Friday, July 18, 2014

Geo 730: July 18, Day 564: High Noon at Interzone

I'll be taking a few days' break from Quartzville to enjoy a spontaneous bit of art that happened at Interzone starting on Tuesday. Every hour, on the hour, IZ denizen Tim snapped a chalk line on the left edge of the shadow cast by the street lamp/telephone/power pole on the northeast corner of 16th and Monroe. Then the lines were bolded and times colored in with sidewalk chalk by Heidi and Erin. Shea drew a silhouette on the two o'clock line, which is the one most parallel to the street. This was shot within a minute of noon; for the time being, it's surprisingly accurate.

Where's the geology in this? If you've followed this blog at all, you know my attitude is that it's all geology, and this is no exception. Under the "12" is asphalt, a mixture of petroleum products, sand and gravel. Under my shadow and in the upper right is concrete, made of lime (CaO) (which in turn is limestone (CaCO3) heated to drive off the CO2) mixed with clay, to which water, sand and gravel are added and allowed to set. The chalk itself is either the same composition as limestone (true chalk) or gypsum (which is softer and easier to work with). These materials are normally powdered, some clay added for a higher degree of consistency and hardness, then pigment and binder added. The result is then molded into the cylindrical form in which we are accustomed to using it.

At a more esoteric level, we're looking at an intersection of geology, geography, horology, and human history. I'll get back to this tomorrow, but I'll leave with a comment and a couple questions: the streets in this area run roughly north-south. Why is the sun at noon casting a shadow so far to the west? Wouldn't you expect the shadow to be falling northwards, roughly parallel to the street, rather than across it?

Photo unmodified. July 18, 2014. FlashEarth location.

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