Surface Velocity Along the Taku / Matthes / Llewellyn Glacier System
These graphs present the surface velocities across the longitudinal extent of the Taku / Matthes / Llewellyn glacier system. These three glaciers comprise a continuous glacial transect 91 kilometers long from sea level at Taku Inlet, northerly across the Continental Divide to the vicinity of Atlin Lake in northern British Columbia. This is an important transect because it allows us to monitor changing patterns of surface velocity and height change along the sensitive maritime/continental boundary.

 


The above graph shows the surface velocity of the Taku / Matthes / Llewellyn glacier system as a function of elevation and distance from Taku Point. This point is on the south side of Taku Inlet and is approximately 1.3 kilometers south of the Taku Glacier terminus.

JIRP has established a series of longitudinal survey profiles throughout the entire Taku Glacier system. The data shown above was collected along Longitudinal A, which begins at Taku Point and continues up the main Taku and Matthes glaciers. It then crosses over the Continental Divide and down the Llewellyn Glacier. Points are surveyed every 500 meters along this longitudinal transect. The magnitude of velocity is indicated by the size of the circles. The white line within the circles shows the surface elevation of the glacier. The effect of valley width and depth on velocity is not considered here. Generally speaking, glacier velocity increases with increasing distance from the glacial divide. Local geomorphic characteristics also have an effect on velocity. For example, 50 kilometers upglacier from the Taku terminus, the valley steepens

 
and narrows, resulting in the local velocity increase in this area.

With the exception of one transverse survey profile five kilometers upglacier from the Taku Glacier terminus and several scattered velocity measurements at the terminus, we have no velocity data for the lower Taku Glacier from the terminus to approximately 14 kilometers upglacier. This is indicated by the data gap in the graph from 0 to 14 kilometers. However, we know from our velocity data at the terminus that the velocity slows relative to the first point surveyed on Longitudinal A (indicated by a velocity of 114 cm/day). Thus, the Taku / Matthes system exhibits a common velocity pattern of increasing velocity from the source to the firn line, and then decreasing velocity from the firn line to the terminus. In the case of the Taku Glacier, the velocity decrease near the terminus is an effect of the radially expanding piedmont lobe at the terminus.

 

Tip: Use the controls below the graph to zoom in and pan around.
 

 

This graph is similar to the one above, but it shows surface velocities at numerous transverse profiles, rather than along the Longitudinal A profile. The transverse profiles extend across the glacier, from one side of the valley to the other. For each of the ten transverse profiles shown here, the minimum, maximum, and mean velocity of the profile is shown. This shows that the cross glacier velocities exhibit the same general pattern of movement as that shown in the first graph for the longitudinal profile. Specifically, velocities are least near the Matthes/Llewellyn divide and increase with increasing distance downglacier on both sides of the divide. Here, Profile 7b shows the velocity increase due to the steepening and narrowing valley. This corresponds with the sharply increasing surface gradient of 5 some 50 kilometers upglacier from Taku Point.