NORTH CASCADE GLACIER CLIMATE PROJECT 1995 REPORT

Mauri Pelto: Director North Cascade Glacier Climate Project

Nichols College, Dudley, MA 01571

For the third consecutive year late summer snowpack was quite low on North Cascade glaciers. The result of substantially more summer melting than winter snow accumulation is a negative mass balance and the continued shrinking of North Cascade glaciers. This year on the average glacier a 0.7 meter slice of glacier was lost to this excess melting. The cause of negative mass balance was a combination of reduced winter season precipitation, in particular from November-January, an early onset of spring melting, and a summer season that was drier than normal and warmer than the long-term average. This summer was not, however warmer than the average summer temperatures of the last 10 years. 

CONTINUED GLACIER RETREAT

The most interesting observation of 1994 was that Milk Lake Glacier north of Glacier Peak has completely disappeared. There are now a few icebergs floating in expanding Milk Lake. This glacier is still shown on the Lime Mountain quadrangle, as quite substantial in size. The glacier ceased to exist probably in the summer of 1992 or 1993.

Table 1 contains the latest measurements of terminus change on both Glacier Peak and Mt. Baker glaciers surveyed during 1993 or 1994 by NCGCP. The retreat has accelerated during the 1990-1994 period. The retreat of these glaciers still leaves each of them longer than they were in 1950. This is not likely to be the case for long since the lower several hundred meters on each of these glaciers is quite inactive. In particular the terminus of the Vista and Ptarmigan Glacier on Glacier Peak show little activity. On Mt. Baker it is the Talum and Mazama Glacier termini that appear most inactive.

Sholes Glacier near Camp Kiser on Ptarmigan Ridge, continues to thin rapidly, although terminus retreat is quite slow. Foss Glacier and Daniels Glacier in the Mt. Daniels area are beginning a period of rapid retreat resulting from a decade of rapid thinning. In both cases the lower section of the glacier has become detached from the upper section. The lower section of the Foss Glacier comprises a third of the glacier's total area. This stagnant ice mass will not last long. The lower 200 meters of Daniels Glacier is detached; however, this section often has heavy snowcover and though clearly separating from the glacier above will not disappear in the near future. Iceworm Glacier on Mt. Daniels no longer has any crevasses, because of the rapid thinning that is reducing glacier movement. This glacier continues to retreat at both the head and terminus of the glacier. Given a continuation of the current climate this glacier will not survive for more than 10 years. 

Fresh snowfall on August 17 on Mt. Daniels

CHANGES IN GLACIER RUNOFF DUE TO CLIMATE AND RETREAT

IN CLE ELUM RIVER BASIN

This basin has witnessed the steady retreat of its glaciers. Table 2 documents the loss of glacier area in Cle Elum Basin since the Little Ice Age Maximum. Beginning about 1850, based on the age of trees on the Little Ice Age moraines, these glaciers began to retreat. By 1958, 14 glaciers remained with an area of 2.5 km2. There was little change from 1958 until 1984. From 1984 to 1994 rapid retreat has reduced glacier area to 1.6 km2.

Summer glacier runoff is the product of glacier covered area and total summer ablation. The glacier-covered area is known, ablation has been measured annually since 1984 on Daniels and Ice Worm Glacier, providing direct determination of glacier runoff. Runoff from the glacier has also been measured in the outlet streams from Daniels and Ice Worm Glacier during each summer since 1986. Comparison of mean summer temperature and total summer ablation has provided an equation for determining ablation from mean summer temperature data at Stampede Pass. This is used to reconstruct mean summer glacier runoff for the 1930's and 1960's (Table 2). Runoff has declined by 50% since the 1930's when Cle Elum Reservoir began operating and by 25% since 1984. The consequent glacier runoff reduction since the 1930's is 3200 acre/feet for the July-September period.

Ice Worm Glacier at the head of Hyas Creek on Mt. Daniels is rapidly shrinking. Since 1985 this glacier has lost 25% of its area. The Upper Ice Worm Glacier has lost 50% of its area since 1965, by 1987 it was no longer a glacier. The remaining snowfield in the Upper Ice Worm area has continued to shrink. The result of the rapid shrinking of these small glaciers is noted in a comparison of mean August runoff in Hyas Creek a short distance below the glaciers (Table 3). A comparison of recent changes in runoff in glaciated and unglaciated basin is noted by contrasting runoff from unglaciated Spinola Creek, the adjacent basin to the south, Hyas Creek and heavily glaciated Daniels Creek. Table 3 indicates the decline in summer runoff has been highest in Spinola Creek and has been moderated to a great extent by the existence of a glacier in Daniels Creek. In Ice Worm Creek the moderation of late summer low flow has declined from 1986 through 1994, as glacier area has declined. It is evident that with the current climate Ice Worm Glacier will cease to exist within the 10-20 years. This will reduce mean August runoff into Cle Elum River by approximately by 360,000 ft3/day. This in conjunction with the retreat of other glaciers in the basin would reduce August streamflow into Cle Elum Reservoir by 10-12%.

