Jökulhlaups in Iceland : sources, release and drainage

Jökulhlaups in Iceland may originate from marginal or subglacial sources of water melted by atmospheric processes, permanent geothermal heat or volcanic eruptions. Glacier-volcano interactions produce meltwater that either drains toward the glacier margin or accumulates in subglacial lakes. Accumulated meltwater drains periodically in jökulhlaups from the subglacial lakes and occasionally during volcanic eruptions. During the 20th century 15 subglacial volcanic eruptions (10 major and 5 minor events) took place, about one-third of all eruptions in Iceland during that century. The release of meltwater from glacial lakes can take place as a result of two different conduit initiation mechanisms and the subsequent drainage from the lake occurs by two different modes. Drainage can begin at pressures lower than the ice overburden in conduits that expand slowly over days or weeks due to melting of the ice walls by frictional and sensible heat in the water. Alternatively, the lake level may rise until the glacier is lifted along the flowpath to make space for the water and water discharges rise linearly, peaking in a time interval of several hours to 1-2 days. In this case, discharge rises faster than can be accommodated by melting of the conduits. The rapidly-rising floods are often associated with large discharges and floods following rapid filling of subglacial lakes during subglacial eruptions or dumping of one marginal lake into another. Jökulhlaups during eruptions in steep ice and snow-covered stratovolcanoes are swift and dangerous and may become lahars and debris-laden floods. Normally jökulhlaups do not lead to glacier surges but eruptions in ice-capped stratovolcanoes have caused rapid and extensive glacier sliding. Jökulhlaups have significant landscaping potential: they erode large canyons and transport and deposit enormous quantities of sediment and icebergs over vast outwash plains and sandur deltas. Jökulhlaups from subglacial lakes may transport on the order of 107 tons of sediment per event but during violent volcanic eruptions the sediment load has been 108 tons. Pleistocene glacial river canyons may have been formed in such catastrophic floods from subglacial lakes. Jökulhlaups have threatened human populations, farms and hydroelectric power plants on glacier-fed rivers. They have damaged cultivated and vegetation areas, disrupted roads on the outwash plains and have even generated flood waves in coastal waters. Iceland is a unique and valuable study-site for glaciovolcanic interactions. This applies to the heat exchange between magma and the glacier, the dynamical response of the glacier to subglacial eruptions, the structure and growth sequence of hyaloclastite ridges and tuyas formed by subglacial eruptions, and jökulhlaups due to volcanic eruptions. The jökuhlaups can be seen as modern analogues of past megafloods on the Earth and their exploration may improve understanding of ice-volcano processes on other planets

Hydrographic measurements in Jökulsárlón lagoon, Iceland

Jökulsárlón lagoon is an enclosed lake bordering the retreating Breidamerkurjökull glacier which flows down from the Vatnajökull ice cap. As the glacier calves most of the ice it releases decays within the lake and the addition of the stored fresh water modifies the water local properties. The lake itself is connected to the North Atlantic Ocean through a narrow channel only ~80 m wide, and all tidal and residual flows in and out of the lake are through this channel. In April 2012 (early spring) we conducted four hydrographic sections from a small boat to determine the early season hydrographic structure of the lake. We conducted two hydrographic sections from the entrance of the channel to sea across the lagoon to the Breidamerkurjökull glacier, one across the centre of the lagoon, and one along, and close to the glacier face. Four months of time series hydrographic data from the channel show that the oceanic tidal pulse into the lagoon is short in duration. The water that enters the lagoon is warm and saline enough to descend rapidly to the greatest depths within the lagoon. With our CTD measurements we have mapped the properties of water across the lake. These reveal the pathway of the Atlantic derived water towards the ice face. The warmest water measured within the lagoon was just below the surface and only adjacent to the glacier face. Whilst this warm water was created from solar input, its location and concentration reveal the complex density driven circulation patterns close to the ice face. Calculated oceanic driven melt rates from the ice face show enhanced oceanographic melting in this near surface layer which contributes to the more substantial deeper melting

