The rapidity with which they occurred is believed to be rare – Ansa /Courier TV
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About 40 kilometers southwest of the Croatian capital Zagreb, after the 6.4 magnitude earthquake in December that killed seven people, large sinkholes appeared. These closed cavities on the bottom are typical in karst regions, generally developed by dissolution of the limestone rock. Although the appearance of sinkholes is not unusual following strong seismic activity, the large number and speed with which they emerged is relatively rare.