Terminus Response Time of North Cascade Glaciers


Mauri S. Pelto, Director  Founded 1983
Nichols College, Dudley, MA    mspelto@nichols.edu

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Updated 11/5/2013

Type 1 glacier with lots of crevassing, indicating higher velocity, and a substantial elevation range leading to high accumulation rates.

Sholes Glacier which has a moderate slope and modest accumulation rates is a Type 2 glacier.

 Lyman Glacier is a type 3 glacier, it has a low slope and low accumulation leading to a slow response to climate change.


Why have North Cascade glacier termini behaved differently this century?  On Snowfield Peak there are three glaciers Colonial, Neve and Ladder Creek which each have behaved differently.  Colonial retreated throughout the century.  Ladder Creek advanced from 1950-1975 and Neve stopped retreating from 1955-1980.  Thus, it is not simply recent climate driven since they share the same climate setting.  We observed the terminus behavior of 38 North Cascade glaciers during the last century to illustrate three different types of glacier response to climate change:
 1) Retreat from the Little Ice Age (LIA) to approximately 1950 followed by a period of advance from 1950-1976, and then retreat since 1976.
2) Rapid retreat from the LIA to approximately 1950, slow retreat or equilibrium from 1950-1976, and moderate to rapid retreat since 1976. 
3) Continuous retreat from the LIA to the present. 
  These types reflect different physical characteristics.

The initial response times (Ts) of North Cascade glaciers to both a  positive and negative mass balance changes resulting from climate change have been observed on 21 glaciers to be 4-16 years.  Thus, when the weather got cooler and wetter beginning in 1946 glacier advances began on Coleman Glacier in 1949 and on all Type 1 glaciers by 1960.  Similarly when the climate turned warmer and drier in 1977, glacier retreat commenced by 1987 on all Mount Baker glaciers, and by 1989 on all North Cascade glaciers.

The time required to reach a new steady state (Tm) for the post Little Ice Age warming was approximately 20-50 years on Type 1;40-60 years on Typ 2 glaciers, and at least 100 years on Type 3 glaciers.  Tm on North Cascade glaciers is a function of glacier velocity, glacier mean accumulation and glacier length.  The glaciers that have the highest mean accumulation and fastest velocity have the most rapid response time.   Velocity increases with increasing slope and increasing thickness.  Thus, in the North Cascades the large glaciers on the volcanoes tend to have the fastest response time. 

Full Report Follows

 Mauri S. Pelto, Department of Environmental Science Nichols College, Dudley, MA 01571: Cliff Hedlund, Oregon State University
Journal of Glaciology

Terminus Data        Glacier Home Page

Foss Glacier Type 3

Challenger Glacier Type 1


Observation of the differing terminus behavior of North Cascade glaciers in response to the same climate changes during the last century (Tangborn and others, 1990), has prompted the evaluation of the terminus behavior of 38 glaciers in the North Cascades for the 1890-1990’s period.  The objective is to determine the characteristics that lead to differential terminus behavior among North Cascade glaciers. 

To complete this task requires examination of the response time of glaciers to climate change.  For any glacier there is a lag time (Ts) between a significant climate change and the initial observed terminus response (Paterson, 1994), this is also referred to as the reaction time of the glacier.  It should be noted that Ts cannot be considered a physical property of a glacier and is expected to depend on the mass balance history and physical characteristics of the glacier.  In this paper Ts is simply defined as the time lag from an observed climate shift to the initial observed change from an advancing to a retreating termini or from a retreating to an advancing termini.    

In addition, for each glacier there is a response time to approach a new steady state for a given climate driven mass balance change (Tm), referred to as length of memory by Johannesson and others (1989). Johannesson and others (1989) defined Tm as the time-scale for exponential asymptotic approach to a final steady state (approximately 63% of a full response), resulting from a sudden change in climate to a new constant climate.  The magnitudes of Ts and Tm are crucial to interpreting past and current glacier fluctuations and predicting future changes (Paterson, 1994; Johannesson and others, 1989).

In nature a step change in climate causing an evolution from an initial to a final steady state never happens (Schwitter and Raymond, 1993).   The variability of climate forcing and the continuous changes in the glacier superimpose new disturbances on the response of the glaciers to previous climate.  This leads to the conclusion that Tm cannot be defined directly from observations in nature.  However, Tm cannot be accurately defined from models alone either. 

In this study we recognize that the response of the terminus is influenced by ongoing changes in forcing, limiting the accuracy of determination of Tm from terminus observations.  We use terminus observations to establish limits on the range of Tm, rather than attempting direct calculation of Tm from observations.  We use terminus observations to establish time limits on the range of Tm.  Our estimates of Tm are based on the understanding that, during a period of relatively constant climate, the glacier should advance to about 2/3 of its final adjustment in its terminus positions and the rate of advance/retreat of the terminus should be reduced to approximately 1/3 over a time period of length Tm. The difficulty of examining terminus response to a specific step change is minimized with respect to the post Little Ice Age warming , because the climate change and associated terminus response is large compared to climate changes and resulting terminus changes that have occurred in the last half-century

(Schwitter and Raymond, 1993; Burbank, 1981; Porter, 1986).  

