36 PARK SCIENCE • VOLUME 28 • NUMBER 2 • SUMMER 2011

Glacier trends and response to climate in ADEMA NPS/GUY National Park and Preserve

By Rob Burrows, Samuel Herreid, Guy Adema, Anthony Arendt, and Chris Larsen Figure 1. Researcher Adam Bucki records data from test pits and an ablation stake at the index measurement site on Kahiltna Glacier.

LACIERS ARE A SIGNIFICANT ter park visitors’ experience. These trends Each of the world’s glaciers is a unique resource of mountain ranges in have a direct infl uence on a wide range of entity and has a diff erent set of physical GAlaska and a dominant feature on hydrologic, ecologic, and geologic systems. characteristics that dictate how it responds Mount McKinley. The glaciers of De- For example, glaciers provide a steady base to changes in mass balance and hence nali National Park and Preserve, , fl ow of freshwater discharge upon which climate. Corresponding to the wide variety are vast, covering 3,779 km2 (1,459 mi2), many ecosystems thrive, and when glacier of mountain shapes and sizes in the Alaska approximately one-sixth of the park’s meltwater and sediment discharge change Range is a large array of shapes, sizes, and area. Each year, these glaciers gain mass because of a change in mass balance, behaviors among glaciers (Molnia 2008). whenever snowfall accumulates at the these ecosystems are altered. Glaciers also Important characteristics that determine surface, and they lose mass primarily advance and retreat in response to changes glacier behavior include size, elevation through surface melting (ablation) during in mass balance, which can create new or range, aspect, slope, number and arrange- the summer. A glacier’s mass balance is destroy existing habitat and contribute to ment of tributaries, the area-altitude distri- the diff erence between accumulation and changes in the climate of alpine regions. bution (hypsometry), and the underlying ablation and describes the overall health of Glacier behavior has a large infl uence on and surrounding geology of the glacier’s the glacier. Generally, the average summer the braided river systems that are a com- basin. Areas with readily erodable bedrock season temperature (May to September) mon feature of the mountain landscapes tend to have large areas of surface ice drives total ablation for any given year and of Alaska. On a global scale, long-term covered by rock debris, which can insulate total winter snowfall drives accumula- trends in glacier mass balance can make the ice on the lower glacier, retarding melt tion. When deviating mass balance trends signifi cant contributions to changes in sea rates, changing fl ow rates, and masking persist for many years they can result in level. areal retreat. Many glaciers in the Alaska signifi cant landscape changes that can al- Range exhibit surge-type behavior, which FEATURES 37

