Okay, they are not literally volcanoes obviously, but I didn't know how else to describe them.
It appears that mineral deposits of some sort have accumulated in 5 or 6 spots on my pool floor. The results are little mounds of hard material about 1 inch in diameter and approximately 1/4 to 1/2 inch tall. I've tried knocking them loose with my pool brush and leaf skimmer, but they won't budge.
My guess is that some dirt or rocks somehow got into the pool over the winter and acted as a "seed" for other minerals to attach. My calcium hardness is on the high side due to high evaporation rates here in SoCal, probably over 750 ppm, but I don't have any scaling on the waterline tiles.
What can I do to remove them. They aren't causing any trouble, but I don't want them to grow and/or spread.