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A GLIMS Case Study of Bering Glacier System, Alaska The Cryosphere, 2, 33–51, 2008 www.the-cryosphere.net/2/33/2008/ The Cryosphere © Author(s) 2008. This work is distributed under the Creative Commons Attribution 3.0 License. Improving estimation of glacier volume change: a GLIMS case study of Bering Glacier System, Alaska M. J. Beedle1,5, M. Dyurgerov2,3, W. Tangborn4, S. J. S. Khalsa1, C. Helm1, B. Raup1, R. Armstrong1, and R. G. Barry1 1National Snow and Ice Data Center, 449 UCB, University of Colorado – Boulder, CO 80309-0559, USA 2Institute of Arctic and Alpine Research, 450 UCB, University of Colorado – Boulder, CO 80309-0450, USA 3Department of Physical Geography & Quaternary Geology, Stockholm University, SE – 106 92 Stockholm, Sweden 4HyMet Inc., 13629 Burma Rd. SW, Vashon Island, WA 98070, USA 5Geography Program, University of Northern British Columbia, 3333 University Way, Prince George, B.C. V2N 4Z9, Canada Received: 19 June 2007 – Published in The Cryosphere Discuss.: 9 July 2007 Revised: 12 March 2008 – Accepted: 12 March 2008 – Published: 7 April 2008 Abstract. The Global Land Ice Measurements from Space comprehensive and accurate. Such accuracy is possible with (GLIMS) project has developed tools and methods that can the increasing volume of satellite imagery of glacierized re- be employed by analysts to create accurate glacier outlines. gions, recent advances in tools and standards, and dedication To illustrate the importance of accurate glacier outlines and to this important task. the effectiveness of GLIMS standards we conducted a case study on Bering Glacier System (BGS), Alaska. BGS is a complex glacier system aggregated from multiple drainage 1 Introduction basins, numerous tributaries, and many accumulation ar- eas. Published measurements of BGS surface area vary from Glaciers are valuable integrators of their local climate and 2 1740 to 6200 km , depending on how the boundaries of this thus, through their changes, indicators of climate change. system have been defined. Utilizing GLIMS tools and stan- Annual field measurements of glacier mass-balance have 2 dards we have completed a new outline (3630 km ) and anal- been undertaken in order to monitor annual change and to ysis of the area-altitude distribution (hypsometry) of BGS understand the relation between glaciers and climate. Such using Landsat images from 2000 and 2001 and a US Ge- measurements of glacier mass-balance are time consuming, ological Survey 15-min digital elevation model. We com- expensive, and arduous. Thus, the vast majority of mass- pared this new hypsometry with three different hypsome- balance programs intentionally select small, easily accessi- tries to illustrate the errors that result from the widely vary- ble, well-defined glaciers with little debris-cover (Fountain et ing estimates of BGS extent. The use of different BGS al., 1999). This legacy of studying a small subset of “simple” hypsometries results in highly variable measures of volume glaciers has resulted in questionable representation of Earth’s change and net balance (bn). Applying a simple hypsometry- complex mountain glaciers (e.g. Dyurgerov and Meier, 1997; dependent mass-balance model to different hypsometries re- Cogley and Adams, 1998). Indeed, few glaciers conform to −1 sults in a bn rate range of −1.0 to −3.1 m a water equiva- the simplistic geographies (morphology and hypsometry) of 3 −1 lent (W.E.), a volume change range of −3.8 to −6.7 km a those with detailed mass-balance studies. W.E., and a near doubling in contributions to sea level equiv- New technology and subsequent techniques have resulted −1 −1 alent, 0.011 mm a to 0.019 mm a . Current inaccuracies in many recent studies using remote sensing to study a in glacier outlines hinder our ability to correctly quantify broader spatial range of glaciers (e.g. Arendt et al., 2002; glacier change. Understanding of glacier extents can become Larsen et al., 2007). Such studies have compared two or more measures of glacier surface height, typically separated on decadal time scales, resulting in vertical height change, Correspondence to: M. J. Beedle volume loss or gain, and an average net balance (bn) rate for ([email protected]) the interim periods. Simple models have also been used (e.g. Published by Copernicus Publications on behalf of the European Geosciences Union. 34 M. J. Beedle et al.: Improving estimation of glacier volume change Fig. 1. Location of Bering Glacier System, Alaska. Bering Glacier System (BGS) is shaded in red. The two meteorological stations used in the PTAA model, Cordova and Yakutat (yellow stars), are indicated to the west and east of BGS. The four glaciers with temporally significant mass-balance records in southern and southeast Alaska, which were tested as possible benchmark glaciers, are also indicated (white and black bordered diamonds). Malaspina Glacier is outlined in red just east of BGS. Braithwaite and Zhang, 1999; Tangborn, 1999; and Paul et et al., 2006; Raup et al., 2006). Unfortunately, the seemingly al., 2002) in order to extend our understanding of glacier simple task of accurately outlining a glacier meets with many