The International Information Center for Geotechnical Engineers

Thursday, 17 May 2018 01:00

An enormous sinkhole opened up in New Zealand, revealing an ancient volcano underneath

Sinkholes aren't rare in the area, but this one is especially large, geologists say

A sinkhole 20m (66 feet) deep and 200m (660ft) long opened up last week on a daily farm in the town of Rotorua, New Zealand. Although it appeared overnight, the hole has been forming unnoticed for up to a century, experts believe. The high-intensity rainfall the area experienced the weekend before has accelerated the process, and the phenomenon has captured the attention of volcanologists, as it turned out that the farm was situated above the crater of a dormant volcano. The area is renowned for its geothermal activity, and similar sinkholes are common on the farm.

"The largest I've seen prior to this would be about a third of the size of this, so this is really big.", said GNS Science volcanologist Brad Scott, adding that ‘the cavity would have been present from all the rainfall events over the last 40, 50, 100 years’. Also impressive is his statement that the dirt in the bottom of the sinkhole was "the original 60,000-year-old volcanic deposit that came out of this crater". "Then there's a stack of about 10 to 12 metres of sediment sitting on top of it from lakes that have formed in this crater the top three meters is volcanic ash." According to Scott, there would be further collapse events as part of the erosion process, that will make the hole grow even bigger. 

Adam Milewski, an associate professor of hydrogeology at the University of Georgia, characterized it as a "cover-collapse sinkhole", since it opened after days of intense rainfall, and believes that by studying the material in it, volcanologists might be able to determine how many times the volcano has erupted in its past. "They're making a good situation out of a bad event. The hard part for all of us is that all of the things we generally like to study are in the ground. So when the ground opens up, it offers geologists a rare glimpse in.", Milewski said.

For Paul Wetmore, an associate professor of geology at the University of South Florida, the sinkhole could have been caused by "caves carved through limestone" below the lava that the volcanologists spotted. But he also believes that lava tubes, which are formed after the cooling of flowing lava and are typically left empty when the lava flow stops, could be blamed for the event.

Watch the stunning drone footage below, showing the massive scale of the sinkhole. The drone was also able to enter, for a closer inspection of the volcanic deposits exposed.


Sources: NZ Herlald, TVNZ, Live Science, The Independent


Read 742 times Last modified on Thursday, 17 May 2018 14:25


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