Gunnar Johnson

Research  

Mountains are the water towers of the world, and of particular interest to me are rock glaciers, poorly understood periglacial features that I believe play an under-appreciated role in alpine hydrology. My dissertation research focuses on rock glaciers of the contiguous United States. Rock glaciers, such as the iconic Gilpin Peak rock glacier (37.990770°,-107.790061°) in the San Juan Mountains of Colorado, are bodies of scree and talus that contain sufficient interstitial ice to allow downslope flow and deformation. My study area encompasses all alpine regions of the contiguous U.S. While rock glaciers are relatively rare in the densely forested, high-precipitation, low-elevation mountains of the Pacific Northwest, they are ubiquitous in higher, drier, colder ranges such as the Rocky Mounatins and Sierra Nevada. Indeed, across most high alpine areas globally, rock glaciers significantly outnumber their more widely known and thoroughly studied “massive ice glacier” cousins. To place rock glaciers in their proper cryospheric context, my collaborators and I compare them to ice glaciers. 

Three major rock glacier themes are explored: spatial distribution controls, meltwater hydrochemistry trends and riparian vegetation influences. To better understand rock glacier spatial distribution controls, a preliminary geospatial inventory of contiguous U.S. rock glaciers was created via manual classification of aerial and satellite images. While there are ~1,500 ice glaciers in the study area, over 10,000 rock glaciers have been identified. To better understand rock glacier hydrochemistry trends, meltwater samples were collected from ~25 pairs of colocated rock glaciers and ice glaciers in the Cascade Mountains, Rocky Mountains and Sierra Nevada. Rock glacier meltwaters are shown to be enriched in nitrate and contain much higher microbial diversity than ice glacier meltwaters. To better understand rock glacier riparian vegetation influences, multispectral satellite imagery of colocated rock glacier and ice glacier meltwater streams is used to generate vegetation indices. Rock glacier meltwater stream riparian vegetation is shown to cover considerably more area, as well grow earlier in and persist longer through the melt season, than ice glacier meltwater stream riparian vegetation.

Middle Teton Glacier (43.731875°,-110.806883°)
Small Unnamed Rock Glacier ( 43.781861°,-110.797555°)
Filtering Meltwater Samples from Isabelle Glacier ( 40.063501°,-105.644894°)
Collecting Meltwater Samples from Adams Glacier ( 46.211912°,-121.505792°)
Measuring Specific Conductance in Snow Dragon Cave Beneath Sandy Glacier ( 45.383122°,-121.716791°)


Publications

Fegel T, Baron J, Fountain A, Johnson G & Hall E (2016) The differing biogeochemical and microbial signatures of glaciers and rock glaciers. Journal of Geophysical Research: Biogeosciences 121: 919-932 DOI: 10.1002/2015JG003236

Johnson G (2015) Hearts, Minds and Touchscreens. Northwest Science 89(1): 104-106 DOI:10.3955/046.089.0112

Chang H, Johnson G, Hinkley T & Jung I (2014) Spatial analysis of annual runoff ratios and their variability across the contiguous U.S. Journal of Hydrology 511(3): 387-402 DOI:10.1016/j.jhydrol.2014.01.066

Chang H, Jung I, Strecker A, Wise D, Lafrenz M, Shandas V, Moradkhani H, Yeakley A, Pan Y, Bean R, Johnson G & Psaris M (2013) Water Supply, Demand and Quality Indicators for Assessing the Spatial Distribution of Water Resource Vulnerability in the Columbia River Basin. Atmosphere-Ocean 51(4): 339-356 DOI:10.1080/07055900.2013.777896


Contact

email: gfj@pdx.edu
advisor: Dr. Heejun Chang





 

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