Ice Sculpting

Ice Sculpting. Image: Julian Thomson.

Image: Julian Thomson.

Glaciers are slowly moving rivers of ice that has accumulated in mountains. In New Zealand there are over 3000 of them, all acting as giant scrapers, carving out valleys with a ‘U’ shaped cross profile, and carrying away rock debris like giant conveyor belts.

When glaciers move
As glaciers move, they pick up rock fragments at their bases (called basal till). This can occur when bedrock gets stuck to the frozen glacier base and is plucked out as the ice continues to flow along. This basal debris then scrapes against the bedrock under the enormous weight of the moving ice. It carves out the valley floor, smoothing and polishing bedrock surfaces. Melt water also erodes the bedrock as it flows in streams along the base of a glacier.

Mount Cook and the Hooker Valley showing numerous glacial features - sharp rock and ice ridges (arêtes), snowfields, ice cliffs, a U shaped valley, moraine covered glacier, truncated spurs, lateral moraine platforms and a terminal lake. Image: Julian Thomson.

Mount Cook and the Hooker Valley showing numerous glacial features - sharp rock and ice ridges (arêtes), snowfields, ice cliffs, a U shaped valley, moraine covered glacier, truncated spurs, lateral moraine platforms and a terminal lake. Image: Julian Thomson.

When glaciers shrink
When glaciers shrink, they leave behind many characteristic landscape features such as scattered boulders (erratics), smoothed and striated rocks, U shaped valleys, truncated spurs, piles of rock debris (moraines) and lakes. Examples of these features can be found in our Mountain Landscapes Gallery.