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Tidewater Glaciers- Hubbard and Columbia Glaciers, AK

Tidewater Glaciers- Hubbard and Columbia Glaciers, AK. Chris Lyles ESS 433. Columbia Glacier 1993 . 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.

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Tidewater Glaciers- Hubbard and Columbia Glaciers, AK

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  1. Tidewater Glaciers- Hubbard and Columbia Glaciers, AK Chris Lyles ESS 433 Columbia Glacier 1993

  2. 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 km^2 (Arendt and others, 2002) • Descends more than120 km from it’s 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

  3. Hubbard Glacier before and after damming of the mouth to Russell Fjord

  4. 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

  5. Hubbard (cont’d) • 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 km^2

  6. Hubbard (cont’d) • 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

  7. 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

  8. 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)

  9. 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

  10. Columbia Glacier- Krimmel 1996 Photo from 1938 (USGS)

  11. Columbia Glacier Stats • 1,000 km^2 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.

  12. Columbia Glacier • 1889 Harriman Expedition Flow from source

  13. Why the Columbia Glacier is important… From page 9 of Austin Post’s autobiography: Columbia Glacier “What was most exciting for me, however, was developing “Calving Theory”and then realizing Alaska’s 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. “

  14. 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.) …

  15. Austin Post Cont’d …Later, Mark’s 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 Post’s Autobiography -The Exxon Valdez supertanker eventually ran aground trying to avoid icebergs released from the Columbia Glacier’s terminus

  16. Krimmel- Columbia Glacier Columbia Glacier’s accumulation is insufficient to sustain it’s 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 km^3 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.

  17. References http://ak.water.usgs.gov/glaciology/columbia/index.htm Krimmell paper- http://ak.water.usgs.gov/glaciology/columbia/reports/fs%20091-96/FS-091-96%20Columbia%20Glacier%20Alaska.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

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