(SI) Velika močvirna ravnica, rezultat tektonskega ugrezanja in ponavljajočih se zasipanj s sedimenti.
PRED ZACETKOM:
Opis tega Geološkega zaklada je dolg. Prosimo, preberite ga in si zapisite naloge za vpis se pred obiskom zaklada!
NALOGE ZA VPIS ZAKLADA
1. Z razgledne tocke lahko vidite vec osamelcev, ki kot otocki predirajo ravnino Barja. Koliko med njimi ima jasno vidne razgaljena kamnita pobocja? Tam so bili kamnolomi.
2. Poiscite siv kamniti portal vrat, ki je prikazan na sliki 5. Stopite pod okvir na strani, ki je oznacena z rdeco puscico. Obrnite se proti zidanemu kamnitemu stebru, vrh katere je plosca z vgraviranimi smermi in imeni vrhov vidnih v daljavi. Pozorno poglejte preko stebra v vrh hriba na obzorju. Zapisite ime vrha lezecega v smeri vasega pogleda.
Glejte sliko 1 (Figure 1, pri angleskem besedilu spodaj): Detajl okvirja slepih vrat v zunanjem zidu cerkve sv. Ane – stojisce za drugo nalogo za vpis zaklada; foto in skica: vane_si;
2a. V primeru slabega vremena, ko oddaljeni vrhovi niso vidni, stopite h kamnitemu stebru, obrnite se proti sivemu okvirju vrat in na vgravirani plosci poiscite ime vrha, ki bi bil viden od okvirja vrat cez kamniti steber (in naprej preko vasega hrbta). Zapisite ime.
3. V vznozju Sv. Ane, v Podpeci, je kamnolom. Kaksen kamen pridobivajo v njem? Kdaj so na tem mestu prvic zaceli lomiti kamen? Za odgovore vam ni treba obiskati kamnoloma.
4. 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 nekatere druge v okolici:
- Geološki zaklad GC3APHF v vasi Jezero,
- lep tradicionalni Nocni zaklad, GC20BHA in
- tradicionalni zaklad Svetla Ana, GC13KHV.
(ENG) Large marshy plain, a product of tectonic sinking and repeated filling with sediments.
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. You can see several isolated hills on the flat Marsh surface from the viewpoint. How many of those hills have visibly exposed rocky hillsides? People used to quarry stones there.
2. Find the grey doorframe shown in figure No.5. Step under the frame on the side shown by the red arrow. Turn towards the stone-built pillar bearing the plate with engraved directions of visible hilltops. Carefully look across the pillar to the hilltop in the distance. Write down the name of the hill in your line of sight.
2a. In the case of bad weather, when distant hills are not visible, step to the stone pillar, turn towards the grey doorframe and find the name of the hill, which would be seen in the line of sight from the doorframe across the stone pillar (and further, behind your back). Write down the name.
3. There is a quarry at the foothill of St. Anna in the village Podpeč. Which stone is quarried there? When has the first quarry started to operate at this site? You don't need to visit the quarry to answer.
4. We would be glad if you added interesting photos from the EarthCache location to your log.
Figure 1: Detail of the doorframe in the outside wall of St. Anna church – standing point for the second logging task; photo and sketch: vane_si;
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 some other caches in the neighbourhood:
- EarthCache GC3APHF at Jezero,
- traditional Night cache, GC20BHA in the Jezero surroundings and
- traditional cache Svetla Ana, GC13KHV.
slovensko besedilo / Slovenian text
tocke poti in dnevniki / waypoints and logs
Visit our web-site Geološki zakladi / EarthCaches
for a complete list of our EarthCaches and a lot of additional information.
(ENG) THE LJUBLJANA MARSH…
… is a wide tectonic depression with a mainly flat surface. It is crossed by numerous streams few of which remain natural. Ljubljansko Barje, or Ljubljana Marsh, is a geographical name for the area between the river Ljubljanica, Vrhnika, Krim and Skofljica. Ljubljana Marsh spreads no more than a few steps from Ljubljana's last suburban streets. This large marshy plain includes almost 160 square kilometres and is marked by an interminable mosaic of grasslands, litter woodlands, fields, ditches and hedges. Here and there, solitary green hillocks rise from this countryside.
