Unprecedented 21st century glacier loss on Mt. Hood, Oregon, USA

Bakken-French, Nicolas; Boyer, Stephen J.; Southworth, B. Clay; Thayne, Megan; Rood, Dylan H.; Carlson, Anders E.

doi:https://doi.org/10.5194/tc-18-4517-2024

Articles | Volume 18, issue 9

https://doi.org/10.5194/tc-18-4517-2024

© Author(s) 2024. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/tc-18-4517-2024

© Author(s) 2024. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 18, issue 9

Research article

|

27 Sep 2024

Research article |

| 27 Sep 2024

Unprecedented 21st century glacier loss on Mt. Hood, Oregon, USA

Nicolas Bakken-French, Stephen J. Boyer, B. Clay Southworth, Megan Thayne, Dylan H. Rood, and Anders E. Carlson

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Final revised paper (published on 27 Sep 2024)
Supplement to the final revised paper
Preprint (discussion started on 05 Feb 2024)

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2024-251', Anonymous Referee #1, 18 Mar 2024

The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-251/egusphere-2024-251-RC1-supplement.pdf

Citation: https://doi.org/10.5194/egusphere-2024-251-RC1
- AC1: 'Reply on RC1', Dylan Rood, 22 Mar 2024
  
  We would like to thank the reviewer for her/his/their highly constructive and thoughtful review. We are happy to see that the reviewer finds our dataset novel and that it provides valuable insights into glacier-climate change interactions. Many beneficial suggestions are provided, and these will be addressed in detail in the response to reviewers document if we are invited to resubmit with revisions made.
  
  In particular, we can readily restructure the methods and results section in the manner in which the reviewer suggests (including moving the detailed descriptions to an appendix) as well as adding information on the volcanic history of Mt. Hood to the introduction. Likewise, we can add a section comparing glacier change on Mt. Hood to that of other western North American mountain ranges where comparable records exist.
  
  The reviewer also suggests using topographic parameters as a proxy for glacier mass balance; we will investigate this method to determine if it is suited for our study at present or would be better left for a follow-up study.
  
  Once again, we thank the reviewer for the careful review and look forward to any more discussion on topics highlighted above.
  
  Citation: https://doi.org/10.5194/egusphere-2024-251-AC1
RC2:
'Comment on egusphere-2024-251', Andrew G. Fountain, 20 Mar 2024

Bakken-French et al., summarize the glacier change on Mt. Hood, Oregon over the past century with an emphasis on the past 20 years. They compiled previous efforts and updated the current glacier extent finding, like everywhere else, the glaciers are receding. The paper is important for local/regional understanding of the glacier changes that have occurred so far this century. While I don't think there is anything wrong with the data collection or the conclusions drawn from the analysis, significant problems remain.
The data collection methods are vague and problems encountered unknown. For example, the margins of the glaciers were mapped using a ground-level GPS and with satellite imagery. How much of the margin was mapped using each? A qualitative answer is fine. Probably not much at the highest, most difficult, and dangerous areas mapped with imagery.

Data sources are not well identified. For example, which Sentinel imagery. The data source for air temperature and precipitation was not exactly identified, was it instrument sourced or reanalysis? Like the Sentinel imagery, no source website was cited and no listing of data sets in an appendix. The uncertainty discussion was arbitrary. A 'conservative estimate' of 7% was applied. Why? Why not 10% or 5%. Any ground-truthing of uncertainty? The authors state that uncertainty was propagated through the time series, but no explanation or equation was provided. Finally, although the authors state they distinguished stagnant debris-covered ice from active ice, no methods were identified. Which brings into question the nature of active glaciers grading into stagnant dead ice. How do we characterize glacier area and length changes under these conditions? This is an important question for glacier change studies, yet it was ignored here.

