CHAPTER
17
Glaciers and perennial snowfields of the
U.S. Cordillera
Andrew G. Fountain, Hassan J. Basagic IV, Charles Cannon, Mark Devisser,
Matthew J. Hoffman, Jeffrey S. Kargel, Gregory J. Leonard, Kristina Thorneykroft,
and Steve Wilson
ABSTRACT
17.1
INTRODUCTION
Of more than 8,000 glaciers and perennial snowfields on 21 mountain ranges in the western U.S.
(excluding Alaska), only 120 are larger than 1 km 2 ,
and just one exceeds 10 km 2 . Where changes in size
are known, the overwhelming majority of glaciers
are shrinking. There are a few that are growing.
These changes, with a few exceptions that relate
mainly to rock debris abundances on the glaciers,
are due overwhelmingly to climate change, though
it is a complex relationship. Analysis of ASTER
(Advanced Spaceborne Thermal Emission and
Reflection Radiometer) imagery has been used in
special case studies, along with published field
data, to track changes in debris loads of glaciers
on Mt. Rainier, show the effects of a lahar from
Mt. Rainier, and track the continued shrinkage of
Grinnell Glacier in Glacier National Park. The
response time of glaciers in the region varies from
under a decade to over a century. Blue Glacier
(Olympic Mountains) is a fast responder; its length,
area, and volume fluctuation history indicates that
it is responding to decadal climate fluctuations as
well as local long-term warming in the 20th and 21st
centuries, which is probably related to greenhouse
gas–driven global warming.
The American Cordillera of the contiguous U.S. is
divided into four major geologic provinces—the
Pacific Province, the Basin and Range Province,
the Rocky Mountains, and the Columbia Plateau—
encompassed by nine states, Washington, Oregon,
California, Nevada, Idaho, Montana, Wyoming,
Colorado, and Utah. Glaciers populate about 21
mountain ranges within the Cordillera (Fig. 17.1).
Although over 8,000 glaciers and perennial snowfields are documented, very few are larger than 1
km 2 and many are just 1–5 ha and are best assessed
systematically by aerial photography or satellite
imagery with resolution of 1 m or better. Most of
the glacierized mountain ranges contain remnants
of glaciers, which are stabilized or retreating slowly
in shadowed and protected niches, where windblown snow, snow avalanches, and rock falls help
nourish and sustain the ice. The study of glaciers in
this region is mainly one of small glaciers <1 km 2 in
the 21 mountain ranges. Only about 120 glaciers are
>1 km 2 , and the largest, Emmons Glacier, is only a
bit bigger than 10 km 2 . All glaciers, with the exception of those on the stratovolcanoes of the northwest, favor north-facing and east-facing aspects
typical of alpine glaciers in the Northern Hemi-
386
Glaciers and perennial snowfields of the U.S. Cordillera
Figure 17.1. Locations of glacier and perennial snowfields in the American Cordillera. Figure can also be viewed
as Online Supplement 17.1.
sphere (Nylen 2004, Granshaw and Fountain 2006,
Sitts et al. 2010, Basagic and Fountain 2011).
Because of the small sizes of most of the glaciers
in the region, aerial photography has been the primary data source used for the analysis. Following
Section 17.2 (‘‘Regional context’’) and a summary/
overview of the distribution and recent changes in
area of glaciers throughout the region (based
mainly on aerial imaging), we present three
ASTER-based case studies, one for a single small
shrinking glacier in Glacier National Park, another
for some larger glaciers of Mt. Rainier, and a third
study for Blue Glacier in the Olympic Mountains.
Although image analysis at ASTER’s spatial resolution is challenged by the small sizes of the glaciers,
a rich variety of glacier features and phenomena are
documented here that have not been reported using
satellite remotely sensed data.
17.2
REGIONAL CONTEXT
17.2.1 Geologic context
Here we offer geologic details of some of the
glacierized ranges to help explain some contrasting
characteristics of this region’s glaciers and associated valleys. The geologic context can help explain
the spatial pattern of debris-covered glaciers versus
glaciers without significant debris.
17.2.1.1.
The Cascade Range
The Pacific Province parallels the Pacific Coast and
is the youngest and most tectonically active in
North America due to its location near active plate
boundaries. The largest Pacific ranges in the U.S.
outside Alaska are the Cascade (northern California, Washington, and Oregon) and Sierra
Regional context 387
Nevada (California) with elevations from about
1,000 m to over 4,300 m. The Cascade Range of
Washington and Oregon south to the Lassen
volcanic complex in northern California hosts
numerous volcanoes, most active in the Holocene,
resulting from subduction of the Juan de Fuca Plate
under the North American Plate along the Cascadia
subduction zone (Brandon and Calderwood 1990).
The basic plate geometry has developed toward the
present configuration over the past 36 million years
(Wood and Kienle 1990).
The magmatic arc of the Cascades is mainly
andesite and dacite and plutonic equivalents. The
glacierized volcanoes are primarily classic stratovolcanoes, and as such are composed of interlayered lava flows, welded and unwelded ash and
other pyroclastic rocks. Because time elapsed
between many eruptions, soil horizons are interspersed with the volcanic layers; consequently, the
volcano flanks are relatively weak. Erosion rates on
the most heavily glacierized volcanoes are among
the highest documented in the world. Mt. Rainier’s
denudation rate, according to sediment loads
analyzed from modern rivers draining the mountain, is 3–8 mm yr 1 (Mills 1976). Though comparable to denudation rates in Alaska’s Chugach
Range, it vastly exceeds the 0.18–0.32 mm yr 1
erosion rates across the Olympic Peninsula
obtained by similar methodology; long-term
erosion rates determined by fission track analysis
reach 1.1 mm yr 1 on Mt. Olympus (Brandon et al.
1998), where the precipitation regime is probably
higher than on Mt. Rainier. The difference in
denudation rates of the two mountains probably
relate to higher glacierization of Mt. Rainier and
possibly differences in lithology between the two
settings.
17.2.1.2
Olympic Mountains
The Olympic Mountains were tectonically uplifted
by convergent plate tectonics. The mountains
largely consist of uplifted metamorphosed sedimentary rocks of the ocean floor and continental margin
(Brandon and Calderwood 1990). As such, there is
substantial mechanical layering of rocks of contrasting strength.
17.2.1.3
Sierra Nevada
The Sierra Nevada, arranged south of the Cascadia
subduction zone, originated with the Mesozoic
intrusion of a massive granitoid batholith into
Paleozoic sedimentary strata and andesitic volcan-
ics. The batholith—mainly granite, granodiorite,
quartz diorite, and similar rocks—is one of the
largest on Earth (Bateman and Eaton 1967, Hirt
2007). Individual glacial valleys cut through and
across plutonic lithologies (Hirt 2007). However,
the petrologic structure is on an immense scale,
and many valleys approach a monolithic petrologic
character.
17.2.1.4
Rocky Mountains
The Rocky Mountains province includes all the
glacierized regions of western Montana, Wyoming,
Colorado, and Utah. Some of the major and most
glaciologically relevant mountain ranges within the
Rocky Mountains are the Front and Gore (Colorado), Wind River and Tetons (Wyoming),
Absoraka/Beartooth and Lewis (Montana), and
the Sawtooth (Idaho). The Rocky Mountains of
Colorado include remnants of layered sedimentary,
metasedimentary, and volcanic rocks; the highest
areas in those ranges where glaciers occur today
are granitoid plutonic rocks. The Wind River
Range, to the north in Wyoming, is granitic resulting from a large batholith uplifted most recently by
the Laramide Orogeny (Frost et al. 1998). The
northern Rockies of the Lewis Range (Glacier
National Park) are mainly sedimentary rocks,
especially carbonates.
