Zidine u Stonu

Povijesni dio

Ovdje u Stonu možete vidjeti dosta geoloških fenomena. Glavna znamenitost u Stonu su gigantske zidine koje okružuju Ston i Mali Ston. Zidine su izgrađene kao obrana Pelješca. Nakon stotina godina (zidine su izgrađene u 14. i 15. stoljeću), zidine još uvijek čvrsto stoje na svom mjestu. Sada ih nazivaju i Europskim kineskim zidom.

Zidine su izgrađene od vapnenca, ali vrijeme i priroda su ostavili svoj trag na zidinama. Trošenje je ogrubilo površinu i dalo zidinama njihovu boju. Nakon mnogih oštećenja koja su na zidinama ostavili zemljotresi i ratovi, zidine (a osobitom Stonska utvrda) su renovirane. Renoviranje je provedeno s istom vrstom kamena koja je korištena i u originalnoj izgradnji zidina. Stoga se sada na istoj lokaciji može pronaći stari i novi vapnenac, te se na taj način može lijepo vidjeti utjecaj trošenja na kamen.

Sada ste čuli dosta toga o povijesti lokacije. Vrijeme je za geološki dio priče.

Trošenje

Općenito, trošenje je prirodni proces koji razbija stijene u manje komade. Postoje dvije glavne vrste trošenja – mehaničko i kemijsko. Mehaničko trošenje je uzrokovano prirodnim elementima poput vjetra, vode, te hladnoće / topline. Navedene pojave fizički otkidaju dijelove stijena. Kemijsko trošenje obuhvaća različite kemijske reakcije koje razbijaju stijene. Također, nekoliko je važnih faktora koji utječu na brzinu trošenja u određenom okruženju.

Trošenje se često zabunom poistovjećuje s erozijom, iako se radi o dvije različite vrste procesa. Trošenje se događa na mjestu i nikakvo kretanje nije uključeno u procese trošenja. Stijene se razbijaju, ali ostaju na svom mjestu. Ukoliko dolazi do pomicanja dijelova stijena s njihove početne lokacije, tada se radi o procesu erozije. Erozija podrazumijeva kretanje fragmenata stijena uz pomoć određenih pokretnih agenata poput zraka, vode ili leda. Prema tome, ukoliko je fragment stijene razbijen kemijskim ili mehaničkim putem, ali je još uvijek na svojoj početnoj lokaciji riječ je o trošenju. Ukoliko dođe do pomicanja fragmenata stijena s njihove početne lokacije, tada je riječ o eroziji.

Trošenje

Izvor: Geologycafe.com

Mehaničko trošenje

Mehaničko trošenje obuhvaća različite procese koji uzrokuju fizičko raspadanje stijena bez promjena u njihovom kemijskom sastavu. Nekoliko je različitih vrsta mehaničkog trošenja: termička ekspanzija, drobljenje ledom, aktivnost biljaka i abrazija.

Termička ekspanzija uključuje širenje i skupljanje minerala unutar stijena pod utjecajem promjene temperature. Stijene sadrže različite minerale koji imaju različite stope širenja i skupljanja pod utjecajem promjene temperature, te stoga nagle promjene temperature (npr. uslijed izmjene dana i noći) mogu izazvati pukotine u stijeni, a u konačnici i postupno raspadanje stijene.

Drobljenje ledom predstavlja raspadanje stijena do kojega dolazi uslijed širenja leda. Do njega dolazi kada voda uđe u pukotine u stijeni, te kada se zbog snižavanja temperature voda unutar stijene zaledi. Uslijed navedenoga dolazi do širenja leda, te početne male pukotine postaju sve veće, te u konačnici dolazi do odlamanja dijelova stijene.

Biljke mogu također uzrokovati odlamanje i raspadanje stijena. Korijenje biljaka i stabala može urasti u postojeće pukotine u stijenama. Kako korijenje raste, dolazi do povećavanja pukotina, te u konačnici može doći do odlamanja dijelova stijena.

