The hole is about 15 metres across.
Geologist Vitor Lamberto told Luda this kind of phenomenon “is typical” in limestone areas and there are “similar” situations in other places in Portugal, though not as big.
Lamberto said that in these areas there are underground rivers, but when the holes they flow through are too narrow for the quantity of water, some upstream caves fill up and start to dissolve the cave roofs and eventually the roofs cave in, leaving these enormous sink holes.
Fortunately no buildings we on the site and no animals are thought to have fallen in the opening.
This has been an extremely wet spring in Portugal, due to the jet stream and Azores anticyclone being much further south than usual, bringing wet weather into Portugal and cold, dry air into the UK, leading to exceptional heath and moor blazes.