100 sinkholes appear after December earthquakes

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A strange and dangerous phenomenon has hit central Croatia.

Huge sinkholes have opened up, dotting the landscape and sometimes swallowing whole houses.

The geological oddity was triggered after two earthquakes, measuring 5.2 and 6.3 on the Richter scale, shook the region, at the end of December.

The quakes killed seven in the largely rural area around the town of Petrinja.

But the sinkholes are a continuing menace.

As low-level tremors continued to erupt, villagers reported more and more of these chasms opening up, filled with groundwater.

“This happened after the quake. After the earthquake there was a lot of rain, which made things much worse. Just water, water, water, everywhere,” says Radojka Vidovic,a  resident of Borojevici village.

In less than two months since the earthquakes, about 100 new sinkholes have been reported in the area.

Although sinkholes are a common occurrence in places rich in limestone deposits, the sheer speed with which they are appearing is taking scientists by surprise as this process usually takes decades or even centuries.

Some holes have emerged under residential houses, forcing residents to evacuate, while others dot backyards and fields, preventing farmers from working the land out of fear of being swallowed by the expanding holes.

Josip Terzic, a hydro geologist from the Croatian Geological Survey, is part of the team studying them.

“We plan several methods (of exploration) here. We have already performed some geophysical profiles, seismic, and also electrical. We plan to do maybe magnetotelluric (electromagnetic) methods here,” he says.

“We will have a site scan screening of this biggest, largest sinkhole, to map the underwater morphology of it. As far as I know, it’s approximately 12 meters deep under the water here.”

Scientists say that this is an unprecedented phenomenon which offers an opportunity to study the way violent events like earthquakes can so rapidly affect sediments and groundwater flows.

Researchers from neighbouring Slovenia and Italy have reportedly already visited the area to help local experts chart and study the holes, and more exploration is planned of largest hole which is 30-metres wide and some 15 metres deep.

But for locals, who mostly subsist on growing corn and potatoes, this is yet another challenge to overcome in a year marked by the coronavirus pandemic and which ended with deadly earthquakes and tremors.

“Well, that 6.2-magnitude earthquake felt pretty unpleasant to say the least,” says Nenad Tomasevic, a resident of Mecencani.

“And after that, these holes started popping up. Experts say that these sinkholes would have formed naturally anyway over time, but the earthquake acted as sort of a catalyst which sped up the whole process, unfortunately. And then we saw smaller sinkholes appearing in the ground.”

These gaping holes, that dot the fields and pull down buildings are another reminder that the natural world can very easily thwart human plans.

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