[ [http://antarcticsun.usap.gov/oldissues2003-2004/Sun011104/icePier.htm “Ice pier serves as bridge to supplies,”] Antarctic Sun. January 11, 2004. McMurdo Station, Antarctica.] ]McMurdo's dock is not without comparison. In 1987 workers constructed a similar pier in Mys Shmidta, a small seaport located in Chukotka, a far-eastern territory adjacent to Alaska on the Arctic Sea. ["Ice floe used as pier," The USSR Weekly Economic Report. British Broadcasting Corporation citing Soviet television. October 16, 1987.] And like, McMurdo, the Arctic ice pier facilitated getting ships to get closer to shore for loading cargo. The pier built in in the former Soviet Union measured more than 700 meters long.
eawater construction
The ice piers deployed at McMurdo Station have grown in sophistication and size since the ice fender prototype. A contemporary pier is approximately 800 feet (244 m) long by 300 feet (90 m) wide and 22 feet (6.7 m) thick. [ [http://www.epa.gov/fedrgstr/EPA-IMPACT/2003/February/Day-14/i3840.htm “Issuance of a Final General Permit to the National Science Foundation for the Ocean Disposal of Man-Made Ice Piers From its Base at McMurdo Sound on Antarctica,”] Federal Register. February 14, 2003 (Volume 68, Number 31).] Fleet operations personnel make the floating pier during the winter. They build upon naturally occurring frozen seawater in McMurdo Sound after the pack ice reaches approximately 0.6 m (2 ft) in thickness. [ [http://www.epa.gov/fedrgstr/EPA-WATER/2003/January/Day-07/w335.htm “Issuance of a General Permit to the National Science Foundation for the Ocean Disposal of Man-Made Ice Piers From its Base at McMurdo Sound on Antarctica,”] Federal Register. January 7, 2003 (Volume 68, Number 4)]
Subsequently, workers construct a snow berm to a depth of several feet along the perimeter of the soon-to-be ice pier. High-volume pumps then flood the pack ice with seawater to a depth of about 10 cm (4 in). The seawater typically freezes solid within 24 hours. Personnel repeat the flooding until they achieve a thickness of 1.5 m (5 ft).
Next a reinforcement mat of approximately 2,100 m (6,900 ft) of 1” (25mm) steel cable is secured to 2” (50mm) steep pipe embedded in the ice pier. The pier overall requires approximately 6,300 m (21,000 ft) of steel cable for construction, according to National Science Foundation permit documentation.
Workers repeat the entire process three more times until the ice pier is approximately 6.7 m (22 ft) thick. Wooden utility poles drilled about four deep into the final ice pier support electrical and telephone service to the pier. Moreover, during the final construction phase, personnel mount shorter poles in the ice edge to serve as bollards to secure the pier to the shore at McMurdo. A 15-20 cm (6-8 in) layer of volcanic gravel tops off the pier to provide a non-slip surface and to insulate the ice from the summer sun.
Experience has shown that ice piers have a lifespan of three to five years. Factors such as stress cracking and erosion shorten the duration. In addition, storm surges, wave action, contact with vessels, and the warm water discharge from ships contribute to degradation of the pier’s seaward edge.
Ice pier limits discovered
Ice pier operations at the world’s most southern port have not been without mishap. The principal threat is onshore winds with accompanying high seas and ocean swells, which can severely damage the ice pier. For example in 1993, high winds and heavy swells caused major cracks in the wharf. Rough seas produced movements of several feet between individual sections of the pier, according to a National Science Foundation (NSF) report. [ [http://www.nsf.gov/pubs/stis1993/opp93105/opp93105.txt "Damage to McMurdo ice pier,"] National Science Foundation Office of Polar Programs. July 14, 1993.] The resulting damage prevented vehicles from traveling onto the pier for repairs.
Conditions worsened the following week when additional storms pushed ice, slush, and sea water onto the pier, flooding about one-half of the dock. The inundation on the pier's seaward side reached three to six-feet high and froze nearly immediately, according to the NSF report. The strategy to repair the storm damage included adding additional restraining cables followed by routine flooding to build up the ice thickness.
Notable incidents with damaged ice piers at McMurdo Station include an event 10 years earlier. The ice pier had been in use four seasons in 1983 when the freighter USNS Southern Cross docked at Winter Quarters Bay. Operation Deep Freeze officials pressed the pier into extended service in order for the freighter to make an unprecedented two supply runs in one season from Port Lyttelton, New Zealand, to McMurdo. ["Race to reach McMurdo Station," The Press, March 23, 1983. Christchurch, New Zealand.] However, efforts to extend the ice pier’s lifespan resulted in a cargo truck breaking through the ice. The driver of the truck standing atop the container leapt to safety, receiving minor injuries.
Maintenance gives way to disposal
Maintenance on the ice pier begins at the end of the austral summer. Equipment operators remove the gravel and store it for the next season. Removing the gravel prevents the gravel’s insulating qualities from inhibiting further thickening of the ice during winter. Winter operations include plowing insulating snow from the dock and flooding the pier with seawater to help sustain the ice strength.
However, when the pier is no longer usable, a permit from the Antarctic Conservation Act allows for an icebreaker to tow the ice pier out to McMurdo Sound and cast it adrift. Preparations for dumping include:
* Pumice surface is removed
* Wooden poles are cut off just above the surface of the ice
* All equipment, materials, and debris are removed
After release at sea, currents and southerly winds drive the ice pier north towards the Ross Sea and into the circumpolar currents of the Southern Ocean. A beacon mounted on the pier allows for tracking and serves as a warning to ships. The pier mixes with pack ice and eventually melts, a process that can take years, according to NSF estimates. Consequently, some 21,000 thousand feet of steel cable and convert|650|ft|m of convert|2|in|mm|sing=on pipe of used in its construction sink to the ocean floor [ [http://www.epa.gov/fedrgstr/EPA-WATER/1999/February/Day-05/w2785.htm Issuance of an Emergency Ocean Dumping Permit to the National Science Foundation for Disposal of an Ice Pier From Its Base at McMurdo Station] , Antarctica, Federal Registry Environmental Documents. February 5, 1999. EDITOR'S NOTE: A method of disposing of the ice pier without polluting the ocean has yet to be deployed.]
U.S. government reports vary regarding the fate of the untreated wooden bollards used in the ice pier. The wood in some instances is reported as weighted so as to sink. Yet a 1999 ocean dumping permit notes that: "the short lengths of wooden poles will float in the ocean for several months before becoming waterlogged and eventually sinking to the ocean floor."
ee also
*Icebreaker
*McMurdo Sound
*McMurdo Station
*Operation Deep Freeze
*Sea ice
*Scott Base
*Winter Quarters Bay
Notes
References
* [http://antarcticsun.usap.gov Antarctic Sun.]
* [http://www.epa.gov/fedrgstr/EPA-IMPACT/ Federal Register Environmental Documents]
* [http://www.nsf.gov National Science Foundation.]
* [http://www.stuff.co.nz/thepress/ The Press; Christchurch, New Zealand.]
* [http://seattlepi.nwsource.com Seattle Post-Intelligencer.]
* [http://www.usatoday.com USA Today]