Abrazija je proces raspadanja stijena do kojega dolazi uslijed trenja. Ovim procesom se komadići stijene otkidaju pod utjecajem drugih fragmenata stijena koi su nošeni vjetrom ili vodom. Fragmenti stijena koji su nošeni vjetrom ili vodom dolaze u izravan kontakt s nepokretnom stijenom i uzrokuju postupno zaglađivanje površine stijene.

Mehaničko vs. kemijsko trošenje

Izvor: Slideplayer.com

Kemijsko trošenje

Kemijsko trošenje obuhvaća procese raspadanja stijena do kojih dolazi uslijed kemijskih reakcija. U tim procesima ne dolazi samo do raspadanja stijena nego i do promjena u njihovom kemijskom sastavu. Procesi kemijskog trošenja su: hidroliza, oksidacija, karbonizacija i izloženost kiselinama.

Hidroliza je proces kemijskog raspadanja stijene do kojega dolazi zbog kontakta s vodom. Do kemijske reakcije dolazi kada voda dođe u kontakt s mineralima iz stijene. Pri tom kontaktu, dolazi do kemijske promjene minerala u stijeni, te zbog navedene kemijske promjene dolazi do slabljenja i u konačnici raspadanja stijene.

Oksidacija obuhvaća reakciju kisika i minerala iz stijene. Stijene mogu biti izložene oksidaciji ako sadrže željezo. Kada željezo iz stijene reagira s kisikom nastaje željezni oksid. S obzirom da željezni oksid nije pretjerano čvrst, kada dođe do oksidacije čvrstoća stijene slabi te lakše dolazi do raspadanja stijene. Stijene koje su izložene oksidaciji su crvene boje jer je željezni oksid također crvene boje.

Karbonizacija uključuje miješanje vode s ugljičnim dioksidom, pri čemu nastaje ugljična kiselina. Ugljična kiselina dolazi u kontakt sa stijenama, te ih pri tome otapa. Jedna od stijena koja je najpodložnija karbonizaciji je vapnenac. Vapnenac sadrži mineral kalcita koji je izrazito topljiv u ugljičnoj kiselini. Karbonizacija je glavni proces stvaranja krškog reljefa i špilja.

Izloženost kiselinama obuhvaća procese s kiselinama različitim od ugljične kiseline. U ovim procesima stijene se raspadaju kada dođu u kontakt s kiselinama. Jedan primjer takvih kiselina koje uzrokuju kemijsko trošenje stijena su kisele kiše. Kisele kiše postaju kisele zbog izloženosti različitim zagađivačima zraka. Kada takve kiše dođu u kontakt sa stijenama dolazi do raspadanja minerala koji čine stijenu. Drugi primjer se odnosi na lišajeve koji rastu na stijenama. Lišajevi stvaraju kiseline, a te kiseline također uzrokuju raspadanje minerala od kojih se stijena sastoji. Do kemijskog trošenja uzrokovanog lišajevima vrločesto dolazi u blizini rijeka i potoka.

Brzina trošenja

Nekoliko je važnih faktora koji utječu na brzinu trošenja stijena. Oni su: (1) izloženost atmosferi, (2) sastav stijene i (3) klima.

Stupanj izloženosti stijena atmosferi može značajno utjecati na brzinu trošenja. Stijene koje su prekrivene zemljom su u manjoj mjeri podložne trošenju jer su manje izložene elementima koji uzrokuju trošenje. Različite stijene imaju različit mineralni sastav, a različiti minerali imaju različit kemijski sastav. Neki minerali u većoj mjeri reagiraju u kontaktu s vodom, kisikom ili drugim elementima, te će se uslijed toga brže trošiti, dok će se drugi minerali trošiti sporije. Također, neki minerali su mekši od drugih, te će i oni biti više pogođeni trošenjem od ostalih. Klima određuje temperaturu i razinu padalina na određenom području, a upravo su temperatura i voda bitni elementi koji određuju brzinu trošenja. U toplim i vlažnim područjima će trošenje stijena biti brže nego u hladnim i suhim područjima.

