scholarly journals Classifying disequilibrium of small mountain glaciers from patterns of surface elevation change distributions

2021 ◽  
pp. 1-16
Author(s):  
Lea Hartl ◽  
Kay Helfricht ◽  
Martin Stocker-Waldhuber ◽  
Bernd Seiser ◽  
Andrea Fischer
Keyword(s):  
High Elevation ◽  
Distinct Pattern ◽  
Surface Elevation ◽  
Elevation Change ◽  
Self Organizing Maps ◽  
Data Set ◽  
Thickness Change ◽  
Mountain Glaciers ◽  
Surface Elevation Change ◽  
Time Periods

Abstract The overall trend of rapid retreat of Alpine glaciers contains considerable variability of responses at the scale of individual glaciers. As a step towards a regional assessment of glacier state that allows a detailed differentiation of single glaciers, we explore the potential of a self-organizing maps (SOM) algorithm to identify and cluster recurring patterns of thickness change at glaciers in western Austria. Using digital elevation models and glacier inventories for three time periods, we compute the frequency distribution of surface elevation change over the area of each glacier in the data set, for each period. The results of the SOM clustering show a distinct pattern shift over time: From 1969 to 1997, surface elevation change occurred at relatively uniform rates across a given glacier. Since 1997, the distribution of surface elevation change at individual glaciers has been far less uniform, indicating accelerated processes of disintegration. Tracking the evolution of individual glaciers throughout the time periods via the clusters highlights both the broader regional trend as well as glaciers that deviate from this trend, e.g. some very small, high elevation glaciers that have reverted to reduced and more uniform volume loss patterns.

scholarly journals Antarctic firn compaction rates from repeat-track airborne radar data: I. Methods

2015 ◽  
Vol 56 (70) ◽  
pp. 155-166 ◽  
Author(s):  
B. Medley ◽  
S.R.M. Ligtenberg ◽  
I. Joughin ◽  
M.R. Van den Broeke ◽  
S. Gogineni ◽  
...  
Keyword(s):  
Accumulation Rate ◽  
Radar Data ◽  
Temporal Variations ◽  
Mass Change ◽  
Surface Elevation ◽  
Elevation Change ◽  
Compaction Rate ◽  
Thickness Change ◽  
Surface Elevation Change ◽  
Spatio Temporal

AbstractWhile measurements of ice-sheet surface elevation change are increasingly used to assess mass change, the processes that control the elevation fluctuations not related to ice-flow dynamics (e.g. firn compaction and accumulation) remain difficult to measure. Here we use radar data from the Thwaites Glacier (West Antarctica) catchment to measure the rate of thickness change between horizons of constant age over different time intervals: 2009–10, 2010–11 and 2009–11. The average compaction rate to ~25 m depth is 0.33 m a−1, with largest compaction rates near the surface. Our measurements indicate that the accumulation rate controls much of the spatio-temporal variations in the compaction rate while the role of temperature is unclear due to a lack of measurements. Based on a semi-empirical, steady-state densification model, we find that surveying older firn horizons minimizes the potential bias resulting from the variable depth of the constant age horizon. Our results suggest that the spatio-temporal variations in the firn compaction rate are an important consideration when converting surface elevation change to ice mass change. Compaction rates varied by up to 0.12 m a−1 over distances <6 km and were on average >20% larger during the 2010–11 interval than during 2009–10.

scholarly journals Rapid changes of Alpine glaciers in Austria tracked by ALS surveys 

2021 ◽  
Author(s):  
Kay Helfricht ◽  
Lea Hartl ◽  
Martin Stocker-Waldhuber ◽  
Bernd Seiser ◽  
Andrea Fischer
Keyword(s):  
Relative Volume ◽  
Surface Elevation ◽  
Ice Thickness ◽  
Mountain Range ◽  
Volume Loss ◽  
Elevation Change ◽  
Thickness Change ◽  
Alpine Glaciers ◽  
Glacier Changes ◽  
Surface Elevation Change

