Linking glacier surface changes to subglacial conduit locations for a temperate Alpine glacier

2020 ◽  
Author(s):  
Pascal Egli ◽  
Bruno Belotti ◽  
Martino Sala ◽  
Stuart Lane ◽  
James Irving
Keyword(s):  
High Spatial Resolution ◽  
Three Dimensional ◽  
Swiss Alps ◽  
Glacier Surface ◽  
Alpine Glacier ◽  
Ice Surface ◽  
Area Of Interest ◽  
Cover Thickness ◽  
Western Swiss Alps ◽  
Surface Changes

<p>It is well understood that topography near the snout of an alpine glacier may evolve quickly due to differential melting depending on exposure to solar radiation and on debris cover thickness. However, the positioning and shape of subglacial conduits underneath shallow ice may also have an important influence on ice creep and thereby on the topography of this region. This relationship could potentially be used to determine locations of subglacial conduits via the detailed observation of glacier surface changes.</p><p>We monitored the ice-marginal zone of the Otemma Glacier in the south-western Swiss Alps with daily UAV surveys at high spatial resolution and with a network of ablation stakes over a period of three weeks. After subtraction of melt measured with ablation stakes, we produced maps of changes in ice surface topography that are due to processes other than melt. In two consecutive summers we conducted three-dimensional GPR surveys in the same area of interest. By looking at these spatially dense grids of GPR measurements, we are able to identify the locations and shape of sub-glacial conduits underneath the ice marginal glacier tongue, for ice thicknesses between 20 m and 50 m. Superposition of the GPR-derived channel maps with those showing the topographic changes suggest a correlation between ice surface changes and processes operating at the glacier bed.</p>

Temperate Alpine glacier surface dynamics linked to collapsing subglacial conduits

2021 ◽  
Author(s):  
Pascal Egli ◽  
Stuart Lane ◽  
James Irving ◽  
Bruno Belotti
Keyword(s):  
Three Dimensional ◽  
Swiss Alps ◽  
Glacier Retreat ◽  
Collapse Mechanism ◽  
Glacier Mass Balance ◽  
Glacier Surface ◽  
Alpine Glacier ◽  
Surface Loss ◽  
Ice Surface ◽  
Surface Melt

<p>If tongues of temperate Alpine glaciers are subjected to high temperatures their topography may change rapidly due to the effects of differential melt related to aspect and debris cover. Independent of local surface melt, the position of subglacial conduits may have an important influence on ice creep and so on changes in topography at the ice surface. This reflects analyses that suggest that subglacial conduits at glacier margins may not be permanently pressurised; and that creep closure rates are insufficient to close subglacial conduits completely. Rapid climate warming may exacerbate this process, due both to surface-melt driven glacier thinning and over-enlargement of conduits due to high upstream melt rates. Over-enlarged conduits that are not permanently pressurised would lead to the development of structural weaknesses and eventual collapse of the ice surface into the conduits. We hypothesise that this collapse mechanism could represent an important and alternative driver of rapid glacier retreat.</p><p>In this paper we combine: (1) an extensive survey of glacier margin collapse in the Swiss Alps with (2) intensive monitoring of the dynamics of such collapse at the Otemma Glacier in the south-western Swiss Alps. Daily UAV surveys were undertaken at a high spatial resolution and with precise and accurate ground control. These datasets were used to generate surface change information using SfM-MVS photogrammetry. Surfaces of difference showed surface loss that could not be related to ablation alone. Combining them with three-dimensional ground-penetrating radar (GPR) surveys in the same zone showed that the surface loss was coincident spatially with the positions of sub-glacial conduits, for ice thicknesses between 20 m and 50 m. We show that this form of subglacial conduit collapse is also happening for several other glaciers in the Swiss Alps, and that this mechanism of snout collapse and glacier retreat has become more common than has hitherto been the case. It also leads to temporal patterns of glacier margin retreat that differ from those that might be expected due to glacier mass balance and ice mass flux effects alone.</p>

scholarly journals Characterization of subglacial marginal channels using 3-D analysis of high-density ground-penetrating radar data

2021 ◽  
pp. 1-14
Author(s):  
Pascal E. Egli ◽  
James Irving ◽  
Stuart N. Lane
Keyword(s):  
Ground Penetrating Radar ◽  
Three Dimensional ◽  
Radar Data ◽  
High Density ◽  
Swiss Alps ◽  
Amplitude Analysis ◽  
Glacier Surface ◽  
Alpine Glacier ◽  
Glacier Terminus ◽  
Ground Penetrating

