▁ago , ▁and ▁caused ▁a ▁huge ▁t sun ami , ▁which ▁left ▁its ▁mark ▁in ▁several ▁places ▁in ▁the ▁eastern ▁Mediter rane an . ▁It ▁may ▁have ▁been ▁the ▁reason ▁the ▁settlement ▁of ▁Atl it ▁Yam ▁( Is rael ), ▁now ▁below ▁sea ▁level , ▁was ▁suddenly ▁abandoned ▁around ▁that ▁time . ▁ ▁The ▁ste ep ▁walls ▁of ▁the ▁valley ▁have ▁suffered ▁subsequent ▁col laps es ▁on ▁numerous ▁occasions . ▁The ▁str ata ▁exposed ▁in ▁the ▁valley ▁walls ▁provide ▁an ▁important ▁and ▁easily ▁accessible ▁record ▁of ▁Et na ' s ▁er upt ive ▁history . ▁ ▁The ▁most ▁recent ▁collapse ▁event ▁at ▁the ▁sum mit ▁of ▁Et na ▁is ▁thought ▁to ▁have ▁occurred ▁about ▁ 2 , 0 0 0   year s ▁ago , ▁forming ▁what ▁is ▁known ▁as ▁the ▁P iano ▁Cal der a . ▁This ▁cal der a ▁has ▁been ▁almost ▁entirely ▁filled ▁by ▁subsequent ▁la va ▁er u ptions ▁but ▁is ▁still ▁visible ▁as ▁a ▁distinct ▁break ▁in ▁the ▁slope ▁of ▁the ▁mountain ▁near ▁the ▁base ▁of ▁the ▁present - day ▁sum mit ▁cone . ▁ ▁Mount ▁Et na ▁is ▁moving ▁towards ▁the ▁Mediter rane an ▁Sea ▁at ▁an ▁average ▁rate ▁of ▁ ▁per ▁year , ▁the ▁mass if ▁sl iding ▁on ▁an ▁un con sol id ated ▁layer ▁above ▁the ▁older ▁s lop ing ▁terrain . ▁ ▁E ru ptions ▁ ▁Historical ▁er u ptions ▁E ru ptions ▁of ▁Et na ▁follow ▁a ▁variety ▁of ▁patterns . ▁Most ▁occur ▁at ▁the ▁sum mit , ▁where ▁there ▁are ▁