Icelandic Glaciers Research Articles

Glacier retreat and landform production on an overdeepened glacier foreland: the debris‐charged glacial landsystem at Kvíárjökull, Iceland

ABSTRACTGlacier recession and landform development in a debris‐charged glacial landsystem characterized by an overdeepening is quantified using digital photogrammetry, digital elevation model (DEM) construction and mapping of the Icelandic glacier Kvíárjökull for the period 1945–2003. Melting of ice‐cores is recorded by surface lowering rates of 0·8 m yr–1 (1945–1964), 0·3 m yr–1 (1964–1980), 0·015 m yr–1 (1980–1998) and 0·044 m yr–1 (1998–2003). The distribution/preservation of pushed and stacked ice‐cored moraine complexes are determined by the location of the long‐term glacial drainage network in combination with retreat from the overdeepening, into which glacifluvial sediment is being directed and where debris‐rich ice masses are being reworked and replaced by esker networks produced in englacial meltwater pathways that bypassed the overdeepening and connected to outwash fans prograding over the snout. Recent accelerated retreat of Kvíárjökull, potentially due to increased mass balance sensitivity, has made the snout highly unstable, especially now that the overdeepening is being uncovered and the snout flooded by an expanding pro‐glacial, and partially supraglacial, lake. This case study indicates that thick sequences of debris‐charged basal ice/controlled moraine have a very low preservation potential but ice‐cored moraine complexes can develop into hummocky moraine belts in de‐glaciated terrains because they are related to the process of incremental stagnation, which at Kvíárjökull has involved periodic switches from transport‐dominant to ablation‐dominant conditions. Glacier recession is therefore recorded temporally and spatially by two suites of landforms relating to two phases of landform production which are likely typical for glaciers occupying overdeepenings: an early phase of active, temperate recession recorded by push moraines and lateral moraines and unconfined pro‐glacial meltwater drainage; and a later phase of incremental stagnation and pitted outwash head development initiated by the increasing topographic constraints of the latero‐frontal moraine arc and the increasing importance of the overdeepening as a depo‐centre. Copyright © 2012 John Wiley & Sons, Ltd.

The Orravatnsrustir palsa site in Central Iceland—Palsas in an aeolian sedimentation environment

The Orravatnsrustir palsa site, located north of the Hofsjokull glacier in Central Iceland, has well developed palsas located in a valley-like depression at 710–715m a.s.l. and stands in remarkable contrast to the surrounding desert-like highland plateau. The purpose of this paper is to give an overview of the Orravatnsrustir palsa site, geographic distribution and geomorphic statistics related to size and permafrost thicknesses of the palsas, including recent changes. Icelandic palsas exhibit characteristics of both organic palsas and lithalsa (frozen mineral soil). They are subjected to intense aeolian deposition of volcanic materials. The palsas are often 40–200cm high, with a 40–80cm thick active layer and permafrost reaching more than 5m depth.Measurements of the size of the palsas and the thickness of the active layer which started in 2001 indicate that their size is decreasing and the thickness of the active layer is increasing. These results are in agreement with the general warming trend which has occurred in Iceland during the last decade.

LiDAR mapping of the Snæfellsjökull ice cap, western Iceland

The surface of the Snæfellsjökull ice cap in western Iceland was mapped with airborne LiDAR in 2008. A comparison with a DTM from 1999 derived by aerial photogrammetry shows that the surface of the ice cap has been lowered by 14.0 m on average during this nine year period, corresponding to an annual average mass loss of 1.25 m w.e. per year when a correction has been made for the different timing of the LiDAR survey and the aerial photographs. The area of the ice cap was reduced from 12.5 km² in 2002 to 10.0 km² in 2008. Based on meteorological observations at Stykkishólmur, ∼60 km to the east of the ice cap, the ice volume reduction indicates a mass balance sensitivity of −1.9 m w.e. a$^{−1}$ °C$^{−1}$ for the ice cap. This is within the range of sensitivities estimated for other ice caps and glaciers in Iceland in recent years. As the average ice thickness of Snæfellsjökull is only 30 m, most of the ice cap is likely to disappear within a few decades if the warm climate of Iceland in recent years persists. The LiDAR DTM has been successfully used to delineate the location of crevasses with an automated procedure based on the calculation of the local curvature of the ice surface.

