The learning point with this earthcache is to get to know tafoni better,
At GZ, you will be able to observe a holey wall, wall with "wounds" and formation failure which consists of what goes under the name tafoni. You will find that these holes and parts of the stone are somewhat uneven, of different sizes and depths. You will find out what this phenomenon is about by reading through the text below, which gives you a good description of what you see based on what you will be studying here at the location. Keep a close eye on the stone to be able to answer the questions below.
Tafoni
Tafoni is a geological formation that resembles a small cave, cave-in, "wound", formation failure, with a round entrance and smooth, concave walls. Generally defined as small less than 1 cm to large, greater than 1 meter cavity features that develop in either natural or man-made works. Tafoni is often found in cliff sides, hills and rocky areas. Tafoni is most commonly formed in granite, sandstone or sandy limestone and is particularly common in semi-arid to arid desert climates. This formation is easy to recognize because of its honeycomb or "mushroom-like" appearance.
The formation of tafoni typically consists of causes such as freezing-thawing, moisture-drying and salt weathering. Honeycomb weathering, a form of salt weathering, is the most common explanation. It occurs when salt accumulates on the surface of permeable rocks, usually by ocean waves, fog or wind. When the salt water evaporates, it leaves the salt behind. The salt works its way into the stone pores, where it crystallizes and pushes the pores open further. These enlarged rock pores are subjected to further weathering, including the aforementioned wetting-drying and freeze-thaw cycles. After a considerable time, the weathering becomes noticeable in the form of tafoni.
There are other theories that explain the presence of tafoni in coastal areas. It is believed that in addition to salt weathering, molluscs and other marine life can also initiate tafoni. They do this by making small holes in the rocky coastlines, where they attach themselves and extract minerals. The hole grows larger over time until eventually the mollusk, or another organism, falls off. The hole is then left to the elements, such as wind, rain and tides. These work together to create the tafoni formations.
Many explanations have been proposed for the origin of taphoney. They include marine wear; wind corrosion; mechanical weathering as a result of short-term temperature variations; chemical weathering of the interior of the rock (core softening) under a protective crust (case-hardening) followed by mechanical removal of the softened material; biogeochemical weathering of lichens; temperature variations affecting salt efflorescence in coastal areas; and salt weathering. In recent times, geologists and researchers have advocated salt weathering as the primary explanation for the formation of tafoni. Currently, tafonia is considered to be polygenetic in origin, and is the result of complex interaction between physical and chemical weathering processes, which include salt weathering and cyclic wetting and drying.
Weathering is the breakdown of rocks, minerals, soil and other materials by direct contact with air, water (ice), temperature fluctuations and biological organisms. Weathering shapes the landscape together with erosion.
The main difference between weathering and erosion is where the process takes place. As weathering crumbles the rocks in place, the erosive forces remove the loose material. Important factors that affect the intensity of weathering are the type of rock, climate and tectonic setting.
Weathering takes place in situ with little or no movement of the decomposition products. It is common to distinguish between mechanical and chemical weathering, but both can have a biological component, and biological weathering can therefore be considered a third main type. Mechanical and chemical weathering can take place simultaneously and thus reinforce each other. In more extreme environments, such as cold and dry or hot and humid, one main type will tend to dominate.
Erosion, on the other hand, is a process that grinds or breaks down material and also transports the loose material, i.e. the breakdown products. Erosion occurs with the help of various agents (i.e. what drives or maintains a process), such as running water, waves, wind, snow, ice or gravity. The decomposition products are transported by one or more agents and can therefore be deposited at varying distances from the source area.
Mechanical weathering
Mechanical weathering is a pure crumbling of the rocks without chemical changes. Changes in temperature and pressure can lead to cracking and, over time, crumbling of the land surface. Mechanical weathering leads to a reduction in clast or particle size, and tends to dominate in cold and dry environments.
An example is frost blasting, which is a type of frost weathering. Another example is peeling and cracking in areas where there are large temperature differences between day and night. The surface of the rock is heated more strongly than the interior, and tensions arise that lead to cracking.
Chemical weathering
Chemical weathering is particularly linked to the dissolving effect of water (rainwater and groundwater), where acidic water will be most effective. Chemical weathering causes a rock's composition to change near the surface. Certain substances in the rocks dissolve very easily, for example the sodium compounds, while others remain unchanged. Like all chemical processes, chemical weathering is faster at higher than at lower temperatures, and is therefore more pronounced in the tropics, where it is hot and humid. The plant cover also plays a major role because it contributes organic acids.
An example of chemical weathering is rust formation. Iron-containing compounds in rocks can react with water and air, and red-brown colored iron oxide is formed.
To log this cache.
To get to log this cache you will have to visit and answer the questions which are related to the coordinates given the earthcache.
When answers are collected, send them to CO for verification.
You can log immediately after answers are sent CO. If there are any questions about your answers CO will contact you.
Logs without answers to CO or with pending questions from CO will be deleted without any further notice.
Please do not include pictures in your log that may answer the questions.
Questions:
1. Answer the questions below by visiting the coordinates.
A. Observe and study the tafoni at GZ! Estimate the average diameter and depth of the tafoni in mm!
B. 1. How much of the area/wall consists of tafoni, and describe what causes the tafoni to decrease and go over to unaffected parts? 2. Do you see any differences in structure, minerals, colors or smoothness in the area/wall with and without tafoni?
C. Based on what you have studied and observed at GZ, what weathering would you say the holes have arisen from in terms of process and reactions? And is erosion part of the process that has taken place here? Describe in your own words!
2. Take a photo of you, the group or the GPS from the location without revealing any of the answers.