17.2.2 Climatic context
Most of the ranges in the American Cordillera were
glaciated during the Pleistocene including many
that no longer have glaciers present today. Most
of the glaciation, however, was from local ice caps
or individual valley glaciers (Denton and Hughes
1981). Continental glaciation of the Late Pleistocene was limited to the northern states of Washington, Idaho, and Montana with lobes of the
Cordilleran and Laurentide Ice Sheets following
the lowlands and merging with local ice caps and
glaciers from adjacent mountain ranges (Waitt and
Thorson 1983). Therefore, the topographic alteration from glacial erosion and deposition are common to most of the ranges in the Cordillera.
The climate of the region is extremely diverse,
from coastal temperate rainforests to deserts, relatively mild marine climates to continental extremes
of cold winters and hot summers. This brief climate
summary is organized in terms of winter snow that
nourishes the glaciers and the summer air temperatures that melt the glaciers. The winter precipitation
388
Glaciers and perennial snowfields of the U.S. Cordillera
climate of the American Cordillera is dominated by
the polar vortex, which moves south in winter also
pushing the Polar Front jet southward advecting
moisture from the Pacific Ocean into the Cordillera
(Davis and Walker 1992). Invasions of cold dry air
from polar continental air masses southward from
Canada into the north central U.S. cool the eastern
side of the Cordillera in winter, extending towards
the west (Mitchell 1976). Interior winter high-pressure systems also form in the Basin and Range
Province cooling the center of the Cordillera
(Mitchell et al. 1976, Davis and Walker 1982).
The summer pattern of air temperatures shows
the influence of cool winds off the Pacific Ocean
along the coastal ranges and into northwestern
Montana (Mitchell et al. 1976), whereas a regional
low-pressure system over the Basin and Range
Province, caused by warm surface temperatures,
affects the interior through Idaho, southern Montana, and Wyoming (Mitchell et al. 1976, Davis and
Walker 1992). Thus, from northwestern Washington State, climate generally becomes drier to the
south and east and warmer during the summer
ablation season. Taken together, this produces a
distribution of glaciers that reach relatively low
elevations and are large in the northwest (Washington) and increase in elevations and become smaller
to the south and east (Fountain et al. 2008).
Temporal variation in the climate of the American Cordillera, besides including the general global
warming trend of the past century, is influenced by
several modes of atmospheric circulation characterized by numerous climate indices. The El Niño–
Southern Oscillation Index (ENSO–SOI) acts on
an interannual temporal scale and a large spatial
scale. During a warm phase (El Niño) the sea surface temperatures (SSTs) are warmer than average
over the central and east Pacific Ocean, with the
opposite during the cool phase (La Niña). For the
American Cordillera, El Niño phases tend to generally cause drier-than-average winters except for
the Sierra where it is wetter; wetter-than-average
winters occur except for the Sierra which has normal winters during La Niña years (Cayan et al.
1999). Acting on an interdecadal scale, the Pacific
Decadal Oscillation (PDO) produces similar
climate variations as the ENSO, although not as
extreme (Mantua et al. 1997). Warm PDO phases
are associated with cool SSTs over the central
North Pacific and warmer SSTs along the west
coast, and vice versa (Mantua 2002). A warm
PDO phase produces an El Niño–like temperature/precipitation pattern such that drier-than-
average winters occur in the northern tier of the
American Cordillera and wetter than average in
the Sierra (Bitz and Battisti 1999, Mote et al.
2005). In this book’s Chapter 33 (‘‘Summary and
climatic context’’) Kargel et al. provide further
insights on the subdecadal to multidecadal climate
oscillations and teleconnections of the eastern
Pacific Basin.
17.3
METHODS
The inventory of glaciers and perennial snowfields
in the American Cordillera is based on U.S. Geological Survey 1:24,000-scale topographic maps
which are derived from aerial photography ranging
from 1943 to 1998 with most imagery (86%) from
1955 to 1990 (Fountain et al. 2007a). Because of
problems with seasonal snow being mistaken by
cartographers as permanent snow the true number
of features, particularly small glaciers and snowfields, is probably smaller. The methods and data
are summarized in Fountain et al. (2007a). Because
we cannot field-check many of the features, we
cannot distinguish between the three categories of
features; therefore we lump them into a single
category of ‘‘glaciers and perennial snowfields’’.
We choose not to use an arbitrary size criterion
to classify active glaciers because we know of small
features (10 4 m 2 ) containing glacial ice and
exhibiting movement. Furthermore, small features
are important to the local hydrological cycle.
Changes in glacier area are derived from groundbased and aerial imagery. Glacier extent from the
ground-based photographs was inferred from
matching landmarks with those found in digital
orthophotographs. Most of the aerial imagery were
vertical aerial photos (1 m ground resolution),
and if they were not georectified we rectified them
by matching ground features from digital orthophotos. Details of the methods are summarized in
the literature cited at the end of this chapter. In
three case studies, below, we utilize satellite remote
sensing as well as published data obtained by airborne and ground-based studies.
17.4
RESULTS
The American Cordillera contains 8,303 glaciers
and perennial snowfields that cover a total of 688
km 2 . These features range in size from 387 m 2 to
10.6 km 2 with a median of 0.014 km 2 ; 928 are larger
Results
than 0.1 km 2 . The largest glacier is the Emmons
Glacier, located on the slopes of Mt. Rainier, a
stratovolcano in Washington. Glacier aspect in
the American Cordillera is typically north to east,
as one would expect in the Northern Hemisphere.
The exceptions to this trend are the glaciers on the
tall stratovolcanoes in the Pacific Northwest, but
also in these cases the glaciers are generally larger
on the north to east–facing sides. Although we do
not address rock glaciers or debris-covered glaciers
in this summary, extensive buried ice exists in the
Cordillera and many of the smaller ice snow features appear to be accumulation zones for subsurface ice.
17.4.1 California
The three main mountain ranges that host glaciers
are the Sierra Nevada, the southern end of the
Cascades represented by the stratovolcanoes Mt.
Shasta and Mt. Lassen, and the Trinity Alps. The
Sierra Nevada extends about 600 km from north to
south along the eastern border of California and
continuously reaches above 3,000 m, with peaks
up to 4,421 m. The Cascade volcanoes abruptly rise
2,300 m to over 4,300 m in the northern part of the
state, while the nearby Trinity Alps are a compact
range with elevations under 2,800 m. The climate of
these mountain regions is characterized by cold wet
winters and hot dry summers. Total water equivalent (w.e.) winter accumulation for alpine regions
ranges from about 330 mm w.e. in the southern
Sierra Nevada increasing northward to >1,350
mm at Mt. Shasta (CDEC 2009). In the Sierra
Nevada, summer temperatures range from 3 to
9 C (PRISM Group 2006). Seasonal precipitation
changes are controlled by migration of the Pacific
High pressure system from the north, which directs
moisture from the Pacific Ocean (Bair 1985). The
inventory shows that 1,788 glaciers and perennial
snowfields, covering 46 km 2 , populate these mountainous regions.
The Sierra Nevada contains 85% of the ice cover
in California, with 1,719 glaciers and perennial
snowfields totaling 39 km 2 located in the central
and southern portions of the range. These features
range in elevation from 2,739 to 4,263 m with a
mean of 3,491 m. However, as reported by Basagic
and Fountain (2011), the number of true glaciers in
the Sierra Nevada, versus non-moving ice (e.g.,
perennial snowfields), is estimated to be 122, covering a total of just 14.89 0.08 km 2 . About 60 of
these features are larger than 0.1 km 2 (Basagic and
389
Fountain 2011), and the largest is Palisade Glacier,
0.8 km 2 . Only 13 glaciers have official names. Based
on these glacier areas and area changes between
1903 and 2004, Basagic and Fountain (2011) estimated ice volume decreasing from 1.09 km 3 in 1903
to 0.43 km 3 in 2004, approximately a 60% volume
loss in one century. We examined glacier area
change with time for 14 glaciers in the Sierra
Nevada for the period 1900 and 2004 and found
that their area decreased by 31% to 78%, averaging
55% (Basagic and Fountain 2011). Rapid retreat
occurred over the first half of the 20th century
beginning in the 1920s in response to warm/dry
conditions and continued through the mid-1970s.