Modelling the 20th and 21st century evolution of Hoffellsjökull glacier, SE-Vatnajökull, Iceland

Abstract. The Little Ice Age maximum extent of glaciers in Iceland was reached about 1890 AD and most glaciers in the country have retreated during the 20th century. A model for the surface mass balance and the flow of glaciers is used to reconstruct the 20th century retreat history of Hoffellsjökull, a south-flowing outlet glacier of the ice cap Vatnajökull, which is located close to the southeastern coast of Iceland. The bedrock topography was surveyed with radio-echo soundings in 2001. A wealth of data are available to force and constrain the model, e.g. surface elevation maps from ~1890, 1936, 1946, 1989, 2001, 2008 and 2010, mass balance observations conducted in 1936–1938 and after 2001, energy balance measurements after 2001, and glacier surface velocity derived by kinematic and differential GPS surveys and correlation of SPOT5 images. The approximately 20% volume loss of this glacier in the period 1895–2010 is realistically simulated with the model. After calibration of the model with past observations, it is used to simulate the future response of the glacier during the 21st century. The mass balance model was forced with an ensemble of temperature and precipitation scenarios derived from 10 global and 3 regional climate model simulations using the A1B emission scenario. If the average climate of 2000–2009 is maintained into the future, the volume of the glacier is projected to be reduced by 30% with respect to the present at the end of this century. If the climate warms, as suggested by most of the climate change scenarios, the model projects this glacier to almost disappear by the end of the 21st century. Runoff from the glacier is predicted to increase for the next 30–40 yr and decrease after that as a consequence of the diminishing ice-covered area.

FLOHOF 2007: an overview of the mesoscale meteorological field campaign at Hofsjökull, Central Iceland

The FLOHOF field campaign took place in the period July 21 to August 24, 2007 on and in the surroundings of Hofsjokull glacier in Central Iceland. During the campaign, 18 automatic weather stations (AWS) recording temperature, humidity, wind speed, wind direction, pressure, and precipitation were deployed on and around the glacier. In addition, atmospheric soundings were performed N and S of Hofsjokull by a tethered balloon, pilot balloons, and two unmanned aerial systems (UAS). An energy balance station, consisting of a net radiometer and an eddy correlation flux measurement station, has also been installed. This paper describes the experimental setup of the campaign and presents first results of the data analysis with respect to transience of mountain-induced gravity waves, the extension of katabatic winds into the surrounding of the glacier, the occurrence of katabatic microfronts, and report on novel approaches to probe the vertical structure of the atmospheric boundary layer by UAS. The observed pressure perturbations related to transient gravity wave activity due to changing inflow conditions were between −2 and 2 hPa in general, with positive values upstream and negative values downstream. Differential heating of the glacier and its surrounding is triggering daytime katabatic flow from the glacier into its surrounding. During the campaign, those katabatic winds typically reached out 4–7 km from the edge of the glacier. During late night in clear sky conditions, frontal-like microstructures have been observed frequently with typical repetition times in the order of 30–60 min indicating the interaction of large-scale synoptic and nighttime katabatic density flows close to the ground. The first research application of the newly developed small unmanned meteorological observer proved the applicability of the system for atmospheric boundary layer research by successfully profiling the atmosphere up to 3.5 km above ground.

A chironomid-based reconstruction of summer temperatures in NW Iceland since AD 1650

Few studies currently exist that aim to validate a proxy chironomid-temperature reconstruction with instrumental temperature measurements. We used a reconstruction from a chironomid percentage abundance data set to produce quantitative summer temperature estimates since AD 1650 for NW Iceland through a transfer function approach, and validated the record against instrumental temperature measurements from Stykkishólmur in western Iceland. The core was dated through Pb-210, Cs-137 and tephra analyses (Hekla 1693) which produced a well-constrained dating model across the whole study period. Little catchment disturbance, as shown through geochemical (Itrax) and loss-on-ignition data, throughout the period further reinforce the premise that the chironomids were responding to temperature and not other catchment or within-lake variables. Particularly cold phases were identified between AD 1683–1710, AD 1765–1780 and AD 1890–1917, with relative drops in summer temperatures in the order of 1.5–2°C. The timing of these cold phases agree well with other evidence of cooler temperatures, notably increased extent of Little Ice Age (LIA) glaciers. Our evidence suggests that the magnitude of summer temperature cooling (1.5–2°C) was enough to force LIA Icelandic glaciers into their maximum Holocene extent, which is in accordance with previous modelling experiments for an Icelandic ice cap (Langjökull).

