Download A preliminary inventory of Alaskan glaciers

World Glacier Inventory — Inventaire mondial des Glaciers
(Proceedings of the Riederalp Workshop, September 1978; Actes de l'Atelier de Riederalp,
septembre 1978): IAHS-AISH Publ. no. 126, 1980.
A preliminary inventory of Alaskan glaciers
A. Post and M. F. Meier
Abstract. The total area of glaciers in the twelve main mountain systems of Alaska is estimated
to be 74 700 km 2 . A total of 1001 glaciers (723 km 2 ) were measured in a glacier inventory of the
Brooks Range.
Un inventaire préliminaire des glaciers de l'Alaska
Résumé. La superficie totale des glaciers des douze principaux systèmes montagneux de l'Alaska
est estimée à 74 700 km 2 . Dans le cadre d'un inventaire des glaciers du Brooks Range, on a
mesuré un nombre total de 1001 glaciers (723 km 2 ).
AN APPROXIMATE ASSESSMENT OF TOTAL GLACIER AREA
The area of glaciers in individual mountain massifs was measured by correcting the
glacier outlines on 1:250 000 scale maps using recent aerial photographs, drawing
closed curves so that the glacier area outside the curve roughly equalled the non-glacial
area within the curve, then integrating the area using a planimeter. This method could
not be used for the Seward Peninsula or the Kilbuk-Wood River Mountains because
of inadequate maps and photographs; a more complete inventory was performed for
the Brooks Range. The results were summed for the twelve main mountain systems
in Alaska (Table 1); the total area is about 74 700 km 2 .
TABLE 1.
North
West
Southwest
Interior
South-central
Southeast
Approximate area of glaciers in Alaska [km 2 ]
Brooks Range
Seward Peninsula
Kilbuk-Wood River Mtns
Aleutian Islands
Alaska Peninsula
Alaska Range
Talkeetna Mtns
WrangeE Mtns
Kenai Mtns
Chugach Mtns
St Elias Mtns
Coast Mtns
Total
723
~3
~230
960
1250
13 900
800
8 300
4 600
21600
11800
10 500
74 700 km 2
Areas of glacier ice within drainage basins can also be measured, but subjective
interpretation of ice divide locations is involved. A complete, glacier-by-glacier
inventory in some regions will be very difficult, but not just because of the large
numbers of glaciers. Some glaciers span political boundaries or drainage basin divides.
Most of the larger glaciers are bounded in part by obscure or constantly changing ice
divides, making objective assessment difficult. A particularly extreme example is Bering
Glacier: it is in and between two countries (USA, Canada), two major drainages
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A. Post and M. F. Meier
(Pacific, Chitina-Copper), and two major mountain ranges, (Chugach and St Elias
Mountains). Furthermore, the main glacier drainage system has at least five differently
named component areas (Stellar, Bering, Columbus, Quintino Sella Glaciers and
Bagley Ice Field), and estimates of its total area range from 1740 to 6200 km 2
depending on how the 'Bering Glacier' is defined (Table 2).
TABLE 2.
What is the area of Bering Glacier? [km2 ]
'Bering Glacier' part of piedmont lobe
Piedmont lobe (mostly ablation area)
Ice drainage to piedmont lobe
'Bering Glacier' and 'Bagley Ice Field' system
Frequently published value
* Includes 490 km 2 in Canada. Total area is only approximate
location of ice divides is very uncertain.
f Preferred value.
1740
2800
5000*f
6200*
5800*
as the
INVENTORY OF THE GLACIERS OF THE BROOKS RANGE
A glacier-by-glacier inventory of the Brooks Range was performed using preliminary
copies of topographic maps of 1:63 350 scale, with glacier margins checked or reinterpreted by comparison with aerial photographs. In this study, 1001 glaciers were
identified and measured, and additional small ones may have been missed. The exposed
ice area is 647 km2 and a total area (exposed plus moraine-covered ice) is 723 km 2 .
Individual glaciers range in area from 0.03 km 2 to 16.8 km 2 , with a mean area of
7.23 km 2 . The amount of glacierized area increases from west to east and from north
to south, as does the altitude of the mountain peaks. Northward facing basins are
more heavily glacierized than the basins facing south. The altitude of the glaciers
ranges from 919 m (base of the lowest) to 2108 m (top of the highest); the mean
altitude weighted by area of all glaciers is 1797 m.
DISCUSSION
Vivian:
We have the same problems on a smaller scale in the western Alps as Meier has shown
us. For example, in the Mont Blanc area, ice drains into the River Po (Italy) and into
the Arve and Rhône (France). There is also a problem in delineation of the different
glaciers flowing out of the same ice caps. These are indeed great problems of glacier
inventory.
Meier:
Yes, I agree.
Miiller:
Would you please indicate what techniques you intend to use for those glacierized
areas where the standard glacier inventory cannot be completed for lack of funds.
Meier:
First, we are measuring a number of parameters for well known or important glaciers
(location, area, maximum and minimum and, sometimes, median altitude, equilibrium
line altitude, classification and snout activity, etc.) In Alaska this is less than 50
glaciers.
Second, we are measuring the total glacier area in major mountain ranges,
A preliminary inventory of Alaskan glaciers
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individual massifs, etc. In some cases, we are dividing these into major drainage basins
also but this is sometimes difficult because the location of the ice divides is not always
certain.
Third, we intend to measure in detail all glaciers in selected small areas in order to
obtain information on lengths, altitudes, etc. by a sampling technique.
Finally, as time and circumstances permit, we will make more complete inventories
such as those for the North Cascades, Sierra Nevada and Brooks Range.
Williams:
Why don't you use a polar planimeter for a more accurate measurement of glacier
areas from topographic maps? Is it a question of personnel and resources or time?
Meier:
We did use a planimeter in some cases, in other cases we counted dots. In either case,
we simplified the glacier outline to speed up the area measurement. We could have
measured the areas more accurately but this would not be consistent with the
approximate nature of the basic data.