Subglacial Volcanic Activity Research Articles

Recurrent outburst floods and explosive volcanism during the Younger Dryas–Early Holocene deglaciation in south Iceland: evidence from a lacustrine record

ABSTRACTLake sediment records give valuable insight into the dynamic events that characterized the last deglaciation in Iceland. Here, we focus on the well‐dated sediment record from Hestvatn, a low‐elevation lake in south Iceland, that features six graded bedding events deposited by outburst floods from glacial lakes dammed by the decaying Iceland Ice Sheet (IIS) in the time period of the Vedde Ash and the G10ka Series tephra. Using climate proxies preserved in the sediment cores, in conjunction with regional glacial geomorphology, we reconstruct the retreat of the IIS in south Iceland, from a marine‐based glacier during the Younger Dryas to a land‐based glacier during the Preboreal. As the ice sheet margin withdrew to the central highlands, ice‐dammed lakes formed along glacier margins. The ice‐dams were occasionally breached, generating large‐scale jökulhlaups (catastrophic outburst floods) that deposited thick turbidite sequences preserved in the sediment record of Hestvatn. The high concentration of volcanic material incorporated within deglacial sediments indicates that along with IIS retreat, subglacial volcanic activity may have helped initiate some of the jökulhlaups. Onset of more stable Holocene conditions was reached after the final turbidite at ~10 ka bp, when the IIS had withdrawn from most of the highlands of Iceland.

Icecap and Subglacial Crustal Deformation Inferred From SAR Pixel Tracking: The 2014 Dike Intrusion Episode in the Bárðarbunga Volcanic System, Iceland

AbstractBárðarbunga is an active volcano beneath the Vatnajökull icecap in Iceland, where a subglacial dike intrusion occurred in 2014. This area has been studied with interferometric synthetic aperture radar, an important geodetic method that measures crustal deformation; however, ice/snow cover on volcanoes impedes the mapping of crustal deformation because of decorrelation problems. Previous geodetic observations have reported deformation signals at ice‐free regions of a major dike formed in 2014 in the Bárðarbunga volcanic system, but direct observations of the subglacial crustal deformation associated with the dike intrusion have been limited. We applied a pixel tracking approach to various satellite synthetic aperture radar (SAR) data over the northern part of the Vatnajokull icecap and the Holuhraun plain. The pixel tracking data revealed not only crustal deformation fields in the ice‐free region of the magma intrusion, which covers only about 20% of the entire length of dike, but also icecap surface movements over the subglacial part of the dike in the ablation area of the Vatnajökull icecap. Signals above the icecap, suggesting subsidence due to subglacial graben formation, are consistent with the dike propagation path inferred from seismicity during the episode. By subtracting the scaled pre‐diking signals from the co‐diking signals, we corrected for the steady‐state icecap flow signals to derive the subglacial crustal deformations. We showed that the inferred subglacial crustal deformation signals can significantly contribute to the improvement of dike opening/faulting distributions. Applying the pixel tracking to satellite images will enable mapping subglacial crustal deformation in the case of subglacial volcanic activity.

A new volcanic province: an inventory of subglacial volcanoes in West Antarctica

Abstract The West Antarctic Ice Sheet overlies the West Antarctic Rift System about which, due to the comprehensive ice cover, we have only limited and sporadic knowledge of volcanic activity and its extent. Improving our understanding of subglacial volcanic activity across the province is important both for helping to constrain how volcanism and rifting may have influenced ice-sheet growth and decay over previous glacial cycles, and in light of concerns over whether enhanced geothermal heat fluxes and subglacial melting may contribute to instability of the West Antarctic Ice Sheet. Here, we use ice-sheet bed-elevation data to locate individual conical edifices protruding upwards into the ice across West Antarctica, and we propose that these edifices represent subglacial volcanoes. We used aeromagnetic, aerogravity, satellite imagery and databases of confirmed volcanoes to support this interpretation. The overall result presented here constitutes a first inventory of West Antarctica's subglacial volcanism. We identified 138 volcanoes, 91 of which have not previously been identified, and which are widely distributed throughout the deep basins of West Antarctica, but are especially concentrated and orientated along the >3000 km central axis of the West Antarctic Rift System.

