezovale in poglabljale svoje struge, menjale svoj tok, nosile in spet odlagale ledeniški drobir. Za čelnimi morenami so vedno znova nastajala nova jezera, ki so jih kasneje s prodom zasuli močni vodotoki. Ob umiku ledenika so se s pobočij prožili zemeljski plazovi in skalni podori. Sava Bohinjka je v postwürmskem obdobju na južnem delu zarezala v morenske in prodne nanose, poglobila svojo strugo in začela teči mimo jezera. Zaradi tega se je tudi izliv Jezernica iz jezera na vzhodni strani pomaknil na današnjo lokacijo na Mlinem, kar je imelo za posledico zmanjšanje obsega in globine jezera.
Nadmorska višina jezera je bila v obdobju največjega obsega na višini 510 metrov, danes pa je na 475 metrih. Tako je globina današnjega jezera za pol manjša od prvotne. Jasno vidne jezerske terase tudi pričajo o procesu postopnega erozijskega oblikovanja jezerske sklede.
Posebnost jezera je, da je vanj po ceveh speljan umetni dotok iz Radovne, iz njega pa vodita dve natežne cevi, iz vsake kotanje jezera. Voda se črpa iz spodnjih plasti jezera in se izliva v Savo Bohinjko. Cevi natege vidite na koordinatah EC. S tem sistemom so povečali pretočnost jezera ( sedaj se voda izmenja iz prejšnjih 4 na 1,5 leta) in obenem zmanjšali onesnaženost.
V letu 2010 so bile v jezeru prvič opažene tujerodne školjke vrste Dreissena polymorpha, s slovenskim imenom »zebrasta školjka« ali »trikotničarka«. Izvira iz rek porečij Volge, Dnjepra in Urala. Zahvaljujoč se svoji naravni trdoživosti, so se kot slepe potnice pritrjene na razna plovila in skrivajoč se v balastnih vodah, razširile po svetu. Je ena izmed 100 najbolj invazivnih vrst organizmov na svetu. V svojem življenju lahko ena sama zebrasta školjka zapusti za seboj na deset tisoče školjk, kar naredi to vrsto za zelo uspešno invazivko. Ker nima naravnih sovražnikov in se razmnožuje z izjemno hitrostjo, bo postopoma zadušila ves jezerski živelj. V kolikor bi se školjke naselile ob obali in prerasle prodnato dno, bi to pomenilo velik udarec za turizem. Njihovi ostri robovi povzročajo ureznine, kar je zelo moteče za kopalce. Nenazadnje, larve (jajčeca) školjke lahko z Jezernico vstopijo tudi v Savo, kar bi dalo tej naravni katastrofi čisto novo dimenzijo. V gospodarstvu delajo škodo na hidroelektrarnah, saj mašijo dovodne cevi turbin, preraščajo zapornice za regulacijo nivoja vode in podobno. Ustrezne rešitve zatiranja zebraste školjke še ni.
NALOGE ZA VPIS:
Obiskali boste štiri točke na katerih se nahajajo razni geomorfološki pojavi, oziroma so vidni od daleč. Na vsaki točki lahko opazite tudi več pojavov, nekateri pa se tudi ponovijo na več točkah. Za lažjo prepoznavo naj jih naštejem:
- skalni osamelec z gradom na vrhu. Bohinjski ledenik je s svojim premikanjem odstranil ves mehkejši material, poglobil površino in ostala je le skala v obliki hriba.
- skalni osamelec s cerkvijo,
- drugi skalni osamelci,
- spremenjena smer toka reke. Reka je v peščene nanose poglobila svojo strugo, spremenila smer toka in začela teči mimo jezera,
- suha struga, nekdanji izliv iz jezera. Jasno vidna oblika rečne struge, vendar brez vode.
- jezerska skleda,
- skalni podori,
- morena, odložen kamniti ledeniški drobir,
- več moren, ledenik se je umaknil in ponovno vrnil,
- sedanji izliv iz jezera,
- jezerske terase, ravnine, ki pričajo o procesu postopnega erozijskega oblikovanja jezerske sklede.
Točke ki jih boste obiskali:
1. Spodnje Seliše: N46° 22.280, E014° 06.895,
2. Dindol: N46° 21.805, E014° 06.730,
3. Mlino: N46° 21.593, E014° 05.954,
4. Pod Osojnico: N 46° 21.310, E 014° 05.260.
Za vsako točko (1 - 4) opišite geomorfološke pojave, ki ste jih opazili in odgovore pošljite na e-pošto. Takoj zatem lahko logirate svojo najdbo. Zelo so zaželjene tudi vaše fotografije.
POMEMBNO!
- Vpisi brez ustrezne spremljajoce e-poste, ki vsebuje pravilne odgovore bodo izbrisani.
- Vpisi, ki vsebujejo odgovore bodo izbrisani.