&lt;p&gt;Unprecedented glacier changes are reported for many mountain regions on earth based on surveys with different spatial resolution and repeat intervals. Eastern Alpine glaciers have been receding since the LIA maximum, with increasing relative volume loss at the beginning of the 21&lt;sup&gt;st&lt;/sup&gt; century. New high-resolution data of surface elevation from ALS surveys enable the analysis of most recent glacier changes at three mountain ranges in western Austria as an impact of climate change.&lt;/p&gt;&lt;p&gt;Surface elevation change rates between 2007 and 2018 increased again in comparison to former periods. Volume loss takes place even in the highest elevation zones, and most of the glaciers are out of an equilibrium state, such that consolidation of mass balance towards zero appears impossible under present climate conditions. The disintegration of low lying glacier tongues and a strong depletion of the firn cover are further signs of rapid glacier changes. The frequency distributions of surface elevation change throughout the area of each glacier show distinct shifts in peak ice thickness change and patterns of surface change distribution that suggest ongoing processes of glacier disintegration. Combining recent surface elevation changes and estimations of the spatial distribution of ice thickness in Austria shows that most of glaciers will vanish in 50 years or less. Only glaciers currently larger than 5 km&amp;#178; can be expected to exist longer at reduced size. At current rates of mass loss, glaciers are projected to retreat entirely to above 2800m in the &amp;#214;tztal and Stubai ranges by 2050. Further concerns arise regarding methods of tracking the future development of the remaining ice bodies. In particular, in the Silvretta mountain range, the majority of glacier margins have to be delineated in debris-covered glacier zones. It is debatable whether some of the smallest glaciogenic features should still be accounted for in glacier inventories or moved to an inventory of transient cryogenic landforms.&lt;/p&gt;

scholarly journals Heterogeneous spatial and temporal pattern of surface elevation change and mass balance of the Patagonian ice fields between 2000 and 2016

2019 ◽  
Vol 13 (9) ◽  
pp. 2511-2535 ◽  
Author(s):  
Wael Abdel Jaber ◽  
Helmut Rott ◽  
Dana Floricioiu ◽  
Jan Wuite ◽  
Nuno Miranda
Keyword(s):  
Spatial Pattern ◽  
Mass Balance ◽  
Temporal Trend ◽  
Sar Interferometry ◽  
Surface Elevation ◽  
Radar Signal ◽  
Elevation Change ◽  
Mass Losses ◽  
Digital Elevation ◽  
Surface Elevation Change

Abstract. The northern and southern Patagonian ice fields (NPI and SPI) have been subject to accelerated retreat during the last decades, with considerable variability in magnitude and timing among individual glaciers. We derive spatially detailed maps of surface elevation change (SEC) of NPI and SPI from bistatic synthetic aperture radar (SAR) interferometry data of the Shuttle Radar Topography Mission (SRTM) and TerraSAR-X add-on for Digital Elevation Measurements (TanDEM-X) for two epochs, 2000–2012 and 2012–2016, and provide data on changes in surface elevation and ice volume for the individual glaciers and the ice fields at large. We apply advanced TanDEM-X processing techniques allowing us to cover 90 % and 95 % of the area of NPI and 97 % and 98 % of SPI for the two epochs, respectively. Particular attention is paid to precisely co-registering the digital elevation models (DEMs), accounting for possible effects of radar signal penetration through backscatter analysis and correcting for seasonality biases in case of deviations in repeat DEM coverage from full annual time spans. The results show a different temporal trend between the two ice fields and reveal a heterogeneous spatial pattern of SEC and mass balance caused by different sensitivities with respect to direct climatic forcing and ice flow dynamics of individual glaciers. The estimated volume change rates for NPI are -4.26±0.20 km3 a−1 for epoch 1 and -5.60±0.74 km3 a−1 for epoch 2, while for SPI these are -14.87±0.52 km3 a−1 for epoch 1 and -11.86±1.99 km3 a−1 for epoch 2. This corresponds for both ice fields to an eustatic sea level rise of 0.048±0.002 mm a−1 for epoch 1 and 0.043±0.005 mm a−1 for epoch 2. On SPI the spatial pattern of surface elevation change is more complex than on NPI and the temporal trend is less uniform. On terminus sections of the main calving glaciers of SPI, temporal variations in flow velocities are a main factor for differences in SEC between the two epochs. Striking differences are observed even on adjoining glaciers, such as Upsala Glacier, with decreasing mass losses associated with slowdown of flow velocity, contrasting with acceleration and increase in mass losses on Viedma Glacier.

