After record rainfall fell on New Zealand’s North Island in May 2018, a farm worker noticed that a sinkhole had formed overnight – and yet he couldn’t quite see its size until the sun came up. Then, with the light of day, the worker realized that the Earth had cracked open, creating a fissure that stretched for hundreds of feet and swallowed up pasture roamed by cows.
Sinkholes that make headlines seem to open instantly, but some can actually take thousands of years to form. They commonly appear in areas that have limestone within their terrain. The sedimentary rock is, you see, easily infiltrated and dissolved by rainwater that becomes acidic after percolating through soil – and gathering a bit of carbon dioxide.