Ljubljana Marsh is the largest Slovene and southern European wetlands. Similar areas are a true rarity in Europe today, due mainly to intensive farming and urbanization. Ljubljana Marsh, home to numerous endangered species, has been proclaimed a Natura 2000 site, and in 2006 a Nature Park as well.
GEOLOGIC HISTORY
Ljubljana Marsh is a part of wider Ljubljana Basin which comprises the entire subsided area, almost 40 km long and relatively flat from Ljubljana to Jesenice. This broader basin has been formed as a result of the strike-slip tectonics since some 30 million years ago. Ljubljana Field north of Ljubljana, and the Ljubljana Marsh south of Ljubljana, are younger, and formed only about two million years ago. The rate of subsidence was relatively high at approximately 1 m in 500 years. The flat surface of the central part of Ljubljana Marsh Basin indicates ongoing subsidence.
Figure 2: Geological map of Ljubljana Marsh, from book Ljubljansko barje, reference No.1
The Marsh is dissected by numerous normal faults. Along the principal faults, individual tectonic blocks were depressed. However, not all the blocks have subsided at the same time and at the same rate. The pattern of faults is relatively dense and largely not mapped since they are not easy to locate below the deep cover of sediments. They can only be reliably established by drilling, or by geophysics. The Marsh floor is deepest in its southeast part, more than 170m in some places!
Some parts of the Marsh basement rise above the younger sedimentary beds. These are the isolated hills. Their geological composition is similar to the borderland. Should one remove the sedimentary cover which fills the Marsh basin at present, an agitated relief would be revealed. Many drills proved Marsh basement has the same rock composition as the hills bordering the Marsh. The northern edge of Marsh is limited by the thrust of Carboniferous-Permian layers, which are positioned over the Triassic layers. The southern edge of Marsh is limited with a fault, which has low angle fault-plane, and layers of the hills are pushed over Marsh floor.
Figure 3: Cross section of Kostanjevica, one of the isolated hills in the Marsh flatland. Kostanjevica is positioned near the northern edge of the Marsh. An example of older Carboniferous sandstone layers pushed over younger Triassic layers; from brochure "Učna pot po Ljubljanskem Barju", reference No.3
DEPOSITION OF MATERIAL IN THE DEPRESSION
The drainage system of the Marsh is quite dense. Streams come both from nearby typical karstic resurgences, such as the sources of Ljubljanica, Bistra and Izica as well as from distant areas, reaching the Marsh as surface streams such as Iska, Borovniscica, Zelimeljscica, Skofeljscica and other smaller creeks. The Ljubljanica River carries its sedimentary load mainly in the form of dissolved limestone and therefore deposits little sediment. However, the surface streams carry large quantities of gravel and sand, especially in spring and autumn, and can deposit them quickly over large areas. In this way, the Ljubljana Marsh has been filled with gravel by surface streams over thousands of years but during periodic lacustrine periods, it was filled with silt and clay. The central base of the Marsh subsided quickly due to this new sedimentary load whilst the rims were stable and perhaps even raised somewhat.
Knowledge of the depositional succession in the Ljubljana Marsh enables the reconstruction of ancient environments. It can be seen that conditions changed fast. Sometimes the Marsh was vast gravel plain with interspersed water surfaces and at other times it was either a shallow lake with rich fauna and flora or uncrossable turf swamp. There were at least three occasions during the deposition of the sedimentary beds of the Marsh when the conditions were favourable for the formation of peat. The youngest and deepest peat seen near the surface was formed during the last lacustrine stage. This was the time of fascine dwellers. Where the thickness of the peat allows it has been excavated and used by the local population for heating as well as by various industries in and around Ljubljana. Today the peat seam is partially preserved near Bevke and south of the Grmez and Babna Gorica hills. Below the peat layer, a whitish clay can be observed in ditch banks. This is the "snail clay" (polžarica) found throughout the Marsh and a good indication of the ancient lake and its rich fauna.
Figure 4: Ljubljana Marsh Cross-section from west to east (Bistra to Lavrica); sediment layers: dolomite basement is green, blue layers include mostly gravel and sand, grey layers consist of silt and clay; red lines represent faults, along which blocks of Marsh floor subsided at a different rate; from book Ljubljansko barje, reference No.1
The oldest sedimentary beds, just above the rocky basement were deposited about 400,000 years ago, and are attributed to the Mindel glaciation period. Overlaying beds at a depth of 90 meters belong to the interglacial periods between Mindel and Riss. Sediments from more than 70 meters deep boreholes were proved to be approximately 100,000 years old. From 44 meters upwards are overlaid by fine-grained sands and silts deposited during the youngest – the Wurm glacial period around 50,000 years ago. The Upper 10 meters of the youngest sediments are less than 4,000 years old and are the result of the sedimentation during the Holocene.
