Analysis of time series of glacier speed: Columbia Glacier, Alaska

Abstract

During the summers of 1984 and 1985, laser measurements were made of the distance from a reference location to markers on the surface of the lower reach of Columbia Glacier, Alaska. The data have numerous gaps, mostly because of inclement weather. The laser measurements were corrected for variations in atmospheric temperature and pressure and for the trajectory of the marker. The marker speed was calculated by using a combination of cubic splines and digital filters to arrive at a data set with 1-hour time intervals. The speed varies from 7 to 15 m/d and has three noteworthy components: (1) a low-frequency perturbation in speed with a time scale of days related to increased precipitation, (2) semidiurnal and diurnal variations related to sea tides, and (3) diurnal variations related to glacier surface melt. The low frequency and tidal period variations are separated by low-pass filtering and subtracting the filtered data from the original data. The variations from melt runoff and tides have the same frequency range and are examined using harmonic analysis and multiple regression with the various forcing functions. The high-frequency portion of the ice speed signal is dominated by tidal influences and to a lesser extent by meltwater influences. The low-frequency portion of the signal is dominated by the effects of precipitation. Kamb et al., 1985] and calving rates. As a result, an intensive field program in August and September 1984 collected data on ice calving, ice velocity, terminus position, meteorological variables, tide stage, and runoff from a marginal river (as a surrogate for subglacial discharge). This program is described in detail by Vaughn et al. [1985]. The purpose of this report is to analyze the ice speed data and relate its variations with variations in the various forcing functions. The primary focus is the ice speed derived from electronic distance meter (EDM) measurements (EDM, Figure 1); temperature, insolation, and precip- Recent glaciological research has indicated a need for the better understanding of the relation between ice flow and subglacial water flow [

Links Between Proglacial Stream Suspended Sediment Dynamics, Glacier Hydrology and Glacier Motion at Midtdalsbreen, Norway

“…The resulting data sets were then re-sampled to produce two-hourly time series of glacier speed for each of the three markers (cf. Walters and Dunlap, 1987). Errors in the time base were generally small (< f6min).…”

Iceberg calving and the glacioclimatic record

“…The seminal work of Austin Post (1975;1980a;1980b;1980c;1980d; provided empirical confirmation of these ideas and also revealed the linear vc/hw relationship (Brown et al, 1982) which explains the catastrophic rates of recession which follow the retreat of a glacier into deep water. The initiation of this kind of retreat has been extensively documented at Columbia Glacier near Valdez (Bindschadler and Rasmussen, 1983;Krimmel, 1987;Krimmel and Vaughn, 1987;Meier, 1979;Meier et al, 1980;1985a;1985b;Rasmussen and Meier, 1985;Sikonia and Post, 1980;Sikonia, 1982;Walters, 1989;Walters and Dunlap, 1987). Because of the efficiency of mass loss of the calving process, calving glaciers can retreat extremely rapidly (at rates of 500-10 000 m a 1 -Mann, 1986) but, for the same reason, their advances are slow, typically 10-40 m a '.…”

“…Williams, 1985;MISR/RAE, 1983). Echelmeyer and Harrison (1989;) measured velocity variation of as much as 35% with the tide, whereas velocities at grounded calving fronts only vary by about 10% with tide (Walters and Dunlap, 1987;Krimmel and Vaughn, 1987;Walters, 1989). Grounded calving events are statistically uncorrelated with the state of the tide (Meier et al, 1980;Brown et al, 1982).…”

Short-period observations of speed, strain and seismicity on Ice Stream B, Antarctica

“…A correlation between marine tides and strain would suggest that tide was affecting the basal water pressure and therefore the flow of the ice stream. A tidal effect on speed was observed on Columbia Glacier, Alaska (Krimmel and Vaughn, 1987;WaIters and Dunlap, 1987) . Also, we found a good correlation between tide and speed on lower J akobshavns Isbne, Greenland (Echelmeyer and Harrison, 1989) .…”