Index

Model

Data

Physics

Results

Analysis

References

Natural Examples

Jakobshavn Glacier

	This is a picture of the velocity flow lines of the ice in the Jakobshavn Glacier in the year 1992.  The velocity of the glacier is 5,700 meters per year (Joughin et al. 2004).
	This is a picture of the velocity flow lines of the ice in the Jakobshavn Glacier.  The red lines are for ice and markers from the year 1992, and the blue lines are for ice and markers from the year 2000.
	This is a picture of the velocity flow lines of the ice in the Jakobshavn Glacier in the year 2000. In 2000 the velocity of the 9,400 meters per year (Joughin et al. 2004).

To see more pictures from the Jakobshavn Glacier click here.  To view a movie of the change in the displacement field with time click here.  These pictures and movie are taken from http://svs.gsfc.nasa.gov/vis/a000000/a003000/a003072/index.html.  Top

This glacier has been speeding up since 1997 with rapid increaces in the velocity from 2000 to 2003 (Joughin et al. 2004).  This is thought to be due to the thinning of the glacier and an increase in the amount of calving that goes on at the edge of the glacier (Van der Veen 2002).  The reason that this glacier is analyzed in great detail is that it is the largest drainer of the Greenland Ice sheet.  This glacier has had large calving events that have been analyzed in great detail to try to see if there is an affect on the Greenland Ice Sheet.  Between the years 1992 and 2000 there was a change in the velocity of the Jakobshavn Glacier.  This change in velocity is thought to be due to the thinning of the ice over the entire glacier.  In the early 1990s there was an increase in size and thickness of the Jakobshavn Glacier, but in 1997 there was a sudden decrease in the thickness of the galcier, which caused there to be an increase in the speed and rate of calving that occurred in the glacier.  (Ramanujan 2004)  This increase in the speed of the glacier due to the thinning and calving events can be seen in the above pictures. In the year 2003 there was a major calving event.  After the event there was a surge in the velocity at the mouth of the glacier.  The surge in the glacier was seen a long distance from the actual calving event.  (Ramanujan 2004, Shirah et. al 2004)  This leads me to believe that the calving events themselves act as a control on the glacier velocity throughout the glacier not just at the margin.  Top

Picture of "Ice Terraces" from Greenland by Leigh Stearns, University of Maine

There seems to be a distinction between small calving events and large ones.  Large calving events like the breaking off of the B-9 and B-15 icebergs in Antarctica do not act the same as small events (Van der Veen 2002).  These systems sometimes speed-up right before calving and then slow down after the calving event.  This happened with the formation of the B-9 iceberg, but the change in velocity before the calving event is probably due to the widening of crevasses in the surface of the Ice Shelf (Keys et al. 1998).  In another study by Angelis and Skvarca in 2003, they found that there seems to be significant increases in the speeds glaciers that once feed the collapsed Larsen Ice Self (LIS).  Evidence that this increase in speed is due to the loss of the ice shelf blocking the glaciers is that the surging occurred directly after the disintegration of the LIS, also there are the presence of "ice terraces" which are stranded ice from when the ice was higher than it is at present.  These ice terraces are 20 to 40 meters above the current glacier surface.  (Angelis and Skvarca 2003)  This change in ice elevation show that there was a recent and rapid change in the level of the glacier.  Top