NW Iceland Research Articles

A global database of historic glacier lake outburst floods

Abstract. Ongoing atmospheric warming has accelerated glacier mass loss in many mountain regions worldwide. Glacier lakes trap part of the glacial meltwater and have increased by about 50 % in number and area since the 1990s. Some of these glacier lakes may empty catastrophically and pose hazards to mountain communities, infrastructure, and habitats. Such glacier lake outburst floods (GLOFs) have caused millions of dollars of damages and fatalities and are one of many concerns about future changes in the magnitude, frequency, and impacts of processes of a shrinking mountain cryosphere. Consistently compiled inventories are thus vital to assess regional and local trends in GLOF occurrence, hazard, and risk. To this end, we studied 769 literature and internet sources and developed a standardized database with 57 attributes that describe and quantify the location, dam type, size, timing, and impacts of GLOFs in nine glaciated mountain regions. Our GLOF inventory also includes details about the lake area before and after the outburst for 391 cases that we manually mapped from optical satellite images since 1984. In total, we compiled 3151 reported GLOFs that occurred in 27 countries between 850 and 2022 CE. Most GLOFs have been reported in NW North America (26 %) and Iceland (19 %). However, the reporting density in our inventory varies. During the 20th century alone, the number of yearly documented GLOFs increased 6-fold. Less than one-quarter of all reported cases feature hydrodynamic characteristics such as flood peak discharge or volume or estimates of loss and damage. Our inventory more than doubles the number of reported GLOFs in a previous global inventory, though gaps in attributes remain. Our data collection process emphasizes the support of local experts in contributing previously undocumented cases, and we recommend applying protocols when reporting new cases. The global database on historic GLOFs is archived at https://doi.org/10.5281/zenodo.7330344 (Lützow and Veh, 2023a) and regularly updated at http://glofs.geoecology.uni-potsdam.de/ (last access: 9 May 2023).

Visitors’ values and perceptions of seal watching management in Northwestern Iceland

Disturbance due to tourism may impact the critically endangered population of harbor seals (Phoca vitulina) in Iceland. Improved seal watching management is a promising strategy for seal conservation in Iceland. Previous research indicates that value orientation of tourists can predict acceptance of wildlife management and awareness of potential impacts of tourism on seals. The goal of this study was to (a) define biospheric and egoistic value orientation of seal watching visitors, (b) investigate how these values correlate with the opinion of visitors towards different management actions and awareness of potential impact of tourism on seals, and (c) investigate which management actions would be acceptable for visitors. Visitor questionnaires were distributed in NW Iceland (n = 597). Results show that seal watching visitors in general had high biospheric values, low egoistic values, and were open to most management actions suggested in the study. High biospheric values were correlated with acceptance of management actions and awareness of the usefulness of regulations. High egoistic values were correlated with low acceptance of management actions and low awareness of the impacts of seal watching. Results will inform managers on how to optimize management strategies at seal watching sites in Iceland and elsewhere.

Trophic dynamics of anadromous brown trout and Arctic charr in NW Iceland and their correlation to salmon lice infection

Anadromous Arctic charr Salvelinus alpinus and sea trout Salmo trutta are commonly found in marine, estuarine and freshwater habitats across the Northern Hemisphere. The marine phase varies between populations but often involves summer foraging in nearshore waters while spawning and overwintering occur in freshwater. The dependence of anadromous salmonids on nearshore habitats makes them vulnerable to increased industrial activity, such as aquaculture developments, that may increase the risk of salmon lice Lepeophtheirus salmonis, infection. Lice infection in wild salmonids depends on farmed fish density but can also be correlated to environmental factors, including foraging ecology. In the current paper we examine niche use and trophic variation of co-occurring Arctic charr and sea trout in northwest Iceland, using stomach contents and stable isotope values of δ13C, δ15N and δ34S. We then test if these factors correlated to salmon lice infection. The salmonid species differed in niche use, for example, in time of marine foraging, with Arctic charr having a longer marine phase than was expected, and in the level of piscivory between both species. Moreover, we show that both environmental factors and individual trophic use are related to salmon lice infection in sea trout. This information may be useful in evaluating the risk and spatial management of sea farming.

