Welcome to a beautiful El Dorado Trails Earthcache. Today you will be learning about weathering and how that effects geological features and various rocks. For the part of the trail, on the east side you should see a nice little rock face or outcropping along the trail. This is where your observations will be made. Following you will find the logging requirements for this earthcache followed by the geological lesson on weather, more specifically on chemical weathering. So I hope you enjoy and have a chance to learn a little something new.
Logging Requirements:
- Who is in your group? How many and cacher names. Only one set of answers need to be sent for the group.
- Describe the rock face (as best you can) focusing on color, texture, and any little features you might see.
- In your own words, briefly describe what chemical weathering is.
- Based on the descriptions of chemical weathering below, and looking at the rock face here, which type of chemical weathering is happening on these rocks? Could there be more than one type happening?
- What type evidence of chemical weathering are you observing on the rocks?
- OPTIONAL: Take a picture with the rock feature at ground zero (selfie, pic with personal item or geocaching name, or a good scenic view). Picture is not required, but they are nice, so please capture the joy of the trek with a picture in your log.
Feel free to log this cache as found once you have sent your answers. If there is a problem or your answers are way off I will reach out and give you a chance to correct the issue. Logs without sent answers or if issues aren’t addressed after contact may be deleted. This is an earthcache and you have to interact and do the lesson, to the best of your ability, but have some fun, be creative, and give it your best effort and you will do fine.
Lesson:
What is weathering? Weathering is the deterioration of substances (rocks, soils, minerals, crystals, wood, artificial materials, etc.) through contact of corrosive elements like: waters, wind, acids, gases, light, biological organisms and so on. Weathering happens on-site with little movements involved, and it is different from erosion which involves transportation and movement of rocks through various agents like water, wind, snow, gravity, etc.
The weathering process is either physical or chemical. Physical weather can be mechanical in nature which would be cause by things like freezing, wind, sand, rain, or other natural forces. It could also be biological in the form of plants and/or animals growing in or through rocks, burrowing, nesting, and so on. Chemical weather is caused more by rocks undergoing chemical reactions and forming new minerals. Chemical weather can also be biological in nature when certain organisms growing on or in the rocks causes chemical changes to take place.
Our focus here will be on chemical weathering. Note, you may see evidence of more than one type of chemical weather here, but also, all along El Dorado Trail you will see these various forms of weathering. My other El Dorado Trails earthcache: GCAM69W - This Extraordinary Metal focuses pretty exclusively on chemical weathering cause by oxygen. For this cache, we are going to focus on the chemical weathering happening just at this location.
Chemical Weathering from Water:
Water is a powerful force and it can cause both mechanical and chemical weathering to occur. Mechanical weathering would occur from water running over or dripping onto the rocks over long periods of time. Chemical weathering from water occurs when the water dissolves minerals within the rocks, producing new compounds as a result. This is called hydrolysis. For example, in granite hydrolysis could/might dissolve the feldspar crystals within the rock causing a chemical reaction resulting in the formation of clay. Clay then weakens the rock making it more brittle. Water can also dissolve calcites in caves causing the formations of stalagmites and stalactites over time. Chemical weather from waters can change the shape of rocks, but it can also change the composition of the water as well, like making water salty over time.
Chemical Weathering from Oxygen:
Oxygen is a reactive element. The process through wich oxygen reacts is called oxidization, and one big and very visible example is rust formation, cause by oxygen reacting to iron in the rocks and sol, oxidizing into iron oxide (rust) changing it to an orange or red color. Red clay we tend to see around the El Dorado County area (and along El Dorado Tails) would be caused by iron in the soil oxidizing and giving the clay that red color (this would actual be both water and oxygen based weathering). Iron oxide is also more fragile, or these rocks are more fragile and you might notice more breaks or sheet formations, especially in larger rock formations.
Chemical Weathering from Acid:
The harsh and abrasive effects of acids. Hydrolysis can have a byproduct when the minerals are altered, acids. Acids can also be produced when water reacts to atmospheric conditions, making the water more harsh and abrasive to the rocks it comes in contact with. Acid on minerals creates a solution weathering. When carbon dioxide reacts with water it creates a common, weaker acid called carbonic acid (carbonation) which can play a part in the formation of caves and sinkholes. Calcite in limestone also dissolve under acidic conditions, which can create open spaces.
Chemical Weathering from Organisms:
Biological organisms can cause chemical changes too. Organisms might cause chemical reactions within minerals in order to obtain minerals from the rock and/or soil, and many chemical changes are possible. Think of it like the organism digesting the rock to turn the minerals into consumable resources needed for survival…in other words, organisms got to eat. Lichens are a great example of organisms causing chemical weathering in rocks. Lichens are kind of a mix between algae and fungi, and they produce weak acids that eat away at and dissolve the rock they grow on. These acids are capable of removing metal ions from bare rock surfaces, like aluminum and silicon. Plant roots are another source of chemical weathering. As the roots expand into the rock acids can then change the minerals they come in contact with. Plant roots also can change soil chemistry through the use of carbon dioxide. With roots also come potential for fungi as well, another potential source for chemical weathering. Fungi living in a symbiotic relationship with the plants/trees they grow on can work to breakdown minerals in the rock to feed back to the plant. Animals can also cause chemical weathering through excretions. For example, bat guano contains reactive chemicals that can breakdown and effect minerals. Humans have major effects as well, through mining, pollution, farming, all things that can lead to changes in the composition of rock and soil over time.
Here Endeth the Lesson:
Those are the four major types of chemical weathering, now be observant and see what observations you can make at this location. What kinds of chemical weathering do you see (or think you might see)? Good luck and I hope you had a little fun and learned a little something.
Parking:
There are no fees for the parking area referenced for hiking this trail, but parking closes in the evenings, so plan accordingly, parking after dark could result in towing, be aware.
Sources:
4 Types and Examples of Chemical Weathering
Wikipedia – weathering (geology)
GC84QZR - Chemical Weathering at Dowdell's Knob
Thekingofbattle (geocacher helped me answer questions and come up with ideas and shared his earthcache on the topic as well to help me focus on ideas)
How To Write an Earthcache: Part I, Part II, Part III