Curved gravel spit, Lake Pukaki, South Canterbury

Lake Pukaki is one of the largest lakes in New Zealand, occupying an old glacial trough that has been carved out by massive glaciers flowing east from the Southern Alps during numerous past ice ages. The present-day lake is over 30 kilometres long and around 5 kilometres wide, an oasis of vivid turquoise surrounded by the dry browns and greys of the semi-arid MacKenzie Country.

Most of the shoreline of Lake Pukaki is made up of rounded gravels, derived from rocks originally brought down from the Alps by glaciers and then by meltwater streams. Wave action and fluctuating lake levels continuously work this gravel into striking beach ridges that change their form with every shift in the weather. The lake’s roughly north-south orientation means that strong northerly and northwesterly winds blowing off the Alps are able to whip up large waves along the length of the lake that are capable of shifting large amounts of gravel during storms.

Prevailing northwest winds mean that much of the gravel movement along the lake’s shores is from north to south which gives rise to some curious formations as gravel is transported around headlands and other obstructions along the shore. The curved spit in this photograph is a classic example in which gravel moving from north to south (right to left in this photograph) has been deposited in the lee of a small headland, causing it to extend southwards and then curve into a graceful shoreward-facing hook as the waves have wrapped around the end of the spit.