Holocene tephrostratigraphy in Vestfirðir, NW Iceland

ABSTRACTWe present a tephra stratigraphical and tephrochronological record from eight lakes in Vestfirðir, NW Iceland. About 50 tephra units have been identified, representing nearly 30 eruptive events originating from five volcanic systems: Hekla, Katla, Snæfellsjökull, Grímsvötn and Veiðivötn‐Bárðarbunga. Most of the tephra layers originate from Grímsvötn, although there is a prominent presence of andesitic to basaltic tephra layers from Hekla in the record. We propose that the previously described Brattihjalli tephra is actually the 6060‐year‐old Hekla Ö tephra marker layer, recording a more north‐westerly dispersal than before and providing new correlation possibilities across Iceland. Thus, the Hekla Ö tephra covers as large an area in Iceland as the Hekla 5, Hekla 4, Hekla 3 and Hekla 1104 tephra layers, emphasizing its importance as a chronological marker. The tephra markers Hekla 1693, V877/Settlement layer, Sn‐1, Hekla 3 and Hekla 4 have been found and, additionally, our study identifies four potential tephra markers, the Katla D1 ∼2750 cal a BP, Katla D2 ∼3700 cal a BP, Reykjarfjörður tephra ∼8800 cal a BP and Dagverðardalur tephra ∼9300–9500 cal a BP. Our data reveal several new tephra layers in Vestfirðir, including chronological markers important for dating and correlation.

Punctuated Holocene climate of Vestfirðir, Iceland, linked to internal/external variables and oceanographic conditions

Emerging Holocene paleoclimate datasets point to a non-linear response of Icelandic climate against a background of steady orbital cooling. The Vestfirðir peninsula (NW Iceland) is an ideal target for continued climate reconstructions due to the presence of a small ice cap (Drangajökull) and numerous lakes, which provide two independent means to evaluate existing Icelandic climate records and to constrain the forcing mechanisms behind centennial-scale cold anomalies. Here, we present new evidence for Holocene expansions of Drangajökull based on 14C dates from entombed dead vegetation as well as two continuous Holocene lake sediment records. Lake sediments were analyzed for both bulk physical (MS) and biological (%TOC, δ13C, C/N, and BSi) parameters. Composite BSi and C/N records from the two lakes yield a sub-centennial qualitative perspective on algal (diatom) productivity and terrestrial landscape stability, respectively. The Vestfirðir lake proxies suggest initiation of the Holocene Thermal Maximum by ∼8.8 ka with subsequent and pronounced cooling not apparent until ∼3 ka. Synchronous periods of reduced algal productivity and accelerated landscape instability point to cold anomalies centered at ∼8.2, 6.6, 4.2, 3.3, 2.3, 1.8, 1, and 0.25 ka. Triggers for cold anomalies are linked to variable combinations of freshwater pulses, low total solar irradiance, explosive and effusive volcanism, and internal modes of climate variability, with cooling likely sustained by ocean/sea-ice feedbacks. The climate evolution reflected by our glacial and organic proxy records corresponds closely to marine records from the North Iceland Shelf.

Winter mass balance of Drangajökull ice cap (NW Iceland) derived from satellite sub-meter stereo images

Abstract. Sub-meter resolution, stereoscopic satellite images allow for the generation of accurate and high-resolution digital elevation models (DEMs) over glaciers and ice caps. Here, repeated stereo images of Drangajökull ice cap (NW Iceland) from Pléiades and WorldView2 (WV2) are combined with in situ estimates of snow density and densification of firn and fresh snow to provide the first estimates of the glacier-wide geodetic winter mass balance obtained from satellite imagery. Statistics in snow- and ice-free areas reveal similar vertical relative accuracy (< 0.5 m) with and without ground control points (GCPs), demonstrating the capability for measuring seasonal snow accumulation. The calculated winter (14 October 2014 to 22 May 2015) mass balance of Drangajökull was 3.33 ± 0.23 m w.e. (meter water equivalent), with ∼ 60 % of the accumulation occurring by February, which is in good agreement with nearby ground observations. On average, the repeated DEMs yield 22 % less elevation change than the length of eight winter snow cores due to (1) the time difference between in situ and satellite observations, (2) firn densification and (3) elevation changes due to ice dynamics. The contributions of these three factors were of similar magnitude. This study demonstrates that seasonal geodetic mass balance can, in many areas, be estimated from sub-meter resolution satellite stereo images.