values based on knowledge of the density Abstract of snow or ice that has accumulated or Glaciers cover approximately one-sixth of Denali National Park and Preserve in Alaska. ablated at that place. Snow and ice ablated They are not only enjoyed by visitors for their scenic and recreational values but are also an during the summer is termed summer bal- important driver of Denali’s diverse ecosystems by defi ning the hydrologic regime, generating ance. The units for water equivalent values landscape-scale braided river systems, and shaping the landforms of the . Scientists from the National Park Service and University of Alaska–Fairbanks have been are meters water equivalent (m w.e.). The researching glacier dynamics and monitoring glacier trends for more than 20 years using sum of the winter and summer balances glacier outlining from satellite imagery, index mass balance measurements, longitudinal is the net balance, which is a measure of elevation profi les, repeat photography, analysis of regional gravity changes, and other the annual gain or loss. Researchers then localized research. Mass balance measurements on the Traleika and Kahiltna glaciers showed extrapolate the point observations to the a cumulative net gain of mass from 1991 to 2003. Since 2003 the mass balance data and entire glacier surface, based on measured satellite-based gravimetric analysis show a net loss of ice mass. Airborne laser and lidar elevation profi les corroborate the mass balance measurements and also show localized or assumed gradients in the various mass changes because of glacier dynamics. Analysis of glacier extent reveals an 8% loss in area balance terms, and calculate the mass since 1950; however, whereas most glaciers lost area, a few surge-type glaciers gained area. balance of the entire glacier. Data from Repeated photographs from historical images help refi ne trends seen in other methods and that glacier may be used to represent other include dramatic examples of smaller glaciers decreasing in size and a surge-type glacier unmeasured glaciers in a region. Glaciers that has not changed as noticeably. Relations to climate trends are complicated and clearly demonstrate the importance of local infl uences on glacier behavior and trends. Losses of chosen to represent broader regions in ice from smaller glaciers and dramatic changes of other glaciers in Alaska suggest that this way are known as “index glaciers,” global climatic change may be overwhelming the dominant infl uence of large-scale climate and are usually chosen based on their oscillations on glacier change in Denali. location, physical characteristics, and ease of access. Key words climate change, Denali, glacier, Kahiltna Glacier, mass balance, In Denali National Park, Larry Mayo (formerly of the U.S. Geological Survey), and Keith Echelmeyer (formerly of the is a periodic acceleration of all or part are the variability and trends of ice loss University of Alaska–Fairbanks) chose the of the glacier to speeds of 10 to 100 times and gain through time? What glaciers are Kahiltna and Traleika glaciers as appropri- the normal quiescent speed. Surge-type representative of and can serve as indexes ate indexes because they capture a broad glaciers may advance in a seemingly of the changes taking place among the range of elevation and climate gradients unpredictable way when other glaciers are larger population of glaciers? Do all Denali spanning from the south to north side retreating. With such a variety of glaciers it glaciers exhibit a melting trend attribut- of the Alaska Range (Mayo 2001). These is imperative to have a thorough charac- able to global or regional climate change? researchers established a single observa- terization of the glacier population and of tion site on each glacier near the long-term which glaciers can represent the popula- equilibrium line altitude (ELA), the ap- tion as study glaciers. Mass balance proximate line at which the average glacier measurements mass balance is zero, and they determined The National Park Service has monitored mass balance gradients that are used to the mass balance of two glaciers in De- Direct fi eld measurements are a vital calculate the entire glacier mass balance nali National Park since 1991. These fi eld component of long-term glacier monitor- from this location. measurements give detailed information ing programs. At the end of the winter on mass variations at specifi c locations, accumulation season, glaciologists probe Index data collected since 1991 tell the but they have limited spatial coverage. snow depths, dig pits, and measure snow story of variability and change in space Recently, satellite and airborne technolo- density to determine the mass gained on and time (fi g. 2, next page). The aver- gies have begun to provide information the glacier over winter (winter balance). age 1991–2010 net balance at the Kahiltna on glacier variations that span broader To track ablation these scientists install Glacier site (shown in fi g. 1) was 0.19 ± 0.27 geographic regions. This article presents vertically oriented stakes in the snow and m w.e., showing that it is just above the long-term fi eld and recent remote sensing ice surface and revisit these locations to long-term ELA, while the average 1991– data sets that we combine in order to as- determine the change of the surface rela- 2010 net balance at the Traleika site was sess the following questions: What are the tive to the height of the stake (fi g. 1). These −0.62 ± 0.32, showing that it is below the spatial patterns of ice loss and gain? What changes are converted to water-equivalent long-term ELA (fi g. 2A). The net balance 38 PARK SCIENCE • VOLUME 28 • NUMBER 2 • SUMMER 2011

Net Balance at the Long-term ELA Cumulative Balance at the Long-term ELA with Five-year Moving Averages with Trend Line 1.5 3.5 Kahiltna Moving Avg Kahiltna KahiltnaKahiltna 3.0 Traleika Moving Avg 1.0 Traleika Traleika Traleika 2.5 0.5 2.0 1.5 0.0 1.0 −0.5 0.5

Net Balance (m w.e.) 0.0 −1.0 Cumulative Balance (m w.e.) −0.5 −1.5 −1.0

1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 AB Balance Year Balance Year

Figure 2. Net and cumulative mass balances on the Kahiltna and Traleika glaciers derived from index stake measurements show relative trends of two of Denali’s largest glaciers. Graph A (left) shows the yearly net balance data adjusted to the long-term equilibrium line altitude, along with the fi ve-year moving averages (solid lines). Graph B (right) shows the cumulative net balance and more correctly shows changes in balance that will drive advance or retreat. The trend lines show neutral to positive net balance, which is strongly tempered by the negative trend since 2004.