Abstract Studying subglacial drainage networks is important for understanding the potential relationship between channel dynamics and rapid glacier recession as well as the role of subglacial channels in subglacial sediment evacuation. In order to delineate the planform geometry of snout marginal subglacial channels, densely spaced ground-penetrating radar (GPR) measurements at a frequency of ~70 MHz were carried out over the snout marginal zones of two temperate glaciers in the southwestern Swiss Alps, the Haut Glacier d'Arolla and the Glacier d'Otemma. Three-dimensional (3-D) data processing and amplitude analysis of the GPR reflection along the glacier bed was used to map the channels. At the Haut Glacier d'Arolla, two relatively straight channels of several meters in width were identified. The positions of these channels correspond well with the locations of channel outlets at the glacier terminus, as well as with fractures appearing on the glacier surface one month after the GPR data acquisition. The latter are believed to represent the beginning of ice collapse above the subglacial channels. At the Glacier d'Otemma, a major subglacial conduit was detected with similar dimensions to those identified at the Haut Glacier d'Arolla, but greater sinuosity. The position of this channel was confirmed by drone-based imagery acquired after glacier margin collapse. Our results confirm that high-density 3-D GPR surveys can be used to map subglacial channels near temperate alpine glacier margins.

scholarly journals Evidence for deep icequakes in an Alpine glacier

2000 ◽  
Vol 31 ◽  
pp. 85-90 ◽  
Author(s):  
N. Deichmann ◽  
J. Ansorge ◽  
F. Scherbaum ◽  
A. Aschwanden ◽  
F. Bernard ◽  
...  
Keyword(s):  
Rayleigh Wave ◽  
Three Dimensional ◽  
Focal Depth ◽  
Vertical Component ◽  
Swiss Alps ◽  
P Wave ◽  
S Wave ◽  
Glacier Surface ◽  
Simultaneous Inversion ◽  
Wave Velocities

AbstractTo obtain more reliable information about the focal-depth distribution of icequakes, in April 1997 we operated an array of seven portable digital seismographs on Unteraargletscher, central Swiss Alps. Over 5000 events were detected by at least two instruments during the 9 day recording period. P-wave velocities (3770 m f) were determined from several calibration shots detonated at the glacier surface as well as in a 49 m deep borehole, whereas S-wave velocities (1860 ms–1) were derived from a simultaneous inversion for Vp/Vs6 applied to 169 icequakes. So far, hypocentral locations have been calculated for over 300 icequakes. Besides confirming the occurrence of shallow events associated with the opening of crevasses, our results show that a small but significant fraction of the hypocenters are located at or near the glacier bed. One event was found at an intermediate depth of about 120 m. Three-dimensional particle-motion diagrams of both explosions and icequakes clearly demonstrate that all vertical component seismograms from shallow sources are dominated by the Rayleigh wave. On the other hand, for events occurring at depths greater than about 40 m, the Rayleigh wave disappears almost entirely. Therefore, a qualitative analysis of the signal character provides direct information on the focal depth of an event and was used as an independent check of the locations obtained from traditional arrival-time inversions. Thus, our results demonstrate that deep icequakes do occur and that simple rheological models, according to which brittle deformation is restricted to the uppermost part of a glacier, may need revision.

scholarly journals A high-resolution image time series of the Gorner Glacier – Swiss Alps – derived from repeated unmanned aerial vehicle surveys

2019 ◽  
Vol 11 (2) ◽  
pp. 579-588 ◽  
Author(s):  
Lionel Benoit ◽  
Aurelie Gourdon ◽  
Raphaël Vallat ◽  
Inigo Irarrazaval ◽  
Mathieu Gravey ◽  
...  
Keyword(s):  
Feature Detection ◽  
Surface Displacement ◽  
Detection Algorithm ◽  
Swiss Alps ◽  
Glacier Surface ◽  
Ice Surface ◽  
Drainage Networks ◽  
Digital Elevation ◽  
Very High Spatial Resolution ◽  
Aerial Vehicle

Abstract. Modern drone technology provides an efficient means to monitor the response of alpine glaciers to climate warming. Here we present a new topographic dataset based on images collected during 10 UAV surveys of the Gorner Glacier glacial system (Switzerland) carried out approximately every 2 weeks throughout the summer of 2017. The final products, available at https://doi.org/10.5281/zenodo.2630456 (Benoit et al., 2018), consist of a series of 10 cm resolution orthoimages, digital elevation models of the glacier surface, and maps of ice surface displacement. Used on its own, this dataset allows mapping of the glacier and monitoring surface velocities over the summer at a very high spatial resolution. Coupled with a classification or feature detection algorithm, it enables the extraction of structures such as surface drainage networks, debris, or snow cover. The approach we present can be used in the future to gain insights into ice flow dynamics.

