Thorvaldur Thordarson

University of Iceland | HI · Faculty of Earth Sciences

The deep roots of volcanic systems play a key role in the priming, initiation, and duration of eruptions. Causative links between initial magmatic unrest at depth and eruption triggering remain poorly constrained. The 2021 CE eruption at Fagradalsfjall in southwestern Iceland, the first deep-sourced eruption on a spreading-ridge system monitored wi...

The Vedde Ash, first described in Norway and dated to ~12000 cal a BP, has been taken to represent tephra derived from a large eruption of the Katla volcano in Iceland and dispersed across the North Atlantic and Europe. However, evidence for tephra layers with similar composition to the Vedde Ash, but of different ages, questions the utility of iso...

The basalts of the 2021 Fagradalsfjall eruption were the first erupted on the Reykjanes Peninsula in 781 years and offer a unique opportunity to determine the composition of the mantle underlying Iceland, in particular its oxygen isotope composition (δ18O values). The basalts show compositional variations in Zr/Y, Nb/Zr and Nb/Y values that span ro...

Pulsating behaviour is observed in volcanic phenomena ranging from caldera collapses to explosions, spattering or lava fountaining. The repeating processes can define irregular, regular or systematically changing patterns. These patterns yield information about the subsurface structure, which often is not considered in detail. We analyse the patter...

Determining the parameters that control fissure-fed lava morphologies is critical for reconstructing the complex emplacement histories of eruptions on Earth and other planetary bodies. We used a geomorphological map of the 2014–2015 Holuhraun lava flow field, in combination with new constraints on lava emplacement chronology and two independently d...

The 2014–2015 Holuhraun eruption extruded >1 km³ of lava in a barren region of the Icelandic highlands. Due to its large volume and the abundance of data for this eruption, Holuhraun is an ideal site to investigate fissure-fed eruption products for comparison with other large lava flows-fields on Earth and other planetary bodies. To characterize la...

Lava that erupted during the 2014–2015 Holuhraun eruption in Iceland flowed into a proglacial river system, resulting in aqueous cooling of the lava and an ephemeral hydrothermal system. We carried out a monitoring study of this system from 2015 to 2018 to document the cooling of the lava over this time, using thermocouple measurements and data-log...

The volcanic sequences in eastern Iceland provide a cross-section of magmatic activity from the Iceland rift system throughout the Miocene. This study focuses on a high precision age determination campaign of a single Miocene volcanic system, the Breiðdalur central volcano and associated dyke swarm, in order to quantify its evolution. The central v...

The 2.1 ka Moinui lava flow field, erupted from the southwest rift zone of Mauna Loa, Hawai`i, exhibits striking textural and geochemical variations, that can be used to interpret magma processes pre-, syn- and post-eruption. From this lava flow, the duration of magma storage and storage conditions, the timescales over which magma is transported to...

Roughness can be used to characterize the morphologies of a lava flow. It can be used to identify lava flow features, provide insight into eruption conditions, and link roughness pattern across a lava flow to emplacement conditions. In this study, we use both the topographic position index (TPI) and the one-dimensional Hurst exponent (H) to derive...

Our understanding of the long-term intrusive and eruptive behaviour of volcanic systems is hampered by a relatively short period of direct observation. To probe the conditions of crustal magma storage below South Iceland, we have analysed compositions of minerals, mineral zoning patterns, and melt inclusions from two Eyjafjallajökull ankaramites lo...

Tephra layers with Icelandic provenance have been identified across the North Atlantic region in terrestrial, lacustrine, marine and glacial environments. These tephra layers are used as marker horizons in tephrochronology including climate studies, archaeology and environmental change. The major element chemistries of 19 proximally deposited Holoc...

To gain insights into crystal–melt separation processes during basalt differentiation, we have studied an 8-m-thick pāhoehoe lava lobe from the Hafnarhraun lava flow field in SW Iceland. The lobe has abundant melt segregations, porous cylindrical and sheet-like structures, generally interpreted as separated residual melts of a lava lobe. We divide...

In the beginning of December 2017, Mt. Agung eruption powered down to minor ash emissions and on the middle of December, aerial photographs of the crater were taken by Indonesia Centre of Volcanology and Geological Hazard Mitigation (PVMBG) showing a steadily growing lava occupying approximately one third of the crater. 3D digital elevation model (...

We present new high-precision major and trace element data on olivine macrocrysts from various volcano-tectonic settings in Iceland and use these data as a proxy for mantle mode and melting conditions. Within individual sampling sites examined (seven lavas and one tephra) olivine-dominated fractional crystallization, magma mixing and diffusive re-e...

