I had intended to take a short trip to northern Virginia this week, to look at Ordovician and Devonian rocks in the Winchester area. The east coast snowstorm put a damper on those plans; I’ve had to dig fossils out from under snowbanks before, and it’s not an experience I’m eager to repeat. Instead, while technically on vacation, I’m at home trying to finish my book chapter before the end of the year.
The images I’ve included in this post have nothing to do with paleontology, but they do present a bit of a geological mystery appropriate to the season. About two weeks ago we had a hard overnight frost in Martinsville. The image at the top is the view through my truck windshield, of the ice crystals that formed on the glass.
Zooming out a bit, you can see that there were actually two types of ice crystals:
Zooming out even more, the real weirdness is apparent; the regions covered by the two types of crystal are defined by the sweep of the windshield wiper blades, with the large crystals covering the area swept by the blades and the small crystals occurring in the unswept areas:
What’s even stranger is that I had not used the wipers in days. My assumption is that the varying amounts of dirt on the different parts of the windshield caused this variation. Perhaps since there was more dirt on the unswept areas, there were more nucleation points for crystals to form, resulting in less room for each individual crystal. I’m not sure about this (mineralogy was not my strongest subject!), so if anyone has an alternate hypothesis feel free to post it in the comments.