SLO
SLOVENSKA OBALA
Debeli rtič je raj za ljubitelje narave in aktivnega preživljanja prostega časa. Peščene plaže in mirni zalivi omogočajo sprostitev ob morju, medtem ko strmi klifi in skalnati izrastki nudijo osupljive razglede na Jadransko morje. Polotok je tudi dom številnim rastlinskim in živalskim vrstam, kar ga naredi še posebej privlačnega za ljubitelje biologije in naravoslovja.
Na tem kratkem, a z geološkega vidika, zelo zanimivem odseku slovenske obale, lahko opazimo številne značilnosti obmorske pokrajine. Tu se stik med morjem in kopnim izraža v obliki strmih klifov, spodmolov in drugih geoloških posebnosti, ki jih je ustvarila erozija. Morje je vplivalo na oblikovanje obale, medtem ko je padavinska voda nadalje raztapljala kamen, kar je privedlo do nastanka impresivnih morsko-obalnih struktur. Ta obalni del je fascinanten za geološke sladokusce, saj prikazuje kompleksnost naravnih procesov, ki oblikujejo obalno pokrajino, in ponujajo edinstven vpogled v geološko zgodovino območja.
VPLIV MORJA
Delovanje morja je omejeno na ozek pas kopnega. Morje deluje na obalo s pritiskom vode, trganjem kamnine, z drobljenjem že odtrganega gradiva in s kemičnim delovanjem. Vse to imenujemo obalna erozija ali abrazija. Zaradi delovanja morja se nekatere obale umikajo, druge pa nastajajo oziroma rastejo. Delovanje je torej lahko erozijsko ali akumulacijsko in je posledica delovanja morskih valov, delno tudi morskih tokov in plimovanja.
MORSKA ABRAZIJA
Ko valovi udarjajo ob obalo, jo spodjedajo, rušijo in »pomikajo« proti kopnemu. Abrazija je odvisna od moči morskih valov, smeri vetra in količine delcev, ki jih vsebujejo valovi in ki skupaj z vodo udarjajo ob obalo. Ko val pljuskne na obalo, s seboj prinese nekaj gradiva in ga odloži, a takoj, ko se voda umakne, gradivo odplakne nazaj v morje. Tako valovi vseskozi premeščajo gradivo vzdolž obale. Erozijski učinki morja so največji na polotokih, rtih in izpostavljenih delih obale. Tu nastajajo klifi. Ti so večji in izrazitejši na obalah, kjer so plasti apnenca ali druge odporne kamnine vodoravne oziroma nagnjene vstran od obale.
Na nastajanje klifov vplivata tudi moč morskih valov in smer vetra. Morski valovi spodjedajo klif do višine, do katere sežejo, zato tam nastane morski spodmol. Pod klifom se v morje spušča zelo položna abrazijska polica, ki je prekrita z odkrušenim gradivom in obalnim peskom. Gradivo z abrazijske police valovi odnašajo in odlagajo v zalivih, ki nastajajo med rti. Ker so kamnine različno odporne proti abraziji, na odpornih delih obale nastajajo manjši izbočeni rti, naravni mostovi in skalni stebri, ki se dvigujejo iz morja.
Slika prikazuje prečni prerez obale z vidinimi različnimi abrazijskimi strukturami, ki jih ustvarijo valovi. Vse te geološke pojave je lepo videti in spoznati med ogledom tega kratkega koščka obale. Spodmol (1). Klif (2). Abrazijska polica (3), ki se nadaljuje v morje (4 in 5).
MORSKA AKUMULACIJA
Akumulacija nastane v zatišnih legah, kjer je gibanje morja počasnejše. Kadar je moč valov in morskih tokov manjša in obala plitva, morje več gradiva nanaša kot odnaša. Posledica morske akumulacije so nizke, peščene reliefne oblike. Glavni pogoji za njihov nastanek so obilje drobirja, razčlenjena obala in podolžni obalni tok. Tipične akumulacijske oblike so peščeni otoki, rti, zemeljske kose, lagune in obalne sipine.
