loped ▁surface , ▁mainly ▁due ▁to ▁the ▁force ▁of ▁gravity . ▁ ▁Mass ▁movement ▁is ▁an ▁important ▁part ▁of ▁the ▁er os ional ▁process , ▁and ▁is ▁often ▁the ▁first ▁stage ▁in ▁the ▁break down ▁and ▁transport ▁of ▁weather ed ▁materials ▁in ▁mountain ous ▁areas . ▁It ▁moves ▁material ▁from ▁higher ▁elev ations ▁to ▁lower ▁elev ations ▁where ▁other ▁er oding ▁agents ▁such ▁as ▁streams ▁and ▁gla ci ers ▁can ▁then ▁pick ▁up ▁the ▁material ▁and ▁move ▁it ▁to ▁even ▁lower ▁elev ations . ▁Mass - mov ement ▁processes ▁are ▁always ▁occurr ing ▁continu ously ▁on ▁all ▁s lop es ; ▁some ▁mass - mov ement ▁processes ▁act ▁very ▁slowly ; ▁others ▁occur ▁very ▁suddenly , ▁often ▁with ▁dis astr ous ▁results . ▁Any ▁per cept ible ▁down - s lo pe ▁movement ▁of ▁rock ▁or ▁sed iment ▁is ▁often ▁referred ▁to ▁in ▁general ▁terms ▁as ▁a ▁lands lide . ▁However , ▁land sl ides ▁can ▁be ▁class ified ▁in ▁a ▁much ▁more ▁detailed ▁way ▁that ▁reflect s ▁the ▁mechan isms ▁responsible ▁for ▁the ▁movement ▁and ▁the ▁velocity ▁at ▁which ▁the ▁movement ▁occurs . ▁One ▁of ▁the ▁visible ▁top ographical ▁manifest ations ▁of ▁a ▁very ▁slow ▁form ▁of ▁such ▁activity ▁is ▁a ▁sc ree ▁slope . ▁ ▁Sl ump ing ▁happens ▁on ▁ste ep ▁hills ides , ▁occurr ing ▁along ▁distinct ▁f ract ure ▁zones , ▁often ▁within ▁materials ▁like ▁cl ay ▁that , ▁once ▁released , ▁may ▁move ▁quite ▁rapidly ▁down hill . ▁They ▁will ▁often ▁show ▁a ▁sp oon - sh