In the North Cascades the disparate terminus behavior of glaciers has been noted by Hubley (1956), Post and others (1971), Tangborn and others (1990) and Pelto (1993). The primary goal of this paper is to examine the observed terminus behavior and glacier geographic characteristics of 38 North Cascade glaciers to determine why the terminus behavior history varies.  The secondary goal is to identify the ranges of Ts and Tm for the response of North Cascade glaciers to climate changes. 


The North Cascade Glacier Climate Project (NCGCP) has been observing terminus behavior on 47 North Cascade glaciers and measuring annual balance on 9 glaciers since 1984 (Pelto, 1993; 1996).   The primary objective of this glacier research has been to identify the magnitude and timing of glacier response to a climate change.  This NCGCP data set is extensive in its breadth, but not in its length of record, extensive USGS aerial photographic collections and the ongoing research by the USGS on South Cascade Glacier have been indispensable to this research in providing long-term records.

Terminus Observations

The magnitude of terminus changes from the Little Ice Age Maximum (LIAM) has been measured on 38 glaciers by utilizing 720 USGS vertical aerial photographs, taken by Austin Post between 1962 and 1979, 150 aerial photographs taken by Richard Hubley at the University of Washington from 1950 to 1955, and 120 photographs taken by J.B. Richardson and William Long of the US Forest Service from 1940 to 1960 (all of these photographs have been donated to NCGCP by William Long, Austin Post, and the USGS).            

Schwitter and Raymond (1993) noted the ease of identification and utility of the well-preserved Little Ice Age moraines for reconstructing former glacier profiles in the North Cascades and elsewhere.  The distance from the typically well preserved, fresh LIA moraines and trimlines to the current glacier front has been measured in each case using a laser ranging device (+1m).  Additionally on each of the 38 glaciers field measurements from the same LIA moraines to the current glacier front was completed on at least two occasions between 1984 and 1998.  The goal being to verify both the LIAM and the actual terminus position changes from 1984-1998.    In cases where the field measurements and photographic measurements differed by more than 20 m the glacier is not used in this analysis.  This was the case on two glaciers. 

Terminus change from 1850-1950 is the distance from the aforementioned LIAM and the position of the glacier terminus as in 1950 noted by Hubley (1956).   Terminus change from 1950-1979 is the change between the position noted by Hubley (1956) and the USGS aerial observations in 1979.  Neither, 1950 or 1979 perfectly match the timing of climate changes noted in the following section; however, they are closest to the climate shifts, beginning in 1944 and 1976 respectively, for which adequate aerial photographic observations were made.  Terminus change from 1979 to the present is based on comparison of the USGS aerial observations and repeated field measurements of the North Cascade Glacier Climate Project from 1984-1998 (Pelto, 1993; 1996).

To determine Ts a group of 21 North Cascade was observed to switch from retreat to advance shortly after 1944, and from advance to retreat shortly after 1976.  Observations of the initial post-1944 glacier advances were made by Long (1955 and 1956) and Hubley (1956).  Observations of the onset of retreat after 1976 are from Heikinnen (1984), NCGCP field observations (Pelto, 1993) and USGS aerial photographs from 1979. 

Glacier Characteristics

On seventeen of the aforementioned 38 glaciers more detailed observations are used to calculate theoretical estimates of Tm for comparison with observations of terminus behavior.  Each of these 17 glaciers had at least five terminus observations during the 1850 to 1998 period (Table 1)(Hubley, 1956; Long, 1955; Meier and Post, 1962; Pelto, 1993; Post and others, 1971).  To be able to calculate Tm terminus velocity u(t), mass balance near the terminus b(t), ice thickness (h) and glacier length (l) have to be determined.  Nine of the 17 glaciers have had annual balance measurements over a span of more than 10 years (Table 1)(Pelto, 1996; Krimmel, 1996).  Krimmel (1999) has observed b(t) and u(t) on South Cascade Glacier.  On the other 16 glaciers b(t) and u(t) have been directly observed for at  least two hydrologic years using stakes drilled into the glacier terminus area by NCGCP (Pelto, 1996; Krimmel, 1999). Measurement of u(t) relied on at least three points, in the lower 25% of the glacier’s length, which is within 200 m of the terminus in each case.    The longer term annual balance measured on nine of these glaciers indicates that the period of record for terminus mass balance measurement (1994-1996) was close to the 1984-1997 mean.

In 1998, Krimmel (1999) observed the length of the South Cascade Glacier.  Glacier length on the other 16 glaciers length has been taken from the most recent USGS maps compiled from aerial photographs between 1982 and 1984, and adjusted for the observed retreat up 1998.

