Skykomish River

Skykomish River: Impact of ongoing Glacier
Retreat on late summer low flows
On the web: www.nichols.edu/departments/glacier/
Contact:
Mauri Pelto, [email protected].
January, 2010, updated January, 2012
North Cascade Glacier Climate Project: Since 1984
Glaciers act as natural reservoirs storing water in a frozen state instead of behind a dam. Glaciers modify streamflow releasing the most runoff
during the warmest, driest periods, summer, when all other sources of water are at a minimum. Annual glacier runoff is highest in warm, dry
summers and lowest during wet, cool summers. The amount of glacier runoff is the product of surface area and ablation rate. The glacier retreat and
loss of glacier runoff has been quite pronounced in the Skykomish River Basin. This fact sheet examines the specific changes in glaciers and glacier
runoff, further details can be provided.
Glacier retreat and changes in summer runoff have been pronounced in the Skykomish River Basin, North Cascades, Washington from 1950-2009.
An analysis comparing USGS streamflow records for the 1950-1985 to the 1985-2009 period indicates that during the recent period the Skykomish
River summer streamflow (July-September) has declined 26% in the watershed, spring runoff (April-June) has declined 6%, while winter runoff
(November-March) has increased 10% (Figure 1). The minimum mean monthly August discharge from 1928-2010 occurred in 2003 and 2005 when
streamflow was 15.1 m3s-1 and 15.2 m3s-1 respectively. From 1929-1985 streamflow was less than 14 m3s-1 during the glacier melt season on a single
day in 1951. From 1986-2007 there were, 217 days with discharge below 14 m3s-1 with nine periods lasting for 10 consecutive days (Figure 2). In
the Skykomish River watershed from 1958-2009 glacier area declined from 3.8 km2 to 2.1 km2. Columbia, Foss, Hinman and Lynch Glacier, the
primary glaciers in the basin, declined in area by 10%, 60%, 90% and 35% respectively since 1958. Annual mass balance measurements completed
from 1984-2009 on Columbia, Foss and Lynch Glacier indicate a mass loss of 13.1 m w.e. Despite 15% higher ablation rates during the 1985-2009
period, the 45% reduction in glacier area led to a 38% reduction glacier runoff between 1958 and 2009. The 38% reduction in glacier runoff did not
lead to a significant decline in the percentage summer runoff contributed by glaciers under average conditions; the contribution has remained in the
range of 1-3% from July-September. The glacier runoff decline impacted river discharge only during low flow periods in August and September. In
August, 2003 and 2005 glacier ablation contributed 1.5-1.6 m3s-1 to total discharge, or 10-11% of August discharge. While declining glacier area in
the region has and will lead to reduced glacier runoff and reduced late summer streamflow, it has limited impact on the Skykomish River except
during periods of critically low flow, below 14 m3s-1 when glaciers currently contribute more than 10% of the streamflow.
Skykomish
10,000
9,000
Discharge (cfs)
8,000
Monthly mean streamflow, in ft3/s
Winter
7,000
Monthly mean streamflow, in ft3/s
Spring
6,000
Monthly mean streamflow, in ft3/s
Summer
5,000
Linear (Monthly mean streamflow, in
ft3/s Winter)
4,000
Linear (Monthly mean streamflow, in
ft3/s Spring)
3,000
Linear (Monthly mean streamflow, in
ft3/s Summer)
2,000
1,000
Spring = -17.782x + 6432.1
Winter = 7.333x + 4117.4
2005
2000
1995
1990
1985
1980
1975
1970
1965
1960
1955
1950
0
Summer = -22.19x + 2782.8
Year
Figure 1. Streamflow at the USGS gaging station on the Skykomish River at Gold Bar. Most notable is the consistently lower summer streamflow
since 1976, despite an increase in annual precipitation during this interval.
35
30
Days of Low Flow
25
20
15
10
5
0
1957 1986 1987 1988 1989 1991 1992 1993 1994 1998 2001 2002 2003 2005 2006 2007
Year
Figure 2: Low flow days during the summer since 1946.
In Figure 3 the change in flow flow for the Gold Bar station for three time periods and the same time period for Gold Bar and South Fork. Note the
ratio of South Fork to Gold Bar is consistently around 0.60. This would suggest the same would be close to true for the south fork for the recent
periods. The most notable change is the substantial decrease in mean summer flows.