This study used optical remote sensors to identify surface hydrothermal alteration and thermal anomalies in Krýsuvík geothermal field. Multispectral Landsat and ASTER satellite images were used to identify hydrothermal alteration minerals and thermal anomalies. A hyperspectral image from Hyperion was used for the analysis of absorption features. Sp...

The cone volcano Anak Krakatau, which is largely built on the steep northeast caldera wall of the 1883 Krakatau eruption, is currently featuring activity on its southwest slope and thus growing into the 1883 caldera and this position makes the edifice unstable. On 22 December 2018, tsunami took place in Sunda strait, the deadliest in this area sinc...

The Holuhraun lava flow was the largest effusive eruption in Iceland for 230 years, with an estimated lava bulk volume of ~1.44 km 3 and covering an area of ~84 km 2. The six month long eruption at Holuhraun 2014-2015 generated a diverse surface environment. Therefore, the abundant data of airborne hyperspectral imagery above the lava field, calls...

The Holuhraun lava flow was the largest effusive eruption in Iceland for 230 years, with an estimated lava bulk volume of ~1.44 km3 and covering an area of ~84 km2. The six month long eruption at Holuhraun 2014–2015 generated a diverse surface environment. Therefore, the abundant data of airborne hyperspectral imagery above the lava field, calls fo...

Strong similarities in Holocene climate reconstructions derived from multiple proxies (BSi, TOC – total organic carbon, δ13C, C∕N, MS – magnetic susceptibility, δ15N) preserved in sediments from both glacial and non-glacial lakes across Iceland indicate a relatively warm early to mid Holocene from 10 to 6 ka, overprinted with cold excursions presum...

Mt. Öræfajökull is one of the most dangerous volcanoes in Iceland with potential for a VEI6 eruption and the generation of many severe associated hazards. It is not a frequently erupting volcano with two eruptions in the last 1100 years, in 1362 and 1727–28. During the 1362 eruption 10 km3 of freshly fallen tephra was emitted, the eruption plume re...

Strong similarities in Holocene climate reconstructions derived from multiple proxies (BSi, TOC, δ¹³C, C/N, MS, δ¹⁵N) preserved in sediments from both glacial and non-glacial lakes across Iceland indicate a relatively warm early-to-mid Holocene from 10 to 6ka, overprinted with cold excursions presumably related to meltwater impact on North Atlantic...

1) Introduction & Objectives Holuhraun lava flow was the largest effusive eruption in Iceland for 230 years, with an estimated lava bulk volume of ~1.44 km3 and covering an area of ~84 km2. The six months (August 2014-February 2015) long eruption at Holuhraun 2014-2015 generated diverse surface environment. Therefore, the abundant information of ai...

The origin of rejuvenated volcanism on mantle plume related oceanic islands remains controversial. One commonly cited model is decompressional melting related to plate flexure from the rapid loading of the lithosphere by the formation of a shield volcano above the plume stem. This model provides testable predictions about the timing and subsidence...

The 2014–2015 Holuhraun fissure eruption provided a rare opportunity to study in detail the magmatic processes and magma plumbing system dynamics during a 6-month-long, moderate- to large-volume basaltic fissure eruption. In this contribution, we present a comprehensive dataset, including major and trace elements of whole-rock and glassy tephra sam...

In the beginning of December 2017, Mt. Agung eruption powered down to minor ash emissions and on the middle of December, aerial photographs of the crater were taken by Indonesia Centre of Volcanology and Geological Hazard Mitigation (PVMBG) showing a steadily growing lava occupying approximately one third of the crater. 3D digital elevation model (...

The 31 August 2014 to 27 February 2015 eruption at Holuhraun created the largest lava flow field in Iceland since the 1783-1784 Laki eruption. Emplacement of a basaltic flow field of this magnitude onto an effectively flat surface (<0.1°) is a rare occurrence. Lava discharge rate, a fundamental variable that controls flow field emplacement, allows...

How a volcano has behaved throughout its past is a guide to its future behaviour. Detailed knowledge of what preceded eruptions from specific volcanoes, and how this can be recognised in real-time, are pivotal questions of this field. Here, the physical history of the magma that erupted in 2010 from the flank of Eyjafjallajökull volcano, Iceland, i...

https://meetingorganizer.copernicus.org/EGU2018/EGU2018-10558.pdf Monitoring the growth of a lava flow field is of interest in densely populated areas where flows threaten roads, houses, other infrastructure and life. Monitoring usually relies on satellite data, ground-based GPS data and modelling of lava flows although they are also accompanied b...

The size distribution of the population of particles injected into the atmosphere during a volcanic explosive eruption, i.e., the total grain-size distribution (TGSD), can provide important insights into fragmentation efficiency and is a fundamental source parameter for models of tephra dispersal and sedimentation. Recent volcanic crisis (e.g. Eyja...