GEOLOŠKE ZNAČILNOSTI SLOVENSKE OBALE
KLIF
Z besedo klif označujemo zelo strmo, vertikalno in včasih tudi previsno steno, sestavljeno iz kamnin ali nevezanih sedimentov, ki se nahaja na stiku kopnega in morja. Več o nastanku klifa in njegovi geološki zgradbi lahko spoznate z geozakladom Flišni velikan. Klifi so pogosto impresivni zaradi svoje velikosti in dramatičnih višin, ki lahko segajo od nekaj metrov do več sto metrov nad morsko gladino. Običajno so tudi pomembni ekosistemi, saj nudijo življenjski prostor številnim rastlinam in živalim, vključno z gnezdilci ptic in specializiranimi rastlinami, ki lahko prenesejo ekstremne pogoje.
RAZPOKA
Razpoka je presledek v kamnini, ki je nastal zaradi delovanja napetosti, pri katerih je kamnina počila in se razprla, premaknila pa se je zelo malo ali sploh ne. Glede na napetosti, ki delujejo v kamnini, delimo razpoke na natezne in strižne. Razpoke, ki so nastale zaradi nateznih sil in so praviloma usmerjene pravokotno na steno, so lahko dolge od nekaj centimetrov do nekaj 100 metrov in v kamnini predstavljajo prevodno pot za raztopine z različnimi količinami raztopljenih mineralov. Ko se iz nasičene raztopine v razpoki kemično izločijo minerali, nastane žila. V Sloveniji so žile najpogosteje zapolnjene s kalcitom in kremenom. Strižne razpoke potekajo vzdolž stene, so zaprte in brez žil.
PRELOM
Drugačna vrsta presledka v kamnini je prelom. Ta razdeli kamnino na dva bloka, ki se med seboj vidno premakneta. Skoraj vsi navpični oziroma prečnoplastni prelomi na klifu so mineralizirani s kalcitom.
ABRAZIJSKI SPODMOL
Abrazijski spodmol je geološka tvorba, ki nastane zaradi erozijskega delovanja valov na obalni pečini. Močni valovi udarjajo ob obalo, s seboj pa lahko prinašajo drobne kamnite delce. Ti delujejo kot abrazivno sredstvo, ki postopoma obrablja spodnji del obalne pečine. Nenehno udarjanje valov povzroča erozijo spodnjega dela pečine, kar vodi do nastanka votline ali spodmola. Ta proces je najbolj intenziven na višini, kjer valovi najbolj učinkovito udarjajo ob pečino. Sčasoma se spodmol povečuje in poglablja. Valovi odstranjujejo material iz spodmola, kar povzroča njegovo širjenje. Ko spodmol postane dovolj velik, zgornji del pečine izgubi oporo in lahko pride do kolapsa. Ta material se nato pogosto odplakne z valovi, kar še dodatno poveča odprtost spodmola.
ABRAZIJSKA POLICA
Na stiku med kopnim in morjem se lahko pojavlja različno široka abrazijska polica. Ta se pod morsko gladino nadaljuje v kamnito podmorsko teraso, ki se na nekaj metrih globine konča s previsom. Višina in naklon skalne stene, prisotnost in širina abrazijske terase ter globina morja se razlikujeta od klifa do klifa. Naklon pečine na Debelem rtiču, kjer je nagnjenost največja, je okoli 70°, abrazijska in podmorska terasa, celotna širina katere krepko presega 100 m, pa je na vsej slovenski obali najbolj položna (približno 4°).
PODVODNI GREBEN
Podvodni svet na skrajnem delu rta, kjer so krušljive plasti klifa najbolj izpostavljene vsakodnevnemu delovanju valov, je nekaj posebnega. Ko abrazijsko polico zalije morje, valovi prično prinašati mulj in drug kamninski drobir. Ta zapolni praznine med posameznimi skladi peščenjaka in tako se pod vodno gladino počasi prične izoblikovati izjemno atraktivni podvodni greben, ki nakazuje smer umikanja rta zaradi intenzivnega delovanja morskih valov. Čez čas peščenjak v morju razpade na drobne zrnce peska in za njim ostane le še obsežna peščena sipina. Razkrije jo zimska oseka, morjeplovce pa nanjo opozarja svetilnik sredi morja.
