The term finger rafting refers to the systematic alternation of interlocking overthrusts and underthrusts involved in this process.
[4] The process of finger rafting as such is commonly observed inside a lead, once a thin layer of ice (at the nilas stage) has formed.
Such a mechanism, and the fact that the upper surface of nilas is already slippery, account for overthrust distances in excess of 100 metres (330 ft) (a length-to-thickness ratio of 1000 to one).
[4][note 2] Rafting and ridging are two possible responses expected from the interaction between two converging ice sheets or floes.
[4][5] The term 'ridging' refers to the process of ridge formation, involving the breaking up of the ice sheet into distinct blocks (which does not happen during rafting).
What this equation shows is that, assuming a representative tensile strength of 0.65 MPa, the maximum thickness for rafting to occur is in the range of 0.2 metres (7.9 in).