This study used optical remote sensors to identify surface hydrothermal alteration and thermal anomalies in the Sveifluháls-Krýsuvík high-temperature geothermal field. The study area is located in a volcanic fissure swarm in the central part of Reykjanes peninsula, in southwest Iceland. The area is characterized by intensive surface alteration, ste...

This study used optical remote sensors to identify surface hydrothermal alteration and thermal anomalies in the Sveifluháls-Krýsuvík high-temperature geothermal field. The study area is located in a volcanic fissure swarm in the central part of Reykjanes peninsula, in southwest Iceland. The area is characterized by intensive surface alteration, ste...

Hurst coefficient (H) for deriving the radiant flux (Φrad) and the crust thickness (∆h). Here, we compare the results derived from satellite images with field measurements. The result from 2 December 2014 shows that a temperature estimate (1096 ◦C; occupying area of 3.05m2) from a lava breakout has a close correspondence with a thermal camera measu...

Volcanic eruptions were included on the UK National Risk Register for the first time in 2012 in reaction to the 2010 eruption of Eyjafjallajökull. Whilst both explosive and effusive eruption scenarios are included, a relatively short duration is ascribed to the former and the latter focuses entirely upon the risks arising from associated volcanic g...

The impact of Holocene eruptive events from hot spots like Iceland may have had significant global implications; thus, dating and knowledge of past eruptions chronology is important. However, at high-latitude volcanic islands, the paucity of soils severely limits 14C dating, while the poor K content of basalts strongly restricts the use of K/Ar and...

An effusive eruption in 2014/15 created a 85 km2 large lava flow field in a remote location in the Icelandic highlands. The lava flows did not threaten any settlements or paved roads but they were nevertheless interdisciplinarily monitored in detail. Images from satellites and aircraft, ground based video monitoring, GPS and seismic recordings allo...

This corrects the article DOI: 10.1038/nature22974.

Abstract In the 60th anniversary of the corner stone placing under the Polish Polar Station at Hornsund (PPSH; Spitsbergen, Svalbard, Norway), a new capsule has been laid down in the vicinity of PPSH. It was made of stainless steel, and included five stainless steel containers, each carrying a message on different themes of our life. The message is...

The separation of volcanic ash and sulfur dioxide (SO2) gas is sometimes observed during volcanic eruptions. The exact conditions under which separation occurs are not fully understood but the phenomenon is of importance because of the effects volcanic emissions have on aviation, on the environment, and on the earth's radiation balance. The eruptio...

Background The eruptions of Eyjafjallajökull (2010) and Grímsvötn (2011), Iceland, triggered immediate, international consideration of the respiratory health hazard of inhaling volcanic ash, and prompted the need to estimate the potential hazard posed by future eruptions of Iceland’s volcanoes to Icelandic and Northern European populations. Method...

We studied the seismic signals that accompanied the 6 month-long, effusive eruption at Holuhraun in 2014/15 in Iceland. The eruption started along a nearly 2 km long fissure, soon focused on fewer vents and had after 20 days focused on one single vent that fed a lava flow field growing to a final size of 85 km2. We analysed the accompanying, long-...

When teaching at a non-English language university, we often argue that because English is the international language, students need to become familiar with English terms, even if the bulk of the class is in the native language. However, to make the meaning of the terms clear, a translation into the native language is always useful. Correct transla...

Aerosols have a potentially large effect on climate, particularly through their interactions with clouds, but the magnitude of this effect is highly uncertain. Large volcanic eruptions produce sulfur dioxide, which in turn produces aerosols; these eruptions thus represent a natural experiment through which to quantify aerosol-cloud interactions. He...

In the period from August 29, 2014, to February 27, 2015, the largest basaltic eruption of the last 200 years in Iceland occurred within the tectonic fissure swarm between the Bárðarbunga-Veiðivötn and the Askja volcanic systems. The eruption took place in the Holuhraun lava field, 45 km northeast of the Bárðarbunga volcano and 20 km south of the A...

Melt inclusions formed during the early stages of magmatic evolution trap primitive melt compositions and enable the volatile contents of primary melts and the mantle to be estimated. However, the syn- and post-entrapment behaviour of volatiles in primitive high-anorthite plagioclase-hosted melt inclusions from oceanic basalts remains poorly constr...

http://meetingorganizer.copernicus.org/EGU2017/EGU2017-16028.pdf Monitoring the change in eruptive style during an eruption, forecasting the height of a plume or distribution of ash or forecasting which areas a lava flow will inundate are important challenges during an eruption. These forecasts are often based on parameters such as effusion rate –...