Complex mass-movement terrains in the western Cascade Range, Oregon

A variety of mass-movement processes interact to formcomplex mass-movement terrains in the western CascadeRange in Oregon. Slow, deep-seated (>5 m depth) processesof creep, slump, and earthflow operate simultaneously andsequentially, resulting in unstable conditions that may initiaterapid, shallow ( Creep movement in western Oregon has been monitoredat rates as high as 15 mm/yr. Relative movement betweendiscrete blocks in the Lookout Creek earth flow ranges up tonearly 10 times as fast. Movement rate accelerates duringperiods of high moisture availability.
Geomorphic observations and tree-ring analysis indicatethat mass-movement terrains may have histories spanningcenturies and possibly millennia.