Recession ceased during the early 1980s. Since the
1980s glaciers resumed retreat. The approximate
synchroneity of area changes in the 14 study glaciers
shows that they exhibit a response to regional
climate; however, the magnitude of changes is
influenced by local topography.
In the Cascades, Mt. Shasta, 4,317 m, is mantled
with seven named glaciers for a total area of 4.9
km 2 . The two largest glaciers in California are
Whitney and Hotlum Glaciers on Mt. Shasta, each
with an area of 1.3 km 2 . Whitney is the longest
glacier in the state (3.2 km). On Mt. Shasta, Howat
et al. (2007) determined that several glaciers
advanced over the second half of the century. Only
a few perennial snowfields are found on Mt. Lassen.
The Trinity Alps contain 35 glaciers and perennial snowfields totaling 1.9 km 2 . While the majority
of these features are snowfields, several small
(0.01 km 2 ) glaciers are located in cirques on the
north sides of Thompson Peak (2,742 m) and
Caesar Peak (2,720 m). In the Trinity Alps, two
glaciers examined lost 77–84% of their area
between 1900 and 1993, but only 10–20% of the
loss occurred over the latter half of the 20th century
(Heermance and Briggs 2005).
17.4.2 Colorado
The Southern Rocky Mountains cross the state of
Colorado, covering an area about 450 km from
north to south and 300 km from east to west.
The mountains are composed of over a dozen
ranges, and rise from base heights of about 1,500
to 2,300 m to numerous peaks over 4,300 m. The
climate of Colorado is continental, and mean
annual temperature ranges from greater than
12 C to the east and west of the mountains down
to below 3 C at the higher peaks (PRISM Group
2006). The high mountains receive between 200 and
390
Glaciers and perennial snowfields of the U.S. Cordillera
900 mm w.e. precipitation during winter (November to March), with greater values to the north and
west (PRISM Group 2006). Mean summer (June to
September) temperatures in the high mountains are
about 4 to 10 C (PRISM Group 2006). The Pacific
Ocean is the prevailing moisture source for
Colorado’s mountains, but in the spring storms
can move north from the Gulf of Mexico bringing
greater amounts of moisture (Bair 1985). In the
mountains, the greatest monthly precipitation
occurs during winter, but thunderstorms are
frequent during summer (Bair 1985).
A total of 141 glaciers and perennial snowfields
are found in Colorado, totaling 4.8 km 2 . The
largest is Arapaho Glacier, 0.24 km 2 , and only six
others are larger than 0.1 km 2 . All 14 named
glaciers are in the Front Range. About 44% of
the ice-covered area in Colorado (48 features) occur
in the Front Range, followed by the Gore Range,
35%; Sawatch Range, 25%; Park Range, 18%;
Medicine Bow Mountains, 10%; San Miguel
Mountains, 4%; and Tenmile Range, 1%. These
glaciers and perennial snowfields vary in elevation
from 3,248 to 4,287 m, with a mean elevation of
3,678 m. Local topography that favors snow accumulation from avalanches and windblown snow
and shades the snow and ice from summer Sun is
important for maintaining these features (Outcalt
and MacPhail 1965).
The glaciers in Rocky Mountain National Park
in the northern Front Range decreased in area by
about 40% during the first half of the 20th century,
grew slightly from the mid-1940s to the end of the
century, and have retreated more rapidly since
(Hoffman et al. 2007). Summer temperature alone
is a good predictor of mass balance but the glaciers
are insensitive to variations in winter snowfall due
to augmentation, up to 12 times, by avalanching
and wind deposition (Outcalt and MacPhail 1965;
Hoffman et al. 2007). The Arapaho and Arikaree
Glaciers, both in the Front Range, rapidly lost mass
in the early 1960s, slightly gained mass from the late
1960s to mid-1970s, and have lost mass since, with
the rate increasing since 2000 (Dyurgerov 2002),
consistent with glacier area change in Rocky Mountain National Park. There is little systematic information on glacier change elsewhere in Colorado,
but comparison of topographic maps from the
mid-20th century and aerial photos from the
1990s indicates little change in glacier area throughout the state during that time period, comparable
with what has been documented in the Front
Range.
17.4.3 Idaho
Of the many mountain ranges in Idaho, three host
glaciers and perennial snowfields, the Sawtooth
Range, Seven Devils Mountains, and the Lost River
Range. The Sawtooth Range is located in central
Idaho and spans 60 km with numerous peaks higher
than 3,000 m elevation. The Seven Devils Mountains are a compact range near the Oregon border
reaching about 2,800 m. The Lost River Range in
east-central Idaho is a fault block stretching for
about 80 km containing several peaks over 3,600
m. Mean annual precipitation in the Sawtooths and
Seven Devils Ranges varies from 500 to 1,250 mm,
the majority of which falls in the winter and spring
(Thackray et al. 2004). The Lost River Range is
more arid, and generally receives less than 1,000
mm of precipitation per year.
Idaho has 208 glaciers and perennial snowfields
covering a total area of about 2.6 km 2 . Thus, the
average size is just 1.3 ha. Only three features
exceed 0.1 km 2 . Most of these features appear to
be perennial snowfields. The Sawtooth Range contains 202 features covering about 2.5 km 2 , or 96%
of the ice-covered area in the state. Aerial imagery
from 2004 indicates that these features have
decreased considerably in size since the middle of
the century. The glacier population in the Sawtooth
may result from this range being the first high orographic barrier encountered by moist Pacific air
masses east of the Cascade Range in Washington.
Six perennial snowfields are found in the Seven
Devils Mountains and cover an area less than 0.1
km 2 . In addition to the inventoried glaciers in the
Sawtooth Range and Seven Devils Mountains,
there is documentation of an active glacier on
Borah Peak in the Lost River Range during the
1970s (Otto 1975, 1977).
17.4.4 Montana
The glaciers of Montana are found in the northwestern part of the state in the Cabinet Mountains,
Flathead–Mission–Swan, Lewis–Livingston, and
Madison Ranges, and in the southern part of the
state in the Absaroka–Beartooth and Crazy Mountains. The climate on the western side of the continental divide, which includes all of the ranges in
the northwestern part of the state is controlled by
Pacific marine air masses that create heavy winter
snowfall. East of the divide, which includes the
Absaroka–Beartooth and Crazy Mountains the
winters are much drier (Bair 1985). At high eleva-
Results
tions in the Lewis Range, average water equivalent
snowfall exceeds 1,400 mm, whereas in the high
elevations of the Beartooth Mountains average
snowfall (w.e.q.) is about 360 mm (PRISM Group
2006).
A total of 1,158 glaciers and perennial snowfields
are found in Montana covering a total area of 68.6
km 2 . About 13% (153) of these features are larger
than 0.1 km 2 and the largest glacier is the Blackfoot
Glacier (1.8 km 2 ). Elevations of the features range
from 1,656 to 3,715 m with a mean of 2,649 m. The
Cabinet Range has three features, all greater than
0.1 km 2 , with a total area of 0.7 km 2 and the
Flathead–Mission–Swan Ranges contain 85 features with a total area of 3.6 km 2 and elevations
from 2,201 to 2,663 m and a mean of 2,444 m.