Mortality associated with drug-induced liver injury (DILI)

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Radio-echo soundings on Icelandic temperate glaciers: history of techniques and findings

Publisher's version (útgefin grein)Since the mid-1970s radio-echo soundings have been conducted on Iceland's temperate glaciers. Since then, low-frequency radar technology has furthered the study of most of the island's ice caps. Their masses and volumes have been quantified and detailed subglacial topographic maps produced which demarcate glacial drainage basins and identify subglacial lakes and volcanoes. Even internal tephra layers have been charted. The resulting data have been used to force and validate models of past and future glacier evolution. Many practical applications in glacier hydrology have come into being, including hydropower management, road and bridge planning and the prediction of catastrophic flood paths from subglacial eruption sites. Finally, emerging landscapes can now be foreseen in places where glaciers may soon disappear. These achievements would not have been possible without the advances in RES technology.The work was supported by The National Power Company of Iceland, The Road and Coastal Administration of Iceland, The Parliament Financial Committee and the Research Fund of Eggert V. Briem. Special thanks to our colleague Eyjólfur Magnússon who processed the digital RES and for fruitful discussion on the paper content. We are grateful to Philip Vogler for improving the English text of the manuscript.Peer Reviewe

Multiple melt plumes observed at the Breiðamerkurjökull ice face in the upper waters of Jökulsárlón lagoon, Iceland

Breiðamerkurjökull flows from the Vatnajökull ice cap and calves into the Jökulsárlón proglacial lagoon. The lagoon is connected to the North Atlantic Ocean through a 6 m deep narrow channel. Four hydrographic surveys in spring 2012, and a 2011 four-month long temperature and salinity time series of lagoon inflow show that the lake has significantly changed since 1976. Warm saline ocean water enters each tidal cycle and descends below the maximum sampled depths. The lagoon has a surface layer of ice melt, freshwater and Atlantic derived water. Beneath 10 m depth an advective diffusive balance is responsible for determining the temperature and salinity of the lagoon waters down to ~90 m. To maintain the observed hydrographic structure, we calculate an upwelling of deep water of ~0.2 m per day. A survey within 30 m of Breiðamerkurjökull showed that the warmest and most saline waters sampled within the lagoon below 10 m depth were adjacent to the glacier face, along with multiple interleaved warm and cold layers. A heat and salt balance model shows that submarine melting along the ice face generates multiple meltwater plumes that are mixed and diluted within 200 m of the ice face

Plastic bed beneath Hofsjökull Ice Cap, central Iceland, and the sensitivity of ice flow to surface meltwater flux

The mechanical properties of glacier beds play a fundamental role in regulating the sensitivity of glaciers to environmental forcing across a wide range of timescales. Glaciers are commonly underlain by deformable till whose mechanical properties and influence on ice flow are not well understood but are critical for reliable projections of future glacier states. Using synoptic-scale observations of glacier motion in different seasons to constrain numerical ice flow models, we study the mechanics of the bed beneath Hofsjökull, a land-terminating ice cap in central Iceland. Our results indicate that the bed deforms plastically and weakens following incipient summertime surface melt. Combining the inferred basal shear traction fields with a Coulomb-plastic bed model, we estimate the spatially distributed effective basal water pressure and show that changes in basal water pressure and glacier accelerations are non-local and non-linear. These results motivate an idealized physical model relating mean basal water pressure and basal slip rate wherein the sensitivity of glacier flow to changes in basal water pressure is inversely related to the ice surface slope.This research was conducted at the California Institute of Technology and the University of Iceland with funding provided by the NASA Crysopherice Sciences Program (Award NNX14AH80G). B. M. was partially funded by a NASA Earth and Space Sciences Fellowship and an Achievement Rewards for College Students (ARCS) fellowship. InSAR data are freely available from the Alaska Satellite Facility via the UAVSAR website (http://uavsar.jpl.nasa.gov).Peer Reviewe

Gatekeeping and referrals from GPs to cardiologists: patients' opinions and registration of information flow

