A New Zealand farm worker was rounding up cows in the early morning last week when he stumbled upon a huge sinkhole that seems to have torn through the property overnight. According to Yasemin Saplakoglu of Live Science, the crater measures around 655 feet long and 65 feet deep; local experts are saying it is the biggest sinkhole they have ever seen.
The farm, located in the Rotorua district of New Zealand’s North Island, sits atop the crater of a long-dormant volcano. Brad Scott, a volcanologist with the research organization GNS Science, tells TVNZ that he was able to see “the original 60,000-year-old volcanic deposit[s]” at the bottom of the newly formed crater. Speaking to Radio New Zealand, Scott notes that he has never before encountered such a large sinkhole in New Zealand—and he believes the gaping chasm will continue to get bigger.
“This will erode back, the sides will continue collapsing and the hole will open over the next decade or so,” Scott explains.
According to New Zealand’s Earthquake Commission, “collapse holes” are quite common in the Rotorua region, which is filled with soft, pumice-based soils. Water seeping into the ground erodes the soil beneath the surface, creating cavities or tunnels. When a sub-surface cavity gets so big that it cannot support the land above it, the ground collapses into a sinkhole.
The United States Geological Survey notes that the formation of sinkholes typically occurs gradually and imperceptibly. But sometimes, dramatic chasms will appear seemingly out of nowhere.
Sinkholes tend to occur along earthquake fault lines—of which there are several in New Zealand—but recent seismic activity is not to blame for the chasm in Rotorua. As the Earthquake Commission explains, “ash or rocks along faults has been smashed up during movement on the fault over thousands of years, so it is more easily washed away during heavy rainfall.” The North Island had, in fact, been experiencing a long period of record rains, according to Sara Gibbens of National Geographic.
By analyzing the ancient volcanic debris revealed by the sinkhole, scientists can learn more about the area’s geologic past. But Colin Tremain, the farm manager who discovered the chasm, is less than thrilled about the new development; he told the Associated Press that he now has to build a fence around the sinkhole so his livestock don’t fall into it.