A glacier is a slowly moving river of ice. Its own weight causes the movement. In fact, to qualify as a glacier, the ice must be thick enough to sink and move on its own weight. Glaciers form where the accumulation of snow exceeds the melt off, or ablation. Most of earth’s glaciers are found in the Arctic and Antarctic, but they are also found in mountain ranges. They are found on every continent, and on some high-latitude islands like New Zealand or Papua New Guinea. Glaciers cover about 10% of the world’s land, with over 5 million square miles of ice.
The aqua color that we often see in glacial ice is due to the fact that air bubbles are squeezed out of the ice, causing it to become denser, and making the ice appear blue. Also, like ocean water, the ice reflects colors at the blue end of the spectrum, while absorbing colors at the red end of the spectrum.
Note the blue color in the crevasses
The National Snow & Ice Data Center lists twelve types of glacier: mountain, tidewater, piedmont, hanging, cirque, ice apron, rock, ice shelf, ice field, ice cap, ice stream, and ice sheet. The glaciers on the South Island of New Zealand are categorized as mid-altitude mountain glaciers. Mountain glaciers develop in high mountainous regions, often flowing out of icefields that span several peaks or even a mountain range.
There are over 3,000 glaciers on the South Island, most of them in the Southern Alps mountain range in Fiordland National Park. New Zealand’s glaciers have been retreating since the late 1800’s, and the rate of retreat has accelerated since 1920, and several of the retreating glaciers have created glacial lakes. A few glaciers have advanced, but the loss of glacier mass far exceeds its creation. We are fortunate to have seen them when we did.
While visiting Milford Sound on the South Island of New Zealand, we had an opportunity to take a flight from Milford to Queenstown that passed over several glaciers. This was my first view of glaciers anywhere, so it was very exciting. There are several glaciers in the area, and we may have seen any of these: Rob Roy, Jura, Dart, Donne, Olivine, Mt. Tutoko, or Grant. Why wasn’t I taking notes!!
On a side note, Milford Sound is not a sound at all, but a fiord (New Zealand spelling). A sound is formed when a river valley is flooded by the sea, a fjord is formed when a glacier retreats, and sea water fills the resulting valley.