In the wetter coastal areas, glacier speeds are commonly 10-30 metres per year, causing large crevasses to form. As the glaciers calve, they can deliver large volumes of freshwater to the world’s oceans, particularly if they are surging at the time and advancing up to several kilometres over just a few years. During the last ice age (some 21,000 years ago), virtually all of Svalbard was covered by a large ice cap, though the timing and rate of retreat after this time is not precisely known.