Helgi Björnsson

Incidence, Presentation, and Outcomes in Patients With Drug-Induced Liver Injury in the General Population of Iceland

BACKGROUND & AIMS Little is known about the incidence of drug-induced liver injury (DILI) in the general population. We investigated the incidence and the quantitative risk of DILI in a population-based cohort. METHODS We performed a prospective study and collected data from 96 individuals diagnosed with DILI in Iceland from 2010 through 2011 (54 women; median age, 55 y). Liver injury was defined based on levels of alanine aminotransferase that were more than 3-fold the upper limit of normal and/or alkaline phosphatase levels more than 2-fold the upper limit of normal. Patients with acetaminophen toxicity were excluded. Drug history and clinical outcome were analyzed. Causality was assessed using the Roussel Uclaf Causality Assessment Method. The patients were registered in prescription databases for outpatients and inpatients. RESULTS The crude annual incidence rate of DILI was 19.1 (95% confidence interval [CI], 15.4-23.3) cases per 100,000 inhabitants. DILI was caused by a single prescription medication in 75% of cases, by dietary supplements in 16% of cases, and by multiple agents in 9% of cases. The most commonly implicated drugs were amoxicillin-clavulanate (21 of 96; 22%), diclofenac (6%), azathioprine (4%), infliximab (4%), and nitrofurantoin (4%). The median duration of therapy was 20 days (range, 8-77 days); 26 patients had jaundice (27%) and 22 patients were hospitalized (23%) for a median of 5 days (range, 2-8 days). Overall 35,252 patients received amoxicillin-clavulanate as outpatients, and DILI occurred in 1 of 2350 (43 of 100,000; 95% CI, 24-70). DILI also occurred in 1 of 9480 patients taking diclofenac (11 of 100,000; 95% CI, 4-24), 1 of 133 patients taking azathioprine (752 of 100,000; 95% CI, 205-1914), 1 of 148 patients taking infliximab (675 of 100,000; 95% CI, 184-718), and 1 of 1369 patients taking nitrofurantoin (73 of 100,000; 95% CI, 20-187). CONCLUSIONS In a population-based study in Iceland, the incidence of DILI was the highest reported to date. Amoxicillin-clavulanate was the most commonly implicated agent. The highest risk of hepatotoxicity was associated with azathioprine and infliximab, but the actual number of cases attributed to these agents was small.

Subglacial lakes and jökulhlaups in Iceland

Active volcanoes and hydrothermal systems underlie ice caps in Iceland. Glacier-volcano interactions produce meltwater that either drains toward the glacier margin or accumulates in subglacial lakes. Accumulated meltwater drains periodically in jokulhlaups from the subglacial lakes and occasionally during volcanic eruptions. The release of meltwater from glacial lakes can take place in two different mechanisms. Drainage can begin at pressures lower than the ice overburden in conduits that expand slowly due to melting of the ice walls by frictional and sensible heat in the water. Alternatively, the lake level rises until the ice dam is lifted and water pressure in excess of the ice overburden opens the waterways; the glacier is lifted along the flowpath to make space for the water. In this case, discharge rises faster than can be accommodated by melting of the conduits. Normally jokulhlaups do not lead to glacier surges but eruptions in ice-capped stratovolcanoes have caused rapid and extensive glacier sliding. Jokulhlaups from subglacial lakes may transport on the order of 10 7 tons of sediment per event but during violent volcanic eruptions, the sediment load has been 10 8 tons.

Ice–volcano interaction of the 1996 Gjálp subglacial eruption, Vatnajökull, Iceland

Volcanic eruptions under glaciers can cause dangerous floods and lahars and create hyaloclastite (fragmented glassy rock) mountains. But processes such as the rate of heat transfer between ice and magma, edifice formation, and the response of the surrounding glacier are poorly understood, because of the lack of data. Here we present observations from the fissure eruption at Vatnajökull ice cap, Iceland, in October 1996. In the 13 days of the eruption 3 km3 of ice were melted and the erupted magma fragmented into glass forming a hyaloclastite ridge 6–7 km long and 200–300 m high under 500–750 m of ice. Meltwater of temperatures of 15–20 °C flowed along a narrow channel at the glacier bed into the Grímsvötn subglacial lake for five weeks, before draining in a sudden flood, or jökulhlaup. Subsidence and crevassing of the ice cap occurred over the eruptive fissure and the meltwater path, whereas elsewhere the glacier surface remained intact, suggesting that subglacial eruptions do not trigger widespread basal sliding in warm-based glaciers.

The thermal regime of sub-polar glaciers mapped by multi-frequency radio-echo sounding

Radio-echo soundings provide an effective tool for mapping the thermal regimes of polythermal glaciers on a regional scale. Radar signals of 320-370 MHz penetrate ice at sub-freezing temperatures but are reflected from the top of layers of ice which are at the melting point and contain water. Radar signals of 5-20 MHz, on the other hand, see through both the cold and the temperate ice down to the glacier bed. Radio-echo soundings at these frequencies have been used to investigate the thermal regimes of four polythermal glaciers in Svalbard: Kongsvegen, Uversbreen. Midre Lovenbreen and Austre Broggerbreen. In the ablation area of Kongsvegen, a cold surface layer (50-160m) thick was underlain by a warm basal layer which is advected from the temperate accumulation area. The surface ablation of this cold layer may be compensated by freezing at its lower cold-temperate interface. This requires that the free water content in the ice at the freezing interface is about 1% of the volume. The cold surface layer is thicker beneath medial moraines and where cold-based hanging glaciers enter the main ice stream. On Uversbreen the thermal regime was similar to that of Kongsvegen. A temperate hole was found in the otherwise cold surface layer of the ablation area in a surface depression between Kongsvegen and Uversbreen where meltwater accumulates during the summer (near the subglacial lake Setevatnet, 250 m a.s.l.). Lovenbreen was frozen to the bed at the snout and along all the mountain slopes but beneath the central part of the glacier a warm basal layer (up to 50m) thick was fed by temperate ice from two cirques. On Austre Broggerbreen. a temperate basal layer was not detected by radio-echo soundings but the basal ice was observed to be at the melting point in two boreholes.