Glacier thickness (h) has been measured on three North Cascade glaciers South Cascade Glacier (Krimmel, 1970), Easton Glacier (Harper, 1993) and Lewis Glacier.   The first two are both comparatively large glaciers for the area.  Each had a maximum mean profile depth of 60-80 m.   These measurements along with those of Driedger and Kennard (1986) on Cascade volcanoes, which yielded a mean thickness of 50 m on Mt. Rainier, and 35 m on Mt. Hood, illustrate that these glaciers are comparatively thin.  On Lewis Glacier the thickness was measured in a moulin that reached the base of the glacier in 1985, 1986 and 1987.  The thickness of each of the other 14 glaciers where direct measurement has not been made is assumed to be 50 m on thin concave or slope glaciers and 100 m on thicker convex or valley glaciers.  In both cases the resulting h is a maximum value, thus the Tm would be a maximum value too (Post and others, 1971).

Climate Data

A good single climate indicator for North Cascade glaciers behavior is the Pacific Northwest Index (PNI), developed by Ebbesmeyer and others (1991).  Figure 1 is a graph of the PNI during this century.  The index is based on March 15 snowpack depth at Paradise on Mt. Rainier, WA, mean annual temperature at Olga, WA., and total annual precipitation at Cedar Lake, WA.  Positive values reflect negative glacier mass balances. 


Since the maximum advance of the Little Ice Age (LIA) there have been three climate changes in the North Cascades sufficient to substantially alter glacier terminus behavior.   During the LIA mean annual temperatures were 1.0-1.5oC cooler than at present (Burbank, 1981: Porter, 1986).   The lower temperatures in the North Cascades led to a snowline lowering of 100 to 150 m during the LIA (Porter, 1986; Burbank, 1981).  Depending on the glacier, the maximum advance occurred in the 16th, 18th, or 19th century (Miller, 1971; Long, 1956).   North Cascade glaciers maintained advanced terminal positions from 1650-1890, emplacing one or several Little Ice Age terminal moraines. 

Retreat from the LIAM was modest prior to a still stand in the 1880’s (Burbank, 1981, Long, 1956).  Miller (1971) mapped the age of terminal moraines in front of Chickamin and South Cascade Glacier and found in each case that a late-19th century moraine was emplaced within 100 m of the LIAM.  On Mt. Rainier, just south of the study area, mapping of terminus changes by (Burbank, 1981) indicate that rapid and continuous retreat of Mt. Rainier glaciers from their LIAM began after the 1880-1885 still stand.   Long (1953) noted that retreat on Lyman Glacier and Easton Glacier became substantial only after 1890.  Long (1955) noted that the Lyman Glacier has been retreating steadily since the 1890’s.  Climate warming and retreat began about 1850, but because of the modest retreat and subsequent stillstand or advance of North Cascade glaciers around 1880, 1890 is used as the approximate time for the climate change that initiated a continuous substantial retreat from the LIA advanced positions in the North Cascades. 

This first substantial climate change was a progressive temperature rise from the 1880’s to the 1940’s.  The warming led to ubiquitous rapid retreat of North Cascade Range alpine glaciers from 1890 to 1944 (Rusk, 1924; Burbank, 1981; Long, 1955; Hubley, 1956). Each North Cascade glacier retreated significantly from its LIAM.   It must be emphasized that the entire retreat noted from the LIAM to 1944 did not occur in the 1890-1944 interval, observations do not exist on most glaciers to distinguish the exact timing of the initial post LIAM retreat, though retreat was minor before 1890 on glacier where observations exist.  Average retreat of glaciers on Mt. Baker was 1440 m from LIAM to 1950 (Pelto, 1993).  Average retreat of the 38 North Cascade glaciers in this study was 1215 m. 

The PNI from 1895-1923 is rising, but has a comparatively low mean (-0.34), that is still capable of generating retreat on North Cascade glaciers, that are all still in advanced positions from the LIA.  The PNI average during the 1924 –1944 was the high at 0.44.  This warm dry period has been noted around the world and in the North Cascades as a period of rapid glacier retreat (Burbank, 1981; Long, 1955; Hubley, 1956).  The second substantial change in climate began in 1944 when conditions became cooler and precipitation increased (Hubley 1956; Tangborn, 1980).  The climate change in 1944 is evident in the PNI record (Figure 1). The mean PNI from 1945-1976 was -0.37. This drop in the PNI average of 0.76 from the previous interval marks the climate change that initiated the advance of some North Cascade glaciers and the more positive mass balance for that period (Tangborn, 1980; Hubley, 1956). 

Hubley (1956) and Long (1956) noted that North Cascade glaciers began to advance in the early 1950s, after 30 years of rapid retreat.    This change was reflected in the mass balance of North Cascade glaciers.  A Runoff-Precipitation model constructed for South Cascade Glacier (Tangborn, 1980) yielded a mean annual balance of –1.15 m/a from 1924-1944, compared to –0.15 m/a from 1945-1976. 

