Niels Oskarsson - Academia.edu (original) (raw)

Papers by Niels Oskarsson

Gradual inflation of magma chambers often precedes eruptions at highly active volcanoes. During e... more Gradual inflation of magma chambers often precedes eruptions at highly active volcanoes. During eruptions, rapid deflation occurs as magma flows out and pressure is reduced. Less is known about the deformation style at moderately active volcanoes, such as Eyjafjallajökull, Iceland, where an explosive summit eruption of trachyandesite beginning on 14 April 2010 caused exceptional disruption to air traffic. This eruption

HAL (Le Centre pour la Communication Scientifique Directe), 1991

The explosive eruption of the 1660 m high ice-capped Eyjafjallajökull volcano in April-May 2010 w... more The explosive eruption of the 1660 m high ice-capped Eyjafjallajökull volcano in April-May 2010 was of moderate size but due to high proportions of very fine-grained ash, its 39-day duration, and prevailing southeasterly jetstream, the ash was widely dispersed and caused unprecedented disruption to air traffic over Europe. After a prolonged period of intrusive activity, a small basaltic flank eruption

International Symposium on the Activity of Oceanic Volcanoes. Ponta Delgada, 4-9 August 1980.The ... more International Symposium on the Activity of Oceanic Volcanoes. Ponta Delgada, 4-9 August 1980.The fluorine content of volcanic rocks from different volcano-tectonic environments in Iceland differs systematically in concert with other petrochemical parameters. The lowest abundance of fluorine (45-220 ppm F) is found in the petrochemically primitive ol-tholeiites of the rift zone. Evolved basalts ranging from ol-tholeiite to qz-tholeiite composition occur in the volcanic centers of the rift zone. These rocks contain 220-450 ppm F, while with alkaline affinities found in volcanic centers outside the rift zone contain up to 1600 ppm F. The variation in fluorine within the different rock suites is believed to reflect varying degree of crustal involvement in their genesis. In the rift zone fluorine chemistry of the basalts is believed to result from mixing with silicic magmas formed by anatexis in the rift zone crust. In the non-rifting volcanic centers the high fluorine results from a par...

Surface ocean fertilisation with iron may affect the marine primary productivity, C-cycles and ev... more Surface ocean fertilisation with iron may affect the marine primary productivity, C-cycles and eventually climate development. Volcanic ash has the potential to release iron on contact with seawater and to stimulate phytoplankton growth (1,2) but the relative importance of volcanism at destructive plate margins (subduction zones, SZ) and intraplate volcanic settings (ocean islands at hot spots) remains unknown. Here we present new results from geochemical experiments with natural seawater and numerous volcanic ash samples from SZ volcanoes in the Pacific Ring of Fire (Alaska, Japan, Kamchatka, Northern and Central America and Papua New Guinea) and hot spot volcanoes (on Iceland and Hawaii). The release of iron as a function of time was determined in situ in seawater by means of Cathodic Stripping Voltammetry. Our experiments show that: A) volcanic ash from both SZ and hot spot volcanic areas mobilise significant amounts of iron, B) with the highest mobilisation rates within the firs...

