Richtis Gorge and Calcareous Tufa
North-side entry to gorge (own photo)
This is an EarthCache, there is no physical container. To log it, you must familiarize yourself with the text below, go to the place indicated by the coordinates and complete the following tasks:
1. Find and observe the calcareous tufa in the Richtis Gorge, what factors do you think influence its formation in this place?
2. Can calcareous tufa be a good building material - why or why not would be?
3. Observe the type(s) of tufa encounter on the hike and why there are different types at different locations (if there are).
4. Take a photo of yourself or your nickname in front of a picturesque waterfall.
The following text may help you with the answers. I invite you to take a walk.
The Richtis Gorge is an extremely picturesque, narrow gorge with a length of about 4 km and a 350 m difference in height between the highest and lowest point. It developed in units of Carboniferous phyllites and quartzites from 360 million years ago. Strong erosion of these formations and various conditions encountered on the way have developed very diverse forms occurring in the gorge. In this Earth Cache, we will look at one aspect closely related to erosion, but still rock-forming - calcareous tufa is common in the Richtis Gorge.
The beauty of the gorge (own photo)
Calcareous tufa – a carbonate rock formed on land as a result of calcium carbonate precipitating from surface waters. Calcite precipitates from fresh waters rich in dissolved CaCO3 – calcium acid carbonate (Ca(HCO3)2). The process of its formation is explained by the following chemical reaction:
Ca(HCO3)2 ↔ CaCO3ℯ + H2O + CO2↑
The formation of calcareous tufa is associated with waters rich in dissolved calcium carbonate, most often encountered in karst areas. There, calcium carbonate is continuously washed out of rock outcrops, as well as through penetration of rock voids in the rock mass. Rainwater absorbs carbon dioxide from the air and soil, creating weak carbonic acid, which dissolves calcite, which builds carbonate rocks. As a result, the water gradually becomes saturated with calcium acid.
Once we have saturated water, specific conditions must still exist for the formation of calcareous tufa. The key one is a sudden change in temperature. CO2 dissolves very well in cold water. When the temperature increases, the solubility of CO2 decreases, while evaporation and the diffusion of gases into the atmosphere increase. This leads to the precipitation of carbonates. We are all familiar with this reaction from the deposition of scale in… household kettles. In nature, such conditions occur when water circulating through the rock mass flows rapidly to the surface in springs. Especially in the initial sections of streams, the bottom, stones, stems or sticks are covered with precipitated calcite mud. The situation is improved by a change in pressure, as well as turbulent water flow. On all kinds of rapids or waterfalls, foamy water and water spray promote faster gas diffusion and, as a result, the precipitation of calcium carbonate. Plants, mosses and algae growing on the bottom and banks of streams also play a certain role. Through the process of photosynthesis, plants assimilate CO2, accelerating the crystallization of carbonates. The precipitated calcite mud lithifies over time, hardens and thickens. Organic material dies and rots, resulting in the formation of pores and rock voids often in the shape of stems and leaves.
Different faces of the calcareous tufa in Richtis Gorge (own photo)
Calcareous tufa is a light-colored rock, from gray to beige. It can occur in a compact form or in a loose form as calcite mud. It shows a low degree of diagenesis, which means that it is not very compact, and additionally very porous, which makes it light. Calcareous tufa is a brittle rock, dusty to the touch. In most cases, it is a monomineral rock - that is, it is made of only one mineral, which is calcite.
There are several types of calcareous tufa, including:
- calcite mud: loose, formed in low-energy water conditions, precipitating from sediment. Often settling around algal thalli and other obstacles.
- limestone tufa: light, highly porous, often brittle limestone derived from the precipitation of calcium carbonate as a result of physiological processes of algae. It is composed of small grains arranged concentrically around thalli.
– travertine: hard and compact in the dry state, with irregular pores, often left over from rotten plant parts. It precipitates both biologically and chemically. It undergoes transformation relatively quickly, the voids are filled with calcite and/or micrite, in larger holes, dripstones similar to those in caves can form. Travertine occurs all over the world and is a popular building material. For example, the façade of St. Peter's Basilica in the Vatican is made of Italian travertine from Tivoli.
– lime sinter: the most compact, non-porous, precipitated exclusively chemically. It builds dripstones in larger travertine voids, for example.
Looking at and touching the calcareous tufa in the Richtis Gorge, we are direct witnesses to the creation of new rock formations. Perhaps it is from this rock you are looking at and touching that someone will build their house in a million years!
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Bibliography:
“Martwice wapienne i trawertyny” – T. Bartuś, AGH
„Geneza i klasyfikacja wapiennych osadów martwicowych” – J. Szulc
https://sitia-geopark.gr/