The structure of the paper has to be revised to be more careful to distinguish between methods and results. Some methods were found in results, and not enough methods were included to explain how some of the results were achieved. The exhaustive descriptive detail of each glacier needs to be moved into an appendix as it is not necessary in the main body of the manuscript. Also, the authors tended to summarize the contents of the tables and figures before engaging with the topic. This is very inefficient. The observation or fact should be stated followed by a citation to the table or figure.

I was puzzled by several of the results. First, Figure 7 shows that greater the changing length of a glacier, greater the elevation change of the terminus. Isn't this to be expected for a glacier on a sloping surface? Is there something else implied here? In Table 2, the p-value of significant varied across the table. There should be a set confidence limit unless otherwise justified. In figures 11 and 12 the delta temperature and precipitation were plotted. I assume delta means difference, but relative to what?

Fundamentally, I think the paper is sound but the problems summarized above require extensive revisions. Also, the text can be tightened considerably. Extensive detailed comments are included on the manuscript. I did not edit the Discussion or Conclusions significantly due to the problems found in the prior sections of the paper. Once they are resolved the contents of the latter parts of the report will become more apparent.

Citation: https://doi.org/10.5194/egusphere-2024-251-RC2
- AC2: 'Reply on RC2', Dylan Rood, 22 Mar 2024
  
  We would like to thank Andrew Fountain for a detailed, constructive, and thought-provoking review of our manuscript. We are happy with his finding that our study is important for local to regional glacier changes that have occurred in this century and that he finds our paper to be sound with no issues raised over our conclusions. That said, Fountain does raise questions about our data collection methods and the structure of the manuscript. In looking at the detailed comments provided in the body of the manuscript, these are all readily addressable if we are invited to submit a revised manuscript.
  
  Briefly, we had provided links to many of our data sources in the reference list, which we can now include directly in the text as well as provide the documentation on the satellite imagery and how these were combined with field GPS measurements. Likewise, we can further discuss and justify our methodology and assumptions as well as our process for delineating active glacier ice from stagnant dead ice and add in discussion of glacier response times with respect to our glacier length-climate regressions. We can restructure our paper in the manner that Fountain suggests, including his suggestions on figures and tables. Basically, we can make every recommended revision by Fountain.
  
  In sum, we would like to thank Andrew Fountain again for his thorough review and look forward to making his suggested changes and revisions if we are invited to submit a revised manuscript.
  
  Citation: https://doi.org/10.5194/egusphere-2024-251-AC2
CC1:
'Comment on egusphere-2024-251', Frank Paul, 21 Mar 2024

Please see my comments in the Supplement.

Citation: https://doi.org/10.5194/egusphere-2024-251-CC1
- AC3: 'Reply on CC1', Dylan Rood, 22 Mar 2024
  
  We would like to thank Frank Paul for his constructive and focused review of our manuscript. In considering his review, we find that we should more clearly delineate the full scope of our methodology and why we focused on mapping only actively flowing glacier ice extent. This can readily be accomplished if we are invited to submit a revised manuscript; his other comments are all easily addressable in such a revision.
  
  Namely, Paul raises difficulties over delineating between active and stagnant ice using satellite imagery. In a revision, we can more clearly layout how the satellite imagery was only an intermediate step in our mapping process and that our active ice margins are based on field mapping. We can then clarify how we made the demarcation between actively flowing ice and stagnant dead ice in the field.
  
  We can also add in a revised manuscript our reasoning on why we mapped only actively flowing glacial ice. Briefly, we are following the methodology of prior such mapping efforts in western North America that focused on changes in aerial extent and length of actively flowing glaciers. Adding a discussion section that compares relative changes in Mt. Hood actively flowing glacier area to changes in actively flowing glaciers in other western North American ranges will hopefully clarify our chosen mapping targets.
  
  In summation, we would like to thank Frank Paul again for his thorough review, noting that we can address his comments through further clarification of our methods and additions to the discussion section if we are invited to submit a revised manuscript.
  
