Kokra je slovenska reka, ki izvira v Karavankah in se kot levi pritok pri Kranju izliva v reko Savo. Dolga
je 34 kilometrov, njeno porečje meri 223 km². Kokra izvira pod Virnikovim Grintavcem v Karavankah,
na višini 825 metrov nad morjem, zahodno od Jezerskega. Kokra je med grebene Karavank in
Kamniško Savinjskih Alp vrezala globoko ozko gorsko dolino. Teče med Storžičem na eni in Grintavci
na drugi strani. Reka ima snežno dežni režim.
Pred izlivom v Savo v Kranju je Kokra v ledenodobno konglomeratno teraso skozi Kranj vrezala skoraj
30 m globoko sotesko – kanjon reke Kokre. Predstavlja pester mozaik vodnih in obvodnih biotopov:
reka, obrežje, prodišča, loka s poplavnim gozdom, skalnati bloki in konglomeratno ostenje.
Učna pot po kanjonu
KANJON V SPRIJETEM PRODU
Posebnost gorske reke Kokre je torej kanjon, ki ga je vrezala na koncu ledenih dob v lastne sprijete
prodne naplavine. Nastanek in obikovanje kanjona sta povezana s tektonskimi premiki in erozijo.
Sprijeti prod imenujemo labor ali konglomerat.
Reka je s seboj prinašala vedno nove plasti sedimentov. Pod njihovo težo se je v nižjih plasteh prod
zgoščeval, preostali prazni prostor med prodniki pa je zapolnilo vezivo. To je lahko mineralni cement
(najpogosteje kremenov ali kalcitni), ki se izloča iz vodne raztopine, lahko drobnozrnata osnova
(peščena, glinena ali lapornata), ali pa oboje.
Prod - Gravel
Glede na geološko zgradbo zaledja, od koder posamezna reka prinaša prodnike, je tudi mineralna
sestava konglomerata (conglomerare - nakopičiti) različna. Med seboj so pomešani prodniki
magmatskih, metamorfnih in sedimentnih kamenin. Glede na sestavo ločimo kremenove, apnenčeve,
dolomitne in druge konglomerate. Konglomerat torej vsebuje individualne kamenčke, odkruške ali
klaste, ki so se z drobnejšim materialom sprijele skupaj. Konglomerat je sedimentna kamenina, ki jo
sestavljajo zaobljeni kamenčki (prodniki), po cemer se loči od brece, ki jo sestavljajo oglati kamencki.
Različni tipi konglomerata vsebujejo različno velike prodnike in različno količino matriksa, ki jih drži
skupaj. Tako konglomerat kot brečo karakterizirajo odkruški, večji od peska (>2mm).
Prod je ponekod slabo sprijet in zaradi zemeljskih sil razpokan. Zaradi raztapljanja apnenega veziva
med prodniki nastajajo v kamnini različno velike votline. Občasno se deli konglomeratnih sten
odlomijo, odlomljeni prodni bloki pa obležijo na pobočjih ali celo v reki.
Konglomerat - Conglomerate
Iz izbranih kosov kamnine so nekdaj izdelovali mlinske kamne, hišne portale in opestnike ali odbojne
kamne. Konglomerat so uporabljali tudi kot gradbeni kamen.
KAJ NAM PRIPOVEDUJE PRODIŠČE V KANJONU?
Prodišče je dinamičen rečni sistem, saj zaradi stalnega delovanja vode nenehno nastaja in izginja.
Vsakič, ko ga obiščemo, je lahko malo drugačno. Prod se odlaga na notranjih delih rečnih zavojev. Če
pogledamo od blizu, lahko opazimo prodnike različnih oblik, velikosti, barv in vzorcev. Ostri kosi
grušča so se na dolgem potovanju iz gora v dolino obrusili in zgladili. Kokra teče po kamninah, pestrih
po geološki starosti ter različnih po nastanku in sestavi.
