Glaciers respond to climate in an attempt to achieve
equilibrium. A glacier advances due to a climate
cooling/snowfall increase that causes positive mass balance. A
climate warming/snowfall decrease leads to negative mass
balances and glacier retreat. To reestablish equilibrium a
retreating glacier must lose enough of its highest ablating
sections, usually at the lowest elevations, so that accumulating
snows in the near the head of the glacier once again are
equivalent to overall ablation, and an equilibrium balance is
approached. If a glacier cannot retreat to a point where
equilibrium is established, it is in disequilibrium with the
climate system. A glacier that is in disequilibrium with present
climate will melt away with a continuation of this climate.
Four lines of evidence indicate that many North Cascade
glaciers are currently in a state of disequilibrium. One key factor
identifies those in disequilibrium-the thinning of the glacier
along its entire length.
1. glacier thinning in the accumulation zone is incompatible
with glacier survival as this indicates the glacier has no
consistent accumulation zone, this thinning is evident in
glaciers where the head of the glacier is retreating and new
rock outcrops are appearing in the accumulation zone. This
is occurring on 10 of 15 North Cascade glaciers surveyed in
detail in 2007.
Published paper on Glacier Survival Forecasts
Longitudinal profiles completed in 1984 and 2005 on twelve North
Cascade glaciers indicate substantial glacier thinning in the
upper portion, accumulation zone, on nine of the twelve
glaciers. This amount of thinning indicates that the
glacier no longer has a substantial accumulation zone. When glacier thinning
substantial in the accumulation zone and comparable to the ablation zone
indicates that there is no point to which the glacier can retreat to achieve
balance measured on nine glaciers yields a mean cumulative
annual balance for the 1984-2006 period of -12.40 m w.e, a net
loss of ice thickness exceeding 14 m. This is a significant
loss for glaciers that average 30-50 m in thickness, 20-40% of
their entire volume lost in two decades.
4. North Cascade glacier retreat is rapid and ubiquitous. All
47 monitored glaciers are currently undergoing a significant
retreat or have disappeared in the case of three of them. Two
of the glacier where mass balance observations were begun,
Spider Glacier and Lewis Glacier, have disappeared. This
retreat on eight Mount Baker glaciers since 1984 that were
advancing in 1975 averages 340 m. The data indicate broad
regional continuity in glacial response to climate.
Above is Honeycomb Glacier. This
glacier has retreated 500 meters in the last 40 years, forming
the new lake, foreground above and exposing an ever expanding
rock island in the middle of the glacier. However,
in the upper reaches of the glaciers it is not thinning, thus,
it could retreat to a new point of equilibrium.
Response to Climate Change
Since the maximum advance of the Little Ice Age (LIA) there have
been three climate changes in the North Cascades sufficient to
substantially alter glacier terminus behavior.
This first substantial climate change was a progressive
temperature rise from the 1880ís to the 1940ís. The warming led
to ubiquitous rapid retreat of North Cascade Range alpine
glaciers from 1890 to 1944 (Long, 1955; Hubley, 1956). Average
retreat of glaciers on Mt. Baker was 1440 m from LIAM to 1950,
and of 38 North Cascade glaciers monitored across the range,
1215 m (Pelto and Hedlund, 2001).
The second substantial change in climate began in 1944 when
conditions became cooler and precipitation increased (Hubley,
1956). Many North Cascade glaciers began to advance in the
early 1950s, after 30 years of rapid retreat. All 11 Mount
Baker glaciers advanced during this period (Hubley, 1956;
The third change began with warmer and drier conditions in 1977
(Ebbesmeyer et al., 1991). By 1984, all the Mount Baker
glaciers, which were advancing in 1975, were again retreating
(Pelto, 1993). Between 1979 and 1984, 35 of the 47 North
Cascade glaciers observed annually by NCGCP were retreating. By
1992 all 47 glaciers termini observed by NCGCP were retreating
(Pelto, 1993). The average retreat from 1984-2004 of Mount Baker
glaciers is 297 m, and on all 47 North Cascade glaciers it has
been 137 m.
At right is the Whitechuck Glacier in 1973 and 2006. The branch of the glacier has disappeared. The lack of crevassing and thinning along its entire length was evident in 1988, indicating glacier disequilibrium, and that it would melt away.
2000,four glaciers had disappeared Lewis Glacier, Spider
Glacier (Right), David Glacier and Milk Lake Glacier (below) (Pelto and Hedlund,
2001). Spider Glacier is shown at right. The current retreat is not confined to the terminus of
glaciers. The head of many glaciers is retreating downslope as
well. On Ice Worm Glacier the head of the glacier has retreated
160 m and the terminus 144 m during the 1984-2005 period.
This retreat on eight Mount Baker glaciers from 1984-2004, that
were advancing in 1975 averages, 340 m. The rate of
retreat has accelerated since 1998.
|The Lower Curtis Glacier on Mount Shuksan advanced from
1950-1975 and has retreated 184 meters from 1987-2004. A
longitudinal profile up the middle of the glacier indicates that
it thinned meters from 1908-1984 and 6 m from
1984-2002 . The thinning has been as large in the
accumulation zone as at the terminus, indicating no point to
which this glacier can retreat and achieve equilibrium with the
||The Columbia Glacier near Monte Cristo has
retreated 135 meters from 1987-2004. A longitudinal
profile up the middle of the glacier indicates that it thinned
meters 57 m from 1911-1984 and 8 m from 1984 to 2002 . The
thinning has been largest in the accumulation zone since
1984, indicating no point to which this glacier can
retreat and achieve equilibrium with the present climate.
Below is the Boulder Glacier which advanced from 1958-1980 and
then began retreating slowly until 1992, when retreat became
The recent 0.6oC temperature rise and 25 %
reduction in mean April 1 SWE in the North Cascades have
resulted in evident disequilibrium of North Cascade glaciers.
Mean annual balances of North Cascade glaciers have average
-0.41 m/a over the past 21 years. The net loss is a significant
portion of the total glacier volume, 18-32%, resulting in
substantial retreat and thinning. The retreat is ubiquitous,
rapid and increasing. There is no evidence that North Cascade
glaciers are close to equilibrium. Their ongoing thinning
indicates that all of the glaciers will continue to retreat in
the foreseeable future. In cases where the thinning is
substantial along the entire length of the glacier, than no
point of equilibrium can be achieved with present climate and
the glacier is unlikely to survive.
The Full paper is in