Tijekom Vaše posjete Stonu trebali biste pronaći odgovore na sljedeća pitanja:

1. Opišite strukturu i izgled kamenja u zidinama
2. Svojim riječima opišite na koji način je trošenje utjecalo na izgled zidina. Je li trenutni izgled zidina nastao u većoj mjeri od kemijskog ili od mehaničkog trošenja?
3. Promotrite utvrdu koja je nedavno obnovljena. Opišite razliku u boji i površini utvrde kada se usporedi sa zidinama. Imajte na umu da je ista vrsta kamena (vapnenac) korištena u oba slučaja.
4. napravite sliku svoje ili osobne pripadnosti zajedno s komadom papira na kojem je ispred zidova kamena napisano vaše ime

Molim, pošaljite odgovore na pitanja. Ne morate čekati na moj odgovor. Ako bude problema s Vašim odgovorima, ja ću kontaktirati Vas. Ali ne vjerujem da će biti nekih komplikacija ;)

Volio bih vidjeti fotografije Vas kod Stonskih zidina. Naravno, to nije zadatak za logiranje. Ako ne želite, ne morate. Ako želite, meni će biti drago ;)

Nadam se da ćete moći naučiti nešto o ovom mjestu. Hvala Vam na posjeti!

Izvori:

Hvala GCEdi koji mi je puno pomogao s ovim geocacheom. Geološki dio sam dobio sa jednog od njegovih geocacheva. On je i preveo ovaj EarthCache na hrvatski. Njegovi izvori za geološki dio su:

1. Alecia M. Spooner, Geology for Dummies, Hoboken: Wiley Publishing, Inc., 2011.
2. Edward J. Tarbuck, Frederick K. Lutgens, Dennis G. Tasa, Earth: An Introduction to Physical Geology (10th Edition), New York: Pearson, 2010.
3. Wikipedia.org
4. Geologycafe.com

The Walls of Ston

The History Part

Here in Ston you can see a lot of geological phenomena. The Main sight of Ston are the gigantic Walls surrounding both Ston and Maliston. They were built as defenceline for the island of peljesac. After hundrets of years (they were built in the 14^th and 15^th century), the walls still stand high. They are now called the “European Wall of China”.

The walls were originally build with limestone, but the time and nature take their toll on the walls. Weathering has roughened the surface and gave the stone and the wall its colour. After a lot of damage on the walls that was caused by earthquakes and the wars that happened since the building of the walls, the walls and especially the forts of Ston get a renovation. The construction is made with the same kind of stone that was used for the original building. So you have old and new lime stone on the same place. This is very good to see the effects on the stone caused by erosion.

Now you heard a lot of history about the side. Now its time for the Geological Part.

Weathering

In general, weathering is natural process that breaks down rocks into smaller pieces. There are two main types of weathering – mechanical and chemical. Mechanical weathering is caused by the elements of nature such as wind, water, and cold / heat. These elements physically break off pieces of rock. Chemical weathering includes various chemical reactions that break down rocks. Also, there are several important factors that affect the rate of weathering in specific environment.

Weathering is often confused with erosion, although they represent two different types of processes. Weathering occurs in place and no movement is involved in weathering. Rocks are broken down but they stay on their location. If rock fragment is moved from its location then the process is called erosion. Erosion involves movement of rock fragments by some flowing agent such as air, water or ice. So, if a rock fragment is loosened, chemically or mechanically, but stays put, it is weathering. Once the rock fragment starts moving, it is erosion.

Weathering

Source: Geologycafe.com

Mechanical Weathering

Mechanical weathering includes various processes that cause physical disintegration of exposed rock without any change in the chemical composition of the rock. There are several different types of mechanical weathering: thermal expansion, frost shattering, plant activity and abrasion.