The Lewis–Livingston Ranges host 603 features
totaling 9 km 2 , 86 of which are greater than 0.1
km 2 ranging in elevation from 1,656 to 3,109 m
with a mean of 2,264 m. The Madison Range contains nine features with a total area of 0.06 km 2 .
The Absaroka–Beartooth Mountains contain 400
features with a total area of 21.8 km 2 , of which
52 features are greater than 0.1 km 2 , and elevation
ranges from 2,641 to 3,715 m with a mean of 3,237
m. Finally, the Crazy Mountains contain 57 features with a total area of 1.9 km 2 , four features
greater than 0.1 km 2 , and the elevation ranges from
2,680 to 3,146 m with a mean of 2,862 m.
Four glaciers in the Lewis Range in Glacier
National Park have retreated about 67% since
1900. They underwent rapid retreat in the 1930s
and 1940s and a slowing and perhaps slight advance
in the 1960s and 1970s, followed by retreat. One of
the park’s largest glaciers, Grinnell Glacier, is
featured in a case study below as an example of
these glacier remnants. Much of the work in the
Beartooth Mountains has focused on the Grasshopper Glacier due to its unusual contents of grasshoppers frozen in the ice (e.g., Kimball 1899). This
glacier and an adjacent one have lost about 70% of
their area since 1898 (Ferrigno 1986, Chatelain
2005)
17.4.5 Nevada
The only glacier/perennial snowfield in Nevada is
on Mt. Wheeler, part of the South Snake Range and
the highest peak in the state, 3,982 m. The feature is
0.9 km 2 and has an average elevation of about 3,350
m.
391
17.4.6 Oregon
The Cascade Range crosses the state of Oregon,
covering an area about 400 km from north to south
and 100 km from east to west. Most of Oregon’s
glaciers are found on the stratovolcanoes that rise
from the surrounding mountains at about 1,200 m
to summits above 3,000 m. Small glaciers are also
found in the Wallowa Mountains that extend about
100 km across northeastern Oregon, rising from
high desert at 1,200 m to peaks at nearly 3,000 m.
The Cascades have a maritime climate, receiving
1,500 to 3,000 mm of precipitation per year, primarily in winter; the inland Wallowa Mountains are
drier, and receive less than 2,000 mm of precipitation per year (PRISM Group 2006).
There are 463 glaciers and perennial snowfields in
Oregon, 29 of which are named, covering 42.5 km 2 .
Most of these features are small, and only 60 are
larger than 0.1 km 2 . The largest glacier in Oregon is
Whitewater Glacier (3.0 km 2 ) on Mt. Jefferson, a
conglomeration of five glacial lobes feeding separate streams, and the longest is Eliot Glacier (3.6 km)
on Mt. Hood. In the Cascades the ice-covered area
on the stratovolcanoes decreases from north to
south with elevations ranging from 1,332 to 3,415
m, with a mean elevation of 2,191 m. Mt. Hood
contains the greatest number of features, 148 (12
named), and largest ice-covered area at 22.7 km 2 .
The glaciers of the northern side are mantled with
rock debris near their termini as a result of frequent
rock avalanches from Hood’s geothermally altered
north face (Jackson and Fountain, 2007). Mt. Jefferson has 35 features covering 5.5 km 2 . The volcanic complex of North and Middle Sister contains
78 features covering 5.4 km 2 . South Sister has 51
features covering 4.4 km 2 , many of which are debris
mantled, and Broken Top has 33 features covering
3.3 km 2 . The tiny (3,000 m 2 ) Lathrop Glacier on
Mount Thielsen is the southernmost glacier in
Oregon and is the smallest named glacier in the
U.S.A. The glaciers of Mt. Hood have a volume
of about 0.34 km 3 , and those of the Three Sisters
about 0.16 km 3 (Driedger and Kennard, 1986). The
Wallowa Mountains host 131 glaciers and perennial
snowfields covering 1.5 km 2 , which vary in elevation from 2,280 to 2,881 m with a mean of 2,625 m.
The largest and only named feature is the Benson
Glacier, most likely the only actual glacier in the
range.
Between 1907 and 2004 the seven largest glaciers
on Mt. Hood lost 34% of their area on average,
retreating through the first half of the 20th century,
392
Glaciers and perennial snowfields of the U.S. Cordillera
advancing or at least slowing their retreat dramatically in the 1960s and 1970s, and then retreating
again, in some cases rapidly (Lillquist and Walker
2006, Jackson and Fountain 2007). The glaciers
with significant debris cover in the ablation zone
retreated more slowly than the other glaciers, with
the debris cover presumably buffering the glacier
from increasing temperatures by thickening when
the mass balance is negative (Jackson and Fountain
2007). Collier Glacier on North and Middle Sisters
has lost over 50% of its area since 1900, but its
retreat may have been exacerbated due to topographic factors (McDonald 1995). Therefore,
change in the glaciers of Mt. Hood is presumably
more representative of the rest of the Cascades.
There is little documentation of glacier change in
the Wallowa Mountains, but Benson Glacier lost
over half of its area between 1920 and 1992 (Skovlin
et al. 2001).
17.4.7 Washington
Both major mountain ranges in Washington are
populated with glaciers, the Cascade Range and
the Olympic Mountains. The Cascade Range is
characterized by large stratovolcanoes, Mt. Rainier
being the tallest at 4,392 m, and in the north, by
rugged mountains with high relief. The Olympic
Mountains occupy an area about 80 km on a side
on the Olympic Peninsula in western Washington.
Washington’s climate, like Oregon’s, is characterized by wet winters and dry summers. The Cascade
Range and the Olympic Mountains receive extensive winter snowfall, commonly 2 m w.e. or more
(LaChapelle 1965; Meier and Tangborn 1965). The
western Olympic Mountains are the wettest place in
the contiguous U.S. Winter air temperatures are
commonly near freezing such that a small change
in air temperature can cause precipitation to occur
as rain instead of snow, thus making snowpacks
and glaciers vulnerable to climatic warming (Mote
et al. 2005).
Washington is the second most glaciated state
in the U.S.A. (after Alaska) with 3,079 glaciers
and perennial snowfields covering 449 km 2 , six
times that of the third most ice-covered state of
Wyoming. The Cascade Range contains 2,693
features covering 412 km 2 . Mt. Rainier, one of
the major Cascade volcanoes and featured in a case
study below, concentrates the largest ice-covered
area, 88 km 2 . The largest glacier in the state is
Emmons Glacier (10.5 km 2 ) on Mt. Rainier. The
Olympic Mountains are closest to the coast and
host 386 features covering 37 km 2 .
In the North Cascades, glacier area decreased by
7% from 1958 to 1998 (Granshaw and Fountain
2006). Percentage-wise, smaller glaciers lost significantly more area than larger glaciers. The wellstudied South Cascade Glacier shrank by 22%
during the same time period (e.g., Bidlake et al.,
2007) while the Blue Glacier in Olympic National
Park saw a terminus retreat of 2% between 1957
and 1997 (Conway et al. 1999). During the period
1940–1990 six glaciers on Mt. Baker fluctuated
between the following three phases: (1) rapid retreat
in the 1940s through 1950s; (2) a period of stable or
advancing glaciers until about 1980; (3) retreat
through 1990 (Harper 1993; Fountain et al.
2007a, b). The glaciers on Mount Rainier decreased
in area by 21% between 1913 and 1994 (Nylen
2004).
Southern Washington’s Mt. Adams is another
large glacier-clad stratovolcano. Sitts et al. (2010)
examined the area change of Adams 12 glaciers
during the 20th century using historical topographic maps and aerial photos. Total glacier area
decreased 49% (31.5 to 16.2 km 2 ) from 1904 to
2006. The glaciers retreated during the first half
of the 20th century, then either slowed their retreat
or advanced from the 1960s to the 1990s. Subsequently, the glaciers resumed their rapid retreat.