Neðst á síðunni er hægt að nálgast greinina í heild sinni með því að smella á hlekkinn Skoða/Opna(view/open)INTRODUCTION: Formal referrals to medical specialists have not been required in Iceland since 1984. In 2006, however, referrals were required for patients to receive reimbursement for cardiologists fees. We studied patients' experiences and opinions on the referral process and explored the potential for quality improvement related to the increase in written communication between referring GPs and cardiologists. MATERIAL AND METHODS: Based on the electronic medical record system, referrals from GPs at Efstaleiti Health Care Center in Reykjavík to cardiologists between 1 June 2006 and 1 April 2007 were analyzed. A total of 344 patients were referred in this period. 245 agreed to participate in a questionnaire study about their opinions on the referral system and 209 (85%) completed the questionnaire. Relevant data on previous contacts with the health care center and received consultants reports from the years 2005-7 were extracted from the record system. RESULTS: Participating patients had a mean age of 72 years, male/female ratio 1:1. Ninety percent (95% C.I. 86-94) regarded the new referral system as more expensive and troublesome, but 89% (95% C.I. 85-94) wanted their cardiologist to send a formal report to the referring GP. The number of reports from cardiologists to the health centre's GPs increased from 43 in 2005 to 326 in 2007. CONCLUSION: Implementation of a referral system led to some dissatisfaction among the patients. On the other hand, it led to a major increase in the information exchange between GPs and cardiologists, in clear accordance with patients' wishes. It would be of interest to study the impact of the increased information flow influenced on the health care delivered.Inngangur: Árið 2006 varð greiðsluþátttaka sjúkratrygginga háð tilvísun heimilislækna til hjartalækna. Tilgangur þessarar rannsóknar var að kanna viðhorf sjúklinga til þessa tilvísanakerfis og hvort breytingin hafi leitt til aukinna samskipta í formi tilvísana og læknabréfa. Efniviður og aðferðir: Árið 2007 var gerð rannsókn á tilvísunum frá heimilislæknum Heilsugæslunnar Efstaleiti, Reykjavík, til sérfræðinga í hjartasjúkdómum. Skoðað var samskiptaform alls 344 einstaklinga sem fengu tilvísun til hjartalækna á tímabilinu 1. júní 2006 til 1. apríl 2007. Þar af samþykktu 245 að taka þátt í viðhorfskönnun um aðdraganda tilvísunar, viðhorf til þessa fyrirkomulags, kostnaðar og fyrirhafnar. Svör bárust frá 209 (85%). Úr sjúkraskrá stöðvarinnar voru jafnframt fengnar upplýsingar um fjölda samskipta hjartasjúklinga við heilsugæslustöðina og fjöldi læknabréfa á tímabilinu 2005 til 2007. Niðurstöður: Meðalaldur sjúklinga var 72 ár og kynjahlutfall jafnt. Níutíu prósent (95% öryggisbil 85,7-93,9) töldu að tilvísanir leiddu til meiri fyrirhafnar og eða auka kostnað. Áttatíu og níu prósent (95% öryggisbil 85,1- 93,5) töldu að hjartalæknir ætti að senda heimilislækni læknabréf. Heildarfjöldi læknabréfa frá hjartalæknum á stofu til heimilislæknanna jókst úr 43 árið 2005 í 326 yfir allt árið 2007. Ályktanir: Niðurstöður benda til þess að tilkoma tilvísanakerfis hafi vakið óánægju meðal sjúklinga. Tilvísanakerfi leiðir hins vegar til faglegs ávinnings með gagnkvæmri miðlun þekkingar fagaðila um sjúklinga sína sem er í samræmi við óskir þeirra sjálfra og líklegt til að auka gæði þjónustunnar

Elevation change, mass balance, dynamics and surging of Langjökull, Iceland from 1997 to 2007