Discharge (cubic feet second)
8000
7000
6000
Skykomish River 1946-1982
5000
4000
3000
2000
1000
0
Skykomish Gold Bar 19852006
Skykomish-Gold bar 19852009
South Fork Skykomish 19461982
Figure 3. Comparison of streamflow in the Skykomish River at Gold Bar and in the South Fork Skykomish for the 1946-1982 period, and then for
Gold Bar to more recent periods of 1985-2006 and 1985-2009. The hydrograph still has two peaks, a rain dominated peak in November-December
and snow melt peak in April-July. The former is supplanting the latter as the major streamflow peak.
Lynch Glacier is on the north side of Mount Daniels, the highest point in the Skykomish Watershed and drains into the South Fork Skykomish
River. In USGS maps of the region the glacier flows down the mountain ending in basin, with a modest fringe of water showing, this configuration
is evident in the 1960 image below. This lake, usually referred to as Pea Soup Lake, expanded rapidly between 1978 and 1983, as the portion of the
glacier occupying this basin disintegrated, by 1988 the lake is fully open water. Lynch Glacier retreated 390 m from 1950-1979, almost all of it
occurring in a rapid breakup of the the glacier in Pea Soup Lake. From 1979-2009 the glacier has retreated 132 m from the lake shore. Annual mass
balance measurements indicate the loss of 13 meters of ice thickness on average. More importantly in 2003 on the upper west section of the glacier
section, a bedrock ridge and scattered outcrops were exposed. The features have continued to expand, indicative of thinning of the glacier in its
accumulation zone, note the rock outcrop on the upper right portion of the glacier in 2007 in the right image. This is an indicator of a glacier that
cannot survive current climate. Lynch Glacier has lost 35% of its area since 1958. As Pea Soup Lake has matured, it has turned from pea green to
turquoise in color.
Figure 4: Lynch Glacier from left to right in 1960 (Austin Post), 1988 and 2007.
Hinman Glacier is on the west side of Mount Hinman drains into the South Fork Skykomish River. This was the largest glacier in the North
Cascades south of Glacier Peak 50 years ago. Today it is nearly gone. Hinman Lake, unofficial name, has taken the place of the lower portion of the
former glacier, which still has a couple of separated relict ice masses. In the USGS map based on 1958 photographs the glacier extends from the top
of Mount Hinman at 2300 meters to the bottom of the valley at 1525 meters (below left). The next image is of Hinman Glacier from the west in 1988,
the Hinman Glacier is now a group of four separated ice masses, three are significant in size still.. Lastly is a 2009 view from the far end, north end
of Lake Hinman up the valley and mountain side that was covered by the Hinman Glacier, now 90% gone compared to 1958. The new lake is one
kilometer long. This is no longer a glacier and is just a few relict pieces of ice as viewed from the 1958 terminus location in 2009, the largest has an
area of 0.05 square kilometers.
Figure 5. At left outline of Hinman Glacier on the 1965 USGS topographic map based on 1958 aerial photographs, in the middle the glacier in 1988
and at right a view from the new Hinman Lake in 2009 at the 1958 terminus location(Tom Davneport).
Foss Glacier is on the Northeast side of Mount Hinman and drains into the South Fork Skykomish River. As recently as 1984 this glacier covered the
majority of this mountain face. Today the glacier is rapidly thinning, separating into smaller parts and retreating. Foss Glacier had by the middle of
August lost all of its snowcover in 1992, 1993, 1994, 1998, 2003, 2005, and 2009. This has led to thinning of the upper reaches of the glacier.
Thinning of the upper reaches of a glacier is an indicator of a glacier that cannot survive current climate. The lower section detached from the upper
section in 2003 and melted away in 2009. Below left is Foss Glacier in 1988, in the middle in 2005 with the 1988 outline, and in 2009. In the latter
two images the snowpack is essentially gone from this dying glacier. Annual balance measurements indicate a loss of over 15 meters of average ice
thickness, which for a glacier that averaged 30-40 m in thickness represents 40-50% of the volume of the glacier lost between 1984 and 2009. The
reduction in glacier extent has been 40% between 1984 and 2009 and 60% between 1958 and 2009.
Figure 65. Foss Glacier at left in 1988, in the middle in 2005 and at right in 2009 taken from the west ridge of the Lynch Glacier.