Glaciers on Mt. Adams show similar trends to those
on Mt. Hood and Mt. Rainier. Sitts et al. (2010)
discerned a correlation between area change and
trends in winter precipitation and summer temperature, but they concluded that century-scale shrinkage trends since the end of the Little Ice Age (late
19th century) have been driven mainly by rising
summer temperatures. Decadal-scale oscillations
in winter precipitation appear to modulate (enhance
or diminish) the effects of temperature on glacier
change, according to the authors. Three local temperature records that they examined showed substantially increased warming rates begin around the
1980s; that climatic shift is thought responsible for
the rapid retreat of Mt. Adams’ glaciers starting
during the late 20th century. Sitts et al. (2010) noted
similar trends in Colorado (Hoffman et al. 2007)
and Montana (Key et al. 2002).
The eruption of Mt. St. Helens on May 18, 1980,
removed the Loowit and Leschi Glaciers, and
beheaded the other glaciers on the mountain (Brugman and Post 1981) such that these glaciers have
disappeared in the years since (Schilling et al. 2004).
The resulting north-facing crater has accumulated
Results
snow and protective layers of rock debris over the
years such that brand-new Crater Glacier is now the
largest on Mt. St. Helens at 1 km 2 (Schilling et al.
2004) and the newest in the American Cordillera, if
not North America. Crater Glacier, despite the fact
that it continues to grow, occurs entirely below its
climatic equilibrium line altitude, a feat made possible by the abundant windblown and avalanched
snow and rock debris contributed by the unstable
crater walls.
17.4.8 Wyoming
Wyoming hosts four distinct glacierized mountain
ranges, the Wind River, the Absaroka, the Teton,
and the Bighorn Mountains, all of which are part of
the Central Rocky Mountains. The Wind River
Range spans roughly 200 km along the continental
divide in west-central Wyoming, and covers about
9,800 km 2 . The range forms a major orographic
barrier, rising roughly 2,000 m from base to crest
(e.g., Gannett Peak 4,209 m) creating a deep precipitation shadow to the east. The Absaroka Range
in northwestern Wyoming runs about 150 km south
from the Montana border, and is roughly 100 km
wide. The range rises about 2,000 m from its base to
a height of 4,000 m at Francs Peak. The Teton
Range is a small range about 100 km from north
to south situated just east of the Wyoming–Idaho
border. The Tetons rise nearly 2,200 m from Jackson Hole to elevations near 4,200 m. The Bighorn
Mountains are located in north-central Wyoming,
covering about 150 km from north to south and
reaching 4,000 m in elevation.
The climate in Wyoming is continental with cold
winters, warm summers, and low precipitation from
Pacific maritime air masses (Bair 1985). In the Wind
River Range, winter air temperatures average about
9 C and summers about 8 C. Annual w.e. precipitation ranges from 200 mm at lower elevations to
almost 1,000 mm at higher elevations, with the
majority occurring in winter as snowfall (Wolken
2000).
Wyoming’s mountains contain 1,477 glaciers and
perennial snowfields totaling 72.1 km 2 , of which
114 are larger than 0.1 km 2 . The mean elevation
of these features ranges from 2,693 m to 4,205 m,
with an overall mean elevation of 3,368 m. The
Wind River Range holds 76% of the ice-covered
area (679 features), the Absaroka Range has 13%
(506 features), the Teton Range contains 10% (276
features), and the Bighorn Mountains account for
1% (16 features). The largest glaciers are found in
393
the Wind River Range, including 82 features larger
than 0.1 km 2 , 25 of Wyoming’s 38 named glaciers,
and the largest glacier in the continental U.S. outside Washington State, Gannett Glacier (3.3 km 2 )
(Pochop et al., 1990).
Since the end of the Little Ice Age the glaciers of
the Wind River Range have generally retreated
(e.g., Wentworth and Delo 1931, Meier 1951,
Marston et al. 1991, Pochop et al. 1989, Wolken
2000). The trend of retreat is similar to trends
observed in Montana and Colorado. A subset of
22 Wind River Range glaciers lost 42% of their area
over the 20th century (Devisser and Fountain, submitted).
17.4.9 Advancing glaciers
The vast majority of glaciers in the contiguous
U.S.A. are retreating, as has been shown here. Certainly all glaciers first documented around 1900 are
smaller now. Over the last 20 years or so some
glaciers have either maintained a quasi-steady position while a few others have advanced. These cases
reflect local circumstances rather than regional/global climate conditions. An extreme case is Crater
Glacier in the crater of Mt. St. Helens, Washington.
After the volcano erupted in the spring of 1980, a
large, north-facing crater was formed. Snow and
rockfall collected at the crater bottom and its
north-facing orientation shaded this accumulation
such that it formed a glacier. The glacier has been
thickening and advancing towards the crater opening (Schilling et al. 2004). A less clear situation is
represented by the northeast-facing glaciers of Mt.
Shasta in northern California. Two glaciers,
Hotlum and Whitney, have been advancing since
the 1940s after a rapid retreat in the prior two
decades (Howat et al., 2007). Since the 1970s the
advance has slowed greatly. Howat et al (2007)
showed that glacier advance is due to anomalously
high winter snowfall that more than compensated
for the increased summer melt due to climate warming. They predict, however, that continued warming
will reverse the glacier behavior in the coming decades.
We note that the glaciers on the stratovolcanoes
of the Cascade Range (California north through
Washington), particularly those on north and
east-facing glaciers, have remained relatively steady
or have retreated little in the past few decades
(Nylen 2004, Jackson and Fountain 2007, Sitts et
al. 2010). This finding corresponds to the findings of
Howat et al. (2007) on Mt. Shasta. In contrast, as
394
Glaciers and perennial snowfields of the U.S. Cordillera
this chapter shows, glaciers elsewhere have
retreated extensively. The stratovolcanoes reach
elevations much higher than that of the surrounding mountain range. Enhanced snowfall in winter
and year-round cool temperatures buffer against
increased summer melt such that the glaciers have
not receded as much as glaciers elsewhere in the
surrounding mountain range.
17.5
CASE STUDIES USING ASTER
17.5.1 Grinnell Glacier, Glacier National
Park, Montana
Key et al. (2002) presented a detailed overview and
specific case studies of the status and recent changes
of glaciers in Glacier National Park, Montana,
U.S.A., including a 143-year-long time series for
Grinnell Glacier. The fifth largest glacier in the
park, with an area of 0.88 km 2 as of 1993, it is just
a remnant of what it was in 1850. Hall and Fagre
(2003) found that, from 1850 to 1979, glaciers in
the Blackfoot–Jackson Glacier Basin in the park
decreased from 21.6 to 7.4 km 2 , a two thirds
decrease, which is about the same change as for
Grinnell Glacier.
The extent of Grinnell Glacier was updated
using ASTER for 2003. We interpolated their
143-year time series every 40 years for 1850, 1890,
1930, and 1970, and superposed those outlines on
an ASTER image from July 29, 2003 (Fig. 17.2).
About one century ago, Grinnell Glacier separated
into two distinct ice bodies, leaving the small,
perched ice apron known as the Salamander Glacier
(Fig. 17.3A, D). In front of the Grinnell, as shown
well in spectacular photos by John Scurlock and
Karen Holzer (Fig. 17.3 and Online Supplements
17.3A, 17.3B, and 17.3C), a lake has formed. The
combined area of Grinnell Glacier and the Salamander now is about 1.1 km 2 , roughly a 62% loss
since 1850. Of the two remnant pieces, the Salamander has been relatively stable since the detachment
occurred, whereas Grinnell Glacier continues to
retreat.