Subglacial volcanic activity above a lateral dyke path during the 2014–2015 Bárdarbunga-Holuhraun rifting episode, Iceland

The rifting episode associated with the Bardarbunga-Holuhraun eruption in 2014–2015 included the first observations of major dyke propagation under ice. Three shallow ice depressions (ice cauldrons) with volumes ranging from 1 to 18 million m3 formed in Dyngjujokull glacier above the 48-km-long lateral path of the magma, at 4, 7 and 12 km from the northern glacier edge. Aircraft-based radar altimetry profiling was used to map the evolution of the cauldrons and construct a time series of the heat transfer rates. Out of the three scenarios explored: (1) onset or increase of hydrothermal activity, (2) convection within vertical fissures filled with water overlying intruded magma and (3) subglacial eruptions, the last option emerges as the only plausible mechanism to explain the rapid heat transfer observed in a location far from known geothermal areas. The thermal signals at two of the cauldrons are consistent with effusive subglacial eruptions. The formation of the northernmost cauldron was more rapid, indicating faster heat transfer rates. Radio-echo sounding data indicate that in contrast to the other two cauldrons, an intrusion of eruptive products occurred into the glacier, reaching 50–60 m above bedrock with the increased magma-ice contact explaining the more rapid heat transfer. We propose that the ~2-m widening associated with graben formation increased the groundwater storage capacity of the bedrock, creating space for the meltwater to be stored, explaining the absence of meltwater pulses draining from Dyngjujokull.

Combination of SAR remote sensing and GIS for monitoring subglacial volcanic activity – recent results from Vatnajökull ice cap (Iceland)

Abstract. This paper presents latest results from the combined use of SAR (Synthetic Aperture Radar) remote sensing and GIS providing detailed insights into recent volcanic activity under Vatnajökull ice cap (Iceland). Glaciers atop active volcanoes pose a constant potential danger to adjacent inhabited regions and infrastructure. Besides the usual volcanic hazards (lava flows, pyroclastic clouds, tephra falls, etc.), the volcano-ice interaction leads to enormous meltwater torrents (icelandic: jökulhlaup), devastating large areas in the surroundings of the affected glacier. The presented monitoring strategy addresses the three crucial questions: When will an eruption occur, where is the eruption site and which area is endangered by the accompanying jökulhlaup. Therefore, sufficient early-warning and hazard zonation for future subglacial volcanic eruptions becomes possible, as demonstrated for the Bardárbunga volcano under the northern parts of Vatnajökull. Seismic activity revealed unrest at the northern flanks of Bardárbunga caldera at the end of September 2006. The exact location of the corresponding active vent and therefore a potentially eruptive area could be detected by continuous ENVISAT-ASAR monitoring. With this knowledge a precise prediction of peri-glacial regions prone to a devastating outburst flood accompanying a possible future eruption is possible.

Imprints of sub-glacial volcanic activity on a glacier surface—SAR study of Katla volcano, Iceland

The Katla central volcano, covered by the fourth largest Icelandic glacier Mýrdalsjokull, is among the most dangerous and active volcanoes in Iceland. Due to the ice cover, several indicators of its volcanic activity can only be identified indirectly. We analysed a total of 30 synthetic aperture radar (SAR) images with special focus on identifying circular and linear depressions in the glacier surface. Such features are indicative of sub-glacial geothermal heat sources and the adjacent sub-glacial tunnel (melt water drainage) system. The time series comprises images from five different SAR sensors (ERS-1, ERS-2, JERS-1/SAR, RADARSAT and ENVISAT-ASAR) covering a time period of 12 years, starting in 1994. Individual SAR scenes only partly map the glacier surface morphology due to the environmental influences on the SAR backscatter intensity. Thus, only surface features detectable in several SAR scenes at the same location were considered and merged to form an overall picture of the surface morphology of Mýrdalsjokull and its modification by sub-glacial volcanic activity between 1994 and 2006. Twenty permanent and 4 semi-permanent ice cauldrons could be identified on the surface of Mýrdalsjokull indicating geothermally active areas in the underlying caldera. An analysis of their size was not possible due to the indistinct outline in the SAR images. The spatial distribution of the geothermally active areas led to a new, piecemeal caldera model of Katla volcano. All cauldrons are connected to tunnel systems for melt water drainage. More than 100 km of the sub-glacial drainage system could be identified under the Mýrdalsjokull in the SAR time series. It has been found that the tunnel systems are not in agreement with estimated water divides. Our results allow improved assessment of areas of potential Jokulhlaup hazard accompanying a sub-glacial eruption.

Glacier–volcano interactions deduced by SAR interferometry

AbstractGlacier-surface displacements produced by geothermal and volcanic activity beneath Vatnajökull ice cap in Iceland are described by field surveys of the surface topography combined with interferograms acquired from repeat-pass synthetic aperture radar images. A simple ice-flow model serves well to confirm the basic interpretation of the observations. The observations cover the period October 1996–January 1999 and comprise: (a) the ice-flow field during the infilling of the depressions created by the subglacial Gjálp eruption of October 1996, (b) the extent and displacement of the floating ice cover of the subglacier lakes of Grímsvötn and the Skaftá cauldrons, (c) surface displacements above the subglacier pathways of the jökulhlaups from the Gjálp eruption site and the Grímsvötn lake, (d) detection of areas of increased basal sliding due to lubrication by water, and (e) detection of spots of temporal displacement that may be related to altering subglacial volcanic activity. At the depression created by the Gjálp eruption, the maximum surface displacement rate away from the radar decreased from 27 cm d−1to 2 cm d−1over the period January 1997–January 1999. The observed vertical displacement of the ice cover of Grímsvötn changed from an uplift rate of 50 cm d−1to sinking of 48 cm d−1, and for Skaftá cauldrons from 2 cm d to 25 cm d−1.