Approximately half the North Cascade glaciers advanced during the 1950-1979 period (Hubley, 1956; Meier and Post, 1962).  Advances of Mount Baker glaciers ranged from 120 m to 750 m,  ana verage of  480 m, and ended in 1978 (Heikkinnen, 1984; Harper, 1993; Pelto, 1993).  All 11 Glacier Peak glaciers that advanced during the 1950-1979 period emplaced an identifiable maximum advance terminal moraine, the mean advance was 295 m.  Of the 47 glaciers that NCGCP has observed during the 1984-1998 period, 15 advanced during the 1950-1978 period. 

The final climate change was a step change in 1977 to a drier-warmer climate in the Pacific Northwest (Ebbesmeyer and others, 1991).  The mean PNI from 1977-1998 was 0.53, even higher than the 1924-1944 period, indicating a warmer drier period that reestablished the ubiquitous retreat of North Cascade glaciers (Pelto, 1993).  This change impacted glacier mass balance, alpine streamflow, and alpine snowpack (Ebbesmeyer and others, 1991).   The impact on North Cascade glacier mass balance is evident from the USGS long-term record of South Cascade Glacier (1958-1998), where mean annual balance was –0.15 m/a from 1958-1976, in contrast to –1.00 m/a from 1977-1998 (Krimmel, 1999).

The retreat and negative mass balances of the 1977-1998 period have been noted by Harper (1993), Krimmel (1994 and 1999), and Pelto (1993 and 1996).  By 1984, all the Mount Baker glaciers, which were advancing in 1975, were again retreating (Pelto, 1993).  In 1997-98, NCGCP measured the retreat of eight Mount Baker glaciers from their recent maximum position (late 1970’s-early 1980’s).  The average retreat had been -197 m.   All of the Mt. Baker termini are still in advance of their 1940 position as observed in photographs from J.B. Richardson, and observations by Austin Post (pers. comm.).  However, the glacier region between the current terminus and 1940 terminus is nearly stagnant on each of the glaciers.  Between 1979 and 1984, 35 of the 47 North Cascade glaciers observed annually by NCGCP had begun retreating.  By 1992 all 47 glaciers termini observed by NCGCP were retreating (Pelto, 1993), and two had disappeared, Lewis Glacier and Milk Lake Glacier. 


                  The time between the onset of a mass balance change and the onset of a significant change in terminus behavior is called the initial terminus response time or reaction time (Ts).  As indicate previously Ts is a descriptive quantity that quantifies the time lag between climate forcing and terminus response for a particular climate event, rather than a physical property of a glacier Ts in this study is based solely on the first observed terminus change from retreat to advance after 1944, and from advance to retreat after 1976.  Ts has been identified from the response of North Cascade glaciers to the relative cooler and wetter weather beginning in 1944 (Hubley, 1956; Long 1955 and 1956; Tangborn, 1980), and to the subsequent warmer and drier conditions beginning in 1977 (Ebbesmeyer and others, 1991; Pelto, 1988; Pelto, 1993; Krimmel, 1994; Harper, 1993).   


Focusing on 21 North Cascade glaciers that responded to these two climate shifTs, all having an area under 10 km2, the initial terminus response invariably is less than 16 years (Pelto, 1993; Hubley, 1956; Harper, 1993).   Table 2 is a list of 21 North Cascade glaciers where Ts has been noted for both advance and retreat for the post-1944 period by Hubley (1956), or Long (1955 and 1956).  In each case the glaciers were observed to be in retreat during the 1940’s, and subsequently each advanced within 16 years of the climate change.  Table 2 also notes the response of the same glaciers from a period of advance by each glacier in the early 1970’s to retreat by 1988, 12 years after the climate change (Pelto, 1988 and 1993; Harper, 1993).  The observed Ts is not significantly different on individual glaciers for initiation of advance, versus initiation of retreat. 

Many North Cascade glaciers did not respond to these two climatic changes.  This may be the result of a longer Ts, or as more likely is either due to an ongoing retreat caused by continuing negative mass balances, or that climate change was insufficient to substantially alter mass balance on these glaciers.


                The 38 North Cascade glaciers, where the terminus history has been determined for the 1890-1998 period exhibit three distinct patterns (Table 3): 1) Retreat from 1890 to 1950 then a period of advance from 1950-1976, followed by retreat since 1976.  2) Rapid retreat from 1890 to approximately 1950, slow retreat or equilibrium from 1950-1976 and moderate to rapid retreat since 1976. 3) Continuous retreat from the 1890 to the present.  Distinction of a glacier’s Type is based solely   on iTs terminus behavior in this analysis. 


                From 1890-1946 a retreat of at least 1000 m occurred on each of the significant glaciers (over 1.0km2) on Mt. Baker and Glacier Peak.  Each of these glaciers is a Type 1 glacier: Mazama, Rainbow, Easton, Squak, Talum and Boulder Glacier on Mt. Baker and, Ermine, Dusty, N. Guardian, Kennedy, Scimitar, Ptarmigan and Vista Glacier on Glacier Peak are used in this study.  The two strato-volcanoes, Glacier Peak and Mt. Baker are the highest peaks in the North Cascades.  The ability to advance was not limited to the high elevation glaciers of the two large volcanoes, as this advance was also noted on other North Cascade glaciers Ladder Creek, Challenger, Quien Sabe, Lower Curtis, Sulphide and N. Klawatti Glacier (Hubley, 1956). 

