[Rennes Templar]

Pardon my ignorance, but what the h*#l is that?

[cogitator]

It's a solidified "toe" of pahoehoe lava. As the lava extrudes in the flow, it forms "toes" (kinda like the way that an amoeba moves) as the lava moves forward. Most of the time the toes stay on the ground; for some reason this one caught some air before solidifying.

[cogitator]

Addition to my previous reply; if you click the HVO link at the top, you can see a lot more images of the flows. I checked, and though this looks large in the picture, it's only about 30 cm (a foot) long. [There are some other ways I could phrase that, but I'll desist... ]