values are shown with their error estimates observations. Implemented jointly by the Repeat laser altimetry to show the relative uncertainty we have National Aeronautics and Space Adminis- profi ling in estimating these values. We adjusted tration and the German Aerospace Center, these values to the long-term ELAs using a GRACE examines time variations in Using airborne laser and lidar, we have predetermined balance gradient, yielding Earth’s gravitation fi eld based on precise measured elevation profi les along the cen- an approximation of the glacier-wide net measurements of orbital variations of a terline of a large number of glaciers in the balance (fi g. 2A). A cumulative sum of the tandem pair of satellites. Data suggest that Alaska Range at multiple times between net balance through time shows that both glaciers in the portion of the Alaska Range 1995 and 2010. These profi les reveal the glaciers generally gained mass from 1991 that Denali National Park and Preserve oc- range and distribution of glacier change to 2003, but began to lose mass after 2004 cupies contributed about 5% to the total of and highlight diff erent glacier responses (fi g. 2B). ice lost from Gulf of Alaska glaciers from occurring in various geographic settings. 2003 to 2009 (updated estimates from In Denali National Park and Preserve the Data from each index site demonstrate Luthke et al. 2008). A correlation analysis data set includes repeated profi les on a the distinct precipitation gradient from with the regional GRACE data from 2003 total of 13 glaciers, with the most extensive the south to the north side of the Alaska to 2009 shows that the Traleika balances data on Muldrow and Kahiltna glaciers. Range, with signifi cantly less winter correlate better with the GRACE data, in- In the most recent measurement interval, snowfall on the north side. Traleika winter dicating Traleika is more representative of 2007–2010, Kahiltna laser profi les indi- balances (average of 0.67 ± 0.19 m w.e.) are regional conditions than Kahiltna. Further cate little change in surface elevation and 40% lower than those of Kahiltna (average index monitoring and GRACE data, along hence volume, which is in close agreement 1.08 ± 0.12 m w.e.). with current and future research, will help with the relatively steady mass balance elucidate the relationship of these data measured at the index site for that period Measurements from the Gravity Recov- to temporal and spatial patterns of other (fi g. 2B). Some minor elevation increases ery and Climate Experiment (GRACE) glaciers and climate in the Alaska Range. (~10 m) were detected on a small portion off er estimates of regional ice loss across of lower reaches of the Kahiltna, likely Alaska that can be compared with our fi eld related to localized ice fl ow dynamics. On FEATURES 39 SAM HERREID, BASED ON UNIVERSITY OF ALASKA–FAIRBANKS DATA

Figure 3. Change in glacier surface area from the 1950s to the present has been about −347 km2 (−134 mi2) or −8%. Glacier surface area was mapped by the U.S. Geological Survey using aerial photographs taken in about 1952. These data were provided in digital form by Berthier (2010) with the addition of minor edits. Glacier surface area was again mapped using satellite imagery from 2003 to 2010. Area loss during this approximately 55-year period is indicated in red, gain is in blue, and areas of no spatial change are in white.

Muldrow Glacier, extensive debris cover 2006 comparison shows thickening of them with extents mapped by the U.S. leads to complex patterns of elevation much of the area “drained” by a 1956–1957 Geological Survey derived from aerial change when laser profi les are compared surge. photography collected in approximately with one another. Additional glacier 1952. The total area in 1952, 4,126 km2 (1,593 change analysis is possible on Muldrow to mi2), decreased to 3,779 km2 (1,489 mi2) in better understand how this surge-type gla- Changes in glacier extent 2003–2010, resulting in a total area change cier redistributes its mass over time. Three of −347 km2 (−134 mi2) or −8%. Uncer- data sets are available: the U.S. Geological We have compiled a new inventory of tainties in these estimates have not been Survey quadrangle topographic maps from glaciers in Denali that will improve our investigated for this region, but we assume about 1952, a high-precision topographic understanding of landscape evolution, an error of +10%, found in a previous map produced by Bradford Washburn in glacier response to climate, and con- study (Nolan et al. 2005). Most glaciers the 1970s, and a lidar map of the glacier tribution of these glaciers to rising sea in the park lost area (fi g. 3) during the produced in 2006. This analysis shows level. We have manually digitized glacier 55-year period, consistent with observa- overall loss of volume on the lower glacier extents from optical band satellite imagery tions of volume loss and increases in mean from about 1952 to 2006, but the 1970s to acquired from 2003 to 2010 and compared summer temperatures observed in other 40 PARK SCIENCE • VOLUME 28 • NUMBER 2 • SUMMER 2011