The color-saturated version of John Scurlock’s
photo (Fig. 17.3B) shows patches of vegetation
developing on the glacial moraines. By comparing
his photo with the ASTER image (Fig. 17.2) and the
interpolated time series of Key et al. (2002), it can
be seen that thin and discontinuous vegetation has
developed on moraine surfaces and bedrock that
became ice free around 1930 and before. Denser
and more continuous vegetation occurs on surfaces
whose ice-free conditions predate the 1850 moraine.
Karen Holzer’s photo (Online Supplement 17.3C)
shows a different perspective of Grinnell Glacier
and reveals the glacier-sculpted mountains nearby,
Figure 17.2. Time series of Grinnell Glacier’s shrinking extent from 1850 to 2003 (data to 1970, Key et al. 2002).
Time series data have been interpolated every 40 years and warped to fit an ASTER VNIR RGB321 false-color image
acquired in 2003. Figure can also be viewed as Online Supplement 17.2.
Case studies using ASTER 395
Figure 17.3. Photo of Grinnell Glacier and the Salamander, Glacier National Park, taken in 2009 by John Scurlock
(A), then color-saturated to highlight vegetation patterns (B), and cropped to show glacier details (C, D). See
Online Supplement 17.3A for a high-resolution version of this figure, Online Supplement 17.3B for Scurlock’s
original image, and Online Supplement 17.3C for one acquired by Karen Holzer (USGS) in 2006. Grinnell Glacier
1,600 m left to right.
shaped by far more extensive and peak-capping
Pleistocene glaciers.
Glaciers in Glacier National Park are small and
receive snow from wind transport, avalanches off
steep headwalls, and from direct snowfall. As the
glaciers retreat deeper into the cirque basins and
small, heavily shadowed niches along the headwall,
the indirect sources of snow become increasingly
important relative to direct snowfall (Basagic and
Fountain 2011).
17.5.2 Glacier changes on Mt. Rainier,
Washington, assessed using
ASTER and MASTER multispectral
and thermal imagery
17.5.2.1
Background
Glaciers on Mt. Rainier (4,392 m), a dormant volcano in the Cascade Range of Washington, exhibit
a stellar array of glaciers as shown in an International Space Station image (Fig. 17.4). These
396
Glaciers and perennial snowfields of the U.S. Cordillera
Figure 17.4. (A) Mt. Rainier glaciers, International Space Station image ISS017E010110 (not orthorectified). (B)
Outlines for north-facing glaciers on orthorectified ASTER 321RGB false-color composite (image acquired August
20, 2010). Outlines for Carbon and Winthrop Glaciers obtained from other recent ASTER images; Emmons outline
extracted from this image. Note the relative rotation of the images (north arrow). Figure can also be viewed as Online
Supplement 17.4.
glaciers are important for their role as signposts of
climate change (Burbank 1982, Nylen 2004,
Oerlemans 2005), freshwater resources (Fountain
and Tangborn 1985, Jansson et al. 2003), and hazards due to glacier outburst floods (Fountain and
Walder 1998, Walder and Driedger 1993). Pyroclastic volcanism and hydrothermal alteration has
produced weak, fractured rocks, glacial erosion has
incised rugged valleys, and glacier thinning and
retreat has debuttressed lateral moraines and
spine-like arêtes. With so much poorly consolidated
rock arranged with precarious support, landslides,
rockfalls, and debris flows generate enormous
amounts of supraglacial debris. The hazard regime
is similar in some respects to that posed by Mt.
Ruapehu, New Zealand, another stratovolcano
(Chapter 29 of this book by Chinn et al.). Though
the hazardous processes are mainly different from
those of the Cordillera Blanca, Peru and the Himalaya, some of the advanced methodologies outlined
Case studies using ASTER 397
by Kargel et al. (2011) potentially could be developed for monitoring of Mt. Rainier, and lessons
learned from Mt. Rainier could be applied to other
ice-capped volcanoes near population centers.
Mount Rainier is recognized as the Cascades’
most dangerous volcano (Walder and Driedger
1993, Hoblitt et al. 1998, Vallance et al. 2003)
due to the proximity of a large human population
vulnerable to eruptive activities. Several population
centers are built directly on debris flow deposits
dating from the last five millennia. Although a
minor eruption occurred in the mid 19th century
(Crandell 1971, Scott et al. 1995) most of the dangerous mass flows appear linked to collapses of
glacial moraines and hydrothermally altered rock
associated with and mobilized by glacier outburst
floods or rainfall/snowmelt events. Given the
extreme and long-term hazards posed by Mount
Rainier, a sustained monitoring program has been
established.
Glacier outburst and rainfall-induced floods
from Little Tahoma Glacier, and other outburst
floods have frequently modified many drainages,
most notably Kautz Creek and Nisqually River,
during historical time (Driedger and Fountain
1989, Walder and Driedger 1993). During November 4–6, 2006, a rainfall-induced flood produced
numerous debris flows around the mountain (Copeland 2009). Flow initiations were close to glacier
termini suggesting that rapid runoff from the
glaciers in combination with the unstable and steep
moraine embankments were the triggers. We might
expect that, as Rainier’s glaciers further recede,
future debris flows will be initiated at higher elevations and on possibly steeper gradients. Clearly,
monitoring of Mount Rainier’s glaciers and
documentation of their recent fluctuations in the
contexts of climate change, volcanic eruptions, outburst floods, and mass movements is important.
Here we offer a remote-sensing case study of three
glaciers on Mt. Rainier (Carbon, Winthrop, and
Emmons), and document their length and debriscover variation, and associated wastage and mass
movements.
17.5.2.2
Methods
Imagery used for this study includes ASTER
orthorectified scaled radiance data (data product:
AST14DMO), which is a NASA Earth Observing
System (EOS) Level 3 data product that incorporates calibrated radiometric and geometric coefficient corrections (Kargel et al. 2005). Addition-
ally, the imagery is terrain-corrected using an
ASTER-derived digital elevation model, and is
mapped onto the UTM coordinate system. The
final product includes 15 orthorectified ASTER
calibrated scaled radiance images, one per band,
having 8-bit DN units (King et al. 2003). Most
images selected were cloud free and acquired during
the mid to late ablation season, thereby minimizing
the occurrence of snowfields and snow patches.
ASTER VNIR bands 3, 2, and 1 were stacked into
standard false-color composite (FCC) image cubes
(using ERDAS IMAGINE 9.3) and projected into
band 321 RGB color space for evaluation and analysis. The spatial resolution of VNIR bands is 15 m.
Glacier extents for 21st century ASTER images
were determined by manual digitizing on FCC
imagery; 20th century extents were extracted by
Nylen (2004), and all glacier extents subsequently
compiled and draped onto ASTER image bases
(Fig. 17.5). Temporal and spatial changes in glacier
termini position were then determined following
Giffen et al. (see Chapter 11 of this book). Briefly,
a downglacier flow vector is defined and a parallel
line is drawn, perpendicular to the flow vector, at
the farthest downvalley extent of the terminus for
each temporal position of the terminus (Fig. 17.5A).
The distance between these lines defines change in
terminus position. All glacier extent measurements
and metric baselines were generated within a geographic information system (GIS) (ArcGIS 9.3).