Figure 5: Ljubljana Marsh topografic map and relief. Isolated hills protrude through the flat surface of the Marsh as islands in the sea. Map and relief clips are from Geopedia, reference No.5
FROM LAKE TO CULTIVATED LAND
Ljubljana Marsh lake, and marsh in the literal sense, has been a result of river Sava deposits at the Northern edge of Marsh depression. Especially during glacial periods, the Sava river deposited enough material to present a barrier. Those deposits have prevented the draining of the Marsh waters and are the main cause of the formation of the lake, which covered the complete flat part of the Marsh. The conditions described above, repeated several times in history. In time, water managed to dig deep enough channels in the barrier to drain the lake. The Marsh formed slowly, after the draining of the lake each time.
The undisturbed natural evolution of the Marsh was terminated with the arrival of man. The swampy area was farmed and settled. From Roman times until today many generations have attempted to drain the Marsh without complete success. One of the most effective projects was the construction of the Gruber channel in 1780 and the removal of ancient mill dams along the river Ljubljanica.
Remains of the original marsh can be found at the foot of the Kostanjevica hill where a swampy meadow is overgrown with vegetation in which peat moss (Sphagnum) prevails.
Since river Ljubljanica has only about 1m of a drop from its source near Vrhnika to Ljubljana, and the draining capability is limited, flooding is still usual after extensive rain.
EARTHCACHE
EarthCache coordinates are set at the best viewpoint above Ljubljana Marsh, the top of the hill St. Anna. It is accessible by foot from villages Podpec, Jezero and Preserje. You reach the hilltop in 30 minutes of leisurely walking from recommended parking areas. And then enjoy in a wide, marvellous view!
Figure 6: A great view of Ljubljana Marsh from EatrthCach! Can you get a better one? Maybe... from a plane or hot air balloon!; photo: vane_si;
References:
1. Ljubljansko Barje, editor: Jernej Pavsic, Drustvo Slovenska matica, Ljubljana 2008;
2. Ljubljansko Barje through Geological Periods, Jernej Pavsic, guidebook, Ljubljana 1989;
3. Ucna pot po Ljubljanskem Barju, ...Mali Plac..., editors: Maja Dremelj and Igor Berginc, obcina Vrhnika, 2005;
4. Ljubljana Marsh Nature Park web site: www.ljubljanskobarje.si
5. Geopedia.si, web-atlas;
Slovensko besedilo
Obiscite naso spletno stran Geološki zakladi / EarthCaches
za seznam vseh nasih Geoloških zakladov in mnogo dodatnih podatkov.
(SI) LJUBLJANSKO BARJE...
... je siroka tektonska udorina s skoraj ravno povrsino. Prepredeno je s stevilnimi vodotoki, od katerih je le malokateri ostal v svoji naravni strugi. Ljubljansko Barje je zemljepisno ime za obmocje, ki lezi med Ljubljano, Vrhniko, Krimom in Skofljico. Razprostira se prav na pragu glavnega mesta, Ljubljane, le nekaj korakov od zadnjih mestnih ulic. Dobrih 150 km2 mocvirne ravnice zaznamuje neskoncen mozaik travnikov, steljnikov, njiv, jarkov in mejic. Sem in tja silijo kvisku nizki zeleni osamelci.
Ljubljansko barje je najvecje slovensko in juznoevropsko mokrisce. Podobna obmocja so danes v Evropi zaradi intenzivnega kmetijstva in urbanizacije ze prava redkost! Ljubljansko barje, dom stevilnim ogrozenim vrstam, je bilo vkljuceno v obmocja Natura 2000 in leta 2006 razglaseno za Krajinski park.