studies (Hartmann and Wendler 2005; Arendt et al. 2009). However, the extent Glacier dynamics will always be strongly infl uenced to which climate changes are expressed as by local features such as terrain, elevation, and local fl uctuations in glacier area is complicated by the unique dynamics, geometry, and weather patterns, but larger-scale climatic patterns and surface cover of each glacier. For example, trends will dominate long-term glacier change. many glaciers have a signifi cant amount of debris covering their lower reaches and terminus areas, which can signifi cantly alter terminus response. In addition nearly all the large glaciers on the north side of the mountain system are surge type, periodically transporting large amounts Comparison to climate in Alaska. We note that the data on which of accumulated mass from an upper trends these trends are based are from relatively reservoir area to the lower terminus area. low-lying areas and are not necessarily In the 55-year period documented here, Climate in much of Alaska is strongly representative of the mountains that the the Muldrow, Peters, and two unnamed driven by seasonal to decadal variations glaciers occupy. glaciers to the east of in sea surface temperature of the Pacifi c experienced surge events that caused sig- Ocean. A multidecadal oscillation driven The glacier and climate link may show us nifi cant terminus advance (shown in blue by these variations is known as the Pacifi c trends in mountainous regions of Alaska. in fi g. 3). Other glaciers have surged over Decadal Oscillation (PDO), which is an in- Arendt et al. (2009) found that 76% of this time but not with enough volume to dex that tracks anomalies in Pacifi c Ocean 46 glaciers measured with repeat laser cause a signifi cant increase in area. sea surface temperatures (Mantua et al. altimetry across Alaska showed increased 1997). The PDO oscillates between positive rates of ice loss since the mid-1990s, with and negative phases on a 20- to 30-year loss driven by increased summer tempera- Repeat photography cycle. In Alaska the positive phase of the tures. Likewise, the benchmark glaciers PDO generally corresponds with higher (Gulkana and Wolverine) monitored by Repeat or comparative photography (fi g. air temperatures (particularly winter tem- the USGS show increased rates of ice loss 4) is a powerful method for document- peratures) and increased cloudiness and since the late 1980s (Van Beusekom et al. ing and communicating glacier change, precipitation, whereas the negative phase 2010). Before 1989, mass balance values allowing us to relate the trends we are tends toward cooler and drier climate of Wolverine Glacier (and South Cascade seeing with index, altimetry, and extent averages (Hartmann and Wendler 2005). Glacier in Washington State) correlated data. We see substantial change in the well with the PDO index; however, a dra- small and medium-sized glaciers at lower A look at regional climate data illustrates matic increase in the rate of loss (driven by elevations. A dramatic example is the East the eff ect of PDO phase shifts on long- increases in summer temperatures) since Teklanika Glacier, a small valley glacier term trends. Between 1951 and 2001 there 1989 appears to be less tied to the PDO that has retreated a great deal in the last was a 1.7°C (3.1°F) increase in the mean and other large-scale climate oscillations century. Other striking examples include annual air temperature in interior Alaska, and is likely forced by global-scale climatic Polychrome, West Fork Cantwell, Sunset, with the greatest increases occurring changes (Rasmussen and Conway 2004). and Hidden Creek glaciers. In the case in winter and spring (Hartmann and of Muldrow Glacier, an aerial photo pair Wendler 2005). The increasing trend is The mass balance data on Kahiltna and shows the terminus only a couple of years largely explained by the shift from a nega- Traleika glaciers do not show dramatic after the surge and then after 47 years tive phase of the PDO (1945 to 1976) to a losses since 1991 as many other glaciers of melting and downwasting (see fi g. 4). positive phase (1976 to 2005). Thus climate in Alaska do. We note that unlike the From farther up on Muldrow Glacier, a trends related to PDO phase shifts (and Wolverine and Gulkana glaciers, these photo pair shows notable loss of glaciers other large-scale climate oscillations) must glaciers have very high-altitude accumula- mantling the mountainside above it, but be considered carefully when calculating tion areas (on the upper reaches of Mount not thinning of the trunk glacier itself. climate averages, establishing climate- McKinley) and thus are very cold and less glacier relationships, and interpreting prone to changes from rising temperature global climate change and warming trends trends. Comparing the periods before and FEATURES 41 S. R. CAPPS R. S. BRADFORD WASHBURN NPS/RON D. KARPILO NPS/RON NPS/GUY ADEMA

