Tearma geolaioch ar chruthu na gciseal de charraigeacha driodair ina sonraionn bristi sa leagan sios no athruithe i nadur an abhar driodair sna planai difriula srathaithe. An tearma ceanna in usaid chun cur sios ar ord na sreabhanna laibhe i gcarraigeacha doigheartha . [1]