Commandeering Potential

Commandeering Potential Daniel A. Barber (bio) Hijacking Sustainability. Adrian Parr. The MIT Press. http://mitpress.mit.edu. 209 pages; cloth, $24.95. Adrian Parr's Hijacking Sustainability contributes to a group of recent publications intending to assess the increasing popularity of environmentalism. Does this popularization empower the movement or dilute it, this scholarship asks? In dialogue with Bill McKibben's Eaarth: Making a Life on a Tough New Planet (2010) and Heather Rodgers's Green Gone Wrong: How Our Economy Is Undermining the Environmental Revolution (2010), Parr explores the terms by which "sustainability culture," as she calls it, has become enmeshed in capitalist and consumerist excess. Parr's is the most theoretically sophisticated of this recent wave of environmentalist critique, and she provides a valuable interpretation of sustainability through the frameworks of Gilles Deleuze and Félix Guattari and Michael Hardt and Antonio Negri. Parr is doing important work by advancing the discourse in this regard, as phenomena as disparate as the rebranding of BP and the evolution of gated communities are investigated for both their theoretical significance and their emplacement within struggles for new possibilities of living in a sustainable future. Parr moves the rubric of sustainability away from a special-interest group of "environmentalists" to a more nuanced analysis of the relationship between economies and ecologies. She broadens the premise of "sustainable design and theory" to encompass "a system of knowledge that shapes subjectivities," indicating that "it creates new ways of feeling, thinking, and intuiting life by charting the powers of art and science together." However, as the book's title indicates, Parr's premise is that such shaping is being hijacked as "the power of sustainability culture is appropriated by the mechanisms of State and corporate culture" to serve their own ends. The two-part structure of the book allows for in-depth analysis of this hijacking–the first part, "The Popularization of Sustainability Culture," presents a series of case studies to describe how "culture can promote a sense of dignity and care for the environment in ways that institutions, bureaucracies, and governments cannot." Each chapter is mainly concerned with a critical description of a given "hijacking" practice, with a few pages at the end describing the transformative role a new cultural approach can play. Parr identifies such counter-tendencies in art, design, and other collective strategies. The second part, "Challenges to Sustainability Culture," explores some of the central problems through which this sustainability culture is being tested. The first part is the strongest. Parr's detailed narratives of various hijackings make for compelling storytelling and are rich in detail. In the context of the ongoing disaster in the Gulf of Mexico, readers now might find the discussion of BP most relevant. Parr debunks the environmental claims of the company's transformation from "British Petroleum" to "Beyond Petroleum" through a thorough analysis of the contradictions contained in the rubric of "socially responsible investment." The most engaging chapter, however, is on Hollywood, where Parr reveals a green celebrity culture that relies on the tropes of image-making developed in Finis Dunaway's recent Natural Visions: The Power of Images in American Environmental Reform (2005). The careful calibration of such public relations efforts obfuscates, Parr argues, the environmental impact of the movie industry—from the large-scale manufacturing and distribution systems to the daily reality of idling trailers and excessive catering. Parr then performs an analysis of the cover of the 2006 "green issue" of Vanity Fair, where Knut—the polar bear once used in a global Coca-Cola advertising campaign—had been photoshopped into an image of Leonardo DiCaprio on site in front of an Icelandic glacier. In Parr's intricate recounting, the plight of the polar bear and legislation to protect it are placed in the context of "the affective power of the bear cub and the commodity value of DiCaprio." Parr's point is that while celebrity activism capitalizes on energies of star power "and puts them to good use in the service of collective life," such energies are still enmeshed in the production of illusions. The image of sustainable activism is not necessarily related to relevant policy or economic shifts, but still holds promise in...

Molecular evidence of the survival of subterranean amphipods (Arthropoda) during Ice Age underneath glaciers in Iceland

A Two endemic groundwater arthropod crustacean species, Crangonyx islandicus and Crymostygius thingvallensis, were recently discovered on the mid-Atlantic volcanic island of Iceland. The extent of morphological differences from closest relatives, endemism, along with the geographic isolation of Iceland and its complete coverage by glaciers 21,000 years ago, suggests that these two species have survived glaciation periods in sub-glacial refugia. Here we provide strong support for this hypothesis by an analysis of mitochondrial genetic variation within Crangonyx islandicus. Our results show that the species is divided into several distinct monophyletic groups that are found along the volcanic zone in Iceland, which have been separated by 0.5 to around 5 million years. The genetic divergence between groups reflects geographic distances between sampling sites, indicating that divergence occurred after the colonization of Iceland. The genetic patterns, as well as the dependency of genetic variation on distances from the tectonic plate boundary and altitude, points to recent expansion from several refugia within Iceland. This presents the first genetic evidence of multicellular organisms as complex as crustacean amphipods which have survived glaciations beneath an ice sheet. This survival may be explained by geothermal heat linked to volcanic activities, which may have maintained favourable habitats in fissures along the tectonic plate boundary in Iceland during glaciations.