scholarly journals CryoSat-2 delivers monthly and inter-annual surface elevation change for Arctic ice caps

2015 ◽  
Vol 9 (3) ◽  
pp. 2821-2865 ◽  
Author(s):  
L. Gray ◽  
D. Burgess ◽  
L. Copland ◽  
M. N. Demuth ◽  
T. Dunse ◽  
...  
Keyword(s):  
Snow Accumulation ◽  
Surface Elevation ◽  
Radar Altimeter ◽  
Elevation Change ◽  
Ice Caps ◽  
Ice Cap ◽  
Winter Snow ◽  
Surface Elevation Change ◽  
Devon Ice Cap ◽  
Arctic Ice

Abstract. We show that the CryoSat-2 radar altimeter can provide useful estimates of surface elevation change on a variety of Arctic ice caps, on both monthly and yearly time scales. Changing conditions, however, can lead to a varying bias between the elevation estimated from the radar altimeter and the physical surface due to changes in the contribution of subsurface to surface backscatter. Under melting conditions the radar returns are predominantly from the surface so that if surface melt is extensive across the ice cap estimates of summer elevation loss can be made with the frequent coverage provided by CryoSat-2. For example, the average summer elevation decreases on the Barnes Ice Cap, Baffin Island, Canada were 2.05 ± 0.36 m (2011), 2.55 ± 0.32 m (2012), 1.38 ± 0.40 m (2013) and 1.44 ± 0.37 m (2014), losses which were not balanced by the winter snow accumulation. As winter-to-winter conditions were similar, the net elevation losses were 1.0 ± 0.2 m (winter 2010/2011 to winter 2011/2012), 1.39 ± 0.2 m (2011/2012 to 2012/2013) and 0.36 ± 0.2 m (2012/2013 to 2013/2014); for a total surface elevation loss of 2.75 ± 0.2 m over this 3 year period. In contrast, the uncertainty in height change results from Devon Ice Cap, Canada, and Austfonna, Svalbard, can be up to twice as large because of the presence of firn and the possibility of a varying bias between the true surface and the detected elevation due to changing year-to-year conditions. Nevertheless, the surface elevation change estimates from CryoSat for both ice caps are consistent with field and meteorological measurements. For example, the average 3 year elevation difference for footprints within 100 m of a repeated surface GPS track on Austfonna differed from the GPS change by 0.18 m.

scholarly journals Surface elevation change and mass balance of Icelandic ice caps derived from swath mode CryoSat-2 altimetry

2016 ◽  
Vol 43 (23) ◽  
pp. 12,138-12,145 ◽  
Author(s):  
L. Foresta ◽  
N. Gourmelen ◽  
F. Pálsson ◽  
P. Nienow ◽  
H. Björnsson ◽  
...  
Keyword(s):  
Mass Balance ◽  
Surface Elevation ◽  
Elevation Change ◽  
Ice Caps ◽  
Surface Elevation Change

scholarly journals Glacier mass-balance determination by remote sensing and high-resolution modelling

2000 ◽  
Vol 46 (154) ◽  
pp. 491-498 ◽  
Author(s):  
Alun Hubbard ◽  
Ian Willis ◽  
Martin Sharp ◽  
Douglas Mair ◽  
Peter Nienow ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Mass Balance ◽  
Mass Flux ◽  
Surface Elevation ◽  
Surface Velocity ◽  
Elevation Change ◽  
Flux Divergence ◽  
Flow Modelling ◽  
Surface Elevation Change ◽  
Divergence Field