Land cover classifications for Carbon, Winthrop,
and Emmons Glaciers quantified total glacier area
and fraction of debris cover. Glacier extent was
determined by manual digitizing on a single 2008
ASTER FCC image (VNIR bands 321RGB), creating polygons for each glacier (Fig. 17.5A). Glacier
polygons were then used to clip a subset image from
the ASTER FCC. Initially, a simple DN threshold
of single-band clipped images was applied, although
it does not accurately discriminate between dirty ice
and debris-free ice, particularly where small clean
ice zones were embedded within heavily debriscovered ice. An unsupervised ISODATA classification (Jensen 2005) using the multispectral (bands
321) FCC yielded a faster and more robust
approach; defining, more accurately, the rich spectrum of ice and debris facies occurring on the
glaciers. ISODATA clustering algorithms typically
require pre-classification inputs including (1) the
maximum number of clusters to be identified, (2)
threshold value specifying minimum percentage of
unchanged pixel classification assignments between
iterations before a forced termination, and (3) the
398
Glaciers and perennial snowfields of the U.S. Cordillera
Figure 17.5. Glacier extent time series for Mt. Rainier’s north and northeast-facing glaciers on ASTER 321RGB
false-color composites. Glacier extents for the 20th century are from Nylen (2004); 21st century extents are from
this work using ASTER imagery. (A) Carbon Glacier showing termini extent measurement method. Note slight
advance 1994 to 2002 (ASTER images: September 24, 2002 and September 30, 2010). (B) Winthrop Glacier
showing 1913 to 1971/1994 advance, followed by recession into this century (ASTER images: July 27, 2004 and
August 23, 2008). (C) Emmons Glacier indicating large 1913 to 1971 recession and formation of vegetated
detached ice-cored lobe, followed by advance and minor retreat to the present day. The detached lobe of Emmons
Glacier remained ice-cored in places as of 2005 (ASTER images: July 27, 2004 and August 20, 2010).
maximum number of iterations before the algorithm is forced to terminate (Jensen 2005). For
Mt. Rainier, 10 classes were identified, with a
95% unchanged pixel threshold, and a maximum
of 6 iterations. The algorithm typically terminated
after three to four iterations because it met the
unchanged pixel threshold. Post-classification
assignments of land cover class were determined
by the user and grouped into four general classes:
ice, ice–debris, debris–ice, debris (Fig. 17.6B),
representing glacier facies spanning pure ice and
pure debris cover, with variable mixtures in
between. The two ‘‘debris’’ classes were merged to
establish total debris cover for each glacier (Fig.
17.6C), and the area and percent debris cover were
calculated within the GIS (note that total debris
cover of Carbon Glacier includes the two debris
classes plus the darkest debris–ice class in the
classification scale).
A simple analysis of change was conducted across
Rainier’s north-facing glaciers. The image pair was
selected for quality (i.e., cloud-free, low-band
saturation) and as close as possible to the same
calendar date to minimize the effects of variable
diurnal, seasonal, and phenological influences. In
this case images were acquired on July 27, 2004
and August 23, 2008, representing a difference of
about 4 years. A few notable change features identified within the difference image indicate the utility
of this technique (Fig. 17.7). Co-registration of
pre-subtraction image pairs was accomplished by
automated generation of numerous (>100) ground
control points (GCPs) between images (ENVI software). GCPs that contributed the highest RMS
errors to the image warp were sequentially deleted;
and co-registration of the image pair was acceptable
when RMSEs of <0.5 pixel were generated for a
first-order polynomial transformation fit between
images (see Chapter 4 for further details of this
method). The images were differenced (the latest
minus the earliest) using the ERDAS IMAGINE
modeler.
Changing terminus positions since 1913 for Mt.
Rainier’s north to northeast-facing glaciers are
shown in Fig. 17.8 and Table 17.1. Burbank
(1982) presented a much longer set of time series
of moraine positions for some other glaciers. The
changing area of debris cover for Mt. Rainier’s
Case studies using ASTER 399
Figure 17.6. (A). Mt. Rainier north and northeast-facing glaciers on ASTER 321RGB false-color composite
(image acquired August 20, 2010). (B) Unsupervised (ISODATA) classification, and post-classification assignment of glacial land cover classes. Classes indicate glacier facies grading from near pure ice to complete debris cover
(debris thicknesses are unknown). (C) Grouped debris cover classes for Winthrop and Emmons Glaciers; and
grouped debris classes plus one debris–ice class for Carbon Glacier (panel B legend). Figure can also be viewed as
Online Supplement 17.5.
Figure 17.7. Winthrop Glacier, Mt. Rainier. (A) Pre-debris flow ASTER 321RGB false-color composite (July 27,
2004). (B) Post-debris flow ASTER 321RGB FCC (August 23, 2008). Note the significant widening of the west
fork of the White River where material from the November 4–6 debris flow denuded vegetation adjacent to the
stream channel. (C) Differenced image (2008 minus 2004) highlights stream widening. Note further the dark-black
patches (bottom and center right of image) where 2004 snow patches are subtracted from areas with no snow in
2008; white patches (bottom center) where 2004 debris areas are subtracted from 2008 snow patches. Yellow circle
represents he presumed proglacial pond initiation site of the 2006 debris flow (Copeland 2009). Figure can also be
viewed as Online Supplement 17.6.
400
Glaciers and perennial snowfields of the U.S. Cordillera
Figure 17.8. Mt. Rainier’s north-facing glacier terminus extents since 1913.
Table 17.1. Mt. Rainier’s north-facing glacier termini extents since 1913 a.
Year
a
Carbon
Winthrop
Emmons
Absolute
(m)
Cumulative
(m)
Absolute
(m)
Cumulative
(m)
Absolute
(m)
Cumulative
(m)
1913
0
0
0
0
0
0
1971
73
73
150
150
1,668
1,668
1994
189
116
136
14
1,066
602
2002
152
37
—
—
—
—
2004
—
—
158
294
973
93
2008
—
—
136
22
—
—
2010
205
—
—
1011
53
38
20th century measurements (Nylen 2004), 21st century measurements (this work—ASTER based).
north-facing glaciers is given in Table 17.2 and illustrated in Fig. 17.9.
Several MODIS/ASTER Airborne Simulator
(MASTER) images were acquired with an oblique
perspective over Mt. Rainier in 2001. MASTER
imagery includes 50 spectral channels ranging from
the visible through the thermal infrared (Hook et al.
2001). Since the MASTER sensor platform is airborne and has oblique look geometry, spatial resolution is variable ranging from 12 to 50 m;
radiometric resolution is 16-bit. One mid-ablation
season VNIR/SWIR/TIR image, acquired on
August 26, 2001, was processed and analyzed for
surface temperatures and detection of temperature
below, at, and above the ice-melting point (Fig.
17.10). We have not georegistered or orthorectified
the MASTER image data, but we use the imagery
simply to show buffering of the surface temperature
at the melting point across the glacier and snow
covered areas, except for a small area near the
summit (which is colder than the melting point)
and the most heavily debris-covered areas, which
are warmer. Nonglacier areas of exposed rock and
vegetation are much warmer than the melting point.
Thus, almost all of the glacier areas were melting,
almost to the summit, at the time the image was
acquired. Continuously but thinly debris-covered
areas of the glacier are buffered near the melting
Case studies using ASTER 401
Table 17.2. Mt. Rainier’s north-facing glacier debris cover since 1913 a.
Year
a
Carbon
Winthrop
Emmons
km 2
Fractional
area
(%)
km 2
Fractional
area
(%)
km 2
Fractional
area
(%)
1913
5.6
66
2.1
14
1.3
10
1971
3.4
42
2.3
24
3.1
28
1994
3.6
45
2.85
31
3.4
30
2010
3.6
50
3.4
38
3.5
32
20th century measurements (Nylen 2004), 21st century measurements (this work—ASTER based).
Figure 17.9. Mt. Rainier’s north-facing glacier debris cover since 1913 (see Fig. 17.2).
point, suggesting the potential utility of thermal
imaging to assist glacier mapping (Taschner and
Ranzi 2002, Ranzi et al. 2004); however, thermalmapping approaches to date have not fully adequately accounted for the heat capacity of debris
layers thicker than one or two centimeters, and so
further development of these approaches is needed.