Evolution of a debris-charged glacier landsystem, Kvíárjökull, Iceland

Please click here to download the map associated with this article. A time-series of 1:12,500 scale maps of the snout and foreland of the Icelandic glacier Kvíárjökull provides a spatial and temporal assessment of landform evolution from a debris-charged glacier snout over a 58 year period between 1945 and 2003. In addition to providing a valuable record of glacier recession over a period of recent global warming, the maps enable the elaboration of existing conceptual models of the debris-charged glacier landsystem based on measurable process-form relationships. Features were identified using a combination of DEM visualization, morphometric analysis, stereoscopic viewing of aerial photographs and field verification. The maps contain twelve colour coded surficial geology units displayed as polygons and various geomorphological features represented by a combination of lines and points. The spatial and temporal evolution of the landforms on the glacier foreland indicate that the snout of Kvíárjökull has been undergoing active retreat and incremental stagnation over the study period. The maps serve as excellent modern landsystem analogues for palaeoglaciological reconstructions in similar climatic and topographic settings.

Glacial Geomorphology at Glasgow

This paper reviews a century of geographical contributions at the University of Glasgow to the development of glacial geomorphology. Significant advances were made from the 1960s, when geographers and topographic scientists began to combine geomorphic and survey expertise in accurately charting spatial and temporal changes in Icelandic glacier snouts and proglacial landforms, providing modern analogues for process-form models (the first glacial landsystems model) and a methodological avenue for quantification. Subsequent expeditions and research projects, involving a range of Glasgow academics, doctoral students and undergraduates, often in collaboration with researchers based elsewhere, have led to numerous conceptual and methodological refinements – and on occasion significant recasting – of this pioneering work. A detailed review is provided of these many contributions, seeking to elaborate their significance against a wider horizon of inquiry into glaciated landscapes, past and present.

The hydration and alteration of perlite and rhyolite

Abstract: The volatile concentrations and thermal characteristics of hydrothermally altered rhyolitic deposits erupted under Icelandic glaciers have been studied by combined differential scanning calorimetry–thermogravimetric analysis–mass spectrometry (DSC–TGA–MS) and X-ray diffraction (XRD). Samples range from pristine obsidians to strongly perlitized and altered fragmental deposits. Four types of samples are determined to have notable differences in total volatile concentrations: obsidians (0.44–3.04 wt%), perlites (2.15–8.15 wt%), obsidian-breccias (8.49–9.41 wt%) and hyaloclastites (3.23–7.78 wt%). DSC–TGA–MS and textural data indicate that the volatile concentration of the perlitic samples increases as the amount of perlitization increases. XRD data show that the volatile-rich samples are rich in the low-temperature zeolite minerals heulandite and mordenite. The temperature at which volatile exsolution occurs is shown to decrease as the volatile concentration increases, reflecting the speciation of water as well as zeolite mineral growth. Supplementary material: Detailed grain-size fraction analysis data in table and histogram form are available at http://www.geolsoc.org.uk/SUP18366 .

Fluid-pressure controlled soft-bed deformation sequence beneath the surging Breiðamerkurjökull (Iceland, Little Ice Age)

The general subject of this paper is subglacial deformation beneath Breiðamerkurjökull, a surging Icelandic glacier. More specifically it discusses the evolution and the role of fluid pressure on the behaviour of subglacial sediments during deformation. During Little Ice Age maximum, the two outcrops studied, North Jökulsarlon (N-Jk) and Brennhola-Alda (BA), were located at 2550 m and 550 m respectively from the front of the Breiðamerkurjökull. Sedimentological analysis at the forefield of the glacier shows thick, coarse glaciofluvial deposits interbedded with thin, fine-grained shallow lacustrine/swamp deposits, overlain by a deformed till unit at N-Jk. BA outcrop shows fine-grained shallow lacustrine/swamp deposits overlain by a deformed till unit. The sequence of deformation events from one outcrop to the other is similar. First, major thrust planes, which were rooted in shallow lacustrine/swamp deposits developed by glacially induced simple shear. Next, the thrusts were folded, indicating the deformation of hydroplastic sediment assisted by moderate fluid pressure. Then clastic dyke swarms crosscut the sedimentary succession, proving that fluid overpressure caused hydrofracturing associated with fluidisation. Finally, as water escaped from the glacier bed, fluid pressure dropped, and normal faulting occurred in brittle-state subglacial sediments. Fluid-pressure variations are related to glacier dynamics. They control the deformation sequence by modifying subglacial rheological behaviour and the nature of the subglacial tectonism.