  Citation: https://doi.org/10.5194/egusphere-2024-251-AC3
EC1:
'reviewer comment on egusphere-2024-251', Ben Marzeion, 02 Apr 2024

We received another reviewer comment from Mauri Pelto, which could not be posted online first, due to technical problems. The review is posted below, and I ask the authors to also take this into account when it comes to the revision of the manuscript.
Ben Marzeion

Review:
The authors provide a detailed report on the rapid recession of Mount Hood, Oregon glaciers in the last ~40 years. Several items must be addressed to make this a useful addition to the literature documenting the rapid demise of these glaciers. There are too few glaciers too discern the impact of geographic characteristics on rate of change, focus less time on trying to discern sensitivity in this regard. Discussion of data from Driedger and Kennard (1984) is imperative. Referencing the response time of Pacific Northwest glaciers to climate change . In the discussion or results relate Mount Hood results to those from Mount Rainer and Mount Baker.
18: “with attendant consequences for water resources” More specifics are warranted here, i.e.. There are PNW observations of significant declines in late summer glacier runoff contributions, which reduces baseflow and minimum flows. What are the water resources utilized for?
30: Worth noting glacier loss in the North Cascades and on Mount Shasta both north and south of study area, there are 31 glaciers in the North Cascades noted as having disappeared in last 30 years in the GLIMS extinct glacier category.
45: Driedger and Kennard (1986) did map all glaciers on the mountain and provided detailed maps of extent and thickness on several glaciers from 1981 field observations. They found an area of 104 million ft2. This information should be incorporated or explain why it is not.
55: Here or later might want to comment on likely cause of this error, that is also evident on North Cascade glaciers in that the glacier footprint used on some of the small glaciers included non-glaciated areas.
92: Particularly in 2021 and 2023 large regional glacier mass balance losses were observed across the PNW, which helped better expose the margins of the glaciers. .
106: Evaluate the ability to use the 1981 extents from (Driedger and Kennard, 1986). This is useful timing because it follows the period of expansion of many of the Cascade glaciers from 1950-1980.
159: What is the mean slope of the steep upper section, steepest part says little.
170: “a 30% decline in its area in the last eight years.”
243: Has the less debris cover been a consistent feature for Coe’s terminus?
250: Up to 60% not a useful metric, provide a steepness metric that is less of a point measurement.
260: What does shallow reference here, slope, snow depth etc?
267: This fits with the rapid area loss seen on Mount Rainier that is leading to loss of glacier status. I have not found on the slopes of Cascade volcanoes that active ice exists below the 0.03 km2 threshold. Report the observed area in 2023 even if below threshold, can use Sentinel imagery for this.
276: Sandy Glacier is the only glacier with a recent/current ice cave system. Other glaciers such as White River have had ice caves in the past.
298: Could add that “The rapid area loss is indicative of large mass balance losses.”
310: Can provide a quantity here as to the significance of the retreat distance.
316: The number of glaciers is too small to discern how important each variable is, this section could be removed. The overall point is regardless of specific characteristics retreat has been significant.
327: Reword –“ When comparing adjacent glaciers, topographic and other factors are key to driving different amounts of retreat.”
