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The
Slow Advance of a Calving Glacier: Hubbard Glacier, Alaska
by D.C. Trabant1, R.M. Krimmel2, K. Echelmeyer3, S. Zirnheld3, D. Elsberg3
1 U.S. Geological Survey, Fairbanks, AK, 99775
2 U.S. Geological Survey, Tacoma, WA, 98402
3 Geophysical Institute, University of Alaska, Fairbanks, AK 99775
Poster presented at the International Glaciological Symposium on Fast Glacier Flow held in
Yakutat, Alaska 10-14 June, 2002
ABSTRACT
Hubbard Glacier is the largest tidewater glacier on the North American continent. It has
been thickening and advancing toward the Gulf of Alaska since it was first mapped by the
International Boundary Commission in 1895 (Davidson, 1903). This is in stark contrast with
most glaciers, which have thinned and retreated during the last century. This atypical
behavior is an important example of the calving glacier cycle. If Hubbard Glacier continues to
advance, it will close the seaward entrance of Russell Fjord and create the largest
glacier-dammed lake on the North American continent in Historic times. This poster shows the
measured changes in ice thickness, ice speed, terminus advance, and fjord bathymetry of
Hubbard Glacier. The lower regions of the glacier have thickened by more than 80 m in the last
40 years, and the entire glacier has increased in volume by 12 km3during that time. Ice speeds
are decreasing near the calving face from a high of 16.5 m d-1in 1948 to 11.5 m d-1in 2001.
The calving terminus advanced at a rate of about 16 m a-1between 1895 and 1948 and accelerated
to 32 m a-1since 1948. However, since 1986, the advance of the part of the terminus in
Disenchantment Bay has slowed to 28 m a-1. NOAA bathymetric data from 1978 and 1999 show that
the sub-sea lee-face of the terminal moraine is advancing at an average rate of 32 m a -1;
confirming the long term advance rate determined from the subaerial calving face in
Disenchantment Bay.
HUBBARD GLACIER
Hubbard Glacier is currently about 123-km long, with a calving face that is 11.4 km in
length and, seasonally, as high as 100 m above sea level. Ice radar thickness measurements in
August 1986 (Mayo, 1989 and Trabant and others, 1991) showed that the glacier bed reaches as
deep as 414 m below sea level about 1.5 km upstream from the terminus. Since 1895, it has
advanced about 2.5 km into Disenchantment Bay. This slow, but persistent advance is the latest
phase of a long-period cycle of alternating slow advances and drastic retreats that has
persisted throughout middle-and late-Holocene in nearly all of Alaska's calving glaciers
(Post, 1975, 1980a,b,c, and d). This cycle has been described by Post (1975) as the calving
glacier cycle.
HISTORIC OBSERVATIONS
Hubbard Glacier has a long documented history. Hubbard Glacier filled all of Yakutat Bay in
about 1130 A.D (Plafker and Miller, 1958). Russell (1891) and Gilbert (1904), interpreting
records of the visits by Malaspina in 1792 and Vancouver in 1794, place the terminus of
Hubbard Glacier south of Haenke Island (see figure above). Tarr and Martin (1914) report that
Russian maps dating from the early 1800's the terminus just north of Haenke Island and a lake
in the Russell Fjord basin. The oral history of the Tlingit Indians of Yakutat includes a
description of the emptying of the lake in Russell Fjord about 1860 (de Laguna, 1972). I.C.
(1891) small map of Hubbard Glacier shows the terminus about 2 km north of Osier Island.