Extremely fast supercooling of water in the anti-Jovian hemisphere of Europa: A speculative model for the fracturing pattern and ascent of brines along cracks

The anti-Jovian hemisphere of Europa (the hemisphere opposite the one facing Jupiter) displays a complex array of fractures, including roughly concentric and arcuate ones. The geometry of this intriguing pattern on the icy surface of Europa resembles the textural features displayed by perlitic volcanic glass. We argue that fast cooling of a rhyolitic magma may serve as an analogue for fast supercooling of water leading to formation of amorphous ice (glassy water). We envisage two possible scenarios for ice melting and subsequent extremely fast supercooling: (1) massive subglacial volcanic activity or (2) a large impact on the anti-Jovian hemisphere. We suggest that extremely fast formation of amorphous ice on Europa would result in a fracture pattern geometrically equivalent to that observed in perlitic glass. Fast supercooling of water will initially lead to brine retention in the ice phase; however, after some time these brines would be laterally rejected toward fractures. Furthermore, as solidification progresses downward, a shrinking ocean would increase brine concentration. These brines would eventually escape to the surface via the fracture network. Finally, high-pressure crystallization of salts within fractures may provide an efficient mechanism for differential plate separation, horizontal movement, and formation of new fractures.

The impact of the 1996 subglacial volcanic eruption in Vatnajökull on the river Jökulsá á Fjöllum, North Iceland

A subglacial volcanic eruption took place in October 1996 beneath the Vatnajökull glacier, Iceland. The volcanic fissure erupted for some 14 days and it extended between two known subglacial central volcanoes. Most of the melt water drained to the south into the Grı́msvötn caldera from where it escaped a month later during a major jökulhlaup (extreme flood) into the glacial rivers flowing to the south from Vatnajökull. At the start of the eruption, the northernmost part of the volcanic fissure extended across the water divide beneath the glacier and into the river basin of Jökulsá á Fjöllum, flowing to the north. A few days later, signs of melt water from the volcanic site were detected in the glacial river Jökulsá á Fjöllum. Distinct changes in the chemical composition of the water were observed. Both discharge and turbidity of the river were somewhat higher than normal for the season, but there was no extreme flood (jökulhlaup). Total dissolved solids (TDS) and conductivity of the river water, as well as bicarbonate, were found to be higher than previously observed. Traces of sulphide and mercury were detected, which are never recorded at normal conditions. The stable isotope ratios, δD and δ 18 O , the 14 C apparent age and the δ 13 C value were also found to be anomalous. In a few weeks the chemistry was back to normal. The chemical changes were most likely caused by a direct flow of melt water from the northernmost part of the main volcanic fissure or from small cauldrons created at the rim of the Bárdarbunga caldera. The flow of melt water to the north from the volcanic centre ebbed soon after or even just before the volcanic eruption in Vatnajökull ended. This experience shows clearly that simultaneous monitoring of chemical changes and flow rate in glacial rivers can deliver valuable data for following subglacial volcanic activity in space and time and may be used to give warning before a major catastrophic flood. Chemical study of glacial rivers can also be used to find out if a jökulhlaup is connected with a simultaneous volcanic eruption or not.

Volcanic and Glacial Landforms on Mount Giluwe, Territory of Papua and New Guinea

Mount Giluwe is a large extinct dome-shaped volcano built up mainly of thin flows of mafic lava rich in potassium. It rises from 2100 m to 4368 m above sea level. During the Pleistocene, it was covered by an ice cap which extended as low as the 3200 to 3500 m level. Although the volcano is dissected by a radial drainage system, cones, craters, lava mounds, lava flow surfaces, and volcanic debris, slopes are well-preserved below the glaciated area. Above this, the original volcanic landforms have been destroyed or modified by glacial activity, and well-preserved lateral moraines, groups of recessional moraines, glacial valleys, cirques, rock basins, and roches moutonnees are present. During the period of maximum glaciation, valley glaciers as thick as 400 m protruded from the edge of the ice cap down preexisting valleys and terminated at elevations between 2750 and 3000 m. On the northeastern side of the volcano, fluvioglacial deposits derived from the valley glaciers formed fans extending onto the Kaugel plain, which is incised 40 m by the present Kaugel River. This incision is almost entirely postglacial. Palagonitic breccia and scoria overlie, and are interlayered with, normal lava flows in the summit area of the volcano. They indicate that some subglacial volcanic activity took place and that there were probably at least two different periods of glaciation. The last glacial period (contemporaneous with the Wurm glaciation of Europe and the Wisconsin glaciation of North America) was the more extensive, covering about 190 km 2 . It was responsible for the development of the existing glacial landforms. Most of the volcanic landforms are older than this last glaciation.