338: Figure 8 does a good job of providing a visual of the acceleration of area loss after ~2000 on five of the seven glaciers. I am not sure of the added value of breaking this up by decade in Figure 9, when measurements do not always fit nicely into decadal periods. If you keep Figure 9 a mechanism to better distinguish periods of gains from those of losses is necessary. Reflect here or in discussion on the comparison with retreats reported from Mount Rainier Figure 10 (Beason et al 2023). Could look at retreat rates of Mount Baker glaciers also (Harper, 1993; Pelto, 2016).
340: This section is really difficult to read just because of how many different area loss rates and periods are mentioned. Let the table and figure provide the details and try to summarize more. All of the information is good, a reader just gets lost in the trees.
380: Several studies have indicated that the strongest temperature relationship to Cascade glacier mass balance is the June-September period, with May and October some years being part of the accumulation season. It is fine to use May-October, but does June-September yield better results?
384: Figure 11 displays well the significant rising trend in annual and ablation season temperature. Worth noting that is sustained over a sufficient period for significant glacier response. There is not a consistent precipitation trend like this since 1980 when area losses began. Would strengthen paper to reference glacier response time for Mount Hood glaciers.
396: This is an excellent statement so add quantitative measures for each of the three either means or greater than values.
422: Should reference the conclusion of Beason et al (2023) about Mount Rainier glacier change. “All 28 glaciers at Mount Rainier are in retreat, losing an average of -0.430 km2 per year parkwide during the last 125 years. Since 2015, this rate has increased to -0.544 km2 per year parkwide.” Harper (1993) good reference for the changes in forcing and terminus response for 1900-1970’s
426: Worth comparing your results to the figure 6 results of O’Neel et al (2019) for the benchmark glaciers.
452: The recent period of sustained warming has also strengthened the temperature signal. Should also note the mass balance climate relationships that drive the terminus changes, they are annually based of course, but because they are not cumulative provide good guidance for interpreting your relationship data. Pelto (2018) notes correlations with annual balance for April 1 SWE and ablation season temperature of greater than 0.64 for all 11 North Cascade glacier noted. O’Neel et al (2019) note the lack of a trend in winter balance at benchmark glaciers, while there is a summer balance trend.
468: Nolin et al (2010) indicated peak water had been reached at Elliott Glacier-“ Our SRM simulations showed that Eliot Glacier discharge increases 13% for every 1°C increase, but decreases 9% for every 10% decrease in glacier area. The recession of the Eliot Glacier in the last century already exceeds this rate; therefore, its discharge has likely been decreasing over time and will continue to decrease.”
Driedger, C L, Kennard, P M 1984 Ice volumes on the Cascade volcanoes: Mount Rainier, Mount Hood, Three Sisters, and Mount Shasta. US Geological Survey. Open File Report 84–581 , https://doi.org/10.3133/pp1365.
Harper JT (1993) Glacier terminus fluctuations on Mt. Baker, Washington, USA, 1940–1980, and climate variations. Arct Alp Res 25:332–340
O’Neel S, McNeil C,Sass L, Florentine C, Baker E, Peitzsch E, McGrathD, Fountain A, Fagre D (2019). Reanalysis of the US Geological Survey Benchmark Glaciers: long-term insight into climate forcing of glacier mass balance. Journal Glaciology, 65, 850–866. https://doi.org/10.1017/jog.2019.66
Pelto, M. (2016). Climate Driven Retreat of Mount Baker Glaciers and Changing Water Resources. SpringerBriefs in Climate Studies https://doi.org/10.1007/978-3-319-22605-7