ABSTRACTGlaciers and ice caps around the world are changing quickly, with surge-type behaviour superimposed upon climatic forcing. Here, we study Iceland's second largest ice cap, Langjökull, which has both surge- and non-surge-type outlets. By differencing elevation change with surface mass balance, we estimate the contribution of ice dynamics to elevation change. We use DEMs, in situ stake measurements, regional reanalyses and a mass-balance model to calculate the vertical ice velocity. Thus, we not only compare the geodetic, modelled and glaciological mass balances, but also map spatial variations in glacier dynamics. Maps of emergence and submergence velocity successfully highlight the 1998 surge and subsequent quiescence of one of Langjökull's outlets by visualizing both source and sink areas. In addition to observing the extent of traditional surge behaviour (i.e. mass transfer from the accumulation area to the ablation area followed by recharge of the source area), we see peripheral areas where the surge impinged upon an adjacent ridge and subsequently retreated. While mass balances are largely in good agreement, discrepancies between modelled and geodetic mass balance may be explained by inaccurate estimates of precipitation, saturated adiabatic lapse rate or degree-day factors. Nevertheless, the study was ultimately able to investigate dynamic surge behaviour in the absence of in situ measurements during the surge.In situ mass balance survey is a joint effort of the Glaciology Group, Institute of Earth Sciences, University of Iceland and the National Power Company (Landsvirkjun). We thank Philippe Crochet and Tómas Jóhannesson from the Icelandic Meteorological Office for providing the gridded climate data and for useful discussions about the climatology of Langjökull. The 2007 lidar data were collected by the UK Natural Environment Research Council Airborne Research and Survey Facility (Grant IPY 07-08). Additional funding was provided by the United States National Science Foundation (Grant No. DGE-1038596), St Catharine’s, St John’s and Trinity Colleges and the University of Cambridge B.B. Roberts and Scandinavian Studies Funds. We thank Cameron Rye for initial help coding the mass balance model.This is the author accepted manuscript. The final version is available from Cambridge University Press via https://doi.org/10.1017/jog.2016.5

Elevation Change, Mass Balance, Dynamics, and Surging of Langjökull, Iceland from 1997 to 2007

Glaciers and ice caps around the world are changing quickly, with surge-type behaviour superimposed upon climatic forcing. Here, we study Iceland’s second largest ice cap, Langjökull, which has both surge- and non-surge-type outlets. By differencing elevation change with surface mass balance, we estimate the contribution of ice dynamics to elevation change. We use DEMs, in situ stake measurements, regional reanalyses, and a mass balance model to calculate the vertical ice velocity. Thus, we not only compare the geodetic, modelled, and glaciological mass balances, but also map spatial variations in glacier dynamics. Maps of emergence and submergence velocity successfully highlight the 1998 surge and subsequent quiescence of one of Langjökull’s outlets by visualizing both source and sink areas. In addition to observing the extent of traditional surge behaviour (i.e., mass transfer from the accumulation area to the ablation area followed by recharge of the source area), we see peripheral areas where the surge impinged upon an adjacent ridge and subsequently retreated. While mass balances are largely in good agreement, discrepancies between modelled and geodetic mass balance may be explained by inaccurate estimates of precipitation, saturated adiabatic lapse rate, or degree day factors. Nevertheless, the study was ultimately able to investigate dynamic surge behaviour in the absence of in situ measurements during the surge.In situ mass balance survey is a joint effort of the Glaciology Group, Institute of Earth Sciences, University of Iceland and the National Power Company (Landsvirkjun). We thank Philippe Crochet and Tómas Jóhannesson from the Icelandic Meteorological Office for providing the gridded climate data and for useful discussions about the climatology of Langjökull. The 2007 lidar data were collected by the UK Natural Environment Research Council Airborne Research and Survey Facility (Grant IPY 07-08). Additional funding was provided by the United States National Science Foundation (Grant No. DGE-1038596), St Catharine’s, St John’s and Trinity Colleges and the University of Cambridge B.B. Roberts and Scandinavian Studies Funds. We thank Cameron Rye for initial help coding the mass balance model.This is the author accepted manuscript. The final version is available from Cambridge University Press via https://doi.org/10.1017/jog.2016.5