Episodic expansion of Drangajökull, Vestfirðir, Iceland, over the last 3 ka culminating in its maximum dimension during the Little Ice Age

Abstract Non-linear climate change is often linked to rapid changes in ocean circulation, especially around the North Atlantic. As the Polar Front fluctuated its latitudinal position during the Holocene, Iceland's climate was influenced by both the warm Atlantic currents and cool, sea ice-bearing Arctic currents. Drangajokull is Iceland's fifth largest ice cap. Climate proxies in lake sediment cores, dead vegetation emerging from beneath the ice cap, and moraine segments identified in a new DEM constrain the episodic expansion of the ice cap over the past 3 ka. Collectively, our data show that Drangajokull was advancing at ∼320 BCE, 180 CE, 560 CE, 950 CE and 1400 CE and in a state of recession at ∼450 CE, 1250 CE and after 1850 CE. The Late Holocene maximum extent of Drangajokull occurred during the Little Ice Age (LIA), occupying 262 km2, almost twice its area in 2011 CE and ∼20% larger than recent estimates of its LIA dimensions. Biological proxies from the sediment fill in a high- and low-elevation lake suggest limited vegetation and soil cover at high elevations proximal to the ice cap, whereas thick soil cover persisted until ∼750 CE at lower elevations near the coast. As Drangajokull expanded into the catchment of the high-elevation lake beginning at ∼950 CE, aquatic productivity diminished, following a trend of regional cooling supported by proxy records elsewhere in Iceland. Correlations between episodes of Drangajokull's advance and the documented occurrence of drift ice on the North Icelandic Shelf suggest export and local production of sea ice influenced the evolution of NW Iceland's Late Holocene climate.

The Drangajökull ice cap, northwest Iceland, persisted into the early-mid Holocene

Abstract Most glaciers and ice caps in Iceland experienced rapid deglaciation in the early Holocene, reaching a minimum extent during the Holocene Thermal Maximum. Here we present evidence of the Holocene glacial history from lake sediment cores retrieved from seven threshold lakes around the Drangajokull ice cap in the Vestfirðir peninsula, NW Iceland. The sediment cores show on/off signals of glacial meltwater activity, as minerogenic material deposited from glacial meltwater alternates with organic-rich material (gyttja) deposited without glacial meltwater. We base the chronology of the sediment cores on 14C ages and geochemical identification of key tephra layers with known ages. A 25-cm thick layer of the Saksunarvatn tephra in Lake Skorarvatn indicates that the northern part of the ice cap had reached a similar size as today or was smaller already by 10.2 cal kyr BP. However, 14C ages of lake sediment cores from the highlands southeast of Drangajokull suggest that this part of the ice cap was larger than today until 7.8–7.2 cal kyr BP. Even today, the Drangajokull ice cap has a different behavior than the main ice caps in Iceland, characterized by a very low glaciation limit. Because palaeoclimatic proxies show an early-mid Holocene temperature optimum in this part of Iceland, we suggest that the persistence of Drangajokull into the early Holocene and, possibly, also the entire Holocene was due to high winter precipitation.

Seasonal, meteorological, tidal and diurnal effects on haul-out patterns of harbour seals (Phoca vitulina) in Iceland

It is of critical importance to identify factors that affect harbour seal haul-out patterns to improve the accuracy of harbour seal censuses. In this study, haul-out patterns of harbour seals (Phoca vitulina) were investigated during different conditions at several major haul-out sites on Vatnsnes peninsula, NW Iceland (65°40′N and 20°48′W), over the 2008–2011 period. A seasonal haul-out pattern was detected among the seals, with the maximum number of seals on land found in July for most of the sites. Analyses of data for harbour seals on Vatnsnes indicate that the main pupping period occurs during late May to the beginning of June and moulting during late July to early August. Abundance at the sites increased with rising air temperature and decreased with increased windspeed and rising tides. However, no evidence that precipitation or cloud cover affected haul-out behaviour of the seals was detected. The diel haul-out pattern was investigated thoroughly in one of the haul-out sites and the results underlined the effect of tidal flucturation, air temperature and wind direction on the haul-out behaviour of harbour seals in the area. Results from this study can be used to improve the survey design when estimating the population size of harbour seals in Iceland and applied more broadly to the study of haul-out behaviour of harbour seals.

