New Zealand's Biggest Ever Sinkhole Just Revealed A 60,000-Year-Old Volcanic Crater

The sinkhole is thought to be the largest in New Zealand. One News New Zealand/YouTube

A massive sinkhole has cleaved the land in two on a dairy farm in New Zealand. Thought to be the biggest sinkhole ever seen on the islands, it is giving geologists a rare glimpse into the heart of an ancient volcano.

The hole has appeared about 15 kilometers (just over 9 miles) south-east of the city of Rotorua, on the north island, and was initially discovered when a farm hand driving a motorcycle at dawn almost ended up in it. Measuring almost 200 meters (650 feet) long and in some places 20 meters (65 feet) wide and just about as deep, it is pretty extraordinary.

“It wasn't until I came down in daylight that I actually saw just how big it was,” said farm manager Colin Tremain, to ABC News. “We'll keep it fenced off as it is to keep stock out, although stock aren't stupid, they're not going to walk into a hole, they can spot danger.”

The appearance of such a massive split in the landscape is likely due to the excessive amount of rain that has fallen on Rotorua over the last few weeks. Over the weekend the region received the highest hourly rainfall, with 51.8 millimeters of water falling over just a single hour on Sunday. To put that into perspective, this is how much usually falls in an entire month.

A state of emergency due to flooding of the community was only lifted yesterday, and it is expected to take months to get the town back on its feet as the water retreats.

It is thought that the hole may have been forming over the last century, as decades of rainfall slowly eroded the underlying sediment. Geologists explained that there are around seven fault lines running across the region, and that as the water percolates through the soil, it preferentially follows these faults, taking the soft limestone with it. The latest deluge seems to have been the final straw, with the huge crack opening up in the ground revealing the cavity that had been formed along this particular fault line.

But geologists hope that it can help give them an insight into this region known as the Earthquake Flat. At the very bottom of the sinkhole, scientists can get a glimpse of the underlying volcanic rock of a 60,000-year-old crater. On top of this, there are at least 10 meters (33 feet) of sediment from when the crater filled with water to become a lake, while the top few meters are thought to be a load of volcanic ash.

The scientists expect that the hole will continue to open up, particularly if there is more heavy rain, and will eventually erode out as it is simply too big to fill.

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