Why a Massive Sinkhole Tore Open in New Zealand

106

New Zealand’s newest sinkhole may be one of its largest. It extends down more than six stories. From end-to-end, it measures just about the length of two football fields. The sinkhole is so large it even exposed 60,000-year-old volcanic soil.

New Zealand volcanologist Brad Scott told a local news outlet it was the largest sinkhole he had ever seen and that it had potential to get even bigger.

The feature appeared on the country’s North Island after a long period of record heavy rains. A local farmworker rounding up cows discovered the opening, narrowly avoiding falling into it while riding his bike. Speaking with New Zealand’s Newshub outlet shortly after the sinkhole appeared, farm manager Colin Tremain said he plans to erect a fence to prevent cows from falling in.

It’s not the first sinkhole to recently open up in the region. Nine additional sinkholes have formed there in the past few years.

New Zealand has several major fault lines running the length of the country, and sinkholes are thought to be more likely to occur near fault lines where soluble rocks wash through. The new sinkhole opened up over pumice terrain, but it’s only one of many sites around the world where the ground is prone to collapsing underfoot.

Where Sinkholes Happen

According to the U.S. Geological Survey, sinkholes open up when groundwater doesn’t drain from the surface and dissolves the rock lying underneath. Limestone and salt beds are often the sources of sudden sinkholes. While New Zealand’s new sinkhole has tall, vertical walls that make it look more like the Grand Canyon, some sinkholes form a rounder bowl shape.

Their formations are often dramatic. As water erodes the ground underneath sinkholes over time, the weight of the land that remains on top eventually becomes too much, and it collapses. In regions where people have built homes or businesses, the sudden collapse can be deadly. Entire homes have been swallowed up by the Earth.

In the U.S., Florida, Texas, Alabama, Missouri, Kentucky, Tennessee, and Pennsylvania have the terrain most conducive to forming a sinkhole, says the USGS’s website.

While less common, sinkholes can also be caused by human land development. Activities like construction and pumping groundwater can make the ground less stable and a sinkhole more likely.

Around the world, any region that has easily dissolvable terrain could potentially develop sinkholes. Mexico and Belize are built on an abundance of soluble rock. Parts of Italy, Slovenia, Croatia, and Russia are also prone to sinkholes.

China is home to the world’s largest cluster of sinkholes and the region’s terrain has, over thousands of years, yielded enormous rock towers and one of the world’s largest systems of caves.


Read More On This At National Geographic News