Ali ste že opazili, da imajo prodišča obliko velike kaplje? Reka ob močnem deževju prestopi bregove,
spreminja prodišče in poplavlja ravnice. Nekdaj so bili na ravnici poplavni gozdovi sive in črne jelše ter
topola, danes pa jih zaradi gospodarjenja ni vec. Rastline, ki naseljujejo prodišče, spadajo med
pionirske vrste. V Kokri so to lapuh ter rdeča in siva vrba. Za njihov obstoj je potrebna naravna rečna
dinamika z odnašanjem in odlaganjem proda.
Kokra in prodišče - Kokra and gravel pit
Prodišča skrivajo v sebi skriti zaklad življenja, ki ga s prostim očesom skorajda ne moremo videti.
Poglejte v zamuljene predele, kjer se skrivajo vodni rakci in ličinke žuželk, na mivki pa lahko opazite
hiteti pajke in hroščke brzce. Tako razgibano in pestro obmocje zato nudi zatocišce in dom številnim,
po življenjskih zahtevah razlicnim živalskim in rastlinskim vrstam.
Kanjon Kokre je zavarovan kot naravna znamenitost v okviru starega mestnega jedra Kranja. V
kanjonu Kokre je urejena učna pot. Izdana je bila tudi zloženka, ki je namenjena predvsem šolskim
skupinam za spoznavanje nastanka soteske, življenja v reki in ob njej in sedanjih geomorfoloških
procesov. Prevedena je tudi v nemški in angleški jezik. Zloženka je na voljo na Zavodu za turizem
Kranj.
ZA VPIS EARTHCACHE TOCKE morate izpolniti naslednje naloge:
1. Oglejte si prodišče v kanjonu. Ali je prodišče pretežno enobarvno ali barvasto? Katera barva prevladuje? Ali veste zakaj? Pomislite, kje izvira reka Kokra!
2. Ali v kanjonu prevladuje konglomerat, breča ali mešanica med njima (konglomeratna breča)?
Ali lahko ugotovite zakaj?
3. Ali tudi ob učni poti lahko v reki Kokri opazimo večje odkruške konglomeratne stene?
4. Staro mestno jedro Kranja leži na konglomeratnem pomolu med rekama Kokro in Savo. Če se
sprehodite po mestu, boste na koordinatah N 46° 14.303 E 14° 21.323 videli markatno stavbo, ki
predstavlja odličen primer uporabnosti konglomerata. Napišite za katero stavbo oziroma njen
del gre?
5. Dodatna, neobvezna naloga: fotografirajte sebe ali GPS sprejemnik na dnu kanjona in
pripnite sliko v svoj vpis.
POMEMBNO!
- Preden vpišete obisk Earthcach točke, pošljite odgovor preko gc profila. Takoj potem lahko vpišete obisk EarthCache točke na spletu – ne potrebujete dodatnega dovoljenja. Če ste fotografirali, prosimo, priložite kakšno fotografijo.
- Vpisi brez ustrezne spremljajoče e-pošte, ki vsebuje pravilne odgovore, bodo sprva kodirani in
kasneje izbrisani!
- Vpisi, ki vsebujejo odgovor bodo izbrisani!
THE RIVER KOKRA
Kokra is a Slovenian river, which rises in the Karavanke (mountain range) and discharges as a left
affluent into the Sava river by the city of Kranj. It is 34 kilometers long, it's river basin amounts to 223
square kilometers. Kokra river rises beneath Virnikov Grintavec in the Karavanke (mountain range),
825 meters above the sea-level, west of Jezersko. Kokra river incised a deep narrow mountain valley
between ridges of the Karavanke (mountain range) and Kamnik-Savinja Alps. It runs between
mountains Storžic and Grintavci. The river has nivo-pluvial regime.
Before the outfall to the Sava river in Kranj, Kokra river has cut almoust 30 m deep gorge into a
conglomerate terrace, dating back to the Ice Age – the Kokra river canyon. It is a variegated mosaic of
aquatic and waterside biotopes comprising the river, bank, gravel pit, meadow with the flooded
woods, rock blocks and conglomerate walls.
An Outdoor Educational Path
THE CANYON IN THE ACCUMULATED GRAVEL
A special feature of the Kokra mountain river is its canyon which cut into its own accumulated gravel
alluvia at the end of the Ice Age. The origin and formation of the canyon are connected with tectonic
movements and erosion. The accumulated gravel is called »labora« or conglomerate.