Global Biogeochemical Cycles, 2011

Surface ocean iron (Fe) fertilization can affect the marine primary productivity (MPP), thereby i... more Surface ocean iron (Fe) fertilization can affect the marine primary productivity (MPP), thereby impacting on CO 2 exchanges at the atmosphere-ocean interface and eventually on climate. Mineral (aeolian or desert) dust is known to be a major atmospheric source for the surface ocean biogeochemical iron cycle, but the significance of volcanic ash is poorly constrained. We present the results of geochemical experiments aimed at determining the rapid release of Fe upon contact of pristine volcanic ash with seawater, mimicking their dry deposition into the surface ocean. Our data show that volcanic ash from both subduction zone and hot spot volcanoes (n = 44 samples) rapidly mobilized significant amounts of soluble Fe into seawater (35-340 nmol/g ash), with a suggested global mean of 200 ± 50 nmol Fe/g ash. These values are comparable to the range for desert dust in experiments at seawater pH (10-125 nmol Fe/g dust) presented in the literature (Guieu et al., 1996; Spokes et al., 1996). Combining our new Fe release data with the calculated ash flux from a selected major eruption into the ocean as a case study demonstrates that single volcanic eruptions have the potential to significantly increase the surface ocean Fe concentration within an ash fallout area. We also constrain the long-term (millennial-scale) airborne volcanic ash and mineral dust Fe flux into the Pacific Ocean by merging the Fe release data with geological flux estimates. These show that the input of volcanic ash into the Pacific Ocean (128-221 × 10 15 g/ka) is within the same order of magnitude as the mineral dust input (39-519 × 10 15 g/ka) (Mahowald et al., 2005). From the similarity in both Fe release and particle flux follows that the flux of soluble Fe related to the dry deposition of volcanic ash (3-75 × 10 9 mol/ka) is comparable to that of mineral dust (1-65 × 10 9 mol/ka). Our study therefore suggests that airborne volcanic ash is an important but hitherto underestimated atmospheric source for the Pacific surface ocean biogeochemical iron cycle.

Bulletin of Volcanology, 2007

The 2010 Eyjafjallajökull summit eruption (Iceland) produced large amounts of fine ash, disturbin... more The 2010 Eyjafjallajökull summit eruption (Iceland) produced large amounts of fine ash, disturbing air traffic across the North-Atlantic and within Europe. Mössbauer spectroscopy of ash-samples and a lava-bomb has been performed to study the material properties and to gain insight into why the volcano produced so vast amounts of fine grained material. Time series of ash samples reveal a changing ferric to ferrous ratio and level of crystallization which can be related to the different phases of the eruption. The lava bomb ...

Mineralogical Magazine, 2008

Long-term climate moderation is commonly attributed to chemical weathering; the greater the tempe... more Long-term climate moderation is commonly attributed to chemical weathering; the greater the temperature and precipitation the faster the weathering rate. To test this widely-held hypothesis, we performed a field study and determined the weathering rates of eight nearly pristine north-east Iceland river catchments with varying glacial cover over 44 y. Statistically significant linear positive correlations were found between mean annual temperature and chemical weathering in all eight catchments and between mean annual temperature and mechanical weathering and runoff in seven of the eight catchments. The runoff, mechanical weathering flux, and chemical weathering fluxes in these catchments are found to increase from 6 to 16%, 8 to 30%, and 4 to 14%, respectively, depending on the catchment for each degree of temperature increase. Positive correlations were found between time and mechanical and chemical weathering for all catchments. In summary, these results demonstrate a significant ...

The Cretaceous-Tertiary Event and Other Catastrophes in Earth History, 1996

ABSTRACT Tektite glasses from Beloc, Haiti, formed by impact melting, show bimodal composition of... more ABSTRACT Tektite glasses from Beloc, Haiti, formed by impact melting, show bimodal composition of doininantly silicic melt of crustal origin (black glass) and a minor CaO-rich melt of sedimentary origin (yellow glass). Low-velocity Mossbauer spectra of the black ...

Geografiska Annaler. Series A, Physical Geography, 1971

CONTENTS lntroduction A. Large-scale polygons Earlier work The distribution of polygons in leelan... more CONTENTS lntroduction A. Large-scale polygons Earlier work The distribution of polygons in leeland Investigated polygon localities Airphoto and thermal infrared scanning experiments in detection of and mapping polygonal ground Discussion of polygonal processes Conclusions B. Palsa areas Earlier work, terminology Investigated palsa localities Discussion and conclusions