Even in 1940 at the height of retreat Type 1 glaciers were extensively crevassed and quite active in the photographs taken by William Long and J.B. Richardson of the National Forest Service (Figure 2).   Today despite moderate to rapid retreat rates of 10-30m/a, all Type 1 glaciers remain extensively crevassed. 

                Each Type 1 glacier was still retreating appreciably in 1940 but had approached close enough to equilibrium that the climate shift beginning in 1944, indicated by a decrease of the mean PNI of approximately 1, brought about a rapid change from retreating to advancing conditions (Hubley, 1956).  The 50 years of continuous retreat reflects Type 1 glacier response to the initial climate shift in approximately 1890, the progressive warming during the 1895-1923 period, and the warmth of the 1924-1944 period (Long, 1955 and Burbank, 1981).  None of the glaciers had achieved a full adjustment by 1940, but certainly seemed to be approaching it, suggesting that Tm is in the 20-30 year range for Type 1 glaciers.

Similarly by 1976 advance had brought these glaciers close enough to equilibrium, as evidenced by the slow rate of terminus change (Harper, 1993), that the modest (10%) recent decline in winter precipitation and rise in summer temperature (1.1oC) resulted in glacier retreat (Pelto, 1993 and 1996; Harper, 1993).  This again indicates that Tm is in the range of 20-30 years.  It must be acknowledged that these glaciers became smaller since the post Little Ice Age warming, and Tm should therefore be shorter. 


                Each of these glaciers retreated substantially from 1890-1950, followed by nearly stable terminus positions between 1955 and 1979, and an increasing retreat rate since 1984.  Type 2 glaciers in this study are Columbia, Watson, Cache Col, Yawning, Sahale, Neve, Ice Worm and Suiattle Glacier.   The maximum retreat or advance of this group was less than 30 m from 1955-1984.  Since 1984 the retreat rate has been increasing for this group of glaciers, average retreat for the 1992-1998 period was 8 m/a.  In 1998 the retreat rate remains modest as the glaciers still seem to be adjusting slowly to climate change. 

An increase in crevassing was noted on the Neve, Yawning and Suiattle Glacier in 1955, but little or no advance occurred, though the retreat did end in the early 1970’s on these three glaciers.  This suggests that that the climate change was insufficient to generate an advance, but did manage to halt the ongoing retreat. 

After continuously retreating from 1890-1950 the Type 2 glaciers had not approached close enough to equilibrium for the 1944 climate shift to stop retreat initially.  This suggests that Tm for Type 2 glaciers is on the order of 40-60 years, since each glacier termini was close to equilibrium after the 1944 climate change, but had not yet attained equilibrium due to the 1890 climate change.  Exponential filtering of the PNI index also indicates that a response time in this range is required to approximately halt the retreat in the period 1944-1976 (Johannesson, personal communication).


                This group includes South Cascade, Honeycomb, Foss, Hinman, Milk Lake, Lyman, Whitechuck, White River, Lewis, Sholes and Colonial Glacier.  Each of these glaciers has retreated continuously throughout this century.  The most rapid retreat period has varied; however, each glacier retreated more than 100 m between 1950 and 1979 and thinned aprreciably, when many North Cascade glaciers were advancing or in equilibrium (Hubley, 1956; Meier and Post, 1962). 

Type 3 glaciers all have a low slope, limited crevassing and in general low velocities for their respective size.  South Cascade Glacier is a typical Type 3 glacier.  Lyman, Hinman, Foss and Colonial Glacier have each lost more than 50% of their area in the last 50 years (Figure 4).  Of these four only Lyman Glacier is still moving at a detectable rate.  The others three had continuously negative mass balances and will disappear with our current climate. None of the Type 3 glaciers has neared a post LIA equilibrium. 

The disappearance of two glaciers in this group, Lewis Glacier in 1989 and Milk Lake Glacier in 1993, illustrates that after nearly 150 years of adjustment these glaciers still had failed and did fail to achieve a new equilibrium.  That none of the glaciers had achieved equilibrium by 1975, after 85 years of retreat, indicates a Tm of at least 60-100 years for Type 3 glaciers.   The complete melting away of Hinman and Foss Glacier may take another 50 years despite their small size.

                South Cascade Glacier is the most studied glacier in the North Cascades.  The USGS has monitored the mass balance since 1952.  The mass balance trend through time indicates that from 1958-1976 mean annual balance was –0.15 m/a (Krimmel, 1999).  The 1945-1975 period of more positive mass balance that generated advance for many North Cascade glaciers, resulted only in smaller negative balances, but a significant ongoing retreat  (Krimmel, 1996).  From 1977-1998 mean annual balance on South Cascade Glacier was –1.0 m/a (Krimmel, 1999), and retreat has been rapid.   During the 1940-1998 period for which terminus observations exist, South Cascade Glacier has not approached equilibrium. 

