The islands of Jabuka and Brusnik are the only 2 Croatian islands, amoung 1185 island in Croatia, that are entirely covered with lava, along with Palagruza, which has only a volcanic origin. These three islands form the area of the "volcanic triangle of Adriatic".
Secondo le teorie geologiche Brusnik e Jabuka come anche alcune parti della baia di Komiza sull’isola di Vis e Palagruza si sono formate grazie all’effusione della lava in mare.