▁five ▁distinct ▁cr aters ▁– ▁the ▁N ortheast ▁Cr ater , ▁the ▁Vor agine , ▁the ▁B oc ca ▁Nu ova , ▁and ▁the ▁S out heast ▁Cr ater ▁Complex ▁( 2 ). ▁Other ▁er u ptions ▁occur ▁on ▁the ▁fl anks , ▁which ▁have ▁more ▁than ▁ 3 0 0 ▁v ents ▁r anging ▁in ▁size ▁from ▁small ▁holes ▁in ▁the ▁ground ▁to ▁large ▁cr aters ▁hundreds ▁of ▁metres ▁across . ▁Sum mit ▁er u ptions ▁can ▁be ▁highly ▁explos ive ▁and ▁spect ac ular ▁but ▁rarely ▁threaten ▁the ▁inhab ited ▁areas ▁around ▁the ▁vol cano . ▁In ▁contrast , ▁fl ank ▁er u ptions ▁can ▁occur ▁down ▁to ▁a ▁few ▁hundred ▁metres ▁alt itude , ▁close ▁to ▁or ▁even ▁well ▁within ▁the ▁inhab ited ▁areas . ▁N umer ous ▁villages ▁and ▁small ▁towns ▁lie ▁around ▁or ▁on ▁con es ▁of ▁past ▁fl ank ▁er u ptions . ▁Since ▁the ▁year ▁AD   1 6 0 0 , ▁at ▁least ▁ 6 0 ▁fl ank ▁er u ptions ▁and ▁count less ▁sum mit ▁er u ptions ▁have ▁occurred ; ▁nearly ▁half ▁of ▁these ▁have ▁happened ▁since ▁the ▁start ▁of ▁the ▁ 2 0 th ▁century . ▁Since ▁ 2 0 0 0 , ▁Et na ▁has ▁had ▁four ▁fl ank ▁er u ptions ▁– ▁in ▁ 2 0 0 1 , ▁ 2 0 0 2 – 2 0 0 3 , ▁ 2 0 0 4 – 2 0 0 5 , ▁and ▁ 2 0 0 8 – 2 0