Hiking the red Triassic, we stopped to admire a wide, round, hissing spring that had been bubbling up CO2, methane, and hydrogen sulfide for a hundred thousand years.
In the Pleistocene this area must have boiled like Yellowstone, for all around were the empty vats of dry springs, thirty to sixty feet deep. If you fell in you could never get out—nor, so far off trail, would you be found. The living spring, presumably as deep, was capped with a peaty mat formed by the accumulated sedge roots of millenia, thick enough—we hoped—to support our weight.
We walked across. It trembled subtly under our feet, like an acqueous drum.