Geodetic mass balance record with rigorous uncertainty estimates deduced from aerial photographs and lidar data – Case study from Drangajökull ice cap, NW Iceland

Abstract. In this paper we describe how recent high-resolution digital elevation models (DEMs) can be used to extract glacier surface DEMs from old aerial photographs and to evaluate the uncertainty of the mass balance record derived from the DEMs. We present a case study for Drangajökull ice cap, NW Iceland. This ice cap covered an area of 144 km2 when it was surveyed with airborne lidar in 2011. Aerial photographs spanning all or most of the ice cap are available from survey flights in 1946, 1960, 1975, 1985, 1994 and 2005. All ground control points used to constrain the orientation of the aerial photographs were obtained from the high-resolution lidar DEM. The lidar DEM was also used to estimate errors of the extracted photogrammetric DEMs in ice- and snow-free areas, at nunataks and outside the glacier margin. The derived errors of each DEM were used to constrain a spherical semivariogram model, which along with the derived errors in ice- and snow-free areas were used as inputs into 1000 sequential Gaussian simulations (SGSims). The simulations were used to estimate the possible bias in the entire glaciated part of the DEM and the 95 % confidence level of this bias. This results in bias correction varying in magnitude between 0.03 m (in 1975) and 1.66 m (in 1946) and uncertainty values between ±0.21 m (in 2005) and ±1.58 m (in 1946). Error estimation methods based on more simple proxies would typically yield 2–4 times larger error estimates. The aerial photographs used were acquired between late June and early October. An additional seasonal bias correction was therefore estimated using a degree-day model to obtain the volume change between the start of 2 glaciological years (1 October). This correction was largest for the 1960 DEM, corresponding to an average elevation change of −3.5 m or approx. three-quarters of the volume change between the 1960 and the 1975 DEMs. The total uncertainty of the derived mass balance record is dominated by uncertainty in the volume changes caused by uncertainties of the SGSim bias correction, the seasonal bias correction and the interpolation of glacier surface where data are lacking. The record shows a glacier-wide mass balance rate of Ḃ = −0.26 ± 0.04 m w.e. a−1 for the entire study period (1946–2011). We observe significant decadal variability including periods of mass gain, peaking in 1985–1994 with Ḃ = 0.27 ± 0.11 m w.e. a−1. There is a striking difference when Ḃ is calculated separately for the western and eastern halves of Drangajökull, with a reduction of eastern part on average ∼ 3 times faster than the western part. Our study emphasizes the need for applying rigorous geostatistical methods for obtaining uncertainty estimates of geodetic mass balance, the importance of seasonal corrections of DEMs from glaciers with high mass turnover and the risk of extrapolating mass balance record from one glacier to another even over short distances.

Climatic variability during the last millennium in Western Iceland from lake sediment records

The aim of this research was to create a decadal-scale terrestrial quantitative palaeoclimate record for NW Iceland from lake sediments for the last millennium. Geochemical, stable isotope and chironomid reconstructions were obtained from a lake sequence constrained by tephra deposits on the Snæfellsnes peninsula, western Iceland. Obtaining a quantitative record proved problematic, but the qualitative chironomid record showed clear trends associated with past summer temperatures, and the sedimentological records provided evidence for past changes in precipitation, mediated through catchment soil in-wash. When the full range of chronological uncertainty is considered, four clear phases of climatic conditions were identified: (1) a relatively warm phase between AD 1020 and 1310; (2) a relatively stable period between AD 1310 and 1510, cooler than the preceding period but still notably warmer than the second half of the millennium; (3) a consistent reduction of temperatures between AD 1560 and 1810, with the coolest period between AD 1680 and 1810; and (4) AD 1840–2000 has temperatures mainly warmer than in the preceding two centuries, with a rising trend and increased variability from c. AD 1900 onwards. The reconstructions show clearly that the first half of the millennium experienced warmer climatic conditions than the second half, with a return to the warmer climate only occurring in the last c. 100 years. Much of the variability of the chironomid record can be linked to changes in the North Atlantic Oscillation (NAO). The reconstructions presented can track low-frequency and long-term trends effectively and consistently but high-resolution and calibrated quantitative records remain more of a challenge – not just in finding optimal sedimentary deposits but also in finding the most reliable proxy. It is this that presents the real challenge for Holocene climate reconstruction from this key area of the North Atlantic.

