CHAPTER 11 Glaciers and Glaciation
264
Before
After
January 31, 2002
March 7, 2002
50km
50km
FIGURE 11.3 These satellite images document
the breakup of the Larsen B ice shelf in early
2002. Look at the lower portion of Figure 11.2 to
see the location of the ice shelf adjacent to the
Antarctic Peninsula. The total area of the ice shelf
that collapsed was 3250 square kilometers (1267
square miles). The average thickness of the ice
was about 220 meters (720 feet). This event
liberated more than 700 billion metric tons of
icebergs. (NASA)
Reykjavik
Vantnajükull
ice cap
ICELAND
D I D Y O U K N O W ?
Because Iceland has active volcanoes
but is also a place with abundant
glaciers, it is often called the “land of
fire and ice.” When volcanoes buried
beneath the island’s ice caps erupt,
they trigger rapid melting that can
cause major floods. Because the
problem is so common here, there is
an Icelandic word, jükulhlaup (“glacier
flood”), to refer to the phenomenon.
See Figure 11.4.
FIGURE 11.4 The ice cap in this satellite image is
the Vantnajükull in southeastern Iceland (jükull
means “ice cap” in Danish). In 1996 the Grimsvötn
Volcano erupted beneath the ice cap, producing
large quantities of melted glacial water that
created floods. (Landsat image from NASA)
or more sides. The shelves are thickest on
their landward sides, and they become
thinner seaward. They are sustained by
ice from the adjacent ice sheet as well as
being nourished by snowfall and the
freezing of seawater to their bases.
Antarctica’ s ice shelves extend over
approximately 1.4 million square kilometers (0.6 million square miles). The Ross
and Filchner ice shelves are the largest,
with the Ross ice shelf alone covering an
area approximately the size of Texas (see
Figure 11.2). In recent years, satellite
monitoring has shown that some ice
shelves are breaking apart. For example,
during a 35-day span in February and
March 2002 an ice shelf on the eastern
side of the Antarctic Peninsula, known
as the Larsen B ice shelf, broke apart and
separated from the continent (FIGURE 11.3).
The event sent thousands of icebergs
adrift in the adjacent Weddell Sea. This
was not an isolated event but rather part
of a trend. Since 1974 the extent of seven
ice shelves surrounding the Antarctic
Peninsula declined by about 13,500 square
kilometers (nearly 5300 square
miles). Scientists attribute the
breakup of the ice shelves to a
strong regional climate warming.
Other Types
of Glaciers
In addition to valley glaciers and
ice sheets, other types of glaciers
are also identified. Covering some
uplands and plateaus are masses
of glacial ice called ice caps. Like ice sheets,
ice caps completely bury the underlying
landscape but are much smaller than the
continental-scale features. Ice caps occur in
many places, including Iceland and several
of the large islands in the Arctic Ocean
(FIGURE 11.4).
Often ice caps and ice sheets feed
outlet glaciers. These tongues of ice flow
down valleys extending outward from the
margins of these larger ice masses. The
tongues are essentially valley glaciers that
are avenues for ice movement from an ice
cap or ice sheet through mountainous terrain to the sea. Where they encounter the
ocean, some outlet glaciers spread out as
floating ice shelves. Often large numbers of
icebergs are produced.
Piedmont glaciers occupy broad lowlands at the bases of steep mountains and
form when one or more valley glaciers
emerge from the confining walls of mountain valleys. Here the advancing ice spreads
out to form a broad sheet. The size of individual piedmont glaciers varies greatly.
Among the largest is the broad Malaspina
Glacier along the coast of southern Alaska.
It covers more than 5000 square kilometers
(2000 square miles) of the flat coastal plain
at the foot of the lofty St. Elias Range
(FIGURE 11.5).
What if the Ice Melted?
How much water is stored as glacial ice?