Columbia Glacier occupies a deep cirque above Blanca Lake ranging in altitude from 1460 m to 1720 m and is the headwaters of the North Fork of
the Skykomish River. Kyes, Monte Cristo and Columbia Peaks surround the glacier with summits over 2200 m. This glacier has the lowest mean
altitude of any substantial glacier in the North Cascades. The glacier is the beneficiary of locally heavy precipitation and orographic lifting over the
surrounding peaks causing cooling of the air mass greater than that expected from the elevation of the glacier. Facing southeast Columbia Glacier is
protected from afternoon sun. During the winters storm winds sweep from the west across Monte Cristo Pass dropping snow in the lee on Columbia
Glacier. Avalanches spilling from the mountains above descend onto and spread across Columbia Glacier. The avalanche fans created by the settled
avalanche snows are 20 feet deep even late in the summer. Nearly a third of the glacier is covered by avalanche fans, but no summer avalanches
have been observed. Columbia Glacier has retreated 134 m since 1984. The head of the glacier has retreated 90 m. Lateral reduction in glacier
width of 95 m in the lower section of the glacier and the reduction in glacier thickness are even more substantial as a percentage. The major issue is
that the glacier is thinning as appreciably in the accumulation zone in the upper cirque basin as at the terminus. This indicates a glacier that is in
disequilibrium with current climate and will melt away with a continuation of the current climate conditions. The glacier has lost 15 m in thickness
since 1984, but still remains a thick glacier, over 75 meters in the upper basin and will not disappear quickly. In 2003, 2004, 2005 and 2009 there
has been nearly a complete exposure of the glacier surface and the loss of all firn and snowcover on the glacier. This exposed more than 50 annual
layers in the 2005 image seen below. Streamflow and ablation are measured each summer on Columbia Glacier. Glacier runoff ranges from 15-30
cfs during the summer melt season from this glacier alone.
Figure 7. Headwaters of the North Fork of Skykomish River emerging from Columbia Glacier in 2009 at left. At right a view of the Columbia
Glacier from its head in 2005 with almost the entire glacier exposed at the start of August.
2012-2013 summer work
We will continue the glacier monitoring in the basin. In addition we will to complete synchronous streamflow measurements during low flow
periods at many locations in the basin (Figure 8). This method allows identification of the percentage of input from each region in the watershed
during a low flow period, information that cannot be gleaned from continuous measurements at a single or pair of gaged stations.
References:
Bach A. 2002. Snowshed contributions to the Nooksack River watershed, North Cascades Range, Washington. Geogr. Rev. 92 (2): 192-213.
Dery S, Stahl K, Moore RD, Whitfield W, Menounos B, and Burford JE. 2009. Detection of runoff timing changes in pluvial, nival and glacial rivers
of western Canada. Water Res. Res., 45, doi:1029/2008WR006975.
Fountain, A and Tangborn, W.V. 1985. 'The effect of glaciers on streamflow variations'. Water Res. Res., 21, 579-586.
Luce CH, and Holden ZA. 2009. Declining annual streamflow distributions in the Pacific Northwest United States, 1948–2006. Geophysical
Research Letters, 36, L16401, doi:10.1029/2009GL039407.
Pelto, M.S. 2011. Skykomish River, Washington impact of ongoing glacier retreat on streamflow, Hydrologic Processes.
Pelto, M.S., 2009. Forecasting Temperate Alpine Glacier Survival from Accumulation Zone Observations. The Cyrosphere 3, 323-350.
Pelto, M.S., 2008. Impact of Climate Change on North Cascade Alpine Glaciers, and Alpine Runoff. Northwest Science, 82: 65-75.
Pelto, M.S., 2006. The Current Disequilibrium of North Cascades glaciers. Hydrologic Processes.,
Pelto, M.S. 1993. Current Behavior of Glaciers in the North Cascades and Effect on Regional Water Supplies. Washington Geology, 21(2), 3-10.
Figure 8. Watershed map indicating the location of suggested locations for instantaneous synchronous flow measurements. Troublesome Creek, N
Fk Skykomish (2), Beckler River (2), S Fk Skykomish, Deception Creek, Miller River, Foss River,
Figure 9. On the following page Is the annual photographs of Columbia Glacier taken from below the terminus each year in early August from 19842008.