  None of the Type 3 glaciers has approached a steady state since the end of the LIA regardless of the fluctuations in mass balance and the low values of the proxy forcing function PNI from 1945-1976.  Type 3 glaciers are still adjusting in part to the post Little Ice Age climate change, which has been reinforced by recent warming. It therefore, seems likely that Type 3 glaciers and South Cascade Glacier are still adjusting to the post LIA warming after a century of retreat and that Tm is at least 75 years.


Each of the three glacier types was established based solely on terminus behavior history; however, it is apparent that each type has specific characteristics (Figure 2-5).   Figure 6 illustrates the different terminus behavior history of North Cascade glaciers.  The slower initial response to climate change of Type 3 glaciers is evident.  The long-term result of the slow start is a more persistent retreat.  Table 3, lists the mean slope, mean altitude and area of each glacier of the 38 glaciers.  Mass balance measurements in the accumulation zone exist for 12 of the glaciers in this study.   Type 1 glaciers have the highest mean elevations (2200 m), largest mean slope (0.42, +0.07), highest measured mean accumulation (Pelto, 1988; 1996), most extensive crevassing and highest measured terminus region velocity (20 m/a, + 3 m/a ).  Type 3 glaciers have the lowest slopes (0.23, +0.06), least crevassing, and lowest mean terminus velocity (5 m/a, + 3 m/a) of any of the glacier types.  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 (Figure 3). 

There is no significant relation between aspect and glacier type.  A larger mean slope, higher accumulation rates, more extensive and higher velocity either reflect or lead to increased glaciers velocities and longitudinal strain rates.   The greater the longitudinal strain rate the faster the glacier can adjust to changing climate conditions (Paterson, 1994).  The terminus region velocities on large alpine glaciers may be quite independent of glacier velocity as a whole.  On the smaller North Cascade glaciers the terminus region velocity is, on the other hand, a good indicator of mean glacier velocity. 

                The three glacier types illustrate that persistent differences in glacier behavior are explainable based on the basic characteristics of the glacier which in turn determine response time, and not unique to specific glaciers.    This is reinforced by the exceptionally high degree of correlation in annual balance between North Cascade glaciers (Pelto, 1997).  The lowest cross correlation value for annual balance, between any pair of nine glaciers observed by the USGS and NCGCP, is 0.79. 

The different behavior of adjacent glacier termini based on differing topographic characteristics in the North Cascades was observed on S. Klawatti and N. Klawatti Glacier (Tangborn and others, 1990).  From 1947-1961 N. Klawatti Glacier lost a volume equivalent to a mean thickness of 8.3m, continuing its ongoing retreat.  S. Klawatti Glacier gained a thickness equivalent to a mean thickening of 5.8 m (Tangborn and others, 1990).  This is not an unusual case in the North Cascades.  Based on the classification of glacier type in this study S. Klawatti is a Type 1 glacier and N. Klawatti a Type 3 glacier.   The difference in the degree of crevassing alone indicates a notable difference in flow.  The adjacent glaciers differing responses fit the overall pattern for glaciers of their respective types in the North Cascades, and are not an anomalous case.  We identified no important microclimatic effects that created differing mass balance conditions on glaciers across the North Cascades (Pelto, 1996 and 1997). 

                An even more poignant example is that of the Neve and Ladder Creek Glacier, which share the same accumulation zone and have termini that both end at approximately 1680 m.  The shared accumulation zone between 2000 m and 2400 m flows into a pass at 2000 m where the glacier turns both east and west.  The Ladder Creek Glacier flows northwest and is a Type 1 glacier and has a steep, shorter terminus, 1200 m to terminus from the pass, comparatively rapid velocity, and was noted to advance by Hubley (1956).  Neve Glacier is a Type 2 glacier, it is slightly larger than the Ladder Creek Glacier and has a longer terminus region, 1920 m from the pass.  This results in a gentler slope and consequently slower velocity.  This glacier did not advance, though crevassing did increase within 500 m of the terminus slowing the retreat to a standstill.

                Observation of different responses of glacier types to a climate change is not unique to the North Cascades.  In Switzerland a sample of 38 glaciers with 150 year long terminus records was classified into, four different classes, with different types of terminus responses for each glacier class (Herren and others, 1999):  1) Large valley glacier such as the Gornergletscher which has retreated rapidly and continuously.  2) Small mountain glaciers such as the Saleina, which has advanced twice during this century, though retreat has been more pronounced.  3) Large mountain glaciers, such as the Tschierva, which follow the same pattern as Saleina except with more significant retreat. 4) Small cirque glaciers, such as the Gran Plan Neve, which has retreated slowly throughout the century.


A primary difficulty in the identification of Tm is that after a climate change climate conditions do not reach a new steady state for periods comparable to the Tm of glaciers.  Each glacier is then adjusting to the continually changing climate conditions and never achieves a steady state, due to the non-steady state climate (Schwitter and Raymond, 1993).  Schwitter and Raymond (1993) noted that these difficulties are minimized with regard to changes from the LIAM to the present, since the basic climate change since the late 1800’s has been from a LIA climate favorable to glaciers and a post LIA climate unfavorable for glaciers.  Changes in North Cascade terminus behavior and glacier thickness from the LIAM to the present are large compared to changes in response to more recent climate changes (Schwittter and Raymond, 1993). 