BIOGENA FORMACIJA
Za podvodnim grebenom se nahaja ena od dveh lokacij večje biogene formacije v slovenskem morju. Z besedo biogena formacije označujemo vse tvorbe, ki so rezultat nalaganja apnenca s strani nekaterih morskih organizmov tekom svojega življenja. Takim organizmom pravimo, da so biogradniki ali biokonstruktorji, saj z ustvarjanjem apnenčastih struktur nudijo možnost za naseljevanje pestre množice organizmov na tako nastala potencialna bivališča.
Najbolj znani biokonstruktorji so koralnjaki (Anthozoa), ki v tropskem in deloma subtropskem okolju ustvarjajo koralne grebene. Poleg koral ustvarjajo grebene tudi nekateri drugi nevretenčarji, kot so trdoživnjaki (Hydrozoa) in cevkasti mnogoščetinci (Polychaeta Sedentaria). Slovenska biogena formacija je sestavljena iz odmrlih delov sredozemskih kamenih koral in njenih živih kolonij.
IHNOFOSILI
Ogromni skalni bloki apnencev (nekdaj deli višje ležečih plasti, ki so se odlomili in padli v morje), na katere naletimo ob sprehodu po morskem obrežju, nudijo odlično priložnost za opazovanje fosilov. Med najbolje opaznimi so predvsem apnenčaste hišice luknjičark (tako imenovanih foraminifer), odlomki bodic in hišk morskih ježkov ter ostanki rdečih alg. Čeprav redkeje, lahko okamnele ostanke živih organizmov, ki jih vidimo s prostim očesom, najdemo tudi v peščenjakih na morski obali. Gre za ostanke debel, včasih listov.
Bolj pogosto pa so se v njih ohranili ihnofosili, sledovi, ki so jih v sedimentu pustile različne živali. Največkrat ne vemo, kateremu organizmu so pripadali, lahko pa iz njihove oblike sklepamo, ali so nastali med kobacanjem, plazenjem, počivanjem, hranjenjem ali kakšnim drugim obnašanjem živali. hnofosile je mogoče odkriti med preprostim obračanjem prodnih kamnov na obali, pomembno pa je, da kamnov po ogledu z obrežja ne odnašamo ali premeščamo. Vrnemo jih tja, kjer smo jih pobrali, saj so dom morskim organizmom, ki se ob oseki skrijejo podnje.
NALOGE ZA VPIS GEOZAKLADA
Odgovore na vprašanja pošljite preko GC profila. Zaklad lahko nato brez čakanja na povratno informacije tudi logirate. V primeru napačnega ali pomanjkljivega odgovora vas obvestim. Vpisi ne smejo vsebovati odgovorov na vprašanja, prav tako pa ne smejo biti vpisani brez poslanih odgovorov. Takšni odgovori bodo nemudoma izbrisani.
Virtualna stopnja 1: ABRAZIJSKA POLICA (01)
- Na tem mestu si priča nastajanju nove abrazijske police, na kateri je še ne dolgo nazaj slonel klif. Katera kamnina jo gradi in kako debeli so ti skladi?
- Če si pobližje ogledaš površino skladov, lahko opaziš izrazit relief (kot da bi bile narisane plastnice). Kako je po tvojem mnenju prišlo do takšnega pojava?
Virtualna stopnja 2: RAZPOKA in PRELOM (02)
- V steni klifa si lahko ogledaš tako razpoko kot tudi prelom v razmaku enega metra. Katera naravna sila je po tvojem mnenju povzročila prelom? Ali gre za navpičnega, vodoravnega ali poševnega?
- Za koliko centimetrov so se skladi premaknili?
Virtualna stopnja 3: ABRAZIJSKI SPODMOL (03)
- V opisu si spoznal kako abrazijski spodmol nastane. Kaj pa se bo po tvojem mnenju zgodilo v primeru, da morje nadaljuje z erozijo flišne stene v spodmolu?
- Spodmolu izmeri dolžino in višino.
Virtualna stopnja 4: PODVODNI GREBEN (04)
- Na vznožju klifa boš opazil sledi podvodnega grebena. Kakšno smer slemenitve ima?
NEOBVEZNO! K vpisu priloži sliko sebe ali predmeta s tvojim GC imenom in datumom obiska, vsekakor pa je zaželjeno, da je na fotografiji viden delček te čudovite slovenske obale.