Thermal expansion includes expansion and contraction of minerals within rocks under different temperatures. Since rocks contain different minerals with different rates of expansion and contraction when exposed to changes in temperature, rapid temperature changes (e.g. change between day and night) can create cracks within rocks and finally cause gradual breakdown of rock.

Frost shattering includes breakdown of rocks due to the expansion of ice. It happens when water enters into cracks that exist within rocks. When temperature drops water freezes and expands and initial small cracks become larger and eventually can break off portions of the rock.

Plant activity can also break down rocks. The roots of plants and trees can grow into cracks that exist within rocks. As roots grow in size, they widen the cracks and can cause pieces of the rock to fall away.

Abrasion includes the process of breakdown of rock by friction. With this process rocks are scraped away by other loose rock and mineral fragments that are carried by air or water. These loose fragments come in direct contact with the stationary rocks and cause gradual smoothing off the surface of rocks.

Mechanical vs. Chemical Weathering

Source: Slideplayer.com

Chemical Weathering

Chemical weathering includes process by which rocks are broken down by chemical reactions. In these processes, rocks are not only broken down into smaller pieces, they are also chemically changed. Types of chemical weathering processes are hydrolysis, oxidation, carbonation and exposure to acids.

Hydrolysis is process that involves chemical breakdown of material when it comes in contact with water. In case of chemical weathering of rocks, chemical reaction happens when rainwater comes in contact with minerals from rocks. As rainwater comes in contact with minerals they are chemically changed and that change weakens the rock.

Oxidation involves reaction of oxygen and minerals within rock. Rocks can be exposed to oxidation if they contain iron. When iron from rock reacts with oxygen it forms iron oxide. Since iron oxide is not very strong, when a rock gets oxidized, it is weakened and crumbles easily, allowing the rock to break down. Rocks that are exposed to oxidation look red because iron oxide is red in color.

Carbonation includes mixing of water with carbon dioxide and creation of carbonic acid. Carbonic acid comes into contact with rocks and dissolves them. One of the most vulnerable rocks to carbonation is limestone as it contains mineral calcite that is very soluble in carbonic acid. Carbonation is the main process responsible for the creation of caves.

Exposure to acids involves acids different from carbonic acid. In this process rocks are broken down when they come in contacts with such acids. One example of acids that cause chemical weathering of rocks includes acid rain. Acid rain becomes acidic by various pollutants in air and when such acid rain falls to the ground and comes in contact with rocks it break down the minerals within rocks. Another example includes lichens that grow on rocks. They also produce acid and that acid can break down minerals within rocks. Chemical weathering caused by lichens is very often near rivers and streams.

Rate of Weathering

There are several important factors that can affect the rate of weathering. They are: (1) exposure to the atmosphere, (2) composition of rock and (3) climate.

The degree of exposure of rocks to the atmosphere can significantly affect the rate of weathering. Those rocks that are covered by ground are less affected by weathering because they are less exposed to elements that cause weathering. Different rocks have different mineral composition and different minerals have different chemical composition. Some minerals are more reactive when mixed with water, oxygen or other elements and will weather more rapidly, while others will weather slowly. Also, some minerals are softer than others and they will be more affected by weathering than others. Climate affects the temperature and rainfall of a region. Both temperature and water are important elements in weathering. Warm, humid environments will have higher rates of weathering than cold, dry environments.

While visiting Ston you should find the answers for all these questions:

1. Describe the Struckture and the look of the Stones in the Wall
2. Describe in your own words how weathering influences the look of the wall. Is it more chemical or more mechanical weathering that caused the look of the wall?
3. Look at the Fort. It is newly renovated. Describe the difference of the Color and Surface on the Fort compared to the Wall. Keep in mind that the same stones (limestone) were used for both.
4. Make a picture of you or a personal belonging together with a piece of paper with your name written on it in front of the walls of ston

Please send me the answers of the questions. You don’t have to wait for an answer. If there is a problem with your answers I will contact you. But I don’t think that there will be any complications ;)

I would love to see pictures of you at the Walls of Stone. This is of course no logging task. If you don’t wan’t, you won’t have to. If you like, I would appreciate it ;)

I hope you could learn something about this place. Thank you for your visit!

