This Earthcache site is dedicated to the multiple tor outcroppings which you can easily see here; it's a great spot to observe these interesting geologic formations. So what exactly is a Tor? A tor is an exposed rock mass of jointed and broken blocks. To learn more about these particular geologic formations, read on below.
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.
After reading the following information, you should be able to easily 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.
- Based on your observations, is this rock part of the Columbia Basalt River Group? Why / Why not?
- (Optional) Find a nearby tor outcropping that impresses you, and post a picture of it in your log (with yourself if you wish).
Tor Outcroppings
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 (wikipedia.org)
Tors are differingly weathered outcrops of rocks (often found on hilltops) that sometimes seem precariously balanced due to 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 what has 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 (water entering cracks, freezing and expanding, thus making the cracks larger, etc.), often collapsing, with trails of blocks called clitter found down and around the nearby slopes.
Possible Source: Columbia Basalts
This entire region of Oregon and Washington is part of what is called the Columbia River Basalt Group. Millions of years ago, this area was a heavily active vulcanic area. Then, from 17.5 MYA (Million Years Ago) to about 6 MYA, multiple lava flows (much like the ones seen in vulcanically active Hawaii today) covered the landscape at regular intervals, leaving behind thick layers (sometimes several hundred feet thick) of basalt, a hard, fine-grained igneous rock that can vary in color, but in this area is generally a rusty hue, due to oxidation of its iron composition.
There are over 300 unique basalt layers that make up the Comulbia River Basalt Group, and especially in the cliffs nearby the Columbia River, it is easy to distinguish various layers of basalt flows. Some dried in a uniform manner that allowed equal cooling, which produced columnar basalt, which looks like columns of rock stacked tightly together. Much of the rock in this area is basalt, which observation can verify.
An example of columnar basalt outcroppings, from the nearby area (wsu.edu)
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.
- Based on your observations, is this rock part of the Columbia Basalt River Group? Why / Why not?
- (Optional) Find a nearby tor outcropping that impresses you, and post a picture of it in your log (with yourself if you wish).
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