The observed terminus record of North Cascade glaciers indicates a range of Tm from 20 to 30 years on Type 1 glaciers, approximately 40-60 years on Type 2 glaciers, and a minimum of 60-100 years on Type 3 glaciers.  How do these values compare to those calculated from the equations of Johannesson and others (1989).  

Johannesson and others (1989), compared two means of calculating Tm:

    Tm=f L /u(t)                 (1)


                  Tm=h/-b(t)                   (2)

Tm in these equations is potentially dependent on four variables: L the glacier length, u(t) velocity of the glacier at the terminus, h the thickness of the glacier, and b(t) the net annual balance at the terminus.  The former equation, which was proposed by Nye (1960), produces longer full response times of 100 to 1000 years, the latter full response times of 10 to 100 years (Johannesson and others, 1989).   The variable f is a shape factor that is the ratio between the changes in thickness at the terminus to the changes in the thickness at the glacier head (Schwitter and Raymond, 1993).  Similar changes in ice thickness will yield a value of f= 1, f=0.5 corresponds to a linear decrease of thickness change from a maximum at the terminus to zero at the head. The mean value of f has been determined as 0.3 (Schwitter and Raymond, 1993), and this value of  f is applied.  This equation is quite sensitive to terminus velocity, which is often spatially inconsistent.  

Table 4 displays the variables used in determining Tm for 17 North Cascade glaciers, the calculated Tm from equation 1, and Tm from equation 2.  Each variable, except h, has been observed on each glacier by the USGS  (South Cascade Glacier) or NCGCP.   

                It is evident that equation 2 yields values that are lower than the estimates of  Tm for North Cascade glaciers of Types 2 and 3 glaciers, but the difference is smaller for Type 1 glaciers.  Equation 1 overestimates Tm and because of the wide spatial variability of u(t), it is not expected to yield a consistently accurate result on alpine glaciers. 

                 South Cascade Glacier, like all Type 3 glaciers, is still adjusting to post LIA warming and the discontinuous but progressive warming of this century.  This is not unique to the North Cascades, many alpine glaciers have not yet fully adjusted to post LIA warming.  The Ptarmigan and Lemon Creek Glacier, Alaska; Gornergletsher and Rhonegletscher in Switzerland; Athabasca Glacier, Canada, and in the Darwin Cordillera, Chile several glaciers have retreated continuously during this century (Marcus and others, 1995; Herren and others, 1999; Holmund and Fuenzalida, 1995).


                North Cascade glaciers had a varied terminal response to the 1944 climate change, with only Type 1 glaciers advancing.  Based on this study, the failure of Type 2 and Type 3 glaciers to advance is a function of their incomplete adjustment to the post LIA progressive warming.  Thus, they were still significantly out of equilibrium in 1944, after approximately a half-century of retreat (Burbank, 1981), and the modest positive mass balances did not trigger a glacier advance.  Pelto (1996) noted the high cross correlation in observed annual balance on North Cascade glaciers (Figure 7).   This similarity is true regardless of glacier type.  This is evidence that microclimates are not the key to differences in behavior.  Instead it is the physical characteristics slope, terminus velocity, thickness, and accumulation rate of the glacier that determines its recent terminus behavior and response time.

 An example is the adjacent N, Klawatti and S. Klawatti Glaciers.  S. Klawatti advanced in the 1950-1975 interval and N. Klawatti continued to retreat.  The glaciers have different area-altitude distributions, to which Tangborn and others (1990) attributed the differential terminus response.  However, the different area-altitude distribution is both a result of slower response and a reflection of the differing topographic setting.  

Porter (1986) noted that many alpine glaciers experienced nearly synchronous reversals in terminus behavior around 1950.  This change in glacier terminus behavior prompted Johannesson and others (1989) to suggest that, alpine glacier behavior is dominated by short-term climate effects.   In the North Cascades, this synchronous reversal to advance and later to retreat of only Type 1 glaciers indicates that in the North Cascades only glaciers close to equilibrium had a reversal in terminus behavior due to the short-term climate effects.  Glacier termini such as the Honeycomb, Lyman, Columbia, Milk Lake, and South Cascade Glacier were only modestly affected by the recent short-term climate changes in the North Cascades.

North Cascade glaciers occupy an exceptionally temperate maritime climate for glaciers.  Ts on North Cascade glaciers are short (Hubley, 1956), ranging from 4-16 years in response to both positive negative mass balance changes.

Tm varies considerably even between similarly sized glaciers in this region.  The key variables that decrease Tm are factors that increase mean glacier velocity, accumulation rates and glacier slopes in particular.  The response times of 30-100 years for most of these small glaciers indicates that with a substantial climate change the initial response may be rapid, but full adjustment is not rapid in the North Cascade Range.              


