Surface Flow Field

Repeated surveys of 110 stakes are used to construct the surface flow field of the study reach. While the bulk of the velocity measurements have focused on weekly variations during the summer season, velocity measurements have been made at time intervals ranging from hours to years. Results from these measurements include:

• Diurnal variations in surface velocity are present. These variations appear to be closely tied to hydrologic input to the basal drainage system.
• Strong seasonal variations in velocity occur, with a summer velocity peak occurring in June. The average velocity of the reach is 82 m/yr during the peak. This is 20% greater than during early or late summer.
• Crevassing causes short wavelength (~10-15 m) velocity anomalies that occur over daily to weekly time intervals. The number of anomalies is proportional to the average surface velocity. These variations occur over the same length scale as important regional velocity variations. This makes the separation of the regional flow field from local transient events difficult over short time intervals.

Surveying velocity markers on the glacier.

Map showing the displacement of 110 velocity markers used to measure the surface flow field. Blue lines are 2 m/yr contours of velocity.