If any technical terms are likely to be remembered by anyone exposed to a bit of geological education, amongst them will be two that are Hawaiian Polynesian words: pahoehoe (‘pa hoy hoy’) and aa (‘a ah’). The first slides around the palate wonderfully while the latter give a sort of worrisome feel as if a large weight is about to land on one’s toes. Aa is lava with a blocky, broken and jagged surface, whereas pahoehoe refers to lava with the appearance of a freshly set torrent of toffee. November’s Picture of the Month is of basaltic lava that looks like it is chewable.