Sources:

Thanks to GCEdo who helped me a lot with this Geocache. I got the geological part from one of his geocaches. He also made the Croatian translation for me. His sources for the geological part were:

1. Alecia M. Spooner, Geology for Dummies, Hoboken: Wiley Publishing, Inc., 2011.
2. Edward J. Tarbuck, Frederick K. Lutgens, Dennis G. Tasa, Earth: An Introduction to Physical Geology (10th Edition), New York: Pearson, 2010.
3. Wikipedia.org
4. Geologycafe.com

Die Mauern von Ston

Der geschichtliche Teil

Hier in Ston könnt ihr viele geologische Phänomene entdecken. Die Hauptatraktion von Ston sind jedoch die gigantischen Mauern die Ston und Maliston umgeben. Die Mauern wurden zum Schutz der Halbinsel Peljesac gebaut. Nach Jahrhunderten (die Mauern wurden ursprünglich im 14. und 15. Jahrhundert gebaut) stehen die Mauern immernoch. Sie werden auch die "europäische Chinesische Mauer" genannt.

Die Mauern wurden aus Kalkstein errichtet. Die Zeit forderte ihren Tribut von der Mauer. Durch Verwitterung wurde die Mauer rauer und dunkler. Nach vielen Schäden durch Erdbeben und Kriegen werden die Mauern und das Fort von Ston renoviert. Für die Renovierung werden die selben Steine hergenommen wie damals beim Bau. Du findest hier also früher und neu verbauten Kalkstein. Dadurch lassen sich sehr gut die Folgen der Verwitterung erkennen.

Genug mit der Geschichte, jetzt gehts zur Geologie.

Verwitterung

Generell ist Verwitterung ein natürlicher Prozess der große Steine in kleiner zerbrechen lässt. Es gibt zwei Typen der Verwitterung: mechanische und chemische Verwitterung. Die Elemente verursachen die mechanische Verwitterung. Wind, Wasser und der Wechsel zwischen warm und kalt bringen die Steine zum brechen. Viele chemische Reaktionen der bestandteile der Steine verursachen die chemische Verwitterung.

Verwitterung und Erosion werden often miteinander verwechselt obwohl der Prozess sehr unterschiedlich ist. Verwitterung findet ohne eine Veränderung des Ortes des verwitternden Gegenstandes statt. Steine zerbrechen, bleiben aber größtenteils an ihrem Platz. Verlassen die gebrochenen Steine aufgrund weiterer Eiflüsse ihren ursprünglichen Platz spricht man von Erosion. Die Bewegung kann durch die Luft, Wasser oder Eis verursacht werden. Zusammengefasst: Das zerbrechen der Steine ist Erosion. Kommt dann "Bewegung" ins Spiel nennen wir das ganze Erosion.

Verwitterung

Quelle: Geologycafe.com

Mechanische Verwitterung

Die mechanische Verwitterung umfasst verschiede Prozesse die physikalischen Zerfall von entblöstem Stein bewirken, ohne dabei die chemische Zusammensetzung des Steins zu verändern. Es giebt hierbei viele verschiedene Typen: Thermale Expansion, Frostschäden, Pflanzliche Aktivitäten und Abrasion (Abtragung von Gesteinsschichten)

Thermale Expansion: der Einfluss von Hitze auf verschiedene Bestandteile des Gesteins. Unterschiedliche Ausdehnung der Bestandteile führt zum zerbrechen des Steins.

Frostschäden: hierbei spaltet gefrierendes, in das Gestein eingedrungenes Wasser das Gestein.

Planzliche Aktivitäten: die Wurzeln von Pflanzen zerteilen bei ihrem Wachstum das Gestein.

