Uncapping subglacial eruption dynamics and glacier response

Informations projet

SURGE

N° de convention de subvention: 895263

DOI

10.3030/895263

Projet clôturé

Date de signature de la CE 13 Mars 2020

Date de début 1 Juillet 2021

Date de fin 30 Juin 2023

Financé au titre de

• EXCELLENT SCIENCE - Marie Skłodowska-Curie Actions

Coût total

€ 184 239,36

Contribution de l’UE

€ 184 239,36

Coordonné par

HASKOLI ISLANDS
Iceland

Periodic Reporting for period 1 - SURGE (Uncapping subglacial eruption dynamics and glacier response)

Période du rapport: 2021-07-01 au 2023-06-30

Résumé du contexte et des objectifs généraux du projet

The overall aim of SURGE was to investigate the dynamics of volcanic eruptions that occur beneath glaciers. We aimed to determine the physical eruption processes that have occurred at Katla volcano, south Iceland, in times of greater glacial extent and to use the volcanic products to reconstruct the past glacial environment at the time of eruption. The Katla central volcano is a 30 km-wide mountain with an ice cap (Mýrdalsjökull) covering most of it. In the last 12,000 years, Katla has erupted frequently through the ice cap, leading to explosive eruptions that have scattered ash across Iceland and the North Atlantic. Despite this, the geology of this large mountain, and the volcanic and glacial processes that have built it, have not been well studied. In addition, while it is known that Iceland has been intermittently covered with ice and that the extent of the ice sheet has varied, there is little empirical evidence for ice thickness and extent at different times around Katla.
The objectives of the SURGE project were to: 1) determine the eruption processes that contributed to mountain-building at three areas around Katla; 2) reconstruct the glacier thickness and extent in these areas; 3) determine the age of lavas in the three areas.
It has been shown that an increase in volcanism in Iceland accompanied the end of the last glaciation. As the ice sheet retreated, pressure was released from the volcanoes leading to more eruptions. How an individual volcano that exhibits a variety of eruption styles, such as Katla, might behave physically under different ice thicknesses is becoming increasingly important to understand as glaciers around the world retreat. In addition, a better understanding of the range of past eruptions at different glacial thicknesses will inform our understanding of the likely hazards during future eruptions at Katla and other similar volcanoes.
This project has contributed three new age-constrained estimates for the minimum thickness of the glacier and it is clear that at the times of eruption, Mýrdalsjökull was thicker and would have been more extensive than the present day. We have found that basaltic lavas erupted underwater on the western flank of Katla (Morinsheiði) at 800 m above sea level 10-20 thousand years ago. This area was covered by the Icelandic Ice Sheet at this time, which allowed a meltwater lake to form and remain stable during the eruption. This shows that the ice surface must have been at least 800 m above current sea level. It is likely Mýrdalsjökull converged with Eyjafjallajökull and an ancient glacier in the Markarfljót valley to the north and that this situation persisted after the last glacial maximum. We have also found that rhyolitic explosive and lava-producing eruptions occurred ~12 thousand years ago, depositing tephra and lava on the northwest and east side of Katla (Enta and Klakkfjöll). These deposits do not show any evidence for a meltwater lake forming in the glacier, but do indicate the eruptions occurred through the glacier with enhanced cooling by the ice and/or water. This suggests that meltwater drained freely from the eruption site. At this time, the glacier was at least 150-250 m thicker than present day.

Travail effectué depuis le début du projet jusqu’à la fin de la période considérée dans le rapport et principaux résultats atteints jusqu’à présent

The three field sites were mapped at 1:5000 scale by a combination of traditional geological mapping and by airborne photogrammetry surveys. The volcanic products were characterised by their physical features, which are indicative of their eruptive processes and environment. Additional petrographic and geochemical analyses of sampled products were carried out to differentiate between mapped units. From these data, eruption and emplacement models were determined for the volcanic products at each field site. Based on the physical evidence, minimum constraints on glacier thickness at the time of eruption were determined. Finally, samples of lava from each field site were taken for age dating by the 40Ar/39Ar geochronological method.

At Morinsheiði, a series of effusive basaltic eruptions occurred in different environments. Initially, glacial meltwater was ponded in the area between Eyjafjallajökull and Mýrdalsjökull at the time of formation, 10-20 thousand years ago. The eruptive products were sourced from the south east of the formation before entering ponded water at least 800 m above sea level. This provides a minimum estimate for ice surface elevation above Morinsheiði at the time of eruption. Emergence of the formation above the water level then gave rise to the emplacement of subaerial lava. Samples from Morinsheiði all have similar chemistry compared with samples from neighbouring formations showing a compositional range from basaltic to basaltic-trachyandesite.
At Enta and Klakkfjöll, explosive and effusive silicic eruptions occurred. Physical evidence for enhanced cooling and confinement, but a lack of evidence for meltwater accumulation, indicates eruptions alongside a glacier and conditions favouring meltwater drainage. The glacier at the time of eruptions was ~150 m thicker than present at Klakkfjöll or 800 m above sea level, and ~200 m thicker than present at Enta or ~1200 m above sea level. The lava ages from these two field sites are both ~12,000 years old.

The results of this project have been presented at 3 international conferences, as a seminar at the University of Iceland, as part of Katla Geopark’s Geodiversity Day, and at the 2022 Researcher’s Night in Reykjavík, Iceland. Three scientific publications are planned and are in preparation. These articles will be made openly accessible.

Progrès au-delà de l’état des connaissances et impact potentiel prévu (y compris l’impact socio-économique et les conséquences sociétales plus larges du projet jusqu’à présent)

Our new geological maps are much more detailed than those previously available, allowing individual volcanic units to be differentiated. The eruption and emplacement models therefore provide a more detailed understanding of pre-Holocene eruptions and mountain-building processes at Katla. In addition, our new geochemical analyses from Morinsheiði lavas and surrounding formations are some of the first geochemical data from pre-Holocene eruptions at Katla. Such models and data contribute to our understanding of long-term volcanic processes, including the range of hazards that may arise at Katla. The results of this project also inform on the past environment at Katla and how volcanic eruptions behave in different glacial environments. We show new empirical, age-constrained evidence for minimum glacier thickness at three locations across the volcano.
The similarity between the geochemical analyses and lava ages from Enta and Klakkfjöll indicate lava and tephra-producing eruptions occurring across multiple parts of the Katla caldera ~12,000 years ago, during the transition from glacial conditions to interglacial conditions. The consistency in chemistry and age of these products with a well-known major tephrochronological marker bed that is found across the North Atlantic support the hypothesis of a major silicic eruption occurring at Katla at the end of the last glacial period. The identification of proximal products of such an eruption offers an exciting chance to understand the processes occurring close to the vent and in association with the glacier.
The results obtained in this project have provided a basis for continued research that will start immediately on the styles volcanic eruptions at Katla and how they are influenced by changing environments.

Location map and photographs of glaciovolcanic formations at Katla volcano, south Iceland.