Near the terminus of the Tasman
Glacier the surface is characterised by surface moraine 1-2 metres deep
covering the ablating ice and sinkholes or moulins. Moulins start off as
small potholes that eventually deepen to join up with meltwater tunnels that
form the maze of the glacial plumbing system. On the Tasman, these moulins
have expanded into large grey circular lakes.
Eventually these systems find
their way to the base of the glacier and out to the terminus where they
discharge themselves into the fluvioglacial system, usually carrying rock
flour. The amount of debris discharged is enormous. The present Tasman River
is at work on a bed of outwash gravels 500 – 1000 metres deep. The river
constantly shifts its pattern, often across tussock land, filling Lake
Pukaki.
