Category Archives: Ice Arch

Ice Arches and Gothic Cathedrals

Soaring towards heaven awash in light, Gothic Cathedrals awed medieval kings, jesters, and peasants alike. Their upward pointing arches allowed walls of stained windows to filter light into these massive buildings when most dwellings from royal castle to decrepit hut were dark, damp, and filthy. While the power of god was both invoked and abused, it was physics and engineering that allowed these cathedrals to scrape the skies. A delicate balance of forces is of the essence to avoid accelerations and collapse.

Arched windows within an arch inside the Cathedral of Reims, France.

Hence it should not surprise that ice arches buttressed by land show similar elegance and stability, but also dramatic collapse. When these ice arches form and collapse is one factor to determine when the Arctic Ocean will be free of ice in summer.

June-10, 2012 ice arch in Nares Strait between northern Greenland and Canada. The arch has been in place since Dec.-8, 2011.

Nares Strait Jun.-10, 2012 image showing land-fast ice between northern Greenland and Canada as well as the ice arch in the south (bottom left) separating sea ice from open water (North Water).

The Nares Strait ice arch forms between December and April most winters. Unlike the medieval cathedrals it consists of blocks of ice. Once in place, the arch shuts down all ice movement. The ocean water under the ice moves undisturbed southward sweeping newly formed ice away. This creates the North-Water polynya, first reported by William Baffin in his ship logs in 1616. The North Water supports wild life for millenia providing food and trading items for people. Even viking remnants from the time the first Gothic Cathedrals were built in Europe were found here: sections of chain mail, iron point blades, cloth, and boat rivets.

I want the ice arch in Nares Strait to collapse as soon as possible so that a Canadian ice breaker can get us to where we like to recover instruments and data that we deployed in 2009. And while I researched the stability of ice arches and studied Moira Dunbar’s 1969 satellite imagery, I came across a wonderful NOVA broadcast on medieval skyscrapers of glass and stone.” PBS stations will show it on Sept.-9, 2012.

Digging a little deeper, I also found a series of Open University podcasts and videos. My favorite 3-minute segment covers lines of thrust where barely connected irregular blocks of wood form a surprisingly stable yet wobbly arching bridge. If you want to build your own arch, then play interactively for fun with the physics of stone arches.

Since I want to understand and predict when the ice arch of Nares Strait collapses, I must understand how medieval architects and engineers designed their Gothic Cathedrals. I will also need understand why some cathedrals are still standing while others collapsed. My icy building blocks in Nares Strait are not as solid as the stones of Reims Cathedral, but unlike the medieval scientists, today we have computers and mathematics to help … as well as more than 800 more years of experience in science and engineering.

Ice Arch off North-West Greenland Locks Ice Motion in Nares Strait

Winter has come to north-west Greenland as the sea ice of Nares Strait has locked itself to land and stopped movement of all ice from the Arctic Ocean in the north to Baffin Bay and the Atlantic Ocean in the south. While there is no sunlight for several more months now during the polar night, the warm ocean beneath the ice emits heat through the ice which becomes visible to heat-sensing satellites. The light yellow and reddish colors show thin ice while the darker bluish colors show thicker ice today:

Dec.-13, 2011 surface brightness temperature of Nares Strait showing an ice arch in Smith Sound separating thin and moving ice (reddish, yellow) from thick land-fast ice (blue).

The prior 2010/11 winter was the first in several years that these normal conditions have returned. The ice arch in Smith Sound did not form in 2009/10, 2008/09, and 2007/08 winters while a weak arch in 2007/08 fell apart after only a few days. Conditions in 2009 were spectacular, as only a northern ice arch formed. Since the ocean moves from north to south at a fast and steady clip, it kept Nares Strait pretty clear of ice for most of the winter as no Arctic ice could enter these waters and all locally formed new “first-year ice” is promptly swept downstream:

March-25, 2009 map Nares Strait, north-west Greenland showing heat emitted during the polar night from the ocean and sensed by MODIS satellite.

The very thin and mobile ice in Nares Strait of 2009 exposed the ocean to direct atmospheric forcing for the entire year. I reported substantial warming of ocean bottom temperatures here during this period. This new 2011/12 ice arch formed the last few days. If it consolidates during the next weeks, then it is very likely to stay in place until June or July of 2012. It decouples the ocean from the atmosphere and, perhaps more importantly, prevents the Arctic Ocean from losing more of its oldest, thickest, and hardest sea ice. This is very good news for the Arctic which has lost much ice the last few years.

For more daily thermal MODIS imagery take a peek at http://muenchow.cms.udel.edu/Nares2011/Band31/ for 2011. Replace Nares2011 with Nares2003 or any other year, and an annual sequence appears. Furthermore, my PhD student Patricia Ryan just sent me a complete list of files that I need to process until 2017. Fun times.