Mystery (to me) rock

[hikeritz]

It's a long shot, but does anyone know the story of this rock? It's in the middle of the Hancock Notch trail (or perhaps the Cedar Brook trail). I noticed it while hiking back to my car after doing the Hancock Loop. Is it natural, or an artifact from the lumber operations? Perhaps it served as the base for some piece of equipment? It's basically flat (other than the radiating lines), and about a meter in diameter.

 

[TCD]

IIRC, an earlier thread explained that this is an artifact from blasting.

 

[peakbagger]

It is artifact from logging although Galehead hut has what I expect are reproductions used to make the flat patio area up front. If the rock was sticking up in an intended haul road and could not be easily moved, a vertical hole would be drilled in the top of the rock down to roughly the level of the ground around the rock. A stick of dynamite would then be dropped down the hole and lit. If things went well the result would be as pictured. A similar effect can be obtained less dramatically using positive coefficient of expansion grout (AKA slow dynamite). The same hole is drilled but instead of dynamite, a the grout is mixed up and poured down the hole. It then sets overnight and in the morning there is a similar result. Reportedly if dynamite was not available in very cold weather water could be poured down the hole and the water would freeze from the outside of the hole inwards and would split the rock. The same approach works with concrete as long as there is no reinforcing bar or mesh in it. Rock is great in compression loading but lousy in tension.

BTW, dynamite was far more readily available in the past, it could be bought at a hardware and farm supply store. It was a pretty standard "tool" for loggers. During the late spring when logging was suspended, the companies that did river drives would send out crews to straighten out the stream beds they used for driving and remove big boulders that might cause a log jam, they used a lot of dynamite but its less obvious as the trails dont run down stream beds. If there was a log jam, dynamite was also used to get the logs moving again.

A good resource on the history of logging practices in the region is this book Tall Trees Tough Men. https://www.amazon.com/Trees-Anecdotal-History-Logging-Log-Driving/dp/0393319172

 

[hikeritz]

Very cool. Thanks for responses.

 

[David Metsky]

It is artifact from logging although Galehead hut has what I expect are reproductions used to make the flat patio area up front.

Yes, the ones in front of Galehead Hut were from construction, not logging.

 

[nartreb]

If my memory can be trusted, there are a couple of places where dynamite was used on a hiking trail, to create a resting spot in the middle of a steep slab. I seem to recall one in the middle of a traverse near the summit of Chocorua, i.e. the Liberty trail, above the cabin.