scholarly journals A high-frequency and high-resolution image time series of the Gornergletscher – Swiss Alps – derived from repeated UAV surveys

2018 ◽  
Author(s):  
Lionel Benoit ◽  
Aurelie Gourdon ◽  
Raphaël Vallat ◽  
Inigo Irarrazaval ◽  
Mathieu Gravey ◽  
...  
Keyword(s):  
Feature Detection ◽  
Detection Algorithm ◽  
Swiss Alps ◽  
Glacier Surface ◽  
Ice Flow ◽  
Ice Surface ◽  
Surface Displacements ◽  
Drainage Networks ◽  
Digital Elevation ◽  
Very High Spatial Resolution

Abstract. The rapid growth of drone technology provides an efficient means to monitor the response of alpine glaciers to climate warming. Here we report a new dataset based on images collected during ten intensive UAV surveys of the Gornergletscher glacial system (Switzerland) carried out approximately every two weeks throughout the summer 2017. The final products, available at: https://doi.org/10.5281/zenodo.1487862 (Benoit et al, 2018), consist in a series of 10 cm resolution ortho-images, Digital Elevation Models of the glacier surface, and Matching Maps that can be used to quantify ice surface displacements and velocities. Used on its own, this dataset allows mapping the glacier and monitoring surface velocities over the summer at a very high spatial resolution. Coupled with a classification or feature detection algorithm, it enables extracting structures such as surface drainage networks, debris or snow cover. The approach we present can be used in the future to gain insights into ice flow dynamics.

scholarly journals Lidar measurement of surface melt for a temperate Alpine glacier at the seasonal and hourly scales

2015 ◽  
Vol 61 (229) ◽  
pp. 963-974 ◽  
Author(s):  
Chrystelle Gabbud ◽  
Natan Micheletti ◽  
Stuart N. Lane
Keyword(s):  
Near Infrared ◽  
Water Pressure ◽  
Laser System ◽  
Lidar Measurement ◽  
Glacier Surface ◽  
Alpine Glacier ◽  
Alpine Valley ◽  
Ice Surface ◽  
Daily Scale ◽  
Surface Melt

AbstractThis study shows how a new generation of terrestrial laser scanners can be used to investigate glacier surface ablation and other elements of glacial hydrodynamics at exceptionally high spatial and temporal resolution. The study area is an Alpine valley glacier, Haut Glacier d’Arolla, Switzerland. Here we use an ultra-long-range lidar RIEGL VZ-6000 scanner, having a laser specifically designed for measurement of snow- and ice-cover surfaces. We focus on two timescales: seasonal and daily. Our results show that a near-infrared scanning laser system can provide high-precision elevation change and ablation data from long ranges, and over relatively large sections of the glacier surface. We use it to quantify spatial variations in the patterns of surface melt at the seasonal scale, as controlled by both aspect and differential debris cover. At the daily scale, we quantify the effects of ogive-related differences in ice surface debris content on spatial patterns of ablation. Daily scale measurements point to possible hydraulic jacking of the glacier associated with short-term water pressure rises. This latter demonstration shows that this type of lidar may be used to address subglacial hydrologic questions, in addition to motion and ablation measurements.

scholarly journals Extension of mathematical background for Nearest Neighbour Analysis in three-dimensional space

2013 ◽  
Vol 11 ◽  
pp. 25-36
Author(s):  
Eva Stopková
Keyword(s):  
Dimensional Space ◽  
Average Distance ◽  
Three Dimensional ◽  
Nearest Neighbour ◽  
Mathematical Background ◽  
Area Of Interest ◽  
Nearest Neighbours ◽  
Anisotropic Function ◽  
Neighbour Analysis ◽  
Three Dimensional Space

Proceeding deals with development and testing of the module for GRASS GIS [1], based on Nearest Neighbour Analysis. This method can be useful for assessing whether points located in area of interest are distributed randomly, in clusters or separately. The main principle of the method consists of comparing observed average distance between the nearest neighbours r A to average distance between the nearest neighbours r E that is expected in case of randomly distributed points. The result should be statistically tested. The method for two- or three-dimensional space differs in way how to compute r E . Proceeding also describes extension of mathematical background deriving standard deviation of r E , needed in statistical test of analysis result. As disposition of phenomena (e.g. distribution of birds’ nests or plant species) and test results suggest, anisotropic function would repre- sent relationships between points in three-dimensional space better than isotropic function that was used in this work.

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