I haven't posted any mystery photos for a long time, but here is an intriguing pattern I caught yesterday. I know how y'all hate a lack of context, so here it is: I was at Bumpass Hell in Lassen Volcanic National Park.
So, what is going on here, and what materials are involved?
I have posted a video of this on Facebook, and I think you can access it here without having to sign up with Facebook:
POSTSCRIPT (9/26): This is a boiling mud pot. The magma providing the heat is at a depth of three miles or so, and groundwater seeping into the crust is heated to beyond boiling, and a vast steam reservoir has developed beneath Bumpass Hell. The steam condenses to hot water near the surface, but is charged with hydrosulferic acid, which does a serious number on the andesite lavas underlying the area. The rock is turned to clay, which forms the gray stuff in the mudpool. The black swirls are actually finely divided iron sulfide, the mineral pyrite. That's right, fool's gold! If you have had a basic class in geology, you may remember that pyrite is black in powder form (the streak). The patterns are hypnotic to watch.