as for heavily debris-covered glaciers where the net ablation at the glacier terminus
might even be zero (e.g. Khumbu Glacier, Nepal; Inoue 1977; Benn and Lehmkuhl
2000). As shown in an earlier study (Kellerer-Pirklbauer et al. 2008), the debriscovered part of Pasterze Glacier exhibited almost identical net ablation rates over a
wide range of altitude intervals during the period 1981–2000. The present study
shows that the steadily growing supraglacial debris cover conserves the glacier ice
and significantly reduces the amount of ice mass loss by about 25 %.
Figure 9.7 reveals that small areas show an increase in surface elevation over the
period 2003–2009. This is related to the fact that there was almost no winter snow
left in 2003 and the firn line was substantially higher than in 2009. The positive
elevation changes observed between 2003 and 2009 at higher altitudes and in areas
less exposed to solar radiation are thus the result of both glacier-hostile conditions
in 2003 and glacier-friendly conditions in 2009. The massive ice loss during the
observation period 2003–2009 is also evident in other places in the European Alps.
Haeberli et al. (2013a) report that the mean specific mass balance of nine Alpine
glaciers (Gries, Silvretta, Vernagt, Hintereis, Kesselwand, Careser, Saint Sorlin,
Sarennes, Stubacher Sonnblick) was À1.2 m a
À1 during the period 1999–2009. This
specific mass balance value is the highest decadal mean measured during the period
1949–2009. A similar accelerated trend in glacier mass loss since the turn of this
century has also been revealed on a global scale at 30 reference glaciers in nine
mountain ranges (Haeberli et al. 2013b).
Direct measurement data on the specific mass balance at Pasterze Glacier have
been available from the Central Institute for Meteorology and Geodynamics
(ZAMG 2013) since the glaciological year 2004–2005 (Table 9.6). The comparison
of mean surface elevation changes obtained using the photogrammetric method
(2003–2009) and direct measurements (2004–2009) reveals very similar results and
confirms the reliability of our method, notwithstanding the caveats mentioned in
Sect. 9.3.2.6. Submergence and emergence velocities of glacier ice cannot be
measured photogrammetrically. Recent measurements at the tongue of Pasterze
Glacier by ZAMG revealed notable emergence velocities only at ablation stakes
close to the icefall (W. Sch€ oner; personal communication 2006). Thus, the
photogrammetrically derived volume change of the glacier in the period 2003–
2009 is presumably close to the real mass loss.
9.5.2 Towards a Big Dead Ice Body
The successful computation of displacement vectors depends on the stability of the
surface texture and the time elapsed between two glacial stages. Ice surfaces are
difficult to monitor over a longer (multi-annual) time span because of changing
surface texture and associated decorrelation of surface radiometry. On the contrary,
a too short observation period would not allow the detection of significant changes.
This is a substantial problem in monitoring the kinematics of glaciers (Ka ¨a ¨b 2005).
Kaufmann et al. (2008) estimated the surface flow velocity at Pasterze Glacier by
9 Glaciological Studies at Pasterze Glacier (Austria) Based on Aerial Photographs
193
might even be zero (e.g. Khumbu Glacier, Nepal; Inoue 1977; Benn and Lehmkuhl
2000). As shown in an earlier study (Kellerer-Pirklbauer et al. 2008), the debriscovered part of Pasterze Glacier exhibited almost identical net ablation rates over a
wide range of altitude intervals during the period 1981–2000. The present study
shows that the steadily growing supraglacial debris cover conserves the glacier ice
and significantly reduces the amount of ice mass loss by about 25 %.
Figure 9.7 reveals that small areas show an increase in surface elevation over the
period 2003–2009. This is related to the fact that there was almost no winter snow
left in 2003 and the firn line was substantially higher than in 2009. The positive
elevation changes observed between 2003 and 2009 at higher altitudes and in areas
less exposed to solar radiation are thus the result of both glacier-hostile conditions
in 2003 and glacier-friendly conditions in 2009. The massive ice loss during the
observation period 2003–2009 is also evident in other places in the European Alps.
Haeberli et al. (2013a) report that the mean specific mass balance of nine Alpine
glaciers (Gries, Silvretta, Vernagt, Hintereis, Kesselwand, Careser, Saint Sorlin,
Sarennes, Stubacher Sonnblick) was À1.2 m a
À1 during the period 1999–2009. This
specific mass balance value is the highest decadal mean measured during the period
1949–2009. A similar accelerated trend in glacier mass loss since the turn of this
century has also been revealed on a global scale at 30 reference glaciers in nine
mountain ranges (Haeberli et al. 2013b).
Direct measurement data on the specific mass balance at Pasterze Glacier have
been available from the Central Institute for Meteorology and Geodynamics
(ZAMG 2013) since the glaciological year 2004–2005 (Table 9.6). The comparison
of mean surface elevation changes obtained using the photogrammetric method
(2003–2009) and direct measurements (2004–2009) reveals very similar results and
confirms the reliability of our method, notwithstanding the caveats mentioned in
Sect. 9.3.2.6. Submergence and emergence velocities of glacier ice cannot be
measured photogrammetrically. Recent measurements at the tongue of Pasterze
Glacier by ZAMG revealed notable emergence velocities only at ablation stakes
close to the icefall (W. Sch€ oner; personal communication 2006). Thus, the
photogrammetrically derived volume change of the glacier in the period 2003–
2009 is presumably close to the real mass loss.
9.5.2 Towards a Big Dead Ice Body
The successful computation of displacement vectors depends on the stability of the
surface texture and the time elapsed between two glacial stages. Ice surfaces are
difficult to monitor over a longer (multi-annual) time span because of changing
surface texture and associated decorrelation of surface radiometry. On the contrary,
a too short observation period would not allow the detection of significant changes.
This is a substantial problem in monitoring the kinematics of glaciers (Ka ¨a ¨b 2005).
Kaufmann et al. (2008) estimated the surface flow velocity at Pasterze Glacier by
9 Glaciological Studies at Pasterze Glacier (Austria) Based on Aerial Photographs
193