Petrogeothermal energy resources within low-temperature areas of Iceland

Iceland remains one of the leading countries in the field of the utilization of geothermal energy worldwide. Despite its knowledge and tremendous experience in the exploitation of mostly high-temperature geothermal energy resources (water and steam), it has been interested in the possibility of harnessing heat from hot rock formations with the implementation of the Enhanced Geothermal System (EGS). This paper presents the main outcomes of the feasibility study of EGS technology within the low-temperature area of the country. It includes broad geological research that constitutes the background for finding a suitable site for an EGS installation and to determine the local thermal parameters together with rock characteristics. To calculate the amount of heat stored within the preordained HDR formation and ascertain that the deployment of the EGS within the lowtemperature area of Holmavik town (NW Iceland) is plausible, the term of static resources of energy was applied. Considering the geological issue, it emerged that within the low-temperature areas of Iceland, there are excellent lithological (mainly porous lava layers) as well as thermal conditions (relatively high heat flow and geothermal gradient values) for the implementation of EGS technology for providing heat for small district heating networks. The amount of energy stored within the designed rock formation turned out to be significant and more than sufficient to cover the energy demands of Holmavik town. The authors also emphasize the importance of running several exchange programs between Polish and Icelandic research and academic centers, with the indication of possible benefits for the Polish geothermal energy sector.

Marine climate variability from Arnarfjörður, NW Iceland, during the Medieval Warm period and early/middle Little Ice Age

A high-resolution sedimentary record from the subarctic fjord Arnarfjörður in northwestern Iceland provides information on local changes in sea ice cover and a regional oceanographic climatic signal reflecting changes in the position of the Polar Front that separates the North Atlantic Current and the East Greenland Current. The 520 cm long sediment core spans approximately 2000 years and thus offers a multi-decadal time resolution during the Medieval Warm Period (MWP) and the early to middle part of the Little Ice Age (LIA). Approximately 150 years from the top of the core were lost during coring. The marine climate reconstruction is based on multi-proxy study with focus on benthic foraminiferal fauna allowing down-core bottom water temperature (BWT_{TF}) estimations based on the statistical transfer function approach. This first of the kind study from Arnarfjörður demonstrates significant variability in the benthic foraminiferal fauna dominated by Cibicides lobatulus, Cassidulina reniforme and Elphidium excavatum, BWT_{TF} variations of ∼3°C, fluctuating from ca. 1.5±1.1 °C to 4.5±0.6 °C. The data is in harmony with previously reported LIA characteristics from the region, which has been described as a period of high amplitude fluctuations, with non-stable conditions and cold bottom waters.

Pristine Arctic: Background mapping of PAHs, PAH metabolites and inorganic trace elements in the North-Atlantic Arctic and sub-Arctic coastal environment

As the ice cap of the Arctic diminishes due to global warming, the polar sailing route will be open larger parts of the year. These changes are likely to increase the pollution load on the pristine Arctic due to large vessel traffic from specific contaminant groups, such as polycyclic aromatic hydrocarbons (PAHs). A well-documented baseline for PAH concentrations in the biota in the remote regions of the Nordic Seas and the sub-Arctic is currently limited, but will be vital in order to assess future changes in PAH contamination in the region. Blue mussels (Mytilus edulis) were collected from remote sites in Greenland, Iceland, the Faroe Islands, Norway and Sweden as well as from urban sites in the same countries for comparison. Cod (Gadus morhua) was caught north of Iceland and along the Norwegian coast. Sixteen priority PAH congeners and the inorganic trace elements arsenic, cadmium, mercury and lead were analysed in the blue mussel samples as well as PAH metabolites in cod bile. Σ16PAHs ranged from 28ng/g dry weight (d.w.) (Álftafjörður, NW Iceland) to 480ng/g d.w. (Ísafjörður, NW Iceland). Mussel samples from Mjóifjörður, East Iceland and Maarmorilik, West Greenland, contained elevated levels of Σ16PAHs, 370 and 280ng/g d.w., respectively. Levels of inorganic trace elements varied with highest levels of arsenic in mussels from Ísafjörður, Iceland (79ng/g d.w.), cadmium in mussels from Mjóifjörður, Iceland (4.3ng/g d.w.), mercury in mussels from Sørenfjorden, Norway (0.23ng/g d.w.) and lead in mussels from Maarmorilik, Greenland (21ng/g d.w.). 1-OH-pyrene was only found above limits of quantification (0.5ng/mL) in samples from the Norwegian coast, ranging between 44 and 140ng/ml bile. Generally, PAH levels were low in mussels from the remote sites investigated in the study, which indicates limited current effect on the environment.