ENG
SLOVENIAN COAST
Debeli Rtič is a paradise for nature lovers and those who enjoy an active lifestyle. Sandy beaches and peaceful coves offer relaxation by the sea, while steep cliffs and rocky outcrops provide stunning views of the Adriatic Sea. The peninsula is also home to numerous plant and animal species, making it especially attractive for biology and natural science enthusiasts.
On this short, yet geologically fascinating stretch of the Slovenian coast, many coastal landscape features can be observed. The interaction between the sea and land is expressed through steep cliffs, overhangs, and other geological formations shaped by erosion. The sea has influenced the formation of the coastline, while rainwater has further dissolved the rock, leading to the creation of impressive coastal structures. This coastal area is a treasure for geology enthusiasts, as it showcases the complexity of natural processes that shape coastal landscapes, offering a unique insight into the geological history of the region.
THE INFLUENCE OF THE SEA
The impact of the sea is limited to a narrow strip of land. The sea affects the coast through water pressure, the breaking of rocks, the fragmentation of already detached material, and through chemical action. This process is known as coastal erosion or abrasion. As a result of the sea's activity, some coastlines retreat, while others form or grow. The effects can be either erosive or accumulative, caused primarily by the action of sea waves, and to some extent by ocean currents and tides.
COASTAL ABRASION
When waves strike the shore, they erode, collapse, and "push" it inland. Abrasion depends on the force of the waves, the direction of the wind, and the amount of particles carried by the waves, which strike the shore along with the water. When a wave crashes against the coast, it deposits some material, but as the water recedes, it washes the material back into the sea. In this way, waves constantly move material along the coastline. The erosive effects of the sea are greatest on peninsulas, headlands, and exposed parts of the coast, where cliffs form. These cliffs are larger and more pronounced on coasts where layers of limestone or other resistant rocks are horizontal or tilted away from the coast.
The formation of cliffs is also influenced by the strength of the waves and the direction of the wind. The waves erode the cliff up to the height they can reach, creating a sea notch. Below the cliff, a gently sloping abrasion platform extends into the sea, covered with broken material and coastal sand. Waves carry this material from the abrasion platform and deposit it in bays that form between headlands. Because rocks vary in their resistance to abrasion, smaller protruding headlands, natural bridges, and sea stacks rise from the sea in the more resistant parts of the coastline.
The image shows a cross-section of the coast with various abrasion structures created by waves. All these geological phenomena are beautifully visible and can be explored during a visit to this short stretch of coastline. Sea notch (1). Cliff (2). Abrasion platform (3), extending into the sea (4 and 5).
COASTAL ACCUMULATION
Accumulation occurs in sheltered areas where the movement of the sea is slower. When the power of the waves and currents is weaker and the coastline is shallow, the sea deposits more material than it removes. As a result, low, sandy landforms develop due to marine accumulation. The main conditions for their formation include an abundance of debris, a dissected coastline, and longshore currents. Typical accumulation features include sand islands, headlands, spits, lagoons, and coastal dunes.
GEOLOGICAL FEATURES OF THE SLOVENIAN COAST
CLIFF
A cliff refers to a very steep, vertical, and sometimes even overhanging wall made of rocks or loose sediments found at the junction of land and sea. You can learn more about the formation and geological structure of cliffs through the Flysch giant earthcache. Cliffs are often impressive due to their size and dramatic heights, ranging from a few meters to several hundred meters above sea level. They also play an important role as ecosystems, providing habitats for many plants and animals, including nesting birds and specialized plants capable of withstanding extreme conditions.
FISSURE
A fissure is a gap in the rock caused by stress, where the rock cracks and opens, but there is very little or no movement. Depending on the stresses in the rock, fissures are divided into tensile and shear types. Fissures created by tensile forces, typically oriented perpendicular to the cliff face, can range from a few centimeters to several hundred meters long. They serve as conduits for solutions containing dissolved minerals. When minerals precipitate from these saturated solutions, veins form. In Slovenia, veins are most often filled with calcite and quartz. Shear fissures run parallel to the cliff, are closed, and lack veins.
FAULT
A different type of gap in the rock is a fault, which divides the rock into two blocks that visibly shift relative to each other. Almost all vertical or cross-bedded faults on cliffs are mineralized with calcite.