During his second visit, Russell (1893) recognized that the fjord, which was later named for
him, had been a glacier-dammed lake. The first surveyed position of the terminus of Hubbard
Glacier was produced by the International Boundary Commission in 1895 (Davidson, 1903), just
before the Harriman expeditions visit in 1899 (Gannett, 1902). Twentieth century investigative
highlights include: marine geologic investigations by Gilbert (1904), Wright (1972), Carlson
and others (1978 and 1992), and Carlson (1989); glaciological investigations by Tarr and
Martin (1906 and 1914), Tarr and Butler (1909), Post (1965 and 1967), Post and Mayo (1971),
Brown and others (1982), Mayo (1988a&b, 1989), and Trabant and others (1991); geological
investigations by Plafker and Miller (1958); oceanographic investigations by Royer (1975) and
Reeburgh and others (1976); and hydrologic investigations by Mayo (1986), Seitz and others
(1986), and National Oceanographic and Atmospheric Administration (1978 and 1999).
CALVING GLACIER CYCLE
Post (1975) described the processes that control the advance and retreat cycles of calving
temperate glaciers. The original description has been augmented by Trabant and others (1991)
and Post and Motyka (1995). The tenets of the hypothesis are that: (1) the primary factor that
influences the advance and retreat of temperate calving glaciers is the water depth at the
calving face; (2) the cycling is not directly related to climate, except perhaps for the
initiation of retreat; and (3) the advance and retreat cycling will continue as long as the
glacier continues to calve. The hypothesis of the calving glacier cycle has been used in
explanations of the anomalous advance and retreat behavior of several calving glaciers in
Alaska, such as Portage (Mayo and others, 1977), Taku (Motyka and Post, 1994), Taku and Le
Conte (Post and Motyka, 1995), Columbia (preeminently by Post, 1975), and the contrasting
advance of Harvard Glacier and retreat of it neighbor, Yale Glacier (Field, 1975).
Surface ice speeds on Hubbard Glacier were photogrammetrically determined from
displacements of crevasses and seracs. The "fixed location" is about 3 km above the 1997
terminus near the center of the glacier (see below). The linear rate of deceleration at the
fixed location is about 0.08 m d-1a-1, and is influenced by the changing strain rate as the
distance to the calving face changes. However, the five speed determinations at the fixed
point were selected to eliminate seasonal speed variations. The 11 "near terminus" speeds
where interpolated as close to the calving face as possible, along a flow line down glacier
from the fixed location. The rate of deceleration of the near-terminus speeds is about 0.05 m
d-1a-1; the seasonal speed variation was not selectively removed from this data subset.
Terminus locations for Hubbard Glacier, 1895, 1948, 1965, 1975, 1986, 1996, 1999, and 2001
from aerial photography and satellite images. The curving line is the ground track of the
airborne laser profiling data. The small circle is the "fixed location" used for interpolating
glacier surface speed and the ray attached to the circle was used for defining the "near
terminus" ice speeds plotted in the figure above. The bathymetric profiles (below right) are
along the red longitudinal line. NOTE: Hubbard Glacier blocked the entrance to Russell Fjord
from May to October, 1986; the August 1986 terminus line shows the ice dam.
Advance of Hubbard Glacier since 1895. The linear trend advance rate prior to 1948 was
about 16 m a-1. Between 1948 and 2001, the termini in Disenchantment Bay and Russell Fjord
advanced at average rates of 32 m a-1and 34 m a-1respectively.
Since the temporary damming of Russell Fjord in 1986, the terminus in Disenchantment Bay
has slowed to 28 m a-1; in Russell Fjord, the terminus continues to advance at 34 m a-1; and
the terminus near the entrance to Russell Fjord is advancing at about 6 m a-1. The entrance to
Russell Fjord will close when the glacier length reaches 123 km in that area.
1978 and 1999 bathymetric surveys by the National Oceanic and Atmospheric Administration
were compared to evaluate the displacement of the submarine terminal moraine of Hubbard
Glacier. The profile (below right) shows an average advance rate of about 10 m a-1. The
integrated average advance rate of 2.1 km width of the seaward face of the moraine between
-120 m and -170 m depth is 32 m a-1; very good agreement with the average rate of terminus
advance.
Maintainer: Rod March
Last update:
Thursday, January 15, 2004 04:45 PM
URL:
http://ak.water.usgs.gov/glaciology/hubbard//reports/2002.06_igs_poster/2002.06_igs_poster.htm
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