Estimates by the U.S. Geological Survey
indicate that only slightly more than
2 percent of the world’ s water is tied up in
264
Before
After
January 31, 2002
March 7, 2002
50km
50km
FIGURE 11.3 These satellite images document
the breakup of the Larsen B ice shelf in early
2002. Look at the lower portion of Figure 11.2 to
see the location of the ice shelf adjacent to the
Antarctic Peninsula. The total area of the ice shelf
that collapsed was 3250 square kilometers (1267
square miles). The average thickness of the ice
was about 220 meters (720 feet). This event
liberated more than 700 billion metric tons of
icebergs. (NASA)
Reykjavik
Vantnajükull
ice cap
ICELAND
D I D Y O U K N O W ?
Because Iceland has active volcanoes
but is also a place with abundant
glaciers, it is often called the “land of
fire and ice.” When volcanoes buried
beneath the island’s ice caps erupt,
they trigger rapid melting that can
cause major floods. Because the
problem is so common here, there is
an Icelandic word, jükulhlaup (“glacier
flood”), to refer to the phenomenon.
See Figure 11.4.
FIGURE 11.4 The ice cap in this satellite image is
the Vantnajükull in southeastern Iceland (jükull
means “ice cap” in Danish). In 1996 the Grimsvötn
Volcano erupted beneath the ice cap, producing
large quantities of melted glacial water that
created floods. (Landsat image from NASA)
or more sides. The shelves are thickest on
their landward sides, and they become
thinner seaward. They are sustained by
ice from the adjacent ice sheet as well as
being nourished by snowfall and the
freezing of seawater to their bases.
Antarctica’ s ice shelves extend over
approximately 1.4 million square kilometers (0.6 million square miles). The Ross
and Filchner ice shelves are the largest,
with the Ross ice shelf alone covering an
area approximately the size of Texas (see
Figure 11.2). In recent years, satellite
monitoring has shown that some ice
shelves are breaking apart. For example,
during a 35-day span in February and
March 2002 an ice shelf on the eastern
side of the Antarctic Peninsula, known
as the Larsen B ice shelf, broke apart and
separated from the continent (FIGURE 11.3).
The event sent thousands of icebergs
adrift in the adjacent Weddell Sea. This
was not an isolated event but rather part
of a trend. Since 1974 the extent of seven
ice shelves surrounding the Antarctic
Peninsula declined by about 13,500 square
kilometers (nearly 5300 square
miles). Scientists attribute the
breakup of the ice shelves to a
strong regional climate warming.
Other Types
of Glaciers
In addition to valley glaciers and
ice sheets, other types of glaciers
are also identified. Covering some
uplands and plateaus are masses
of glacial ice called ice caps. Like ice sheets,
ice caps completely bury the underlying
landscape but are much smaller than the
continental-scale features. Ice caps occur in
many places, including Iceland and several
of the large islands in the Arctic Ocean
(FIGURE 11.4).
Often ice caps and ice sheets feed
outlet glaciers. These tongues of ice flow
down valleys extending outward from the
margins of these larger ice masses. The
tongues are essentially valley glaciers that
are avenues for ice movement from an ice
cap or ice sheet through mountainous terrain to the sea. Where they encounter the
ocean, some outlet glaciers spread out as
floating ice shelves. Often large numbers of
icebergs are produced.
Piedmont glaciers occupy broad lowlands at the bases of steep mountains and
form when one or more valley glaciers
emerge from the confining walls of mountain valleys. Here the advancing ice spreads
out to form a broad sheet. The size of individual piedmont glaciers varies greatly.
Among the largest is the broad Malaspina
Glacier along the coast of southern Alaska.
It covers more than 5000 square kilometers
(2000 square miles) of the flat coastal plain
at the foot of the lofty St. Elias Range
(FIGURE 11.5).
What if the Ice Melted?
How much water is stored as glacial ice?
Estimates by the U.S. Geological Survey
indicate that only slightly more than
2 percent of the world’ s water is tied up in