1. THE PAINSTAKING

W. Colgan, H. Rajaram, W. Abdalati, C. McCutchan, R. Mottram, M. Moussavi and S. Grigsby. 2016. Glacier Crevasses: Observations, Models and Mass Balance Implications. Reviews of Geophysics. 53: 119-161.

I’m pretty meticulous in general, but an invitation to contribute to Reviews of Geophysics forces thoroughness to the next level. Review articles are beasts by nature. In this case, our goal was to summarize everything ever written about crevasses for a dual science and safety motivation. We ended up surveying sixty years of crevasse research, from field observations to numerical modeling to remote sensing, in an epic tome that weighs in at 43 typeset pages with 238 citations. That’s about four times longer than a typical article for me. This review also describes how crevasses can influence glacier mass balance, and synthesizes some emerging theories on crevasse formation. Did you know, that, while crevasses are often conceptualized as initiating at the ice surface and propagating downwards, there is compelling evidence that they can initiate at several meters depth and then propagate upwards?

Illustrative schematic of various crevasse types.

2. THE INSIGHTFUL

J. MacGregor, W. Colgan, M. Fahnestock, M. Morlighem, G. Catania, J. Paden and S. Gogineni. 2016. Holocene deceleration of the Greenland Ice Sheet. Science. 351: 590-593.

Showing that ice flow in the Greenland Ice Sheet interior has been slowing down over the last 9000 years is about as “big picture” as it gets for me. This article is a personal touchstone for the unexpected collaborative jewels that might be unearthed at small workshops. Joe was presenting ice-sheet radar stratigraphy that suggested interior ice flow had slowed down over the past 9000 years. I was presenting an ice flow model that suggested the gradual replacement of soft Last Glacial Period ice with hard Holocene ice was resulting in an ongoing slowdown of ice flow. This ice-sheet slowdown is accompanied by ice-sheet thickening. This means that the evolution of ice-sheet form and flow over past millennia directly imprints on our altimetry measurements of mass balance today. This prompts the question: how much of the satellite-observed interior thickening is due to the ice sheet’s ongoing response to the last deglaciation?

A: Holocene-averaged surface speed inferred from radiostratigraphy. B: Present-day satellite-observed surface speed. C: Difference in surface speed between (Present-day minus Holocene-averaged).

3. THE SENSATIONAL

W. Colgan, H. Machguth, M. MacFerrin, J. Colgan, D. van As and J. MacGregor. 2016. The abandoned ice-sheet base at Camp Century, Greenland, in a warming climate. Geophysical Research Letters. 43: 8091-8096.

At 30K downloads and counting, this study is approaching “pop-sci” glaciology. Our goal was presenting Camp Century as a microcosm for the multi-national and multi-generational challenges presented by climate change. Everything about Camp Century, from its construction to abandonment, is undeniably sensational. But, importantly, the ultimate fate of Camp Century is still subject to our collective climate choices. It’s only under the business-as-usual climate pathway that Camp Century will experience net melt by 2100. If we implement strong climate action, however, consistent with the Paris Agreement, Camp Century will continue to experience net snowfall into the foreseeable future. I think directly addressing the political implications of these climate pathway choices is a unique aspect of this study. The subsequent – on ongoing – media interest in this publication has been overwhelming. Camp Century has definitely deflected my career trajectory!

Surface mass balance in Northwest Greenland during the 1950s (A) and 2090s (B). The blue shading denotes the accumulation area where surface mass balance is positive. C: Surface mass balance, and its components, at Camp Century during 1950–2100.

4. THE INNOVATIVE

W. Colgan, W. Abdalati, M. Citterio, B. Csatho, X. Fettweis, S. Luthcke, G. Moholdt, S. Simonsen and M. Stober. 2015. Hybrid glacier Inventory, Gravimetry and Altimetry (HIGA) mass balance product for Greenland and the Canadian Arctic. Remote Sensing of Environment. 168: 24-39.

Reconciling satellite altimetry and gravimetry measurements has probably been my greatest technical struggle, but also my greatest technical achievement. Ice-sheet mass balance is normally assessed using either altimetry or gravimetry, with the mass balance results from these approaches then compared at ice-sheet scale. Here, in contrast, our goal was to merge both altimetry and gravimetry data into a single spatial mass-balance product that is self-consistent with both sensors. This means digging deep into both ICESat-1 and GRACE-1 measurements, and getting familiar with their complementary strengths and limitations. While NASA and ESA program officers are strongly encouraging of hybrid sensor products, it seems difficult for scientists to agree on the most appropriate way to hybridize altimetry and gravimetry data. Right now, hybrid sensor products are still sufficiently novel that the Ice Sheet Mass Balance Inter-Comparison Exercise (IMBIE) does not include them!

Inferred land-ice mass balance simultaneously consistent with ICESat-1 altimetry and GRACE-1 gravimetry over the Sep-2003 to Oct-2009 period. Black lines denote regional sectors.

5. THE QUIRKY

W. Colgan. 2014. Considering the ice excavation required to establish and maintain an open ice pit. Journal of Cold Regions Engineering. 28: 04014003.

Simulating ice flow into an open pit mine is, without a doubt, my most esoteric work. But, if you're into non-linear ice physics like me, you may also find this rather fascinating. When you excavate an open pit through a glacier, it creates unnaturally steep ice walls, in which the ice flow is incredibly non-linearly dependent on driving stress. The ice gradients you create in an open ice pit yield driving stresses that you would never actually find in nature. Serving as an expert reviewer for a geotechnical assessment of the Kumtor Mine in Kyrgyzstan, which includes an open ice pit, got me interested in this topic. In this study, however, I simulate the larger open ice pit proposed for the Isua Prospect in Greenland. I may also count this applied glaciology study among my favorites as it is was my first sole-authored publication!

Cross-sectional ice velocity 2.5 years (A) and 10.0 years (A) intro excavating a open ice pit with a 3:1 ice slope. The black line denotes the initial ice-sheet profile, and the red line denotes the ice pit wall.

W. Colgan. 2011. Modeling the influence of surface meltwater on the ice dynamics of the Greenland Ice Sheet. Ph.D. Thesis. University of Colorado. [.pdf]

W. Colgan. 2007. Reconstructing the recent accumulation history and mass balance trends for high elevation regions of the Devon Island Ice Cap in the Canadian Arctic. M.Sc. Thesis. University of Alberta. [.pdf]