Hydrological characteristics of the drainage system beneath a surging glacier

A rare combination of natural circumstances permits assessment of current theories on water flow beneath glaciers. Outburst floods from the subglacial lake Grímsvötn in Iceland took place before, during and after surging of Skei∂arárjökull, the glacier beneath which the outburst floods drain. The observable drainage patterns associated with these floods show the different nature of the basal water conduit system of the glacier during surge and non-surge phases. During surge conditions, basal water is dispersed slowly across the bed in a distributed drainage system; but when the glacier is not surging, water is transported rapidly through a system of tunnels.

Surges of glaciers in Iceland

Abstract Surges are common in all the major ice caps in Iceland, and historical reports of surge occurrence go back several centuries. Data collection and regular observation over the last several decades have permitted a detailed description of several surges, from which it is possible to generalize on the nature of surging in Icelandic glaciers. Combining the historical records of glacier-front variations and recent field research, we summarize the geographic distribution of surging glaciers, their subglacial topography and geology, the frequency and duration of surges, changes in glacier surface geometry during the surge cycle, and measured velocity changes compared to calculated balance velocities. We note the indicators of surge onset and describe changes in ice, water and sediment fluxes during a surge. Surges accomplish a significant fraction of the total mass transport through the main outlet glaciers of ice caps in Iceland and have important implications for their hydrology. Our analysis of the data suggests that surge-type glaciers in Iceland are characterized by gently sloping surfaces and that they move too slowly to remain in balance given their accumulation rate. Surge frequency is neither regular nor clearly related to glacier size or mass balance. Steeply sloping glaciers, whether hard- or soft-bedded, seem to move sufficiently rapidly to keep in balance with the annual accumulation.

Eight centuries of periodic volcanism at the center of the Iceland hotspot revealed by glacier tephrostratigraphy

A record of volcanic activity within the Vatnajokull ice cap has been obtained by combining data from three sources: tephrostratigraphic studies of two outlet glaciers, a 415-m-long ice core from northwestern Vatnajokull, and written records. The record extends back to a.d. 1200 and shows that the volcanic activity has a 130–140 yr period. Intervals of frequent eruptions with recurrence times of three to seven years alternate with intervals of similar duration having much lower eruption frequency. In comparison with other parts of the plate boundary in Iceland, eruption frequency is greater, episodes of unrest are longer, and intervals of low activity are shorter. The high eruption frequency may be the result of a more sustained supply of magma, owing to the areas location above the center of the Iceland mantle plume. When combined with historical data on eruptions and earthquakes, our data indicate that rifting-related activity in Iceland as a whole is periodic and broadly in phase with the volcanic activity within Vatnajokull.

Estimating the Spatial Distribution of Precipitation in Iceland Using a Linear Model of Orographic Precipitation

A linear model of orographic precipitation that includes airflow dynamics, condensed water advection, and downslope evaporation is adapted for Iceland. The model is driven using coarse-resolution 40-yr reanalysis data from the European Centre for Medium-Range Weather Forecasts (ERA-40) over the period 1958–2002. The simulated precipitation is in good agreement with precipitation observations accumulated over various time scales, both in terms of magnitude and distribution. The results suggest that the model captures the main physical processes governing orographic generation of precipitation in the mountains of Iceland. The approach presented in this paper offers a credible method to obtain a detailed estimate of the distribution of precipitation in mountainous terrain for various conditions involving orographic generation of precipitation. It appears to be of great practical value to the hydrologists, glaciologists, meteorologists, and climatologists.

Glacio-meteorological investigations on Vatnajökull, Iceland, summer 1996: an overview

We give an overview of a glacio-meteorological experiment carried out in the summer (melt season) of 1996 on the largest European ice cap, Vatnajökull, Iceland (area 8000 km2; altitude range: from sea level to about 2000 m). The main goal was to understand how the energy used in the melting of snow and ice is delivered to the surface. Many meteorological stations were operated simultaneously on the ice cap, at almost all of which profile measurements were made. Cable balloons and radiosondes were used to probe the vertical structure of the boundary layer. It appears that the flow near the surface is katabatic most of the time, with the height of the wind maximum varying between a few metres and a few tens of metres. It is only during the passage of intense storms that the katabatic wind in the melt zone disappears. Global radiation increases significantly with altitude. Surface albedo varies enormously in space and time, with very low values (≈ 0.1) being found at many places because of the melt out of volcanic ash layers. If we consider the total melt in the period 22 May–31 August 1996, we conclude that radiation typically provides two-thirds of the melt energy, and turbulent exchange of heat one-third. At locations high on the glacier, turbulent exchange becomes less significant.

Glaciohydraulic supercooling in Iceland

We present evidence of glaciohydraulic supercooling under jokulhlaup and ablation- dominated conditions from two temperate Icelandic glaciers. Observations show that freezing of sediment-laden meltwater leads to intraglacial debris entrainment during normal and extreme hydrologic regimes. Intraglacial frazil ice propagation under normal ablation-dominated conditions can trap copious volumes of sediment, which forms anomalously thick sections of debris-rich ice. Glaciohydraulic supercooling plays an important role in intraglacial debris entrainment and should be given more attention in models of basal ice development. Extreme jokulhlaup conditions can result in significant intraglacial sediment accretion by supercooling, which may explain the concentration of englacial sediments deposited in Heinrich layers in the North Atlantic during the last glaciation.