▁need ▁not ▁occur ▁every ▁year ▁to ▁be ▁considered ▁active . ▁ ▁The ▁area ▁in ▁which ▁most ▁ice ▁wed ges ▁remain ▁active ▁is ▁along ▁the ▁per ma f rost ▁zone . ▁The ▁number ▁of ▁active ▁ice ▁wed ges ▁that ▁are ▁crack ing ▁year ly ▁is ▁consist ently ▁decl ining ▁as ▁they ▁become ▁in active . ▁ ▁In active ▁In active ▁ice ▁wed ges ▁are ▁wed ges ▁that ▁are ▁no ▁longer ▁crack ing ▁and ▁growing . ▁Through out ▁the ▁winter ▁months , ▁the ▁w edge ▁does ▁not ▁split ▁and ▁therefore ▁in ▁the ▁summer ▁no ▁new ▁water ▁is ▁added . ▁ ▁Cast s ▁In ▁areas ▁of ▁past ▁per ma f rost , ▁ice ▁wed ges ▁have ▁m elt ed ▁and ▁are ▁no ▁longer ▁filled ▁with ▁ice . ▁The ▁w edge , ▁which ▁is ▁now ▁empty , ▁is ▁filled ▁with ▁sed iment ▁and ▁d irt ▁from ▁the ▁surrounding ▁walls . ▁These ▁are ▁called ▁ice ▁w edge ▁cast s ▁and ▁are ▁used ▁to ▁estimate ▁the ▁climate ▁of ▁hundreds ▁of ▁thousands ▁of ▁years ▁ago . ▁ ▁Types ▁Ice ▁wed ges ▁have ▁histor ically ▁been ▁class ified ▁into ▁two ▁main ▁categories : ▁ep igen etic ▁and ▁sy ng en etic . ▁The ▁type ▁of ▁an ▁ice ▁wed ges ▁refer ▁to ▁the ▁way ▁in ▁which ▁the ▁w edge ▁grows ▁over ▁time . ▁Rel atively ▁recent ▁field ▁studies ▁have ▁revealed ▁a ▁new ▁type ▁of ▁ice ▁w edge : ▁anti - s y ng en etic . ▁Currently , ▁these ▁are ▁the ▁only ▁three ▁distinct ly ▁class ified ▁types ▁of ▁ice ▁wed ges