Lime-Tuff @ South-Crete

*****

Welcome to the magical world of geology in Crete. Here you can get to know great geologically interesting places and thus a lot about our earth. We love Crete, nature, people and many other things have fascinated us for years. Maybe you already know one or the other Earthcache from us. Today we would like to show you another interesting topic.

Tufa

Is also known as spring lime, spring tuff or stream tuff. It is a young, porous secondary sedimentary rock. Why secondary ? Because primary limestone sediments from different geological eras are re-sedimented after dissolution, weathering or precipitation. One possibility is karstification. In addition to processes of physical weathering, chemical processes of carbonic acid weathering primarily take place during karstification. In the brittle limestone of a more or less developed karst system, carbonated water dissolves the carbonates to the point of saturation. If the lime transported in dissolved form comes under different environmental conditions, it can be deposited again through chemical precipitation. The two processes can be viewed as two different equilibrium states of a reversible chemical process. The other possibility is the precipitation of dissolved lime. Interactions of karst water and carbon dioxide (underground or when re-emerging to the surface) can trigger the process of lime precipitation. Especially in karst caves and after karst springs, considerable amounts of lime can sediment, as the dissolved lime precipitates again under various chemical and physical conditions.

Formation of tufa

The lime from the water is mainly deposited in cold stratified springs (tufa springs). This happens very often in karst areas. There are also a few other factors:

1. a relatively low discharge from the respective source,

2. a relatively large evaporation surface,

3. a favorable corridor of water temperatures,

 4. a change in pressure conditions and

 5. specific ion concentrations.

If karst water flows over moss carpets, algae carpets or colonies of cyanobacteria, large amounts of lime can be precipitated if the organisms remove carbon dioxide from the karst water for their assimilation (photosynthesis). The removal of carbon dioxide increases the pH value of the water and the solubility of lime decreases, the lime precipitates. The lime sediments can grow at rates of 0.01 mm/year for inorganic and up to 20 mm/year for organic co-induced precipitation. The precipitated lime forms a fine-crystalline crust around all relatively dormant small material (sand, small stones, twigs, leaves, ferns, moss, algae slime). Structures or cushions growing upwards and forwards are created by pouring over layers on small waterfalls or steps in stream terraces.

In order to be able to log this Earthcache as a found, go to the listed coordinates. Attention ! Especially on weekends there can be a lot more going on here! Then the arrival or departure will be anything but not easy! The beach and tavernas nearby are very popular and very busy at weekends. During the week it is much more relaxed. You can normally park near the listed coordinates. Opposite the tavern, a small staircase goes down towards the sea. Go down this to the small waterfall (listed coordinates). Answer us the questions asked -before- you log. If something is wrong, we will contact you. We must delete log's without answers. Afterwards you can enjoy at a great natural spectacle. If you swim towards the creek from the beach and put on your diving mask, you can see a great effect of what happens when fresh water meets salt water.

Here the questions:

1. Which (numbers of) factors for the formation of the tufa can you see here on site?

2. What special feature can you see in the area of ​​the waterfall that leads to the formation of tufa?

3. Describe the temperature of the water, does that correspond to the formation of the tufa?

4. What is the growth rate for inorganic precipitation approximately in 100 years?

5. What is the growth rate for organically induced precipitation in about 6 months?

6. Take a photo of yourself in front of the waterfall and attach it to the log or send it with the answers.

Have fun and enjoy crete 😊

EC made by Patchwork-Rudel

Sources: Wikipedia, own observations on site