                The comments of Roger LeB Hooke, M. Hoelzle, W. Haeberli, T. Johannesson, M. Sturm and J.G. Cogley have been most helpful.  The USGS maps and photographs provided by Austin Post and David Hirst were essential to this project.  The fine ongoing research initiated by Mark Meier and currently guided by Robert Krimmel of the USGS on South Cascade Glacier provided essential long-term data. 




1850-1950 1950-1979 1980-1998
Mazama 0.44 -2350 450 -117 2200
Rainbow 0.37 -1370 512 -148 1850
Easton 0.35 -2420 608 -97 2250
Squak 0.45 -2500 305 -160 2350
Talum 0.55 -1975 275 -161 2400
Boulder 0.5 -2560 743 -143 2350
Ermine 0.46 -1800 170 -108 2400
Dusty 0.42 -1800 280 -218 2350
N. Guardian 0.43 -1550 160 -120 2400
Kennedy 0.48 -1700 330 -151 2100
Scimitar 0.46 -1600 350 -98 2100
Ptarmigan 0.5 -1050 75 -39 2250
Vista 0.28 -1900 105 -105 2150
Quien Sabe 0.4 -1250 55 -89 2350
Lower Curtis 0.36 -645 225 -82 1650
Ladder Creek 0.31 -1230 105 -52 2100
Sulphide 0.38 -1775 210 -101 2100
TYPE 2          
Cache Col 0.46 -360 -25 -46 1950
Columbia 0.18 -560 -15 -70 1600
Watson 0.4 -320 -21 -55 1650
Neve 0.24 -720 -25 -48 2150
Sahale 0.5 -260 -12 -53 2400
Sholes 0.3 -1170 -57 -50 1850
Yawning 0.39 -310 35 -31 1850
Lynch 0.36 -160 -390 -88 2150
Ice Worm 0.33 -925 0 -55 2150
Daniels 0.5 -960 -20 -121 2200
White River 0.2 -780 -140 -98 2200
Suiattle 0.3 -2400 15 -23 2100
TYPE 3          
Lewis 0.25 -65 -80 -182 * 2100
Colonial 0.27 -230 -81 -52 2000
Lyman 0.23 -1020 -408 -113 2000
Foss 0.36 -975 -86 -112 2050
Hinman 0.21 -410 -300 -711 1950
S. Cascade 0.17 -1800 -350 -295 1900
White Chuck 0.22 -1300 -330 -170 2150
Honeycomb 0.17 -1750 -290 -338 2250
Milk Lake 0.17 -400 -190 -210* 1900

                         Advance               Retreat

Glacier             Observed             Observed

Coleman                 1949                        1979

Easton                    1960                        1989

Deming                  1955                        1986

Boulder                  1954                        1985

Squak                     1955                        1985

Rainbow                1955                        1985

Kennedy                1955                        1986

Chocolate                1950                        1986

N. Guardian           1955                        1986

Dusty                     1955                        1986

Ptarmigan                1960                        1988

Vista                       1960                        1988

Ermine                    1955                        1986

Ladder Creek         1955                        1987

Eldorado                1955                        1984

Quien Sabe           1955                        1984

Yawning                1955                        1986

Lower Curtis        1955                        1987

Challenger           1955                        1985

Price                     1954                        1987

Chimney Rock     1955                        1987


Table 2.  Date of first observed advance following the 1944

climate change.  Date of the first observed retreat following

the climate change  

 in 1976-77.

Table 4. The Termius Response time Calculations for North Cascade Glaciers
Glacier l u(l) h b(l) ^l Tm1a Tm1b Tm2 Tmo
Colonial 1.5 0.003 50 -4.5 -0.31 167 250 11 150+
Columbia 1.6 0.004 100 -4.5 -0.61 133 200 22 150+
Daniels 0.8 0.009 50 -4 -0.96 30 45 12 100
Easton 4 0.024 75 -6.5 -2.42 55 83 12 100
Foss 1 0.004 50 -4.5 -1.06 83 125 11 150
Honeycomb 4.4 0.006 100 -6 2.36 244 366 16 150+
Ice Worm 0.5 0.002 50 -4 -0.93 83 125 12 100
Kennedy 2.4 0.02 100 -6 -1.6 40 60 16 100
Ladder Creek 2.6 0.025 100 -5 -1.23 35 52 20 100
Lewis 0.3 0.001 25 -2 -0.28 100 150 12 150
Lower Curtis 1.8 0.02 100 -5.5 -0.54 30 45 18 100
Lyman 0.6 0.005 50 -5 -1.43 40 60 10 150+
Lynch 1.2 0.012 100 -4 -0.45 33 50 25 150+
Neve 3.5 0.008 100 -4.5 -0.8 146 220 22 100
Rainbow 2.7 0.015 100 -5 -1.37 60 90 20 100
South Cascade 3.1 0.008 80 -6 1.5 129 193 13 150+
Yawning 0.8 0.005 50 -4 -0.31 53 80 12 100


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