Figure 4. Modern photos of glaciers compared with images taken from early scientists and explorers help researchers interpret long-term rates of change. From top to bottom, left to right in pairs: Muldrow Glacier terminus 1959 (soon after the 1956–1957 surge) and again in 2006, Teklanika Glacier 1919 and again in 2004.

after the 1976 PDO-induced climate shift, from the cold period known as the Little Summary and conclusion there was an approximately 20% increase Ice Age (16th to 19th centuries) to the in autumn and winter precipitation that warmer 20th century. Continued loss of Monitoring glacier behavior and trends would have off set some of the eff ects of glacial mass from about 1952 to present using a variety of techniques provides in- the increased air temperatures. We also may be driven by the temperature increase sight into the complexity of glacier change note that average annual temperature for associated with the 1976 shift in PDO. and increases our ability to distinguish lo- Alaska’s interior region from 1976 to 2001, Analysis of terminus retreat on two of cal eff ects from regional and global trends. although shifted above the 1951 to 1976 Denali’s eastside glaciers shows West Fork Formal glacier monitoring in Denali began values, reveals a slight decreasing trend Cantwell Glacier has been retreating at a in 1991 and has tracked mass balance (Hartmann and Wendler 2005). This, constant rate from about 1950 to pres- trends on two large valley glaciers, with together with the snowfall increases, could ent and Middle Fork Toklat Glacier has trends neutral to positive from 1991 to 2003 explain the mass balance observations been retreating at an increased rate from and negative since 2003. Parkwide analysis on Kahiltna and Traleika, which indicate 1992 to 2002. Unfortunately, more recent of glacier extent change since the 1950s cumulative mass gains during a portion of volume loss data for these smaller glaciers indicates a consistent trend of glacial re- that period (fi g. 2B). and others in the vicinity are not available treat, except for glaciers that have surged. to indicate if the rate of ice mass loss has Longitudinal surface elevation profi ling The loss of glacier mass in the smaller, increased since the mid-1990s as on many and repeat photography reveal relative lower-altitude glaciers in the eastern other glaciers in Alaska. Further research stability in larger glaciers, but dramatic portion of the park (as seen in the repeat and monitoring may elucidate these rates. long-term mass loss on small, relatively photography) is in part due to the shift low-elevation, valley glaciers characteristic 42 PARK SCIENCE • VOLUME 28 • NUMBER 2 • SUMMER 2011