The river carried with it ever new layers of sediments. Under their weight, the gravel in lower layers
condensed, while the rest of the empty space among the boulders was filled by binder. This can be
mineral cement (most often, silica or calcite) which separates itself from the aqueous solution, fine-
grained basis (sandy, clay or marly), or both.
Konglomeratna stena - Conglomerate wall
Depending on the geological structure of hinterland from which a river carries boulders, the mineral
structure of the conglomerate also differs. Mixed amongst themselves are boulders of magma,
metamorphic and sedimentary rock. As to the structure, we differentiate limy, dolomitic and other
conglomerates. A conglomerate is a rock consisting of individual clasts within a finer-grained matrix
that have become cemented together. Conglomerates are sedimentary rocks consisting of rounded
fragments and are thus differentiated from breccias, which consist of angular clasts. Different tipes of
conglomerate consists different size of clasts. Both conglomerates and breccias are characterized by
clasts larger than sand (>2mm).
In some places, the gravel is loosened and cracked due to earth movements. There are holes of
different sizes arising in the rock due to the limestone cement dissolving between gravel stones.
From time to time, parts of the conglomerate walls break off, and the broken parts remain lying on
the slopes or in the river.
Spodmoli in luknje - Rock shelters and holes
In the past, people would produce mill stones, house portals and kerbstones from conglomerate. It
was also used as a building material.
WHAT IS THE GRAVEL PIT IN THE CANYON TELLING US?
A gravel pit is a dynamic river system. Due to constant water activity, the river system continuously
springs up and disappears. Every time you visit it, it can look significantly different. The gravel is
deposited on the inner side of the river bends. Taking a close look, one can see gravel stones of
various forms, sizes, colours and patterns. During their long way from the mountains down the
valley, the sharp pieces of gravel are ground down and smoothed. The Kokra river flows along the
rocks which differ significantly in their geological age as well as in their formation and composition.
Have you ever noticed that gravel pits form a large drop? During heavy rain, the river overflows its
banks, changes the gravel pit and floods the meadows. In the past, there were many flooded woods
in such places, consisting of grey and black alder and poplar trees. However, due to the forest
economy, these woods are gone. The plants growing on the gravel pit are from the pioneer species.
In Kokra, among these species you can find coltsfoot and purple and Resemary Willow tree. These
trees require natural river dynamics, meaning that the gravel is carried away and deposited.
Rastje - Plants
Gravel pits represent a hidden tresure of life which is hardly seen to the naked eye. Take a look into
the covered holes where clear water crayfish and insect larvae are hiding. On the sand, you can see
spiders and hastening tiger beetles. Such a dynamic and variegated area thus represents a shelter
and a home to numerous and in terms of vital necessities extremely variegated flora and fauna.
It is protected as a natural site and part of Kranj’s old town centre. There is an educational trail in the
Kokra canyon. A brochure has been printed, meant primarily for acquainting school groups with the
creation of the canyon, life in the river and waterside as well as the current geomorphologic
processes. The brochure has been translated into German and English. It is available at Tourist Board
Kranj.
TO LOG THIS EARTHCACHE you have following tasks:
1. Look at the gravel pit in the canyon. Is the gravel pit predominantly one or multi-colored?
Which color is prevalent? Do you know why? Consider where the Kokra river rises!
2. In the canyon, does conglomerate, breccia or mixture of both (conglomerate breccia) prevail?
Do you know why?
3. Are there in the Kokra river to be noticed major shivers of the conglomerate wall also along
the educational path?
4. The Kranj old town centre lies at the conglomerate dock between the Kokra and Sava river. If you stroll
through the town, you shall find on coordinates N 46° 14.303 E 14° 21.323 a prominent building, which illustrates an excellent example of the conglomerate’s usability. Write down which building or it’s part is in question?
5. Additional, not obligatory task: take a photo of yourself or your GPS receiver in the canyon
and upload it to your log.
IMPORTANT!
- Before logging, send your answer through my gc profile. 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!