Tidewater Glaciers- Hubbard and Columbia Glaciers, AK

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Tidewater Glaciers- Hubbard and Columbia
Glaciers, AK

• Chris Lyles
• ESS 433

Columbia Glacier 1993
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Seasonal fluctuations in the advance of a
tidewater glacierand potential causes Hubbard
Glacier, Alaska, USAJ. Brent RITCHIE, Craig S.
LINGLE, Roman J. MOTYKA, Martin TRUFFER

• Area of interest
• Examining Seasonal Fluctuations at the Hubbard
  Glacier terminus in Disenchantment Bay and
  Russell Fjord near Yukutat, AK
• Background
• Hubbard is the largest non-polar tidewater
  glacier in the world at 2450 km2 (Arendt and
  others, 2002)
• Descends more than120 km from its origin- Mount
  Logan (5959m), Yukon, Canada
• Calving face ranges from 60-100 m a.s.l. and the
  curvilinear face has a width of 11.5 km

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Hubbard Glacier before and after damming of the
mouth to Russell Fjord
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Why is the Hubbard such an interesting glacier to
study?

• 1) Asynchronous response to climate with respect
  to regional glacier trends and climate, but can
  be used to measure climate trends on longer
  timescales
• 2) Nice illustration of the dominant controls on
  tidewater glacier extent
• Takes into account the alternative perspectives
  regarding glacier calving
• water discharge at the bed (Sikonia, 1982)
• submarine melting important for seasonal
  fluctuations at the terminus of a calving face
  (Motyka and others, 2003). Fresh water drainage
  and saline water forced convection
• height of ice face above flotation (Van der Veen
  2002), incorporates ice speed and ice thickness
  at the terminus

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Hubbard (contd)

• Also mentions calving rates with respect to water
  depth at the terminus as valid over longer
  timescales, but not seasonally. Must take into
  account the complex nature of calving dynamics
• Seasonal surface ice speeds and water temperature
  are two forcing mechanisms for terminus
  fluctuations
• Observed changes in sea surface temperature of
  10-12 degrees
• Closely proximal Valerie Glacier effects the
  Hubbard terminus as it surges with a periodicity
  of several years
• Largest non-polar tidewater glacier in the world-
  2450 km2

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Hubbard (contd)

• Closure of Russell Fjord effects the Situk River
  access, an area of economic importance
• Also known to be in the advance phase of the
  tidewater glacier cycle- this is rapid retreat
  followed by a stabilization, then slow advance
• These advancing calving glaciers are driven by a
  large AAR, which then advance into fjords by
  remobilizing subglacial sediments and pushing
  their terminal marine shoals
• The advance can be from a few meters up to tens
  of meters per year
• Retreat rates are of far greater magnitudes-
  ranging from 100 to 1000 meters per year
• Retreating glaciers find stability when reaching
  the neck of the fjord or a place where the fjord
  bottom rises above sea level

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The terminus of Hubbard Glacier was divided into
five sections

• Section A- is made up of ice that flows from
  Valerie Glacier as defined by the medial moraine
  separating Valerie Glacier from the main branch
  of Hubbard Glacier. Here the terminus not only
  calves into Disenchantment Bay, but it also
  terminates on a mudflat
• Section B- is defined as ice flowing down from
  the main branch of Hubbard Glacier and
  terminating into the waters of Disenchantment Bay
• Section C- is defined by its proximity to
  Gilbert Point (and is of importance because it is
  the area where closure of the adjacent Fjord
  could occur following a surge of the Valerie
  Glacier, or of the Hubbard itself)
• Section D- calves into the waters of Russell
  Fiord
• Section E- terminating on land, section E is
  advancing over glacier outwash deposits of nearby
  Variegated Glacier

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Conclusions- seasonal factors influencing
terminus postion

• (1) changes in ice speed and calving rate
• (2) position of the moraine shoal, which
  stabilizes the terminus in an overall sense, and
• (3) seasonal increases in seawater temperature
  and subglacial freshwater discharge (which drives
  convection at the calving front)

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Conclusions- Hubbard

• Build-up of marine shoal by accumulating sediment
  and allowing glacier to readvance and occupy
  Gilbert Point Gap- blocking the entrance to the
  Russell Fjord and upstream fishery
• Surge in Valerie Glacier could assist in a
  readvance
• Damaging outburst floods possible from the
  damming of the Russell lake

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Columbia Glacier- Krimmel 1996
Photo from 1938 (USGS)
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Columbia Glacier Stats

• 1,000 km2 in 1995
• rapid retreat- 10 km in 12 years (as of date of
  publication)
• 27 meter submerged terminal moraine depth limits
  the size of iceberg that can be released into
  Upper Columbia Bay and into Prince William Sound.

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Columbia Glacier
1889 Harriman Expedition
Flow from source
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Why the Columbia Glacier is important
From page 9 of Austin Posts autobiography Columb
ia Glacier What was most exciting for me,
however, was developing Calving Theory and then
realizing Alaskas Columbia Glacier potentially
could drastically retreat many miles while
calving innumerable dangerous icebergs. These in
turn, could menace supertankers en-route to and
from Valdez, southern terminal of the Alaska
pipeline then in its final stages of
construction.
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When I told Mark of my suspicions, he immediately
realized this was a serious hazard that should be
investigated. This was undertaken with a joint
trip to Reston, VA, USGS headquarters. Here Mark
made presentations at the Directors Office where
it was given very close attention and some
emergency funding for field studies promised.
Mark then gave the identical presentation to the
U. S. Coast Guard headquarters where it got no
response at all other than being passed off by
Admiral Price as interesting speculation.
Obviously we were going to get no funding from
the Coast Guard if this was the extent of their
responsibility to insure ship safety! (With one
exception Captain Kohlmyer later did inspect the
glacier and proposed a giant rope-barrier to
restrain icebergs, a clever scheme quite
universally ridiculed.)
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Austin Post Contd
Later, Marks presentation was given at Valdez,
Alaska to representatives of the City and
Pipeline officials. Here the response was
emotional and hostile to the extreme Get out of
town stupid Stateside Bureaucrats! We know what
our glacier is doing! - excerpts from Austin
Posts Autobiography -The Exxon Valdez
supertanker eventually ran aground trying to
avoid icebergs released from the Columbia
Glaciers terminus
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Krimmel- Columbia Glacier
Columbia Glaciers accumulation is insufficient
to sustain its present state- it has been
thinning by 20 meters per year (lower glacier
area). Low AAR when compared to the Hubbard
(0.9) Total volume lost (between 1982 and 1994)
is estimated at 40 km3 Tidewater glaciers are
extremely sensitive to changes in the climate
(albeit not good indicators as they are extremely
fickle) and as such retreat rapidly into deep
water, leaving their terminal marine shoals
behind which intensifies the calving experienced
by the glacier.
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References
http//ak.water.usgs.gov/glaciology/columbia/index
.htm Krimmell paper- http//ak.water.usgs.gov/gla
ciology/columbia/reports/fs20091-96/FS-091-9620C
olumbia20Glacier20Alaska.pdf Seasonal
fluctuations in the advance of a tidewater
glacier and potential causes Hubbard Glacier,
Alaska, USA J. Brent RITCHIE, Craig S. LINGLE,
Roman J. MOTYKA, Martin TRUFFER