Abrasion: Reibung durch andere Gegenstände, Luft und Wasser.

Abrasion includes the process of breakdown of rock by friction. With this process rocks are scraped away by other loose rock and mineral fragments that are carried by air or water. These loose fragments come in direct contact with the stationary rocks and cause gradual smoothing off the surface of rocks.

Mechanische vs. Chemische Verwitterung

Quelle: Slideplayer.com

Chemische Verwitterung

Hierbei handelt es sich durch chemische Vorgänge die die Steine zerbrechen lassen. Hierbei verändert sich auch die chemische Zusammensetzung des Gesteins. Die Vorgänge heisen hier: Hydrolyse, Oxidation, Karbonisierung und Zersetzung durch Säure.

Hydrolyse: eine Reaktion von Wasser mit den mineralien im Gestein. Durch die Reaktion wird der Stein geschwächt.

Oxidation: eine Reaktion der Luft mit den Bestandteilen des Gesteins. Das beste Beispiel hierfür ist Rost bei Eisenerzen.

Karbonisierung: durch die Vermischung von Wasser und Karbon Dioxid wird Karbonsäure erzeugt. Diese zersetzt das Gestein.

Zersetzung durch Säure: Natürlich Säuren greifne bestandteile des Gesteins an und zersetzen diese.

Stärke der Verwitterung

Es giebt eine Faktoren die die stärke der Verwitterung beeinflussen. Diese sind der Zugang zur Luft, die Zusammensetzung des Gesteins und das Klima des Ortes.

Je stärker das Gestein der Luft ausgesetzt ist desto schneller verwittert es. Je nach Zusammensetzung des Gesteins ist es mehr oder weniger anfällig für eine der oben genannten Vorgänge der chemischen Verwitterung. Das Klima macht den Unterschied bei der Temperatur und dem Wetter. in warmen, feuchten Gebieten ist die Verwitterung stärker als in kalten, trockenen Gebieten.

Während deines Besuchs in Ston solltest du folgende Fragen beantworten können:

1. Beschreibe die Oberfläche und Farbe der Steine in der Mauer
2. Beschreibe wie die Verwitterung das Aussehen der Steine beeinflusst hat. Ist es eher chemische oder mechanische Verwitterung?
3. Schau dir nun das Fort an. Es wurde frisch renoviert. Beschreibe den Unterschied der frischen, wenig verwitterten Steine zu den alten verwitterten Steine. Denk daran: es wurde das selbe Gestein verwendet.
4. Macht ein Foto von euch oder einem persönlichen Gegenstand und einem Zettel mit eurem Namen vor der Mauer von Ston

Sendet mir eure Antworten einfach zu. Ihr dürft sofort loggen. Ich melde mich dann sobald ich eure Antworten gelesen habe, aber ich denke dass es keine schwierigkeiten geben sollte. ;)

Ich würde mich sehr über Bilder von Euch an der Mauer oder dem Fort freuen. Das ist natürlich keien Aufgabe. Wenn ihr nicht wollt müsst ihr nicht, aber wenn ihr lust habt würde ich mich sehr freuen :)

Ich hoffe ihr konntet einiges über diesen Ort lernen. Danke für euren Besuch!

Quellen:

Danke an GCEdo der mir sehr viel bei diesem Earthcache half. Der Geologische Part stammt nahezu komplett von Ihm. Außerdem verdanke ich ihm die kroatische Übersetzung ohne die dieser Earthcache nicht sein könnte. Edos Quellen für den geologischen Teil waren:

1. Alecia M. Spooner, Geology for Dummies, Hoboken: Wiley Publishing, Inc., 2011.
2. Edward J. Tarbuck, Frederick K. Lutgens, Dennis G. Tasa, Earth: An Introduction to Physical Geology (10th Edition), New York: Pearson, 2010.
3. Wikipedia.org
4. Geologycafe.com