Citation: https://doi.org/10.5194/egusphere-2024-251-EC1
- AC4: 'Reply on EC1', Dylan Rood, 02 Apr 2024
  
  We would like to thank Mauri Pelto for a thoughtful and very constructive review of our manuscript. We are happy with his finding that our study is detailed and that he finds no issues over our conclusion of rapid recession of Mount Hood glaciers. Pelto does provide several points and changes to the manuscript that will definitely improve the paper. In looking at the detailed comments provided in the body of the manuscript, these are all readily addressable if we are invited to submit a revised manuscript.
  
  Briefly, we can add further discussion of Driedger & Kennard (1986) to our paper and their 1981 observations of Mt. Hood glaciers. We can also remove the discussion of geographic influences on glacier responses given the number of glaciers on Mt. Hood. We will add discussion of the response time of Pacific Northwest glaciers as well as section discussion our results in light of glacier changes on Mount Rainier and Mount Baker
  
  In sum, we would like to thank Mauri Pelto again for his very helpful review and look forward to making his suggested changes and revisions if we are invited to submit a revised manuscript.
  
  Citation: https://doi.org/10.5194/egusphere-2024-251-AC4

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload

ED: Reconsider after major revisions (further review by editor and referees) (04 Apr 2024) by Ben Marzeion

AR by Dylan Rood on behalf of the Authors (14 May 2024)

EF by Lorena Grabowski (17 May 2024) Manuscript Author's response Author's tracked changes Supplement

ED: Referee Nomination & Report Request started (21 May 2024) by Ben Marzeion

RR by Mauri Pelto (02 Jun 2024)

Suggestions for revision or reasons for rejection

The authors provide a detailed report on the rapid recession of Mount Hood, Oregon glaciers in the last ~40 years. This manuscript is significantly improved over the last version. The authors included a detailed discussion of data from Driedger and Kennard (1984). Added significant detail on the water resource usage by agriculture. Referenced the response time of Pacific Northwest glaciers to climate change. Contrasted Mount Hood glacier response in much greater detail with response of glaciers on Mount Rainer and Mount Baker. The items noted below can strengthen the paper, and clarify a few points; however, collectively I do not think this rises to the level of requiring a further review.
38: The GLIMS extinct data base was created after 2018 in 2023. I submitted the 33 glaciers to GLIMS in 2023.

80: Fabulous new information on agriculture in the basin.

83: Might be worth noting that the two small hydropower plants have 4.4 MW of installed capacity.

125: The combination of satellite imagery delineation of margins with ground truth mapping relative to the images, is a robust effective technique.

146: Reword removing excellently which is not a well-defined term-provide a range “Manual remote-sensed ice limits comparisons with direct field observations, yielded extent differences that were small enough (x-y m2) to make it difficult to quantify. "

196: Reword “Pelto (2018) determined the best fit between mass balance and ablation temperature to be May-September or June-September for glaciers in Washington.”

297: The mass balance loss is not inferred in this case. Given the rate of area retraction there is a substantial mass balance loss.

300: Your images in Figure 3 are quite useful at illustrating the darkening of the glaciers, beyond even debris covered areas, which further increases mass losses.

335: May want to observe that the lack of a relationship with precipitation does not indicate it is not important just that no long-term trend exists for precipitation.

350: Did the Frans et al. (2016) model include albedo changes which increase mass loss?

375: Which salmon runs, species and season timing from Thieman et al (2021) suggests spring Chinook, or Summer Steelhead?

385: Suggest rewording to not lead with Contrary....” We document from field observations that the glaciers of Mt. Hood retreated, and most likely lost mass, in the 21st century, losing ~40% of their area (seven largest glaciers) in the last 23 years and ~18% of their area (all glaciers) in the last seven to eight years at unprecedented rates with respect to the last 120 years (1.73±0.17 % yr-1 and 2.40±0.02 % yr-1 , respectively). This is contrary to geodetic mass balance change from remote sensing data only (Menouos et al, 2019)

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RR by Frank Paul (11 Jun 2024)

ED: Reconsider after major revisions (further review by editor and referees) (11 Jun 2024) by Ben Marzeion

AR by Dylan Rood on behalf of the Authors (01 Jul 2024) Author's response Manuscript

EF by Anna Glados (05 Jul 2024) Author's tracked changes Supplement

ED: Referee Nomination & Report Request started (05 Jul 2024) by Ben Marzeion

RR by Frank Paul (28 Jul 2024)

ED: Publish subject to minor revisions (review by editor) (02 Aug 2024) by Ben Marzeion

AR by Dylan Rood on behalf of the Authors (08 Aug 2024) Author's response Author's tracked changes Manuscript

ED: Publish as is (14 Aug 2024) by Ben Marzeion

AR by Dylan Rood on behalf of the Authors (14 Aug 2024) Author's response Manuscript

Short summary

Repeat photography, field mapping, and remote sensing find that glaciers on Mt. Hood, Oregon, have lost about 25 % of their area in the first 2 decades of the 21st century and 17 % of their area in the last 7–8 years. The 21st century recession rate is more than 3 times faster than the 20th century average and 1.9 times faster than the fastest period of retreat within the 20th century. This unprecedented retreat corresponds to regional summer warming of 1.7–1.8°C relative to the early 1900s.