Excellent AVIRIS image cubes are also available
for Mt. Rainier; the latest scene was acquired July
19, 1996. Crowley and Zimbelman (1997) used an
AVIRIS cube to investigate the mineralogy of Mt.
Rainier, though they did not examine glaciers.
17.5.2.3
Historic changes of Mt. Rainier’s
glaciers
From the 1850s through the 1970s Mt. Rainier’s
glaciers lost mass with average thinning of 43 m
w.e. (Burbank 1982). Little mass change occurred
from 1892 to 1910, but from 1910 to 1979 the mass
balance averaged 0.47 m yr 1 w.e. Ice volume
shrank by 25% between 1913 and 1994, averaging
0.09 km 3 lost per glacier (Nylen 2004). Sisson et al.
(2011) determined a 14% ice volume loss on Mt.
Rainier between elevation surveys in 1970 and
2007/2008. From 1913 to 2008 the average terminus
position of 10 glaciers (Fig. 17.4A) retreated by
14.7 m yr 1 (Nylen 2004, Copeland 2009). The
two most heavily debris-covered north-facing glaciers, Carbon and Winthrop, retreated little, 1.8 m
yr 1 during 1913 to 2010 (Figs. 17.5 and 17.8; Table
17.1); the remaining eight glaciers, those having
southerly or less northerly aspects and generally less
debris coverage, retreated an average of 17.9 m
yr 1 . Nylen et al. (2004) shows a strong inverse
correlation between debris cover and retreat rate,
402
Glaciers and perennial snowfields of the U.S. Cordillera
Figure 17.10. MASTER image acquired August 26, 2001 (oblique view, not georegistered or orthorectified) of
Mt. Rainier. (A) Band 753RGB false-color composite (equivalent to ASTER 321RGB). (B) MASTER band 47-7-1
(equivalent to ASTER 14-3-1 RGB). (C) MASTER band 48 (equivalent to ASTER TIR band 14), showing nearfreezing areas as moderate gray, colder areas as dark, and warmer as white. Figure can also be viewed as Online
Supplement 17.7.
with the less debris-covered glaciers retreating far
more rapidly than the heavily debris-covered ones;
clearly, debris cover provides a net protective role
against ablation. Emmons Glacier has advanced in
recent decades (Figs. 17.5C and 17.8) since a large
rockfall event in 1963 that deposited debris onto the
glacier (Driedger, 1986) this probably acts to reduce
ablation.
Wastage of Mt. Rainier’s glaciers is a response to
climate warming that increases melt in summer and
increases the probability of precipitation falling as
rain rather than snow (Nylen 2004, Mote et al.
Summary and conclusions 403
Figure 17.11. Record of surface area for Blue Glacier excluding Snow Dome, a region of ice connected to Blue
Glacier, over the past 94 years. The period of advance between 1960 and 1980 is clearly evident, as is the return to
the previous rate of retreat. ASTER imagery indicates that the retreat shown in Fig. 17.12 after 1990 continued from
2002 to 2010 at about the same rate.
2005). Geothermal heat is not considered an important factor affecting glacier size. The most geothermally active parts of the volcano are in the
caldera and perhaps along the caldera rim. In some
spots melting due to geothermal input approaches
or exceeds local snowfall. An elaborate system of
ice caves containing fumaroles has been mapped
(Zimbelman et al. 2000). Geothermal heat along
the flanks of the volcano are low, probably inconsequential.
17.5.3 ASTER and field studies of
Blue Glacier, Olympic Mountains,
Washington
Blue Glacier has been monitored since 1939 (Armstrong 1989, Conway et al. 1999) and field monitoring and frequent airborne surveys have been
conducted by the University of Washington, the
U.S. Geological Survey, National Park Service,
and more recently by Portland State University.
Blue Glacier has retreated for most of the past 94
years, except for a small readvance from 1960 to
1980 and a brief period of terminus stability from
1980 to 1985 (Fig. 17.11; Spicer et al. 1986, Conway
et al. 1999). Retreat resumed after 1985 and has
continued through the ASTER era to the present
(2012). From 2002 to 2010 images (Fig. 17.12), the
retreat of Blue Glacier’s terminus was 93 20 m
(about 11 m yr 1 ), almost the same average rate
as Conway et al. (1999) indicate—14 m yr 1 —for
the period 1985–1997. The fluctuations in retreat
history—including the advance from 1960 to
1980, indicate that this glacier is not now responding to the end of the Little Ice Age; rather, retreat is
a response to more recent climatic fluctuations,
including an overall pattern of nearly a century of
retreat that is consistent with the effects of a general
warming climate (Fig. 17.12). Recent studies of the
change in glacier surface areas for all perennial
snow and ice masses in the Olympic Mountains
suggests that this rate of retreat is continuing.
17.6
SUMMARY AND CONCLUSIONS
Glaciers in the western U.S.A. are in a state of
overwhelming dominant retreat and thinning.
Retreat in some regions is faster than others, probably due to the interaction of several issues in-
404
Glaciers and perennial snowfields of the U.S. Cordillera
Figure 17.12. ASTER VNIR band 321 false-color composite image of glaciers in the Olympic Mountains,
Washington, U.S.A., including Blue Glacier, northwards (up) from the center of the top image. Snow in these
images is white; exposures of recrystallized glacier ice are bluish; exposed rock and soil (including debris-mantled
ice) is dark (almost black as processed here); and vegetation is red. The bottom set of three images, acquired in
different years but within the summer season, highlights the difficulty of acquiring images at minimum snow cover.
In the July 11, 2002 scene (lower left), the previous winter’s snow still mantles almost the whole glacier area, and
snowfields exist well beyond the glacier limits. In the middle panel, acquired July 30, 2009, snow is at about the
minimum extent; and in the panel at lower right (September 3, 2010), snow again covers much of the glacier’s
surfaces, but snowfields external to the glacier are few. Despite transient snowfields persisting into the summer,
changes in the terminus position have been assessed. Figure can also be viewed in higher resolution as Online
Supplement 17.8.
cluding altitude, debris cover, and glacier size. The
response time of glaciers in the region varies from
under a decade to over a century. Blue Glacier
(Olympic Mountains) is a fast responder due to
its high mass throughput and steep slope; its length,
area, and volume fluctuation history indicates that
it is responding to decadal climate fluctuations as
well as local long-term warming in the 20th–21st
centuries, which is probably related to greenhouse
gas–driven global warming.
Heavily debris-covered glaciers (such as those of
Mt. Rainier) retreat less rapidly than debris-free
glaciers due to the insulating effects of the debris.
Smaller cirque-type glaciers can be relatively
climate insensitive due to local effects of solar shadowing and additional snow accumulation via avalanches. A few glaciers are not retreating, such as
Whitney Glacier on Mt. Shasta and the brand new
Crater Glacier in Mt. St. Helens. These two exceptions to the overall trend are certainly unusual. For
Whitney Glacier the advance is ascribed to locally
enhanced snow accumulation, and for Crater Glacier it occupies a newly formed north-facing crater
due to the eruption of Mt. St. Helens.
Conventional application of ASTER imagery to
the glaciers in Glacier National Park and Mt. Rainier has proven useful. Of particular interest is the
application of MASTER airborne imagery in the
References 405
near infrared to thermal infrared wavelengths to
distinguish thinly debris-covered ice from ice-free
debris and thick debris cover over ice.
17.7
ACKNOWLEDGMENTS
ASTER data courtesy of NASA/GSFC/METI/
Japan Space Systems, the U.S./Japan ASTER
Science Team, and the GLIMS project. MODIS/
ASTER (MASTER) airborne simulator data courtesy of NASA/Airborne Sensor Facility at Ames
Research Center/Jet Propulsion Laboratory, and
the EROS Data Center.
17.8
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