Pitch Lake is forty hectares of natural asphalt at La Brea, on the southwest coast of Trinidad, and it is firm enough to walk on. Oil rises up a fault from far below, loses its lighter parts at the surface, and leaves the tar behind; at the centre it is 76 metres deep. About a quarter of the crust stays soft, so you cross on a guide's line, over plates of hard pitch and between the pools. That line ends where the surface starts to look wrinkled and freshly poured — the middle, which people here call the Mother of the Lake, and where you are told to go no further. Your boot presses into the crust and it takes the shape the way cool wax would, every toe in relief. Later in the day the print has softened and begun to close over.
Rain gathers in the folds of the pitch into pools that run warm, clear and faintly sulphurous, with gas coming up past you in strings of small bubbles. People climb in for aching joints, and the guides know which pockets have firm ground under them. At the southern edge the lake is a working mine: diggers cut 180 tonnes a day and carry it off for export. Against forty hectares seventy-six metres deep, that is centuries of digging. By the next morning fresh pitch has welled up and smoothed the cuts flat again. The whole thing circulates, very slowly. Old tree trunks work their way up and stand black and half drowned in the tar, and Amerindian tools and even a human skull have surfaced this way. Walter Raleigh caulked his ships here in 1595 and noted that the pitch does not melt in the sun. He was right about the physics: it softens at about twice the temperature ordinary road bitumen takes. The strangest thing it has brought up is water. Microbes live inside droplets sealed in the oil, and the water they live in never fell as rain: it is ancient brine, carried up from deep below along with the pitch.