THE DISEQUILBRIUM OF NORTH CASCADE, WASHINGTON GLACIERS

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1 THE DISEQUILBRIUM OF NORTH CASCADE, WASHINGTON GLACIERS CIRMOUNT 2006, Mount Hood, OR Mauri S. Pelto, North Cascade Glacier Climate Project, Nichols College Dudley, MA

2 NORTH CASCADE GLACIER CLIMATE PROJECT Terminus behavior measured on 47 glaciers. Annual balance measured on 10 glaciers. Longitudinal Profile mapping on 14 glaciers. Identification of the response of glaciers to climate change Monitoring changes in glacier runoff.

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4 Glacier response to climate change Climate Change can cause variations in both temperature and snowfall, causing changes in mass balance. A glacier with a sustained negative balance is out of equilibrium and will retreat to reestablish equilibrium. A glacier with sustained positive balance is also out of equilibrium, and will advance to reestablish equilibrium.

5 Equilibrium versus Disequilibrium Glacier retreat results in the loss of the low-elevation region of the glacier. Since higher elevations are cooler, the disappearance of the lowest portion of the glacier reduces overall ablation, thereby increasing mass balance and potentially reestablishing equilibrium. However, if the mass balance of a significant portion of the accumulation zone is negative, it is in disequilibrium with the climate and will melt away without a climate change.

6 Evidence for Disequilibrium The magnitude of the retreat of all 47 glaciers observed, resulting in the loss of 5 out of 47 North Cascade glaciers. Cumulative annual balance loss of meters from , with average glacier thickness of meters. Thinning in the accumulation zone approximating thinning in the ablation zone on Columbia, Colonial, Daniels, Foss, Ice Worm, and Lower Curtis Glacier.

7 Glacier Disequilibrium Identification The key symptom of a glacier in disequilibrium is thinning along the entire length of the glacier. Such as on Foss Glacier below.

8 Accumulation zone of Columbia Glacier, August 2005

9 Whereas a glacier retreating to a point of equilibrium will thin predominantly in the lower section of the glacier. For example, Easton Glacier will likely shrink to half its size, but at a slowing rate of reduction, and stabilize at that size, despite the warmer temperature, over a few decades.

10 Why Measure Glacier Mass Balance? Mass balance is the dominant control of future terminus behavior. Annual mass balance is the best measure of annual climate and its impact on a glacier and is viewed as one of the most sensitive natural recorders of climate Annual balance is what we determine on North Cascade glaciers. This is the mean net change in glacier thickness measured on a fixed date each year. It is reported as an average value of snow or ice lost in meters of water equivalent gained or lost.

11 Lynch Glacier Mass Balance Measurement Network: Dots indicate accumulation measurement sites. This is a high density of 200 pts/km 2. The result is excellent accuracy, mean densities in the traditional methods is less than 20 pts/km 2.

12 Crevasse Stratigraphic mass balance measurements provides a two dimensional view of snowpack thickness.

13 Crevasse Stratigraphy Determined in vertically walled crevasses the snow layer can be traced from crevasse to crevasse and can be corroborated with probing as well. As a result the accuracy of this method is higher than snowpits or probing where only a point measurement is obtained.

14 Probing

15 The annual balance records indicate the high degree of correlation between nine North Cascade glaciers including South Cascade Glacier observed by the USGS North Cascade Glacier Annual Balance Columbia Daniels Foss Ice Worm Lower C urt is Lynch Rainbow Yawning So ut h C ascad e Easton -4 Year

16 Glacier Cumulative Annual Balance: The negative trend has increased. North Cascade Glacier Cumulative Annual Balance Years

17 Terminus Behavior : Rapid retreat of all glaciers period: Type 1 glaciers advance; Type 2 glaciers approach equilibrium; Type 3 glaciers continue retreat : Increasing retreat of all North Cascade glaciers. Disappearance of a significant number of glaciers. The differing response of the three glacier types is due to the difference in response time.

18 Glacier Type Characteristics Type 1 have the highest mean elevations (2200 m), largest mean slope (0.42, +0.07), highest measured mean accumulation, most extensive crevassing and highest measured terminus region velocity (20 m/a, + 3 m/a ). Type 2 glaciers have on average, a lower slope (0.35, +0.08), a lower terminus region velocity (7 m/a, +4 m/a), less crevassing, and a lower mean accumulation rate than Type 1 glaciers. Type 3 glaciers have the lowest slopes (0.23, +0.06), least crevassing, and lowest mean terminus velocity (5 m/a, + 3 m/a).

19 Easton Glacier 1992: Type 1

20 Easton Glacier 2003: A retreat of 300 m in 10 years.

21 Boulder Glacier Type

22 Lower Curtis Glacier 1985 and 2003 Type 1: A vigorous glacier that is still retreating ( 130 meters since 1987) and thinning dramatically.

23 Lower Curtis Glacier 2006

24 Lynch Glacier 1978 Type 2: Wide active front reaching Pea Soup Lake, which it filled in 1976.

25 Lynch Glacier 1992 Type 2: Narrow inactive front no longer in contact with lake, has retreated 120 m since 1984.

26 Columbia Glacier Type

27 Columbia Glacier Type : The terminus is thick and retreat has been 5 m/ year. However, thinning has been dramatic.

28 Surface elevation change on longitudinal profiles from three glaciers. 30 Longitudinal Profile Elevation Change Lower Curtis Easton Columbia elevation change (m) Distance from Terminus Benchmark

29 1800 Columbia Glacier: Changes in longitudinal profile shows thinning from terminus to glacier head indicating no safe place to retreat to. This is common on many North Cascade Changes glaciers. in surface elevation on Columbia Glacier Little Ice Age elevation (m) Distance (km)

30 Whitechuck Glacier (Post and Scurlock). Type 3 glacier.

31 Whitechuck Glacier Type 3: The former location of the north branch, which retreated more than 1000 meters from 1985 to 2002.

32 Foss Glacier 1988 and 2005 Type 3

33 Causes of glacier mass loss has been declining Winter Snowpack as noted on April 1 at USDA Snotel sites. Since precipitation has not declined this is a result of rising temperature causing winter melting and increased rainfall. North Cascades April 1 SWE SWE (m) April 1 SWE Linear ( April 1 SWE) 0.50 y = x Year

34 Glacier mass loss is also due to rising summer temperatures in the North Cascades, as noted here for Diablo Dam which is representative of the entire range. Ablation Season Temperature Temperature (C) Mean C Linear (Mean C) Year

35 Ice Worm Glacier another case of disequilibrium

36 Canadian Rockies have glaciers in disequilibrium

37 Grinnell Glacier 1940 and 2005 in disequilibrium

38 Conclusions All North Cascade glaciers have thinned significantly since The mean annual balance of -.41 m has led to an average thinning of 9.5 m, 15-30% of the entire glacier volume. All North Cascade glaciers are retreating significantly, and 5 of 47 monitored annually have disappeared. Not much left of Ice Worm Glacier below. The result is less summer glacier runoff.