ABRASION NOTCH
An abrasion notch is a geological formation created by the erosive action of waves on a coastal cliff. Powerful waves strike the shore, often carrying small rock particles with them. These particles act as an abrasive, gradually wearing away the lower part of the cliff. Continuous wave action erodes the base of the cliff, leading to the formation of a cavity or notch. This process is most intense at the height where the waves hit the cliff most effectively. Over time, the notch deepens and expands. As waves remove material from the notch, it enlarges. When the notch becomes large enough, the upper part of the cliff loses support, leading to a collapse. The collapsed material is often washed away by the waves, further enlarging the notch.
ABRASION PLATFORM
At the junction between land and sea, a varying-width abrasion platform can appear. This platform continues underwater as a rocky submarine terrace, which ends with an overhang at a few meters depth. The height and slope of the cliff, the presence and width of the abrasion platform, and the sea depth vary from cliff to cliff. The slope of the cliff at Debeli Rtič, where it is steepest, is around 70°, while the abrasion and submarine terrace, which exceeds 100 meters in total width, is the most gently sloped on the Slovenian coast (approximately 4°).
UNDERWATER REEF
The underwater world at the extreme tip of the headland, where the fragile layers of the cliff are most exposed to daily wave action, is something special. When the abrasion platform is submerged, waves begin depositing silt and other rock debris. This material fills the gaps between individual layers of sandstone, slowly forming an exceptionally attractive underwater reef that marks the retreat of the headland due to the intense wave action. Over time, the sandstone in the sea disintegrates into fine grains of sand, leaving behind an expansive sand dune. This dune is revealed during the winter low tide, and sailors are warned of it by a lighthouse in the middle of the sea.
BIOGENIC FORMATION
Behind the underwater reef lies one of the two larger biogenic formations in the Slovenian sea. The term biogenic formation refers to all structures resulting from the deposition of limestone by certain marine organisms during their lifetimes. These organisms are called biobuilders or bioconstructors because, by creating calcium carbonate structures, they provide habitats for a wide variety of organisms that settle in these newly formed potential living spaces.
The most well-known bioconstructors are corals (Anthozoa), which form coral reefs in tropical and partly subtropical environments. Besides corals, other invertebrates, such as hydrozoans (Hydrozoa) and tube-dwelling polychaetes (Polychaeta Sedentaria), also build reefs. The Slovenian biogenic formation consists of the dead parts of Mediterranean stony corals and their living colonies.
ICHNOFOSSILS
The large limestone boulders (once parts of higher-lying layers that broke off and fell into the sea) found along the seashore provide an excellent opportunity for observing fossils. Some of the most visible fossils include foraminifera (tiny limestone-shelled organisms), fragments of sea urchin spines and shells, and remnants of red algae. Though rarer, fossilized remains of organisms that can be seen with the naked eye are sometimes found in the sandstones along the coast. These can include pieces of wood, and occasionally, leaves.
More commonly, the sandstones contain ichnofossils, which are traces left by various animals in the sediment. While it's often difficult to determine the specific organisms responsible, their shapes can reveal whether the traces were made by crawling, burrowing, resting, feeding, or some other behavior. Ichnofossils can be discovered by simply turning over pebbles along the shore, but it's important not to remove or displace the stones after viewing them. They serve as homes for marine organisms that hide beneath them during low tide.
TASKS TO LOG AN EARTHCACHE
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Virtual Stage 1: ABRASION PLATFORM (01)
- At this location, you are witnessing the formation of a new abrasion platform, where the cliff once rested not long ago. What type of rock forms this platform, and how thick are these layers?
- If you take a closer look at the surface of the layers, you can notice a distinct relief (as if contour lines were drawn). What do you think caused this phenomenon?
Virtual Stage 2: FISSURE and FAULT (02)
- In the cliff wall, you can observe both a fissure and a fault, just one meter apart. What natural force do you think caused the fault? Is it vertical, horizontal, or oblique?
- How many centimeters have the layers shifted?
Virtual Stage 3: ABRASION NOTCH (03)
- The description explained how an abrasion notch forms. What do you think will happen if the sea continues to erode the flysch wall inside the notch?
- Measure the length and height of the notch.
Virtual Stage 4: UNDERWATER REEF (04)
- At the foot of the cliff, you will notice traces of an underwater reef. What is the direction of its ridge?
OPTIONAL! Attach a photo of yourself or an object with your GC name and the date of your visit. Ideally, the photo should also include a part of this beautiful Slovenian coast.