Topographic controls on glacier sediment–landform associations around the temperate North Patagonian Icefield

Glacier sediment–landform associations are commonly used as interpretive and predictive tools to reconstruct the nature of past glacial events. Here we provide a regional-scale study of the sediments and landforms around the temperate North Patagonian Icefield, an area with outlet glaciers that terminate in the full range of environments possible in a temperate glacier setting (land-terminating, lake-terminating and tidewater-terminating). We present a regional-scale geomorphological map and sedimentological data collected at 11 outlet glaciers of the icefield. Key sediments and landforms include large tracts of ice-scoured bedrock, extensive sandar, terminal moraines, ice-contact glaciofluvial landforms and evidence of paraglacial slope adjustment following glacier recession. The sediments and landforms developed around the North Patagonian Icefield contrast with those previously identified at other temperate outlet glaciers in Iceland and Alaska, and we argue that this is largely a result of topographic controls on glacier terminal environment (e.g. local relief, topography and geomorphological setting).

Geological Resources for Tourism in North and South Iceland

In August 2008, I visited some rift zones, volcanoes, and glaciers in Iceland, and was impressed with Iceland's nature and Icelandic activities for harnessing it. I would like to introduce you to some of the geological tourist attractions in Iceland.

Surging glacier landsystem of Tungnaárjökull, Iceland

Please click here to download the map associated with this article. A1:30,000 scale map of the snout and proglacial landscape of the surging Icelandic glacier Tungnaárjökull, based upon aerial photography from 1995, immediately after a surge, allows an assessment of the spatial variability in landform-sediment imprints of catastrophic glacier advance across upland bedrock ridges. The ice-margin parallel alignment of the bedrock ridges locally strongly directs proglacial meltwater drainage and initiates strong compression in the ice during surging, resulting in the development of prominent ice-cored hummocky moraine composed of glacifluvial sediment. Diagnostic surge landforms elsewhere on the foreland include thrust block and push moraines, overridden ice-cored thrust block moraines, crevasse squeeze ridges, long flutings, hummocky moraine and ice-cored, pitted outwash.

Icelandic glaciers

Icelandic glaciers

The Little Ice Age glacier maximum in Iceland and the North Atlantic Oscillation: evidence from Lambatungnajökull, southeast Iceland

This article examines the link between late Holocene fluctuations of Lambatungnajokull, an outlet glacier of the Vatnajokull ice cap in Iceland, and variations in climate. Geomorphological evidence is used to reconstruct the pattern of glacier fluctuations, while lichenometry and tephrostratigraphy are used to date glacial landforms deposited over the past /400 years.Moraines dated using two different lichenometric techniques indicate that the most extensive period of glacier expansion occurred shortly before c. AD 1795, probably during the 1780s. Recession over the last 200 years was punctuated by re-advances in the 1810s, 1850s, 1870s, 1890s and c. 1920, 1930 and 1965. Lambatungnajokull receded more rapidly in the 1930s and 1940s than at any other time during the last 200 years. The rate and style of glacier retreat since 1930 compare well with other similar-sized, non-surging, glaciers in southeast Iceland, suggesting that the terminus fluctuations are climatically driven. Furthermore, the pattern of glacier fluctuations over the 20th century broadly reflects the temperature oscillations recorded at nearby meteorological stations. Much of the climatic variation experienced in southern Iceland, and the glacier fluctuations that result, can be explained by secular changes in the North Atlantic Oscillation (NAO). Advances of Lambatungnajokull generally occur during prolonged periods of negative NAO index. The main implication of this work relates to the exact timing of the Little Ice Age in the Northeast Atlantic. Mounting evidence now suggests that the period between AD 1750 and 1800, rather than the late 19th century, represented the culmination of the Little Ice Age in Iceland.