change beyond the few glaciers with detailed annual field complications. studies. Whether we compare remotely sensed glacier sur- Complications which hinder an accurate outline include faces to derive surface height change or use models of glacier different definitions of what should be included as glacier mass-balance the glacier surfaces being assessed must be lat- within an outline and the exceeding complexity of many erally constrained, or, in other words, extent of the glaciers glacier systems. In this paper we address these two com- must be outlined. Accurate glacier outlining is perhaps the plications by 1) illustrating the facility of a common glacier most basic of glacier measurements, but one of significant definition developed by and utilized for the Global Land Ice importance. A glacier’s outline yields measurements of sur- Measurements from Space (GLIMS) project, and 2) applying face area and length; and, when projected to a horizontal sur- this glacier definition to a study of mass-balance and volume face and combined with a digital elevation model (DEM), an change of the complex Bering Glacier System (BGS), Alaska outline leads to a glacier’s distribution of area with elevation (Figs. 1 and 2). (hypsometry). Perhaps most importantly, a glacier’s outline defines the surface area with which any measure of surface 1.1 This study height change or mass-balance will be integrated to obtain an estimate of a glacier’s bn. Errant glacier outlines result in in- The GLIMS project at the National Snow and Ice Data Cen- accurate measures of glacier volume change and bn (Arendt ter, University of Colorado (Raup et al., 2006, 2007; Raup and Khalsa, 2006) is creating standardized methodology and The Cryosphere, 2, 33–51, 2008 www.the-cryosphere.net/2/33/2008/ M. J. Beedle et al.: Improving estimation of glacier volume change 35 Fig. 2. Bering Glacier System. Glacier outlines digitized in GLIMSView displayed in Google EarthTM. Surging Bering Glacier System (SBGS) and Steller Glacier (includ- ing Steller Lobe) are outlined in red. Together the SBGS and Steller Glacier comprise the Bering Glacier System. Nunataks are outlined in light green and debris-cover is outlined in dark green. The yellow line is the border between Alaska (west) and Yukon Territory, Canada (east). tools, and a common glacier database through which the sci- The comparisons within this study yield: 1) an illustration entific community can pursue more accurate and more acces- of the importance of accurate glacier outlining via a common, sible knowledge of glacier characteristics and change, lead- or at least explicitly stated, glacier definition; 2) accurate, ing to better monitoring of the world’s glaciers in regards to transparently-defined outlines and hypsometries of BGS; 3) past, present, and future climatic change. This study, within a discussion of BGS mass-balance and volume change re- the broader GLIMS project, aims to address the importance sults for the second half of the 20th century from three mod- of accurate glacier outlining and hypsometry creation – es- els; and 4) a discussion of some of the problems facing the pecially in regards to large, complex glaciers – as well as to glaciological community in regards to accurately outlining demonstrate the facility of GLIMS methodology and tools. and understanding some of the world’s major glaciers. To do so we compare the results achieved when integrating net balance estimates (from three different models) with four 1.2 Bering Glacier System different BGS hypsometries. In addition we examine charac- teristics such as debris-cover, surge dynamics, and multiple Previous studies have noted the complexity of BGS. In their flow divides, which complicate studies of glacier extent and preliminary inventory of Alaska glaciers, Post and Meier change. (1980) use BGS as “a particularly extreme example.” www.the-cryosphere.net/2/33/2008/ The Cryosphere, 2, 33–51, 2008 36 M. J. Beedle et al.: Improving estimation of glacier volume change Table 1. Official Bering Glacier System nomenclature. This table describes some of the Official (US Board on Geographic Names) Bering Glacier System (BGS) nomenclature that often leads to confusion when defining the component parts of BGS. Name Description Bering Glacier Entire piedmont lobe (Bering Piedmont Glacier), including Steller and Bering Glacier Piedmont Lobes Steller Lobe Portion of piedmont lobe fed by Steller Glacier Steller Glacier Tributary feeding Steller Lobe Central Medial Moraine Band Moraine covered ice between Steller and Bering Lobes Bering Lobe Portion of piedmont lobe fed by the main trunk glacier Central Valley Reach Central portion of main trunk glacier feeding Bering Lobe Bagley Ice Valley Main accumulation area both east and west Waxell Glacier West branch of Bagley Ice Valley Bering Glacier System Entire glacier flowing to the Bering Piedmont Glacier It is in and between two countries (USA, Canada), two Recently, remote sensing, via aerial photography and major drainages (Pacific, Chitina-Copper), and two major satellite imagery, has afforded analysts the means of visual- mountain ranges, (Chugach and St.
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