Geology, 2001

The fertilization potential of newly erupted and well-preserved ash from the 2000 Hekla eruption ... more The fertilization potential of newly erupted and well-preserved ash from the 2000 Hekla eruption in Iceland was measured for the first time by flow-through experiments. As previously shown, (1) the North Atlantic Ocean, including the subarctic seas surrounding Iceland, is the largest net sink of the world's oceans for atmospheric CO 2 , owing to biological drawdown during summer; (2) almost complete consumption of phosphate in chlorophyll-rich areas of the North Atlantic Ocean might limit primary production; and (3) in the southern Pacific Ocean and parts of the equatorial Pacific Ocean iron might limit primary production. We found through laboratory experiments that volcanic ash exposed to seawater initially releases large amounts of adsorbed phosphate, 1.7 mol•g ؊1 •h ؊1 ; iron, 37.0 mol•g ؊1 •h ؊1 ; silica, 49.5 mol•g ؊1 h ؊1 ; and manganese, 1.7 mol•g ؊1 •h ؊1. Dissolution of acid aerosols adsorbed to the surface of the ash caused the high initial release of major and trace elements. Because of the instantaneous dissolution of adsorbed components when newly erupted volcanic ash comes in contact with the ocean surface water, macronutrients and ''bioactive'' trace metals are released fast enough to become available to support primary production.

Journal of Volcanology and Geothermal Research, 2002

Dissolution of igneous feldspar and the formation and occurrence of secondary feldspar in tholeii... more Dissolution of igneous feldspar and the formation and occurrence of secondary feldspar in tholeiitic basalts from the Hengill volcanic centre, in SW Iceland was studied by microprobe analysis of cuttings from two ca. 2000 m deep geothermal wells. Well NG-7 in Nesjavellir represents a geothermal system in a rift zone where the intensity of young, insignificantly altered intrusions increases with depth. Well KhG-1 in Kolviarho ¤ ll represents the margin of a rift zone where the intensity of intrusives is lower and the intensity of alteration higher. This marginal well represents altered basaltic crust in an early retrograde state. The secondary plagioclase in both wells is mainly oligoclase, occurring in association with K-feldspar and chlorite þ actinolite. The texture of this assemblage depends on the lithology and intensity of alteration. In Nesjavellir (NG-7) the composition of secondary albite-oligoclase is correlated with the host-rock composition. This connection is not apparent in more intensely altered samples from Kolviarho ¤ ll (KhG-1). The influence of temperature on composition of secondary Na-feldspar is unclear in both wells although Ca is expected to increase with temperature. Any temperature dependence may be suppressed by the influence of rock composition in Nesjavellir and by retrograde conditions at Kolviarho ¤ ll. The absence of clear compositional gradients between igneous plagioclase and secondary feldspar and between Na-feldspar and K-feldspar suggests that secondary feldspars formed by dissolution precipitation reactions.

Geology, 2017

Primitive basalt melt inclusions from Borgarhraun, northern Iceland, display large correlated var... more Primitive basalt melt inclusions from Borgarhraun, northern Iceland, display large correlated variations in CO 2 and nonvolatile incompatible trace elements (ITEs) such as Nb, Th, Rb, and Ba. The average CO 2 /ITE ratios of the Borgarhraun melt inclusion population are precisely determined (e.g., CO 2 /Nb = 391 ± 16; 2σM [two standard errors of the mean], n = 161). These data, along with published data on five other populations of undegassed mid-oceanic ridge basalt (MORB) glasses and melt inclusions, demonstrate that upper mantle CO 2 /Ba and CO 2 /Rb are nearly homogeneous, while CO 2 /Nb and CO 2 /Th are broadly correlated with long-term indices of mantle heterogeneity reflected in Nd isotopes (143 Nd/ 144 Nd) in five of the six regions of the upper mantle examined thus far. Our results suggest that heterogeneous carbon contents of the upper mantle are longlived features, and that average carbon abundances of the mantle sources of Atlantic MORB are higher by a factor of two than those of Pacific MORB. This observation is correlated with a similar distinction in water contents and trace elements characteristic of subduction fluids (Ba, Rb). We suggest that the upper mantle beneath the younger Atlantic Ocean basin contains components of hydrated and carbonated subduction-modified mantle from prior episodes of Iapetus subduction that were entrained and mixed into the upper mantle during opening of the Atlantic Ocean basin.