They are called "sinkholes", whose existence is due to very deep caves in the subsoil.
It is not the case, more catastrophic, of Mexico City, which according to scientists is slowly sinking, but we are dangerously close: in Croatia have opened more than 100 holes in the ground. The inhabitants of two villages about 40 kilometers from the capital Zagreb are afraid of where to put their feet. From just before 2021 to the end of January, sinkholes have popped up like flowers in a field. Not only in the countryside areas, but also under the houses of the citizens of Mečenčani and Borojevići, who have suffered damages such as collapses and cracks.
The citizens' fear: "We don't know if we will have to leave"
"We don't know if we will be forced to leave. These holes are dangerous because they open suddenly with the water leaking out", so Stojan Kresojevic described a nightmarish situation. According to the Croatian Geological Institute, there are 54 sinkholes that have opened up in about 30 days. But the AFP news agency, collecting information on the field, has arrived at a much more disturbing estimate, according to which the sinkholes could be as many as 100.
What are sinkholes and why do they suddenly appear
These are sinkholes, openings up to 30 meters wide and 15 meters deep, which occur in areas whose subsoil is characterized by the presence of underground cavities and caverns. In fact, Croatia is home to dozens of caves, three of which are deeper than 1,000 meters. But sinkholes can also be the consequence of seismic phenomena, and it is no coincidence that Croatia, in December 2020, was hit by a magnitude 6.4 earthquake that killed seven people and injured 26.
For scientists, it is entirely plausible that ground movement caused the vault of these giant caves to collapse, thus creating dozens and dozens of sinkholes. "Even without earthquakes, the ground above such cavities would collapse and depressions would form, as has occasionally happened in the past, but earthquakes have accelerated and intensified these processes." This is the thesis of the Croatian Geological Institute.
The phenomenon recently observed in the Balkans brings to mind another spectacular and dramatic collapse, which occurred on the other side of the world: this is the huge sinkhole opened on the coast in Australia.