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Comment on “wastage of the Klutlan ice-cored moraines, Yukon Territory, Canada” by Driscoll (1980)
QUATERNARY
RESEARCH
Comment
22, 259 (1984)
on “Wastage Yukon Territory,
of the Klutlan Ice-Cored Moraines, Canada” by Driscoll (1980)
In his calculation of wastage rates of the Klutlan moraines Driscoll(l980) uses three different definitions of ablation season. Apart from being confusing, all probably seriously underestimate the length of the ablation period. Driscoll states that an “entire ablation season” is estimated as 70 days (p. 41), the “effective ablation season” as 90 days (p. 39), and finally that the period of “net ablation of the stagnant ice core” is estimated as extending from “late May to October 1” (Table 2). Thus, there are three different estimates of the ablation period: 70, 90, and 120 days. At Davis in Antarctica, I have seen melt at air temperatures of - 15°C. Similar observations are recorded in the literature. Over austral summer 19790980 we recorded rock surface temperatures 20°C higher than air temperatures. Again, this is commonly reported in the literature. At Davis I estimate the ablation period occurs whenever air temperatures are above - 10°C. Applying this criterion at Klutlan would give an ablation period from mid-March to mid-October or approximately 200 days. This extends the ablation season considerably beyond Driscoll’s three estimates. After lengthy calculations based on various data and assumptions Driscoll presents two summaries of the wastage of Klutlan over the past 1000 yr. However, his pictorial summary of the composite curve (Fig. 14) is not described by his mathematical summary (Eq. 9). Equation 9 (p. 47) is stated to describe the composite curve (Fig. 14) of wastage on Klutlan. If we include the negative sign omitted from Eq. 9 (but shown on p. 48) it reads y = lo-
However, solving this equation for various values of y and t does not give the composite curve shown in Figure 14 as shown by the results below: Eq. 9 Figure 14
t
t
3380 1515 950
0
2;3
0
180
Estimating from the curve of Figure 14, a more realistic equation would be y =
lo-0.00237'+2.255
Thus, the rate of down wastage is 0.0024 my - ’ or about 50% faster than that calculated by Driscoll. Interestingly, Driscoll’s rate (0.0016 my-‘) is two orders of magnitude slower than the 0.3 my-’ calculated by Watson (1980, p. 55) for the same moraine. It is also one order of magnitude slower than the 0.05 my - ’ I have estimated for Flanders Moraine, Antarctica (Pickard, 1984) even though Klutlan is considerably warmer and wetter. REFERENCES Driscoll, F. G. (1980). Wastage of the Klutlan icecored moraines, Yukon Territory, Canada. Quarernary Research 14, 31-49. Pickard, J. (1984). Surface lowering of ice-cored moraine by wandering lakes. Zeirschrift fiir Geomorphologie, in press. Watson, R. A. (1980). Landform development on moraines of the Klutlan Glacier, Yukon Territory, Canada. Quaternary Research 14, 50-59. JOHN PICKARD* Antarctic Division
Kingston, Tasmania, Australia
0.0016083r+2.436
where y is thickness of ice in meters of the ice at time I in years.
O.iOl 1.0 0
r Present address: School of Biological Sciences and Quaternary Research Unit, Macquarie Univer;sity, Sydney, Australia. 259 0033-5894/84 $3.08 Copyright All rights
0 1984 by the University of Washington. of reproduction in any form reserved.
RESEARCH
Comment
22, 259 (1984)
on “Wastage Yukon Territory,
of the Klutlan Ice-Cored Moraines, Canada” by Driscoll (1980)
In his calculation of wastage rates of the Klutlan moraines Driscoll(l980) uses three different definitions of ablation season. Apart from being confusing, all probably seriously underestimate the length of the ablation period. Driscoll states that an “entire ablation season” is estimated as 70 days (p. 41), the “effective ablation season” as 90 days (p. 39), and finally that the period of “net ablation of the stagnant ice core” is estimated as extending from “late May to October 1” (Table 2). Thus, there are three different estimates of the ablation period: 70, 90, and 120 days. At Davis in Antarctica, I have seen melt at air temperatures of - 15°C. Similar observations are recorded in the literature. Over austral summer 19790980 we recorded rock surface temperatures 20°C higher than air temperatures. Again, this is commonly reported in the literature. At Davis I estimate the ablation period occurs whenever air temperatures are above - 10°C. Applying this criterion at Klutlan would give an ablation period from mid-March to mid-October or approximately 200 days. This extends the ablation season considerably beyond Driscoll’s three estimates. After lengthy calculations based on various data and assumptions Driscoll presents two summaries of the wastage of Klutlan over the past 1000 yr. However, his pictorial summary of the composite curve (Fig. 14) is not described by his mathematical summary (Eq. 9). Equation 9 (p. 47) is stated to describe the composite curve (Fig. 14) of wastage on Klutlan. If we include the negative sign omitted from Eq. 9 (but shown on p. 48) it reads y = lo-
However, solving this equation for various values of y and t does not give the composite curve shown in Figure 14 as shown by the results below: Eq. 9 Figure 14
t
t
3380 1515 950
0
2;3
0
180
Estimating from the curve of Figure 14, a more realistic equation would be y =
lo-0.00237'+2.255
Thus, the rate of down wastage is 0.0024 my - ’ or about 50% faster than that calculated by Driscoll. Interestingly, Driscoll’s rate (0.0016 my-‘) is two orders of magnitude slower than the 0.3 my-’ calculated by Watson (1980, p. 55) for the same moraine. It is also one order of magnitude slower than the 0.05 my - ’ I have estimated for Flanders Moraine, Antarctica (Pickard, 1984) even though Klutlan is considerably warmer and wetter. REFERENCES Driscoll, F. G. (1980). Wastage of the Klutlan icecored moraines, Yukon Territory, Canada. Quarernary Research 14, 31-49. Pickard, J. (1984). Surface lowering of ice-cored moraine by wandering lakes. Zeirschrift fiir Geomorphologie, in press. Watson, R. A. (1980). Landform development on moraines of the Klutlan Glacier, Yukon Territory, Canada. Quaternary Research 14, 50-59. JOHN PICKARD* Antarctic Division
Kingston, Tasmania, Australia
0.0016083r+2.436
where y is thickness of ice in meters of the ice at time I in years.
O.iOl 1.0 0
r Present address: School of Biological Sciences and Quaternary Research Unit, Macquarie Univer;sity, Sydney, Australia. 259 0033-5894/84 $3.08 Copyright All rights
0 1984 by the University of Washington. of reproduction in any form reserved.