Geospatial Rock Glacier Inventory of the American West
a
Gunnar Johnson & Dr. Andrew Fountain
b
Portland State University: School of the Environment
a) PhD student, gfj@pdx.edu
Glaciers Hiding in Plain Sight
While massive ice glaciers are a fundamental element
of the alpine cryosphere, rock glaciers are also a major
component in many regions. Perennial ice features in
mountains span a continuum of ice content, with alpine
glaciers at one end and stagnant rock glaciers at the
other. While alpine glaciers are easily identified using
traditional remote sensing techniques, rock glaciers
present challenges due to their surface composition,
which is, radiometrically, virtually identical to
surrounding talus and scree. Visual clues like flow
banding and surface deformation, such as that exhibited
by Gilpin Rock Glacier (Figure 1), are sufficient for
identification of most rock glaciers but difficult to
automate. As such, no continental scale inventories of
rock glaciers exist. I will fill this gap with a manually
classified inventory based on visual identification of
rock glaciers from satellite images.
Project Objectives
●
●
●
Identify several thousand rock glacier points
Delineate several hundred rock glacier polygons
Describe American West rock glacier distribution
Figure 1: Gilpin Rock Glacier, Colorado
Image Credit: Bob Webster 2011
Rock Glacier Identification
Using the inventory of alpine glaciers and perennial
1
snowfields developed by Fountain and others and
topographic parameters found during an extensive
literature review, primary search criteria applied were
elevation, slope, aspect and land cover type. These
factors were used to target areas across the contiguous
U.S. for brute force (lots of coffee!) manual image
b) Professor of Geology & Geography, andrew@pdx.edu
classification. Rock glaciers identified were assigned a
classification of 1-3.
Figure 4: Rock glacier delineation and ancillary GIS data extraction
Class 1: Rock glaciers that exhibit extensive flow
banding, over-steepened terminal slopes and are
almost certainly currently active
● Class 2: Rock glaciers that exhibit some flow
banding, distinct marginal slopes and were very likely
recently active
● Class 3: Rock glaciers that appear to be deflated
Class 1 or 2 features and are not likely still active
●
The preliminary rock glacier inventory contains nearly
10,000 features found in 10 western states (Figure 3).
Figure 2: From left to right examples of feature class 1, 2 and 3
Image Credit: Google Earth 2014
Figure 3: Contiguous U.S. rock glacier distribution
State
CA
Rock
Mean
Glacier Elevation
Count
(m)
835
3,416
CO
4,048
3,595
ID
2,282
2,739
MT
1,770
2,716
NM
110
3,575
NV
50
3,013
OR
64
2,439
UT
858
3,239
WA
255
1,982
WY
772
3,109
All
11,044
2,982
Rock Glacier Delineation
Representative rock glacier points were then
translated to polygon delineations to extract existing
GIS data (Figure 4). A digital elevation model (DEM)
and derivative slope and aspect rasters are shown for
example, but geology, precipitation, air temperature and
many other ancillary data sets have been evaluated.
These data will be used to develop automated
classification methods applicable to South America and
Asia, where rock glacier distribution is even less certain.
DEM
slope
aspect
Implications & Continuing Work
Statistical models of rock glacier distribution will
inform both automated classification techniques and the
landscape scale ecological and geomorphic significance
of such features. Diverse microbial communities thrive
2
beneath alpine glaciers , and initial investigations show
those inhabiting rock glaciers are even more robust,
many playing an active role in nitrogen cycling. Recent
3,4
findings from Colorado have shown rock glaciers to
be rich sources of stream nitrate, but without an
inventory of features to extrapolate these findings to,
the true influence of rock glaciers is unknowable.
Acknowledgments: Sincere thanks to Portland State University, the Western Mountain Initiative, the
U.S.G.S., the U.S.F.S. and Dr. Jill Baron at Colorado State University.
References
1) Fountain AG, Hoffman M, Jackson K, Basagic H, Nylen P & Percy D (2007) Digital outlines and
topography of the Glaciers of the American West, U.S.G.S. Open-File Report 2006-1340
2) Hodson A, Anesio AM, Tranter M, Fountain A, Osborn M, Priscu J, Laybourn-Parry J, et al. (2008) Glacial
ecosystems. Ecological Monographs, 78(1):41-67
3) Baron JS, Schmidt TM & Hartman MD (2009) Climate-induced changes in high elevation stream nitrate
dynamics. Global Change Biology, 15(7):1777-1789
4) Williams MW, Knauf M, Cory R, Caine N & Liu F (2007) Nitrate content and potential microbial signature of
rock glacier outflow, Colorado Front Range. Earth Surface Processes and Landforms, 32(7):1032-1047