This graph shows the year-to-year and cumulative surface height change along the longitudinal centerline of the Vaughan Lewis Glacier at the base of the Vaughan Lewis Icefall. The glacier at this location is some 500 meters lower in elevation than its source accumulation area. Ice from the accumulation area flows 500 meters through the Vaughan Lewis Icefall and generates a series of large wave ogives, with one ogive being created each year.

A longitudinal profile containing 179 survey points was established at the base of the Icefall in 2001. This profile begins in the trough immediately upglacier of the crest of the first wave ogive and continues downglacier nearly 1.8 kilometers to a point where the amplitude of the ogives becomes zero. The glacier's surface elevation, and the wavelength and amplitude of the ogives is represented by the uppermost plot in the graph, referenced to the right-hand Y-axis.

Download the GPS Survey Data (Excel format)

  
The animated plots show the magnitude of year-to-year change. These plots are referenced to the left-hand Y-axis and show the spatial variation of height change along the length of the profile. The elevation range between Point 1 and Point 179 is only 100 meters, not great enough to discern a strong elevation controlled ablation pattern.

Being in the ablation zone, this area - along with the lower Llewellyn Glacier - has experienced the greatest surface lowering that we have measured on the Juneau Icefield. The cumulative effect of the individual year-to-year height change is shown by the bold white plot, labeled 2001 to 2007. During this six year time period, the surface has lowered an average of 17 meters - nearly 3 meters per year - along the longitudinal survey profile, with a maximum of 22 meters.

 

  
Tip: Right-click the graph and choose among the options to control the animation.


 

As with the first graph above, this graph depicts the surface change of the Vaughan Lewis Glacier longitudinal profile. This graph however, shows the surface elevation along the profile for each year surveyed, rather than the numerical height change from one year to the next.

The crests and troughs of the first eleven wave ogives is easily seen. The greatest amplitude in 2001 - roughly 20 meters - is seen at the first three ogives. Ogives 4 and 5 are within a transitional zone, downglacier from which the amplitude decreases to zero beyond ogive 11. By 2007 the amplitude at the first three ogives decreased to

Download the GPS Survey Data (Excel format)

  
roughly 10-12 meters, and the average wavelength has also slightly decreased. The most significant change however, is seen in the dramatic decrease of the surface elevation throughout the length of the profile. This decrease averages 17 meters, with a range from -5.4 meters to -22 meters. The combined amplitude and wavelength reduction from 2001 to 2007 likely indicates a reduction in mass flowing through the Vaughan Lewis Icefall, which is corroborated by other survey data showing a lowering of the surface - about 1.5 meters per year - above the Icefall.

 
Tip: Right-click the graph and choose among the options to control the animation.

© 1999-2009 Scott McGee
scott @ crevassezone.org
Last updated 04/13/09 02:24 PM