The effect of land based seal watching tourism on the haul-out behaviour of harbour seals (Phoca vitulina) in Iceland

The effect of land-based seal watching on the haul-out pattern of harbour seals (Phoca vitulina) was investigated between June and August of 2008–2010 on Vatnsnes, NW Iceland. The results showed that the behaviour and spatial haul-out pattern of seals was affected by the tourists. In 2009 the seals were more likely to be vigilant during periods when tourists had access to the area, compared to a period when tourists were not allowed in the area. Also, in 2010 the likeliness of the seals being vigilant increased as the number of tourists in the area increased. In addition, seals were more likely to be vigilant when tourists behaved in an active way. During the post weaning period, which coincided with the peak of the tourist season, a significantly higher proportion of seals hauled out on the skerry located farthest away from land, compared to a skerry closer to land. Seals also preferred to haul out further away from land when the number of tourists in the area increased. Single tourists and couples behaved more passively compared to families and tourist groups of more than two adults. All tourist group types were significantly more active in an approaching zone than in the seal watching zone. Education of tourists, for example through a code of conduct built on these results, is advisable to minimise disturbance of seals in the area.

Impact of Medieval Fjord Hydrography and Climate on the Western and Eastern Settlements in Norse Greenland

Abstract A comparison of the Medieval fjord hydrography and climate regime of the main Norse settlements in Greenland demonstrates important differences in the timing of sea-ice expansion and storminess when comparing the Western and Eastern Settlement regions. The Western Settlement, as well as the northern hunting grounds around Disko Bugt, had already experienced major climate deterioration in the first decades after AD 1200. This regime shift in West Greenland included an expansion of fjord and sea ice (“West Ice”) in coastal waters as well as a drastic atmospheric cooling and an increase in storminess, mainly in the summer season. In contrast, environmental conditions in the Eastern Settlement deteriorated notably later, i.e., around AD 1400. At that time, ice conditions became much more severe, whereas the previously prevailing strong wind activity decreased, which was coeval with a general decrease in aeolian activity in West Greenland, eastern Canada, and NW Iceland. Summer blockage of the fjord e...

GIS analysis of cirques on Vestfirðir, northwest Iceland: implications for palaeoclimate

This study presents the first regional analysis of cirques on Vestfirðir, NW Iceland, using a Geographical Information System (GIS). The length, width, elevation of cirque‐floor, latitude and the distance to the modern coastline (both ocean and fjord coastlines) of cirques were quantified using ArcGIS. The topographical analysis revealed a total of 100 cirques on western and northern Vestfirðir. Several additional cirques are present, but they had poorly defined toewalls, making the cirque‐floor difficult to identify. Mean cirque length is 515 m and mean cirque width is 752 m. The modal orientation of the aspect of cirques is northeast, with a strong secondary mode to the northwest. Cirques at low elevations are more abundant close to the ocean, whereas cirques further from the ocean are present at high elevations. Three techniques were used to reconstruct past equilibrium‐line altitudes (ELAs) of cirque glaciers: the cirque‐floor method, the altitude‐ratio method and the accumulation‐area ratio method. The largest range of past ELAs is generated from the cirque‐floor method with values from 40 up to 730 m. Mean past ELA values range from ∼395 to 423 m depending on the method used to reconstruct former ELAs. A strong positive relationship is observed between past ELA values and distance to the ocean demonstrating the importance of access to a moisture source for glacier survival. This relationship is stronger than the relationship between former ELAs and latitude. Based on the small size of cirque glaciers, it is likely that even minor fluctuations in the Irminger Current and the East Greenland Current influence cirque glaciation on Vestfirðir.

