using differential SAR interferometry. Their study revealed that only ERS-1/2
Tandem Mission images with a time interval of 1 day can be successfully applied
for surface flow analyses of mid-latitude glaciers during the summer period. On a
large scale, Heid and Ka ¨a ¨b (2012) studied regional signals of glacier flow changes
using Landsat data. These authors calculated the average rate of decline of glacier
flow velocity per decade for five regions with negative specific mass balances
(Pamir, Caucasus, Penny Ice Cap of Baffin Island, Alaska Range and Patagonia).
Their results show that velocity decreased in recent decades (mid-1980s up to 2011)
at an average rate per decade of 43 % in the Pamir, 25 % on Penny Ice Cap, 20 % in
Patagonia, 11 % in the Alaska Range and 8 % in the Caucasus.
We successfully quantified surface flow velocity at two Pasterze Glacier test
sites (LTS, UTS) with supraglacial debris despite the decorrelation problem
outlined above. LTS shows a distinct flow component from the valley side towards
the valley center. This movement pattern is related to the effect of differential
ablation. Recent changes in the glacier flow pattern are also revealed by morphological evidence at bedrock outcrops in the proglacial area showing two different
striation generations. The dominant striation direction detected is parallel to the
valley axis. These older striations are superimposed by younger striations pointing
towards the valley center (Kellerer-Pirklbauer 2009). UTS is located below the
icefall, which is well known for the fastest flow velocities at Pasterze Glacier
(Wakonigg and Lieb 1996; Kaufmann et al. 2008). Long-term glacier flow data
from the cross profile BSL (see Fig. 9.4) indicate that the mean decadal velocity at
this profile decreased from 46 m a
À1 in 1981–1990 to 21 m a
À1 in 2001–2010. Our
measurements confirm this recent decline of flow velocity in this fast moving area.
A further decline in flow velocity of the glacier tongue is very likely if we
consider the ongoing disintegration of the icefall. The pace in the separation of the
glacier tongue from the main glacier is high considering the rapidly increasing rock
outcrops in the icefall. It is very likely that the two remaining glacier-ice connections at the southwest side of the icefall will separate in the near future. The main
remaining icefall at the north side will last substantially longer. However, if glacier
recession continues at this pace, the tongue of Pasterze Glacier will – at least for a
brief period of time – form a regenerated glacier (Benn and Evans 2010) within the
next few decades. By then, the tongue of the remaining glacier will only be fed by
Table 9.6 Mean surface
elevation changes at Pasterze
Glacier during the period
2004–2009 based on direct
mass balance measurements
Period
Mean surface elevation change [m a
À1
]
2004–2005
À0.990
2005–2006
À1.355
Mean 2004–2006
À1.173
2006–2007
À1.491
2007–2008
À1.563
2008–2009
À1.232
Mean 2006–2009
À1.429
Mean 2004–2009
À1.326
Data from ZAMG (2013)
194
V. Kaufmann et al.
Tandem Mission images with a time interval of 1 day can be successfully applied
for surface flow analyses of mid-latitude glaciers during the summer period. On a
large scale, Heid and Ka ¨a ¨b (2012) studied regional signals of glacier flow changes
using Landsat data. These authors calculated the average rate of decline of glacier
flow velocity per decade for five regions with negative specific mass balances
(Pamir, Caucasus, Penny Ice Cap of Baffin Island, Alaska Range and Patagonia).
Their results show that velocity decreased in recent decades (mid-1980s up to 2011)
at an average rate per decade of 43 % in the Pamir, 25 % on Penny Ice Cap, 20 % in
Patagonia, 11 % in the Alaska Range and 8 % in the Caucasus.
We successfully quantified surface flow velocity at two Pasterze Glacier test
sites (LTS, UTS) with supraglacial debris despite the decorrelation problem
outlined above. LTS shows a distinct flow component from the valley side towards
the valley center. This movement pattern is related to the effect of differential
ablation. Recent changes in the glacier flow pattern are also revealed by morphological evidence at bedrock outcrops in the proglacial area showing two different
striation generations. The dominant striation direction detected is parallel to the
valley axis. These older striations are superimposed by younger striations pointing
towards the valley center (Kellerer-Pirklbauer 2009). UTS is located below the
icefall, which is well known for the fastest flow velocities at Pasterze Glacier
(Wakonigg and Lieb 1996; Kaufmann et al. 2008). Long-term glacier flow data
from the cross profile BSL (see Fig. 9.4) indicate that the mean decadal velocity at
this profile decreased from 46 m a
À1 in 1981–1990 to 21 m a
À1 in 2001–2010. Our
measurements confirm this recent decline of flow velocity in this fast moving area.
A further decline in flow velocity of the glacier tongue is very likely if we
consider the ongoing disintegration of the icefall. The pace in the separation of the
glacier tongue from the main glacier is high considering the rapidly increasing rock
outcrops in the icefall. It is very likely that the two remaining glacier-ice connections at the southwest side of the icefall will separate in the near future. The main
remaining icefall at the north side will last substantially longer. However, if glacier
recession continues at this pace, the tongue of Pasterze Glacier will – at least for a
brief period of time – form a regenerated glacier (Benn and Evans 2010) within the
next few decades. By then, the tongue of the remaining glacier will only be fed by
Table 9.6 Mean surface
elevation changes at Pasterze
Glacier during the period
2004–2009 based on direct
mass balance measurements
Period
Mean surface elevation change [m a
À1
]
2004–2005
À0.990
2005–2006
À1.355
Mean 2004–2006
À1.173
2006–2007
À1.491
2007–2008
À1.563
2008–2009
À1.232
Mean 2006–2009
À1.429
Mean 2004–2009
À1.326
Data from ZAMG (2013)
194
V. Kaufmann et al.