of the eastern portion of Denali National contributed data to the long-term record, Nakicenovic, N., and R. Swart, editors. 2000. Park and Preserve. These patterns of ice including Keith Echelmeyer, Phil Brease, Emissions scenarios. Cambridge University loss are somewhat unique to the western Larry Mayo, Adam Bucki, Jamie Roush, Press, Cambridge, UK. Available at http:// interior Alaska Range and on the larger Pam Sousanes, Chad Hults, Ron Karpilo, www.grida.no/publications/other/ipcc_ glaciers appear to contrast with increasing Denny Capps, and others. sr/?src=/climate/ipcc/emission/index.htm. rates of ice loss from USGS benchmark Nolan, M., A. Arendt, B. Rabus, and L. Hinzman. glaciers and large glaciers that border the 2005. Volume change of McCall Glacier, Gulf of Alaska. References Arctic Alaska, from 1956 to 2003. Annals of Glaciology 42:409–416. Arendt, A., J. Walsh, and W. Harrison. Continued glacier monitoring, along with 2009. Changes of glaciers and climate in Rasmussen, L., and H. Conway. 2004. Climate enhanced climate monitoring, will allow northwestern North America during the late and glacier variability in western North for correlations between climate and 20th century. Journal of Climate 22(15):4117– America. Journal of Climate 17:1804–1815. glaciers to be refi ned. Glacier dynamics 4134. SNAP (Scenarios Network for Alaska Planning). will always be strongly infl uenced by local Berthier, E., E. Schiefer, G. Clarke, B. Menounos, 2009. Projected climate change scenarios for features such as terrain, elevation, and and F. Remy. 2010. Contribution of Alaskan Denali National Park and Preserve. Available local weather patterns, but larger-scale glaciers to sea-level rise derived from satellite from http:// www.snap.uaf.edu/fi les/docs/ climatic patterns and trends will dominate imagery. NatureGeoscience 3(2):92–95. Climate_Change_Sums/Denali_ClimSum.pdf. long-term glacier change. Projected cli- Hartmann, B., and G. Wendler. 2005. The Van Beusekom, A. E., S. R. O’Neel, R. S. March, mate change scenarios up to the year 2080 signifi cance of the 1976 Pacifi c Climate L. C. Sass, and L. H. Cox. 2010. Re-analysis for Denali indicate a possible increase Shift in the climatology of Alaska. Journal of of Alaskan benchmark glacier mass-balance in summer temperature of 3°C (5.4°F) Climate 18:4829–4839. data using the index method. Scientifi c and a 25% increase in winter precipita- Investigations Report 2010-5247. U.S. Luthke, S. B., A. Arendt, D. Rowlands, J. tion, along with a 6°C (10.8°F) increase in Geological Survey, Reston, Virginia, USA. average winter temperature (SNAP 2009). McCarthy, and C. Larsen. 2008. Recent glacier mass changes in the Gulf of Alaska This scenario uses the “intermediate” CO 2 region from GRACE mascon solutions. emissions scenario (A1B) from the IPCC Journal of Glaciology 54(188):767–777. About the authors Special Report on Emissions Scenarios (Nakicenovic and Swart 2000). Glacier Mantua, N. J., S. R. Hare, Y. Zhang, Rob Burrows ([email protected]) is a mass balance modeling will be required J. M. Wallace, and R. C. Francis. 1997. A physical scientist. Sam Herreid (sjherreid@ to determine whether the projected Pacifi c decadal climate oscillation with alaska.edu) is a student researcher. Guy impacts on salmon. Bulletin of the American temperature increases would be off set by Adema ([email protected]) is a Natural Meteorological Society 78:1069–1079. the increased amount of precipitation. Resource Team leader. Anthony Arendt In addition the National Park Service is Mayo, L. R. 2001. Manual for monitoring glacier ([email protected]) is an assistant evaluating the likely impacts on visitation responses to climate at Denali National Park, research professor. Chris Larsen (chris and recreation, along with changes to hy- Alaska, using the index site method. Denali [email protected]) is assistant research drologic and geomorphic conditions and National Park contractor’s report. Glacier professor. Burrows and Adema are with Gnome Consulting, Anchorage, Alaska, USA. dependent habitats. Denali National Park and Preserve, Alaska; Molnia, B. F. 2008. Glaciers of Alaska. (With Herreid, Arendt, and Larsen are with the sections on: Columbia and Hubbard Geophysical Institute, University of Alaska– Acknowledgments tidewater glaciers, by R. M. Krimmel; The Fairbanks. 1986 and 2002 temporary closures of Glacier monitoring work in Denali has Russell Fiord by the Hubbard Glacier, by B. F. Molnia, D. C. Trabant, R. S. March, and been the result of a long-term collabora- R. M. Krimmel; and Geospatial inventory tion between park staff and staff from and analysis of glaciers: A case study for the the Geophysical Institute at the Uni- eastern Alaska Range, by W. F. Manley.) In versity of Alaska–Fairbanks. The NPS R. S. Williams, Jr., and J. G. Ferrigno, editors. Inventory and Monitoring Program and Satellite image atlas of glaciers of the world. the Central Alaska Network have been USGS Professional Paper 1386-K. U.S. primary supporters of routine monitor- Government Printing Offi ce, Washington, ing work. Numerous fi eldworkers have D.C., USA.