Geology Reference
In-Depth Information
level (>2 m) and thickness between 10 and 20 m. Ice shelves
usually have great horizontal extent and a level or gently
modulating surface. The growth of an ice shelf occurs by
annual snow accumulation and also by the seaward exten-
sion of land glaciers. Limited areas may be grounded.
2. Ice stream: part of an inland ice sheet in which the ice
flows more rapidly but not necessarily in the same direc-
tion as the surrounding ice. Margins are sometimes clearly
marked by a change in direction of the surface slope but
may be indistinct.
3. Iceberg: a massive piece of ice of greatly varying shape,
calved from land glaciers or sometimes from ice shelves or
ice streams. They are usually protruding 5 m or more above
sea level with total thickness of about eight times the pro-
truding height. Some icebergs are grounded but most of
them are afloat. Small icebergs are called bergybits.
4. Glacier tongue: projecting seaward extension of a
land glacier, usually afloat. In the Antarctic, glacier
tongues may extend over tens of kilometers.
5. Ice island: a large piece of floating ice protruding
about 5 m above the sea level, which has broken away
from an ice shelf. They have a thickness of 30-50 m and
an area in the range from a few thousand square meters to
500 square kilometers or more. They are characterized by
a regularly undulating surface giving a ribbed appearance
from the air. The largest ice shelf in the Arctic, the Ward
Hunt ice shelf, is located on the north coast of Ellesmere
Island, Nunavut, Canada. This ice shelf is believed to
have been in place for 3000 years, occupying an area of
approximately 400 km
2
by 1980s. Satellite images obtained
in 2002 confirmed the split of this ice shelf. This has gen-
erated a few ice islands that continued to float in the high
Arctic. Section 5.2 presents information about high Arctic
ice islands. Fragments of ice islands are found in different
areas in the Arctic Basin.
The most commonly observed forms of floating ice of
land origin are icebergs and ice islands. They may exist
within sea ice cover. However, since they are much thicker
than the surrounding sea ice they can be identified visu-
ally or in remote sensing images. Icebergs are classified
according to their shape or size. Categories based on each
criterion are presented in
MANICE
[2005]. Shape‐based
categories start from small growlers and bergybits (height
above sea surface less than 1 m and between 1 and 5 m,
respectively) up to very large bergs (height above sea sur-
face >75 m). The largest iceberg in the Arctic was observed
off the Baffin Island in 1882. It measured 13 by 6 km with
20 m freeboard. Most Arctic icebergs measure few hun-
dred meters in length or width. However, icebergs in the
Arctic are much smaller than in the Antarctic as will be
explained later. A few shape‐based types of icebergs are
shown in Figure 2.75. Icebergs calve from the glaciers
(a)
(b)
(c)
(d)
(e)
(f)
Figure 2.75
Different shapes of icebergs: Tabular (a), Non‐Tabular (b), Pinnacle (c), Wedge (d), Blocky (e), and
Domed (f).
