Finger rafting

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).

Aerial photograph showing two thin ice sheets (made of nilas ) that are moving toward each other. Along the length of the contact between the two sheets, segments where one sheet climbs onto the other alternate with others where it is the other way around. The lighter areas are where the ice thickness has doubled due to the overlapping process. This pattern is known as finger rafting . In many cases, it is highly systematic.
Finger rafting in the Weddell Sea , Operation IceBridge photo, 2017.
Idealized three-dimensional representation of finger rafting, It occurs when two thin ice sheets converge toward each other.
Finger rafting derives its name from its resemblance to the interlocking of fingers. Note that the fingers shown here are not interlaced normally (with all ten fingers showing from the top), but interlaced as in finger rafting (with only five fingers visible from either the top or bottom). [ note 1 ]
Rafted ice observed during MOSAiC Expedition in June 2020.