Geomorphology and the Little Ice Age extent of the Drangajökull ice cap, NW Iceland, with focus on its three surge-type outlets

Detailed geomorphological maps from the forefields of three surging outlets of the Drangajökull ice cap, northwest Iceland, are presented. The maps are based on field studies in 2011–2013, high resolution orthorectified aerial photographs recorded in 2005–2006, and airborne LiDAR data from 2011. The maps cover an area of about 40–60km2 each. Furthermore, we present an overview map that covers the area surrounding the Drangajökull ice cap. Landforms and sediments were manually registered in a geographic information system (ESRI ArcGIS 10). We mapped glacial landforms such as flutes, ice-sculpted bedrock, hummocky moraine, kame terraces, and moraines. Fluvial landforms include outwash plains/sandur, pitted sandur, and eskers. In addition raised beaches were mapped. The Little Ice Age (LIA) maximum extent of Drangajökull and its outlet glaciers are fingerprinted by surficial till deposits and freshly glacially scoured bedrock. Sediments distal to the LIA deposits were recorded and consist mainly of late Weichselian and early Holocene sediments and locally weathered bedrock. Periglacial activity is demonstrated by patterned ground, mainly occurring on the 500–700m high plateaux, and three rock glaciers. At least 3–4 surge events are described from each of the outlet glaciers, occurring over the last three centuries. In contrast to most other surge-type outlets from Icelandic ice caps, the Drangajökull outlets are confined within valleys, which affect the forefield geomorphology. Glaciofluvial landforms, moraines, and a thin sheet of till with numerous boulders are characteristic for the forefields of the Drangajökull outlets.

Structure of regional dykes and local cone sheets in the Midhyrna-Lysuskard area, Snaefellsnes Peninsula (NW Iceland)

This paper provides the first detailed structural description of 48 vertical dykes, 384 inclined sheets and two large intrusions and the geometry (strike, dip direction and dip) of 1116 fractures in the central area of the Snaefellsnes peninsula, NW Iceland. Our data show a more complex setting than that depicted by the WNW-ESE en-echelon trend of the volcanic structures at the surface. In the Miocene basement lavas, dykes dominantly strike N50–100°E whereas other directions are also present with a higher dispersion. Two main swarms of centrally dipping sheets have also been recognized, focussing towards two areas. Sheet dips range from 2 to 75° with the higher frequency between 10 and 45°. In section view, there is no systematic variation of sheet dip with distance from the focus area. Gabbro and granophyre laccoliths are present in the studied area but cross-cutting relations indicate that most of the inclined sheets are younger. Comparison with regional tectonics suggests that the N50–80°E-striking dykes are coherent with emplacement under the stress field of the pre-6 Ma Snaefellsnes Rift dominated by a NNW-SSE-directed least principal stress (σ3). The N80–100°E dykes and the late Quaternary WNW-trending sub-aerial volcanic features are instead consistent with the development of a more recent E-W, right-lateral shear zone affecting the Snaefellsnes peninsula. Coherent sets of fractures have also been found. Within the inclined sheet swarms, the stress tensor rotated in response to an excess magma pressure linked to two underlying magma chambers of lobate shape, located at an estimated depth of about 400 and 500 m below sea level. This local magmatic stress also produced the centrally inclined fracture swarms that have been found in this area.

Holocene denudation rates from the superhumid southernmost Chilean Patagonian Andes (53°S) deduced from lake sediment budgets

Holocene denudation rates and their regional variations in the superhumid and temperate climate of the southernmost Patagonian Andes are poorly surveyed. Therefore we have investigated denudation in five small lake catchments (0.11–1.62km2) across a precipitation gradient from 600 to >9000mmyr−1 in southernmost Chile at 53°S. Variations in denudation rates can be defined most precisely by using small catchments and short time spans (Holocene) thus can be related to variable bedrock types, vegetation cover, elevation, and climate. Minimum physical denudation rates were determined from sediment budgets based on sediment echosounder data and physical properties of sediment cores. The Holocene denudation rates vary from 0.08mmkyr−1 in the highly elevated, bare granitic rock catchments to 9.01mmkyr−1 in the low and vegetated catchments with a basement of sedimentary rocks. These values are comparable with those from similar areas in Norway, Sweden, and NW Iceland. The high annual precipitation in the study area has only a minor effect on denudation. Enhanced geomorphic activity during paraglacial conditions caused a faster denudation after the glacier retreat until either the clastic, glacial detritus was removed or the catchment was covered with vegetation. Chemical comparisons between basement rocks and lake sediments indicate a pronounced chemical denudation in catchments with peaty soils and low soil water pH values of 3 to 5. The Holocene surface lowering rates are on average 200 fold lower than Cenozoic surface lowering rates calculated from fission-track data for the southern Andes. This discrepancy can be explained by significantly higher erosion rates during glacial periods.