Viri: Tekst: Remec-Rekar 2005, 2011; Turizem Bled, 2005; Melik, 1930; Špela Gorjanc 2012; Slike: Špela Gorjanc 2012, Greenslovenia, I-love-slovenija, Green Nuclear Butterfly, Geopedia; Video: Turizem Bled, Narodni muzej Slovenije
ENGLISH VERSION:
Lake Bled lies at an altitude of 475 meters and is surrounded by three higher-lying alpine plateaus, altitude 1300 m: Pokljuka, Mežakla and Jelovica. In its vicinity flows three rivers: Sava Bohinjka, Sava Dolinka and Radovna. Fortunately, none of those rivers flow into the lake, as this would burry lake's basin with a gravel. Surface of the lake is 1.45 km ², length 2100 m and width 1380 m. Near the lake leads a walking path by which you can get around the lake in an hour. In the summer, the lake is popular among swimmers, since the water temperature reaches 25°C in July. The whole water is exchanged in one and a half year. The largest fish in the lake are catfish. They reach nearely the size of 2 meters.
Today's image of Bled corner with moraine hills, solitary rocks, river terraces, gravel deposits, abandoned riverbeds and lake itself, is the result of Bohinj glacier action and later actions of river flows. Bohinj Glacier has deepened the existing natural tectonic depression and behind the frontal moraines was formed a lake.
The oldest rocks in the area of Bled are medium Permian limestone and limy breccia, which are found on the hill Straža. Middle Triassic dolomite, which is one of hard rocks, is located at Osojnica and on the island. Middle Triassic marl consists the western part of the Castle hill and in surrounding area Mala Zaka. From the last glaciation can be found the extensive moraine in north area (Gorje, Zasip and Bled).
Bohinj Glacier has before the 15.000 to 20.000 years with his activity (grinding and deepening landscape; gravel depositing) created in Bled typical glacial landscape.
Between ice ages rivers have deepened its river beds, after that deposited glacial gravel and than changed their way of flow. This process was continuously repeated. Behind the frontal moraines were repeatedly made new lakes, which were later filled with gravel deposites. When the glacier melted down, the unsupported slopes started to collapse landslides and rockfalls. In the southern part of Bled, river Sava Bohinjka (in the post-Age period) deepened its bed into the moraine and started to run past the lake. Therefore also an outflow Jezernica from the lake (on the east side) was moved to its current location (on the south side) at the Mlino and the effect was reduction of volume and depth of the lake.
The lake maximum altitude in the past period was at 510 meters and today is at 475 meters. Thus the depth of the lake is reduced on less than a half. Today are clearly visible terraces, which testify about gradual erosion process of the lake bowl.
Catchment of Lake Bled:
Special feature of the lake is that, it is into the lake channeled(through the pipes) flow of river Radovna, while simultaneously lead two tensile pipes out from each lake basin. Water is pumped from the lower layers of the lake and flows into the river Sava Bohinjka. Siphon pipes you can see on the EC coordinates. With this system is increasing fluidity (whole water in lake is changed every 1.5 years, before every 4 years) and reducing pollution.
In the lake, in 2010, was for the first time observed a Zebra mussel, named in latin Dreissena polymorpha. It comes from the Volga, Dnepr and Ural river basins. Thanks to its natural persistence, they were expanded around the world as secret passenger attached to the various vessels and hiding in the ballast water. A single Zebra mussel can leave in its live tens of thousands new shells. Since they have no natural enemies and they are reproduced with exceptional speed, gradually suffocate the entire lake organisms. There would be a major problem in tourism, if mussels settled on the coast and grew gravelly bottom. Their sharp edges cause cuts, which is very disturbing for swimmers. Finally, larvae (eggs) shells can also enter into the Sava river, which would give this natural disaster, a whole new dimension. They doing economy damage to hydroelectric power plants, since clogging intake turbine pipes and overgrown barrier for regulation water level. Appropriate solutions of oppression zebra mussels is not finding yet.
TASKS FOR ENTRY:
You will visit four points on which are visible various geomorphological features. At every point you can see even more features, some are also repeated at several points. For easier identification let me list them:
- solitary rock, with a castle on top. Bohinj Glacier, with its moving remove all soft material, deepened surface and there is remained just a rock in form of the hill.
- solitary rock, with a church on it,
- other solitary rocks,
- changed direction of river flow. River deepened its bed into the gravel deposits and changed direction of river flow to run past the lake.
- dry riverbed, a former outflow of the lake. Clearly visible shape of the riverbed, but without water.
- lake bowl,
- rockfalls,
- moraine, gravel transported by a glacier and then deposited.
- several moraines, gravel deposits which are evidence that the glacier repeatedly withdrew and returned again.
- the current outflow from the lake,
- lake terraces, flat surfaces which testify about gradual erosion process of the lake bowl.
Points to be visited:
1. Spodnje Selise: N46°22.280, E014°06.895,
2. Dindol: N46°21.805, E014°06.730,
3. Mlino: N46°21.593, E014°05.954,
4. Under Osojnica: N46°21.310, E014°05.260.
For each point (1 - 4) explain what geomorphological features you've seen and send the answers to my e-mail. Immediately afterwards, you can log your find. They are highly desired your own favorite photos.
IMPORTANT!
- Entries without proper accompanying e-mail, which contains the correct answers will be deleted.
- Entries that contain the answers will be deleted.
Sources: Text: Remec-Rekar 2005, 2011, Bled, 2005; Melik, 1930; Špela Gorjanc 2012; Pictures: Špela Gorjanc 2012, Greenslovenia, I-love-Slovenia, Green Nuclear Butterfly, Geopedia; Video: Turizem Bled, National Museum of Slovenia
Additional Hints
(Decrypt)
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