Note: This is an Earthcache. Put simply, that means it is not a traditional cache, but its purpose is to help educate those who find it about some geologic aspect of the area they find themselves in. To log this cache, you will NOT be looking for a typical geocache container (in fact, there IS no container to find). Rather, to prove you were here and learned something you'll need to find the answers to the given questions (found at the end of this description), which you will then email me, the owner (this is the same process for ALL Earthcaches).
So go ahead and log your experience while here, submit photos, etc., but email your answers to me (not in your visit log) to get credit for "finding" this cache. If it seems too complicated, don't sweat it too much (as long as I can see that you made an honest effort to answer all of the questions, that is fine). Remember that the purpose of this is to learn something, and most importantly, to have fun! Also, feel free to email me with any questions you may have, I'd be happy to help.
Note: This cache is accessible from the road's right of way; there is no need to cross any fences you may see to get this cache; simply park at the designated areas to observe the outcroppings.
Tor
The word itself comes from Celtic (meaning hill), and in fact if you ever visit Great Britian, you can see many such examples of this landform with the word 'tor' included even in the name.
Right: Helman Tor, found in Cornwall, Great Britain.
Tors are weathered outcrops of rocks (usually found on hilltops) that seem precariously balanced due to the erosion of the rock which once surrounded them. Joints and cracks that appeared in the original solid rock were attacked by rainfall and a variety of mechanical weathering. The rock that is now visible is that which remained uneroded--for the time being at least, as eventually these rocks will also weather and erode away as well.
Tors may develop in a range of different rock types including granite, volcanic rocks, metamorphic rocks, & hard sedimentary rocks like quartzite or sandstone. Formation processes and ages can vary.
Formation
One theory for their formation says that tors start out as solid bedrock. At some point, the bedrock becomes exposed, and then chemical and physical weathering processes go to work. Even before it is exposed however, other weathering processes may occur, breaking down the bedrock within the earth. Once exposed, the harder elements persist, while the softer more weathered material is eroded away.
Bedrock often has naturally occuring joints in it, where the bedrock is cracked. Where these joints are closely spaced, the larger crystals in the rock readily disintegrate to form a sandy regolith/gravel. This is readily stripped off by solifluction or surface wash when not protected by vegetation. In desert environments, flash floods often perform this function.
Where joints happen to be unusually widely spaced, core blocks (hard solid remnants of the bedrock) can survive and escape above the weathering surface, developing into tors. These can be monolithic, but are more usually subdivided into stacks, often arranged in avenues. Each stack can comprise several tiers or pillows, which may become separated: sometimes these pillows will weather away until they are just balanced on top of other rocks; rocking pillows (rocks that can be easily rocked back and forth) are called logan stones. These stacks are vulnerable to frost action, often collapsing, with trails of blocks called clitter found down and around the nearby slopes.
Constant Weathering
Weathering is a constant process. Tors are continually subjected to weathering and erosion. One of the most destructive weathering influences on tors is Frost Action, which occurs when water gets inside the rocks, then freezes and expands, and causes the rock to split apart. This further breaks apart the harder stones that make up the tor, and eventually the tor will weather away too.
Right: Frost action example.
Water can also cause chemical weathering. Water can bring all sorts of different minerals along with it, which can chemically react with the stone and minerals therein. These processes can also weaken the rock, and lead to weathering, flaking, etc.
Biological weathering is another possibility. Creatures such as snails, plants, fungus, etc. often secrete different chemicals and acids into the environment around them, which can weaken the rock. Other forces, such as water, wind, etc. can then more easily weaken and weather and erode the rock. The nearby lichen is a possible candidate, as are other organisms that may grow along the surface. Additionally, plants growing can pry the rocks apart with their roots, a type of physical weathering.
Another destructive force is salt weathering. Basically, the salt can arrive on the rock in a number of ways; it may be in the nearby soil, and rain or wind can deposit it on the surface of the rock. Sometimes the salt may originate in the rock itself.
However it gets there, once there it will eventually crystallize. The arrival of water will help catalyze the formation of salt crystals (which grow and expand), thus causes stress to the rock around the salt, thereby flaking off grains and pieces (much like frost action).
Above Left: Another fine example of a tor, near Kisuma, Kenya.
Conclusion
Although tors are magnificent, they wouldn't exist without weathering. Ironically, weathering is what will eventually lead to their demise as well. I hope that in visiting this earthcache, you've learned something new. Thanks for visiting!
In conclusion, remember: to log this cache, use the following info, your surroundings and head to answer the following questions. Email me the appropriate answers (don't post them in your log, or per Earthcache guidelines your post will have to be deleted), and most of all, have fun!
- Pick a nearby tor outcropping. Describe its size, number of tiers, rock composition, etc. Is its composition the same as the other tors you can see nearby? What does this confirm?
- What is a "pillow"? Describe the tallest stack of "pillows" that you can see.
- Based on your observations, what weathering processes do you think helped create these tors? Will they continue? Why / why not?
- (Optional) Find a nearby tor outcropping that impresses you, and post a picture of it (with yourself if you wish).
This cache was created by an