GEOLOSKA ZGODOVINA
Ljubljansko barje je del vecje Ljubljanske kotline, ki obsega celotno ugreznjeno podrocje, dolgo skoraj 40 km, skorajda ravno od Ljubljane do Jesenic. Ta, sirsa kotlina je zacela nastajati kot posledica tektonskih premikov ob zmicnih prelomih pred priblizno 30 milijoni let. Ljubljansko polje, severno od Ljubljane in Ljubljansko barje juzno, sta mlajsa, nastala pred priblizno dvema milijonoma let. Pogrezanje je bilo relativno hitro, priblizno 1 m v 500 letih. Popolna izravnanost osrednjega dela barja kaze, da se pogrezanje se vedno nadaljuje.
Slika 2: Geoloska karta Ljubljanskega barja, iz knjige Ljubljansko barje, vir st. 1
Barje je razkosano s stevilnimi prelomi. Posamezni tektonski bloki so bili razmaknjeni vzdolz glavnih prelomov, vendar vsi Bloki niso tonili istocasno in ne enako hitro. Vzorec prelomov je precej gost in v glavnem slabo kartiran, ker jih je tezavno locirati pod debelimi sloji usedlin in nanosov. Zanesljivo jih lahko dolocimo le z vrtinami ali geofizicnimi raziskavami. Dno Barja je najgloblje na jugovzhodnem delu, kjer ponekod seze celo vec kot 170 m pod povrsino!
Nekateri deli kamninske podlage pa se kljub temu dvigajo nad mlajse sloje sedimentov. To so nizki osamelci. Njihova geoloska sestava je enaka sestavi kamnin robnih pobocij ob barju. Ce bi kdo s carobno palicico s temeljne kamninske podlage Barja odstranil vse usedline, bi ocem razkril zelo razgiban, grudast relief. Mnoge vrtine dokazujejo, da ima kamninska podlaga barja enako sestavo kot obrobna pobocja. Severni rob Barja je omejen z narivom karbonsko-permskih plasti, ki lezijo na triasnih. Juzni rob Barja pa je omejen s prelomom pod majhnim kotom in so juzno lezece plasti potisnjene na plasti dna Barja.
Slika 3: Prerez osamelca Kostanjevica. Osamelec lezi blizu severnega roba Barja. Prikazan je primer nariva starejsih karbonskih slojev pescenjaka, ki so potisnjeni cez mlajse, triasne dolomite; iz prospekta Ucna pot po Ljubljanskem Barju, vir st. 3
ODLAGANJE MATERIALA V KOTLINI BARJA
Sistem odvodnjavanja je na Barju precej gost. Vodotoki so od povsem kraskih, ki do roba Barja pritecejo pod zemljo, naprimer Ljubljanica, Bistra in Izica, pa do povrsinskih, ki pritecejo, kot so Iska, Borovniscica, Zelimeljscica, Skofeljscica in drugi manjsi potoki. Ljubljanica nosi material predvsem v obliki raztopljenega apnenca in zato, ceprav najvecji vodotok, odlaga le malo usedlin. Povrsinski vodotoki pa prinasajo velike kolicine proda in peska, se posebej spomladi in jeseni in jih lahko hitro odlozijo na velikih povrsinah. Na ta nacin se je Ljubljansko barje tisocletja zapolnjevalo s prodom povrsinskih tokov, v vmesnih, ponavljajocih se obdobjih ojezeritve, pa sta se odlagala melj in glina. Pod vedno vecjo tezo novih usedlin, se je osrednji del dna Barja hitreje pogrezal, medtem ko so robni predeli ostali bolj stabilni in se pod dolocenimi pogoji lahko celo dvignili.
Poznavanje zaporedja odlaganja usedlin in nanosov na Barju omogoca dolociti pogoje, ki so vladali temu obmocju skozi zgodovino. Razvidno je, da so se razmere hitro spreminjale. Vcasih je bilo Barje obsirna planjava prekrita s prodnimi nanosi in prepredena z vodotoki in vodnimi povrsinami, v naslednjem obdobju pa je bilo plitvo jezero bogato z rastlinami in zivalmi ali pa neprehodno sotno mocvirje. Vsaj trikrat so nastopile ugodne razmere za nastajanje sotnega mahu. Najmlajsi in najgloblji sloji sote, ki so vidni blizu povrsine, so nastali v obdobju zadnje ojezeritve. To je bilo obdobje mostiscarjev. Kjer je debelina sote to dopuscala, so jo rezali in uporabljali za gretje lokalni prebivalci in tudi razlicne industrije v Ljubljani in okolici. Danes so plasti sote delno ohranjene blizu Bevk ter juzno od Grmeza in Babne Gorice. Pod soto se nahaja plast svetle gline imenovane polzarica, ki jo najdemo po celotni povrsini Barja, kar je dober pokazatelj nekdanjega jezera in njegove bogate zbirke zivali.
