The essential difference between glaciers and icebergs is that a glacier is a (relatively) permanent ice formation on land, while an iceberg is a comparatively short-lived free-floating body of ice on an ocean or, potentially, a sea or large lake. Icebergs are typically formed where glaciers lie along an ocean shore, and where chunks of ice can break off and float into the open ocean. Although this definition implies that icebergs are usually quite small, the largest icebergs can in fact be larger than small glaciers.
– About Glaciers –
A glacier is a mass of ice which exists year-round, distinguishing it from temporary snow and ice formations which build up over a single winter and then melt away over the following spring and summer. Instead, over long periods of time, glaciers undergo a continuous cycle, adding new snow (which is eventually buried by more snow and compressed into ice) during the winter, receding somewhat in the summer, and then growing again the following winter. The immense mass of a large glacier carves deep U-shaped grooves into the rock on which it rests.
Most people live in relatively temperate zones and therefore are familiar with glaciers only in the most hostile environments to which we occasionally subject ourselves: high mountain ranges, like the European Alps and the North American Rockies. In the latter, for example, the Columbia Icefield is a particularly noted interconnecting set of glaciers. However, in the polar regions, glaciers are much more common, and can be found across vast swathes of, for example, the island of Greenland in the north, and the continent of Antarctica in the south.
Normally, as stated, glaciers are essentially permanent ice bodies. However, this is the case only so long as temperatures remain cold enough for the glacier to recover from the summer melt. If temperatures are cold enough (as they have been at certain points in the past, glaciers can grow, in some cases rapidly (particularly rapid glacial growth is what marked the beginning of the last Ice Age). If temperatures are warm, however, glaciers melt more in summer than they grow in winter, and thus recede, theoretically until they vanish entirely. Currently most glaciers around the world are receding on an annual basis, and some have now vanished entirely.
– About Icebergs –
Icebergs, by contrast, are free-floating bodies of ice in water, which are not expected to survive and grow on this sort of long-term basis. The difference between glaciers and icebergs, essentially, is that a glacier is a relatively permanent body of ice on land, while an iceberg is a temporary body of ice in the water. In most cases, icebergs result when large chunks of ice break off a glacier in the Arctic or Antarctic which meets or overhangs the shoreline. Icebergs also result in the Arctic in the spring, when the ice which blankets the pole during the winter breaks up and drifts south.
Because icebergs are extremely large, melting can take many months or more. For this reason, icebergs which break off, or “calve” in northern or southern regions can actually drift well to the south, posing a significant danger to commercial shipping. (It was, of course, an iceberg which resulted in the infamous sinking of the Titanic in 1912.)
We tend to assume that icebergs are relatively “small” (a size distinction which actually means they may be dozens or hundreds of feet long). Much larger icebergs are possible, however, in certain conditions in the far north and far south. Very large Arctic icebergs were, during the early Cold War, home to temporary signals listening posts set up by both the American and Soviet intelligence services, featuring buildings and ice airstrips.
In the south, extremely large icebergs sometimes calve off the Antarctic ice sheet (the size and frequency of this massive ice sheet calving is increasing as a result of the warming climate). In 2002, for example, a 5500-square-kilometre ice sheet broke off of the Ross Ice Shelf in Antarctica and was designated Iceberg C-19. C-19 broke up into two pieces, which have subsequently broken up farther. However, according to the U.S. National Ice Center, the largest piece of the iceberg, C-19A, still measured 16 miles long by 4 miles wide in 2009, seven years after it broke off Antarctica. Similar icebergs the size of small states break off Antarctica and drift north towards countries such as New Zealand and Australia.
The current general warming trend (regardless of whether it is human-caused or not) means that glacial ice along shorelines is melting faster than previously, but also that winter sea ice does not form as thickly or over as wide an area. Eventually, therefore, the number of icebergs will also decline significantly.