AbstractAn indirect methodology for determining the distribution of mass balance at high spatial resolution using remote sensing and ice-flow modelling is presented. The method, based on the mass-continuity equation, requires two datasets collected over the desired monitoring interval: (i) the spatial pattern of glacier surface-elevation change, and (ii) the mass-flux divergence field. At Haut Glacier d’Arolla, Valais, Switzerland, the mass-balance distribution between September 1992 and September 1993 is calculated at 20 m resolution from the difference between the pattern of surface-elevation change derived from analytical photogrammetry and the mass-flux divergence field determined from three-dimensional, numerical flow modelling constrained by surface-velocity measurements. The resultant pattern of mass balance is almost totally negative, showing a strong dependence on elevation, but with large localized departures. The computed distribution of mass balance compares well (R2 = 0.91) with mass-balance measurements made at stakes installed along the glacier centre line over the same period. Despite the highly optimized nature of the flow-modelling effort employed in this study, the good agreement indicates the potential this method has as a strategy for deriving high spatial and temporal-resolution estimates of mass balance.

scholarly journals Net Budget and Flow of South Cascade Glacier, Washington

1965 ◽  
Vol 5 (41) ◽  
pp. 547-566 ◽  
Author(s):  
Mark F. Meier ◽  
W. V. Tangborn
Keyword(s):  
Steady State ◽  
Surface Elevation ◽  
Elevation Change ◽  
Glacier Surface ◽  
Surface Elevation Change ◽  
Long Valley ◽  
Valley Glacier ◽  
Ice Velocity ◽  
The Mean ◽  
Velocity Averages

AbstractIce velocity, net mass budget and surface elevation change data were collected over the length and width of a small (3.4 km. long) valley glacier from 1957 to 1964. Ice velocities range up to about 20 m./yr.; three prominent velocity maxima along the length of the glacier correspond to maxima in surface slope. Net mass budgets averaged over the glacier surface range between − 3.3 m. of water equivalent (1957–58) and +1.2 m. (1963–64). Except for the year 1960–61, curves of net budget versus altitude are parallel. During the period 1958–61 the glacier became thinner at a rate averaging 0.93 m./yr. The net budget and thinning data are internally consistent. Relations between emergence velocity, net budget and surface elevation change are examined at four specific points on the glacier surface and as functions of distance along the length of the glacier. Emergence velocity averages about −0.5 m. in the upper part of the glacier and about +1.0 m. in the lower part. Ice discharge and ice thickness are also calculated as functions of distance. The discharge reaches a peak of 8.8 × 105m.3of ice per year 2.2 km. from the head of the glacier. The mean thickness of the glacier is about 83 m. A steady-state distribution of net budget is used to calculate a steady-state discharge, which is 2.2 times larger than the present discharge.

scholarly journals Modeling of firn compaction for estimating ice-sheet mass change from observed ice-sheet elevation change

2011 ◽  
Vol 52 (59) ◽  
pp. 1-7 ◽  
Author(s):  
Jun Li ◽  
H. Jay Zwally
Keyword(s):  
Accumulation Rate ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Temporal Variations ◽  
Mass Change ◽  
Surface Elevation ◽  
Effective Density ◽  
Elevation Change ◽  
Surface Elevation Change ◽  
Elevation Changes

AbstractChanges in ice-sheet surface elevation are caused by a combination of ice-dynamic imbalance, ablation, temporal variations in accumulation rate, firn compaction and underlying bedrock motion. Thus, deriving the rate of ice-sheet mass change from measured surface elevation change requires information on the rate of firn compaction and bedrock motion, which do not involve changes in mass, and requires an appropriate firn density to associate with elevation changes induced by recent accumulation rate variability. We use a 25 year record of surface temperature and a parameterization for accumulation change as a function of temperature to drive a firn compaction model. We apply this formulation to ICESat measurements of surface elevation change at three locations on the Greenland ice sheet in order to separate the accumulation-driven changes from the ice-dynamic/ablation-driven changes, and thus to derive the corresponding mass change. Our calculated densities for the accumulation-driven changes range from 410 to 610 kgm–3, which along with 900 kgm–3 for the dynamic/ablation-driven changes gives average densities ranging from 680 to 790 kgm–3. We show that using an average (or ‘effective’) density to convert elevation change to mass change is not valid where the accumulation and the dynamic elevation changes are of opposite sign.

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