Lava and something like a "found kanji." I don't have time to locate my Nelson's kanji dictionary, but I feel confident that there's really a kanji there.
As for the rest, it's lava I exposed in 2011. When I exposed it, it was reddish. But over time, it blackened -- except where I filled a crack with cinders. A couple of weeks ago I cleaned out the cinders, and there was the original color and patina. I should ask a geologist what kind of process masks and then reveals lava color. It's interesting.
My son has just now convinced me to go to Instagram with the HDI. I won't abandon this site, though. Stay tuned.