Slika 4: Prerez Ljubljanskega Barja od zahoda proti vzhodu (od Bistre do Lavrice); plasti usedlin: zelena je dolomitna podlaga, modro oznaceni sloji vsebujejo v glavnem prod in pesek, sivo oznaceni sloji vsebujejo vecinoma melj in glino, rdece linije predstavljajo prelome vzdolz katerih so razlicno hitro pogrezali bloki barjanskega dna; iz knjige Ljubljansko barje, vir st. 1
Najstarejsi sloji usedlin, lezeci neposredno na kamnitem dnu so bili odlozeni pred priblizno 400.000 leti in so pripisani Midelski ledeni dobi. Plasti nad temi, na globini 90 m pripadajo medledeni dobi med Midlom in Rissom. Usedline globlje od 70 m so stare priblizno 100.000 let. Od globine 44 m proti povrsju Barja s nahajajo drobnozrnati peski in melji odlozeni v casu zadnje – Wurmske ledene dobe, pred priblizno 50.000 leti. Zgornjih 10 m usedlin je nastalo v Holocenu in so mlajse od 4000 let.
Slika 5: Topografska karta in relief Ljubljanskega Barja. Osamelci ravno povrsino Barja prebadajo kot otoki morje. Karta in relief sta s spletnega atlasa Geopedia, vir st. 5
OD JEZERA DO OBDELANIH POVRSIN
Jezero na Ljubljanskem Barju in barje v pravem pomenu beseda sta nastajala zaradi nanosov, ki jih je reka Sava odlagala na severni rob Barja. Sava je naplavinsko prepreko intenzivno gradila med ledenimi dobami. Ti nanosi so preprecevali normalen odtok voda z Barja in so glavni vzrok za nastanek jezera, ki je zapolnilo celotno ravnino Barja. Opisane okoliscine so se skozi zgodovino ponovile veckrat. Vsakic je voda s casom dovolj poglobila odtocne kanale v naplavinski oviri, da je odtekla iz jezera. Temu je pocasi sledilo nastajanje barja.
Naravni cikli Barja so se koncali s prihodom ljudi. Mocvirno zemljisce je bilo poseljeno in obdelovano. Vse od rimskih casov do danes so stevilne generacije poskusale osusiti Barje, a vselej brez dokoncnega uspeha. Doslej najucinkovitejsi projekt je bila izgradnja Gruberjevega kanala v letu 1780 in odstranitev starih mlinskih jezov vzdolz Ljubljanice.
Ostanke prvotnega barja lahko najdemo v vznozju Kostanjevice, kjer je mocviren travnik prerascen z rastlinstvom v katerem prevladuje sotni mah.
Ljubljanica ima od izvirov pri Vrhniki do Ljubljane, na razdalji 20 km, vsega priblizno 1 m padca in omejene moznosti odtoka. Zato je poplavljanje vecjih povrsin Barja po mocnejsih padavinah tudi danes se vedno obicajen pojav.
GEOLOŠKI ZAKLAD
Koordinate so postavljena na najlepse razgledisce nad Ljubljanskim barjem, na vrh Sv. Ane. Pes je dostopen iz vasi Podpec, jezero in Preserje. Od predlaganih izhodisc je do vrha pol ure zlozne hoje. Potem na vrhu lahko uzivate v sirokem, cudovitem razgledu!
Slika 6: S koordinat Geološkega zaklada je velicasten pogled na Ljubljansko barje! Bi lahko kje bil boljsi? Morda... z letala ali balona. foto: vane_si;
Viri:
1. Ljubljansko Barje, urednik: Jernej Pavsic, Drustvo Slovenska matica, Ljubljana 2008;
2. Ljubljansko Barje through Geological Periods, Jernej Pavsic, guidebook, Ljubljana 1989;
3. Ucna pot po Ljubljanskem Barju, ...Mali Plac..., urednika: Maja Dremelj in Igor Berginc, obcina Vrhnika, 2005;
4. Krajinski park Ljubljansko Barje, spletna stran www.ljubljanskobarje.si
5. Geopedia.si, spletni atlas;
tocke poti in dnevniki / waypoints and logs