CHANGES IN NORTH CASCADE ALPINE RUNOFF

Examination of runoff records from nine North Cascade streams indicate three significant changes in alpine runoff in the North Cascades for the 1985-1993 period (Table 4). 1) A 30% increase in mean November runoff primarily reflecting two large storm events in 1990 and 1991.

2) An increase by 16% of February-April runoff, despite below average precipitation, reflecting increased early season melting. 3) Decreased June-September runoff. Annual runoff has changed only moderately due to a slight drop in annual precipitation. Increased spring flow raises flood and erosion potential during an already high water period. Reduced summer runoff stresses aquatic ecosystems during a low flow period.

Changes in North Cascade sreamflow are the same in glacier and non-glacier streams from November-May. However, there is a significant difference in the change in summer runoff. The reduction of runoff from July-September has averaged 36% in Newhalem Creek Basin and Skykomish River Basin, each with less than 1% glacial cover. The reduction for the July-September period has ranged from 12 to 14% in Thunder Creek, Stehekin River and North Fork Nooksack River basins, which are the three basins with more than 3% glaciated area. This illustrates that a significant change in late summer runoff has occurred in the North Cascades and that this change is less pronounced in glacier basins, demonstrating the critical role glaciers play late in the summer in moderating late summer low flow periods (Table 4).

NCGCP has had a busy year in terms of publications (listed on last page). The Pack and Paddle, and Wild Cascades articles have generated a lot of scientific and reader interest. In addition I have also received substantial donations to the glacier photo archive from Hans Sauter and Austin Post, and Fred Darvill will be meeting with me to review photos this summer. I am currently arranging with the National Park Service through Jon Riedel to house this collection in Marblemount. Hopefully by the summer of 1996 it will be in place. If you have any photos or slides documenting the position of glacier termini from the 1950s-1980's that you are willing to donate please send them my way. After I analyze each I will catalog and place in the archive.

Table 1: Glacier Retreat 1984 to 1993* or 1994 on Mt. Baker and Glacier Peak glaciers monitored by NCGCP.

Retreat in Meters

MT. BAKER

Boulder 105

Coleman 135

Easton 47 *

Mazama 92

Rainbow 113

Squak 38*

Talum 116* 

GLACIER PEAK

Ermine 65

Kenneday 103

Ptarmigan 57

Scimitar 62

Vista 80

Table 2. Change in Glacier area in the Cle Elum River Basin since the maximum of the Little Ice Age. Runoff is listed in acre/feet because that it the unit local water resource managers use.

Year Number of Glacier Summer Glacier 

Glaciers Area Runoff

1850 -- 8.6 km2 17,500 acre/feet

1930 -- 3.2 6,500

1958 14 2.5 5,000

1984 11 2.1 4,300

1994 9 1.6 3,300

Table 3. August Runoff in heavily glaciated Daniels Creek, Moderately glaciated, Hyas Creek and unglaciated Spinola Creek. All three streams drain the west side of Mount Daniels. Runoff is reported in ft3/sec.

Year Spinola Hyas Daniels

1986 10.7 8.1 13.5

1987 9.1 7.8 13.9

1988 12.3 7.3 12.1

1989 12.1 7.4 12.9

1990 11.8 7.0 12.4

1991 16.1 8.2 15.8

1992 8.0 5.6 10.4

1993 8.7 6.3 10.4

1994 7.3 5.4 10.2

Table 4. Percentage change in mean monthly discharge on five North Cascade streams gauged by the USGS from the 1950-1980 to the 1985-1993 period. Note the much larger decrease in summer runoff in basins with less than 1% glacier covered area (Newhalem, Skykomish), compared to Stehekin 3%, Nooksack 12% and Thunder 14% glacier cover.

Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Annual

Newhalem - 3 +46 -17 - 8 +16 +15 +29 + 8 -17 -33 -37 -37 - 2

Skykomish -14 +41 -32 - 1 + 4 + 4 +18 - 8 -25 -37 -35 -36 - 8

Stehekin - 8 +56 -9 -22 + 5 +28 +20 - 3 -19 -21 - 9 -13 - 6

Nooksack - 6 +26 -25 - 6 + 7 +19 +34 + 9 - 5 -12 - 6 -18 0

Thunder - 9 +37 -16 - 2 + 2 +19 +31 +12 - 6 -13 - 7 -20 - 1

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