Significant retreat of glaciers terminating in Hornsund Fjord (Southern Spits− bergen, Svalbard) has been observed during the 20 th century and in the first decade of the 21 st century. The objective of this paper is to present, as complete as possible, a record of front positions changes of 14 tidewater glaciers during this period and to distinguish the main factors influencing their fluctuations. Results are based on a GIS analysis of archival maps, field measurements, and aerial and satellite images. Accuracy was based on an as− sessment of seasonal fluctuations of a glacier's ice cliff position with respect to its mini− mum length in winter (November-December) and its maximum advance position in June or July. Morphometric features and the environmental setting of each glacier are also pre− sented. The total area of the glacier cover in Hornsund Fjord in the period of 1899-2010 diminished approximately 172 km 2 , with an average areal retreat rate of 1.6 km 2 a −1 . The recession rate increased from~1 km 2 a −1 in first decades of the 20 th century up to~3 km 2 a −1 in years 2001-2010. The latest period was more thoroughly studied using optical satellite images acquired almost every year. The importance of glacier morphology and hypso− metry, as well as fjord bathymetry and topography is analyzed. Large glacier systems with low slopes terminating in deeper waters are retreating faster than small steep glaciers ter− minating in shallower water. A relation between mean annual air temperature and aerial retreat rate of tidewater glaciers was found for long time scales. A sudden temperature in− crease, known as the early 20 th century warming in Svalbard, and an increase in tempera− tures during recent decades are well reflected in deglaciation rate. Influence of sea water temperatures on calving and retreat of glaciers was considered and is significant in short−time intervals of the last decade. Surge events are non−climatic factors which com− plicate the record. They are reflected in front advance or fast retreat due to a massive calv− ing depending on the relation between ice thickness and water depth. Despite the influ− ence of many factors, the response of tidewater glaciers to climate change is evident. The average linear retreat rate of all the tidewater glaciers in Hornsund amounted to~70 ma −1 in 2001-2010 and was higher than the average retreat of other Svalbard tidewater glaciers (~45 ma −1 ). Thus, glaciers of this basin can be considered as more sensitive to climate than glaciers of other regions of the archipelago.

Based on observations and model calculations, the retreat over the last two decades of Hansbreen, a tidewater glacier in southern Spitsbergen, Svalbard, is investigated. The observations of the calving-front position between 1982 and 1998 show an abrupt retreat in 1990, which is suggested to be related to a depression in the glacier bed. The observed seasonal variations of the front position are mainly due to variations of the calving rate. The observations of Hansbreen further indicate that during periods of slow front-position changes, melting at the water-line may play an important role in triggering the process of calving.The evolution of Hansbreen between 1982 and 1998 is simulated with a numerical model for the dynamics of tidewater glaciers. Using a flotation criterion for calving in which for each time-step the part of the glacier terminus which is below a critical height above buoyancy is removed, we are able to reproduce the observed rapid retreat of Hansbreen through the depression in the glacier bed. From the observations and model calculations, we conclude that the rapid retreat is mainly an effect of basal topography in the terminus region and not a direct response to a change in mass balance.

Hansbreen, a medium size tidewater glacier in Southern Spitsbergen (Svalbard) is one of the most intensively studied glaciers in the Arctic. This work presents new digital elevation models of its surface and basal topography based on data collected during GPS/GPR campaigns conducted in the spring seasons of 2005 and 2008, as well as on other recent topographic/bathymetric sources. The mean thickness of the glacier is calculated as 171 m and its volume is estimated to be 9.6 (±0.1) km 3 . The main feature of the bedrock morphology is a vast depression that is overdeepened below sea level and extends as far as 11 km upstream from the glacier front. This depression is divided into four individual bas− ins by distinct sills that are related to the main geological/tectonic features of the area. The bedrock morphology affects considerably the glacier's surface topography. The influence of bedrock and surface relief on the subglacial drainage system geometry is discussed. Vast depressions on the glacier surface favor concentration of meltwater and development of moulin systems.

To improve our understanding of Svalbard‐type polythermal glacier drainage, hydraulic geometry models of the subglacial hydrology of two contrasting glaciers in Svalbard have been constructed. The models are tested against a uniquely long and rich set of field observations spanning 45 years. Digital elevation models (DEMs) were constructed from bedrock data measured with ground penetrating radar and surface data of two medium‐sized polythermal glaciers, Hansbreen and Werenskioldbreen, in south‐west Spitsbergen. Hansbreen has a low angle bed with over‐deepenings and a calving front, while Werenskioldbreen has steeper bed and terminates on land. Together they are representative of many Svalbard glaciers. The DEMs were used to derive maps of hydraulic potential and subglacial drainage networks. Validation of the models was done using field observations including location mapping and speleological exploration of active moulins, positions of main river outflows, dyetracing and water chemistry studies, and observations of water pressure inside moulins. Results suggest that the water pressure is generally close to ice overburden pressure but varies greatly depending on local conditions such as bed location, the thickness of cold ice layer, the thickness of the glacier and seasonal changes in meltwater input.

In this study, we assess the accuracy and precision of digital elevation models (DEM) retrieved from aerial photographs taken in 2011 and from Very High Resolution satellite images (WorldView-2 and Pléiades) from the period 2012–2017. Additionally, the accuracy of the freely available Strip product of ArcticDEM was verified. We use the DEMs to characterize geometry changes over Hansbreen and Hornbreen, two tidewater glaciers in southern Spitsbergen, Svalbard. The satellite-based DEMs from WorldView-2 and Pléiades stereo pairs were processed using the Rational Function Model (RFM) without and with one ground control point. The elevation quality of the DEMs over glacierized areas was validated with in situ data: static differential GPS survey of mass balance stakes and GPS kinematic data acquired during ground penetrating radar survey. Results demonstrate the usefulness of the analyzed sources of DEMs for estimation of the total geodetic mass balance of the Svalbard glaciers. DEM accuracy is sufficient to investigate glacier surface elevation changes above 1 m. Strips from the ArcticDEM are generally precise, but some of them showed gross errors and need to be handled with caution. The surface of Hansbreen and Hornbreen has been lowering in recent years. The average annual elevation changes for Hansbreen were more negative in the period 2015–2017 (−2.4 m a−1) than in the period 2011–2015 (−1.7 m a−1). The average annual elevation changes over the studied area of Hornbreen for the period 2012–2017 amounted to −1.6 m a−1. The geodetic mass balance for Hansbreen was more negative than the climatic mass balance estimated using the mass budget method, probably due to underestimation of the ice discharge. From 2011 to 2017, Hansbreen lost on average over 1% of its volume each year. Such a high rate of relative loss illustrates how fast these glaciers are responding to climate change.