These are the black sand beaches of Playa Negra, Costa Rica. The photo is of 2 women of my family about to leave footprints these in these sands. Due to their black colour they absorb more heat in the summer than the usual light coloured sand, and at times are too hot to walk on. The black sand is due to erosion of black basaltic lava that flowed out of volcanoes in this region millions of years ago.