Mass balance of three Svalbard glaciers reconstructed back to 1948

A simple model using upper-air meteorological variables in the NCEP-NCAR Reanalysis database is used to model seasonal components of mass balance of three glaciers in Svalbard. The model was originally developed for glaciers in North America, and has been applied to glaciers in Norway, Sweden and Iceland. Over the period for which mass balance data are available for the three Svalbard glaciers, the model fit yields r2 values ranging from 0.46 to 0.61 for winter balance Bw and from 0.56 to 0.59 for summer balance B­s . Sensitivity to + 1 ° C warming was about -0.36 m yr-1 water equivalent (w.eq.), caused mainly by increased ablation and secondarily by shift of precipitation from snow to rain. Sensitivity to a 10% increase in precipitation was about + 0.06 m yr-1 w.eq. The model, calibrated over the period of observations, was used to extend the mass balance series back to 1948. At annual resolution, observed mass balance of the three glaciers correlates poorly with both the North Atlantic Oscillation (NAO) and with glaciers in Norway. Over two multiyear periods, the strongly positive NAO period 1990–1996 and the period afterward, glaciers in both Svalbard and especially Norway showed a pronounced decline in Bw. However, Bs for Svalbard glaciers was not more strongly negative after 1996, in contrast to glaciers in Norway.

Glacio‐isostatic deformation around the Vatnajökull ice cap, Iceland, induced by recent climate warming: GPS observations and finite element modeling

Glaciers in Iceland began retreating around 1890, and since then the Vatnajökull ice cap has lost over 400 km3 of ice. The associated unloading of the crust induces a glacio‐isostatic response. From 1996 to 2004 a GPS network was measured around the southern edge of Vatnajökull. These measurements, together with more extended time series at several other GPS sites, indicate vertical velocities around the ice cap ranging from 9 to 25 mm/yr, and horizontal velocities in the range 3 to 4 mm/yr. The vertical velocities have been modeled using the finite element method (FEM) in order to constrain the viscosity structure beneath Vatnajökull. We use an axisymmetric Earth model with an elastic plate over a uniform viscoelastic half‐space. The observations are consistent with predictions based on an Earth model made up of an elastic plate with a thickness of 10–20 km and an underlying viscosity in the range 4–10 × 1018 Pa s. Knowledge of the Earth structure allows us to predict uplift around Vatnajökull in the next decades. According to our estimates of the rheological parameters, and assuming that ice thinning will continue at a similar rate during this century (about 4 km3/year), a minimum uplift of 2.5 meters between 2000 to 2100 is expected near the current ice cap edge. If the thinning rates were to double in response to global warming (about 8 km3/year), then the minimum uplift between 2000 to 2100 near the current ice cap edge is expected to be 3.7 meters.

Imprints of sub-glacial volcanic activity on a glacier surface—SAR study of Katla volcano, Iceland

The Katla central volcano, covered by the fourth largest Icelandic glacier Mýrdalsjokull, is among the most dangerous and active volcanoes in Iceland. Due to the ice cover, several indicators of its volcanic activity can only be identified indirectly. We analysed a total of 30 synthetic aperture radar (SAR) images with special focus on identifying circular and linear depressions in the glacier surface. Such features are indicative of sub-glacial geothermal heat sources and the adjacent sub-glacial tunnel (melt water drainage) system. The time series comprises images from five different SAR sensors (ERS-1, ERS-2, JERS-1/SAR, RADARSAT and ENVISAT-ASAR) covering a time period of 12 years, starting in 1994. Individual SAR scenes only partly map the glacier surface morphology due to the environmental influences on the SAR backscatter intensity. Thus, only surface features detectable in several SAR scenes at the same location were considered and merged to form an overall picture of the surface morphology of Mýrdalsjokull and its modification by sub-glacial volcanic activity between 1994 and 2006. Twenty permanent and 4 semi-permanent ice cauldrons could be identified on the surface of Mýrdalsjokull indicating geothermally active areas in the underlying caldera. An analysis of their size was not possible due to the indistinct outline in the SAR images. The spatial distribution of the geothermally active areas led to a new, piecemeal caldera model of Katla volcano. All cauldrons are connected to tunnel systems for melt water drainage. More than 100 km of the sub-glacial drainage system could be identified under the Mýrdalsjokull in the SAR time series. It has been found that the tunnel systems are not in agreement with estimated water divides. Our results allow improved assessment of areas of potential Jokulhlaup hazard accompanying a sub-glacial eruption.