Pacific Northwest Glacier Mass Balance 2013

North Cascades Climate Conditions:
The 2013 winter accumulation season featured 93% of mean (1984-2013) winter snow accumulation at the long term USDA Snotel stations in the North Cascades, Washington (Figure 1). The melt season was exceptional by several measures. The mean summer temperature from June-September and July-September at Lyman Lake is tied with the highest for the 1989-2013 period (Figure 2). The average minimum temperature at Lyman Lake was the highest since 1989 for the July-September period, and tied with the highest for the June-September period (Figure 3). SeaTac airport minimums were high as well indicating the regional nature.

Glacier Mass Balance:
Snow depth was measured at a 30 m spacing across the entire glacier on August 4th. The position of the snowline indicates the location where snow depth is zero. Assessment of stakes emplaced in the glacier from Aug. 3-20 indicates mean ablation during the period of 7.8 cm/day. Assessment of ablation from remapping of the snowline on Sept. 1 indicates mean ablation of 7.5 cm/day during the August 4th-Sept. 1st period. A preliminary map of Sholes Glacier mass balance for Aug. 8th is seen below (Figure 6). The contours are in meters of water equivalent, which is the amount of water thickness that would be generated if the snow or ice was melted. Note the similarity of the 1.75 m contour and the Sept,. 12th snowline.The best measure of ablation over the period from August 4th to Sept. 12th is the shift in the snowline, as identified in satellite imagery (Figure 7 and 8). The snow depth at a particular location of the snowline on Sept. 12th indicates the snow ablation since August 4th. Observations of the snowline margin on Aug. 20, Sept. 1 and Sept. 12 indicated mean ablation of 7.4 cm per day from Aug. 4th to Sept. 12th.

sholes 2013 August melt
Figure 4 Comparison of snowpack on Sholes Glacier on August 4th and September 1st, 2013

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Figure 5. Sholes Glacier snow depth measurement network

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Figure 6. Snow depth distribution in snow water equivalent on Sholes Glacier on Aug. 8th, 2013.

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Figure 7 August 4th satellite image showing snowline on Sholes Glacier from Landsat imagery.

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Figure 8. September 12 snowline on Sholes Glacier from Landsat imagery

Snow depth observations on Easton Glacier on the bench below the main icefall at 2000 m, yielded an average depth of 3.1 m on Aug. 10th. The bench was completely snowcovered on Aug. 10th. GPS measurements of the snowline on Sept. 15th indicate ablation of 2.75 m since Aug. 10th. This is an ablation rate of 7.6 cm of snow melt per day. This is 0.2 cm/day higher than Sholes Glacier. The time period is not identical either. The southern orientation of Easton Glacier typically leads to higher ablation rates at specific elevations than on Sholes Glacier. Satellite observations of the change in snowline position compared to snow depth observations from Aug. 4th to Sept 12th indicate mean ablation of 7.2-8.0 cm/day.

On the four Mount Baker glaciers a total of 380 snow depth measurements were made on (Figure 9). The initial mass balance assessment is -0.78 m on Columbia Glacier. -1.58 m on Easton Glacier, -0.5 m on Foss Glacier, -0.76 m Ice Worm, -0.85 m on Lower Curtis Glacier, -0.40 m Lynch Glacier, -1.85 m on Rainbow Glacier, -1.7 m on Sholes Glacier and -1.15 m on Yawning Glacier. easton crevasse depth
Figure 9 Snow depth in crevasse on Easton Glacier.

columbia glacier Ba 2013
Figure 10 Mass balance map for Columbia Glacier in meters of water equivalent.

On the Juneau Icefield in southeast Alaska the ablation season was warmer and longer than normal. The result was snowlines rising above average at Lemon Creek and Taku Glacier, where the Juneau Icefield Research Program measures mass balance. For Taku Glacier the ELA was 1050 m, 75 m above an equilibrium snowline, and 1115 m, 100 m above an equilibrium snowline for Lemon Creek Glacier. The final mass balance for these glaciers will be in the -0.5 to -1.0 m range for both. Further north the USGS reports preliminary results, from there two Alaskan benchmark glaciers, which indicate that Gulkana Glacier in the Alaska Range, mass balance was the 5th most negative year. At Wolverine Glacier in the Kenai Mountains mass balance will likely be the most negative on record. In British Columbia both the Helm Glacier and Place Glacier are observed annually for mass balance. On Sept 12, 2013 Landsat imagery indicates limited remaining snowcover on both of these glaciers. The snowline is at 2050 m on Helm Glacier and 2300 m on Place Glacier, red arrows. The snowcovered area is less than 20% on Helm Glacier and 30% on Place Glacier, which will lead to large negative mass balances (Figure 11 and 12). Hence, all 16 glaciers examined here will have significant negative mass balances in 2013.

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Figure 11. Landsat image indicating the snowline on Sept. 24, 2013 on Lemon Creek and Taku Glacier.

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Figure 12 Helm Glacier in Landsat imagery 9-12-2013

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Figure 13 Place Glacier in Landsat imagery 9-12-2013

Mass balance 2011 North Cascades, Washington and Juneau Icefield, Alaska

In the summer of 2011, the North Cascade Glacier Climate Project completed 430 measurements of snowpack on 10 glaciers using probing and crevasse stratigraphy. This is much less than our normal number because of the exceptionally deep snowpack. The probe we use was 5 meters long, beyond that only crevasses could be used. The mass balance was quite positive for the first time since 2002. The combination of a La Nina and a negative PDO almost always deliver a mass balance in the North Cascades, 9 of 11 times (Pelto, 2008). The March-May period was the coldest and wettest spring ever in the North Cascade region. Summer was also cool in the region. This led to positive balances ranging from +1.2 to +2.2 m, the first year with significant mass balance since 1999. The first image below is the preliminary mass balance map for the Lynch Glacier in 2011, indicating the measurement points, black dots, and the blue contour line is the snowline. The cumulative mass loss since 1984 is still 12 meters, or 20-30% of the total volume of these glaciers, second image below. . Below is the field season captured in images.

Fourteen hundred kilometers north the Juneau Icefield glaciers did not fare as well. As part of the Juneau Icefield Research Program mass balance measurements are made every summer on the Taku and Lemon Creek glaciers. This summer the program was headed by Jay Fleisher, the mass balance portion was spearheaded by Chris McNeil and Toby Dittrich, Portland Community College. Satellite imagery from Sept. 11, 2011 indicates the snowline at the end of the melt season was just over 1000 meters on Taku Glacier and nearly 1100 meters on Lemon Creek Glaciers. This is higher than average and indicates negative mass balances for both glaciers. Snowpit and probing measurements at 40 locations, will yield a more specific mass balance, than provided by the snowline. The snowline is quite similar to 2009 and 2010 with snowpack depths generally a bit lower, 2009 and 2010 were also negative mass balance years. The snowpits are typically 2-4 meters deep and quite an effort to dig, the image below is from Cathy Connor at University of Alaska Southeast. The cumulative mass balance loss since 1953 on Lemon Creek Glacier is 25 meters, 15 meters since 1984.