Björn Oddsson

Ash generation and distribution from the April-May 2010 eruption of Eyjafjallajökull, Iceland

The 39-day long eruption at the summit of Eyjafjallajökull volcano in April–May 2010 was of modest size but ash was widely dispersed. By combining data from ground surveys and remote sensing we show that the erupted material was 4.8±1.2·1011 kg (benmoreite and trachyte, dense rock equivalent volume 0.18±0.05 km3). About 20% was lava and water-transported tephra, 80% was airborne tephra (bulk volume 0.27 km3) transported by 3–10 km high plumes. The airborne tephra was mostly fine ash (diameter <1000 µm). At least 7·1010 kg (70 Tg) was very fine ash (<28 µm), several times more than previously estimated via satellite retrievals. About 50% of the tephra fell in Iceland with the remainder carried towards south and east, detected over ~7 million km2 in Europe and the North Atlantic. Of order 1010 kg (2%) are considered to have been transported longer than 600–700 km with <108 kg (<0.02%) reaching mainland Europe.

Gradual caldera collapse at Bárdarbunga volcano, Iceland, regulated by lateral magma outflow

Driven to collapse Volcanic eruptions occur frequently, but only rarely are they large enough to cause the top of the mountain to collapse and form a caldera. Gudmundsson et al. used a variety of geophysical tools to monitor the caldera formation that accompanied the 2014 Bárdarbunga volcanic eruption in Iceland. The volcanic edifice became unstable as magma from beneath Bárdarbunga spilled out into the nearby Holuhraun lava field. The timing of the gradual collapse revealed that it is the eruption that drives caldera formation and not the other way around. Science, this issue p. 262 Magma flow from under the Bárdarbunga volcano drove caldera collapse during the 2014 eruption. INTRODUCTION The Bárdarbunga caldera volcano in central Iceland collapsed from August 2014 to February 2015 during the largest eruption in Europe since 1784. An ice-filled subsidence bowl, 110 square kilometers (km2) in area and up to 65 meters (m) deep developed, while magma drained laterally for 48 km along a subterranean path and erupted as a major lava flow northeast of the volcano. Our data provide unprecedented insight into the workings of a collapsing caldera. RATIONALE Collapses of caldera volcanoes are, fortunately, not very frequent, because they are often associated with very large volcanic eruptions. On the other hand, the rarity of caldera collapses limits insight into this major geological hazard. Since the formation of Katmai caldera in 1912, during the 20th century’s largest eruption, only five caldera collapses are known to have occurred before that at Bárdarbunga. We used aircraft-based altimetry, satellite photogrammetry, radar interferometry, ground-based GPS, evolution of seismicity, radio-echo soundings of ice thickness, ice flow modeling, and geobarometry to describe and analyze the evolving subsidence geometry, its underlying cause, the amount of magma erupted, the geometry of the subsurface caldera ring faults, and the moment tensor solutions of the collapse-related earthquakes. RESULTS After initial lateral withdrawal of magma for some days though a magma-filled fracture propagating through Earth’s upper crust, preexisting ring faults under the volcano were reactivated over the period 20 to 24 August, marking the onset of collapse. On 31 August, the eruption started, and it terminated when the collapse stopped, having produced 1.5 km of basaltic lava. The subsidence of the caldera declined with time in a near-exponential manner, in phase with the lava flow rate. The volume of the subsidence bowl was about 1.8 km3. Using radio-echo soundings, we find that the subglacial bedrock surface after the collapse is down-sagged, with no indications of steep fault escarpments. Using geobarometry, we determined the depth of magma reservoir to be ~12 km, and modeling of geodetic observations gives a similar result. High-precision earthquake locations and moment tensor analysis of the remarkable magnitude M5 earthquake series are consistent with steeply dipping ring faults. Statistical analysis of seismicity reveals communication over tens of kilometers between the caldera and the dike. CONCLUSION We conclude that interaction between the pressure exerted by the subsiding reservoir roof and the physical properties of the subsurface flow path explain the gradual near-exponential decline of both the collapse rate and the intensity of the 180-day-long eruption. By combining our various data sets, we show that the onset of collapse was caused by outflow of magma from underneath the caldera when 12 to 20% of the total magma intruded and erupted had flowed from the magma reservoir. However, the continued subsidence was driven by a feedback between the pressure of the piston-like block overlying the reservoir and the 48-km-long magma outflow path. Our data provide better constraints on caldera mechanisms than previously available, demonstrating what caused the onset and how both the roof overburden and the flow path properties regulate the collapse. The Bárdarbunga caldera and the lateral magma flow path to the Holuhraun eruption site. (A) Aerial view of the ice-filled Bárdarbunga caldera on 24 October 2014, view from the north. (B) The effusive eruption in Holuhraun, about 40 km to the northeast of the caldera

Monitoring Subglacial Volcanic Eruption Using Ground-Based C-Band Radar Imagery

The microphysical and dynamical features of volcanic clouds, due to Plinian and sub-Plinian eruptions, can be quantitatively monitored by using ground-based microwave weather radars. In order to demonstrate the unique potential of this remote sensing technique, a case study of a subglacial volcanic eruption, occurred in Iceland in November 2004, is described and analyzed. Volume data, acquired by a C-band ground-based weather radar, are processed to automatically classify and estimate ash particle concentration. The ash retrieval physical-statistical algorithm is based on a backscattering microphysical model of fine, coarse, and lapilli ash particles, used within a Bayesian classification and optimal regression algorithm. A sensitivity analysis is carried out to evaluate the overall error budget and the possible impact of nonprecipitating liquid and ice cloud droplets when mixed with ash particles. The evolution of the Icelandic eruption is discussed in terms of radar measurements and products, pointing out the unique features, the current limitations, and future improvements of radar remote sensing of volcanic plumes.

Emerging technology monitors ice-sea interface at outlet glaciers

Recent melting in Greenland and Antarctica has led to concerns about the long-term stability of these ice sheets and their potential contributions to future sea level rise. Marine-terminating outlet glaciers play a key role in the dynamics of these ice sheets; recent mass losses are likely related to increased influx of warmer water to the base of outlet glaciers, as evidenced by the fact that changes in ocean currents, calving front retreats, glacial thinning, mass redistribution based on satellite gravity data, and accelerating coastal uplift are roughly concurrent [e.g., Holland et al., 2008; Wouters et al., 2008; Jiang et al., 2010; Straneo et al., 2012; Bevis et al., 2012]. However, collecting quantitative measurements within the dynamic environment of marine outlet glaciers is challenging. Oceanographic measurements are limited in iceberg-laden fjords. Measuring ice flow speeds near the calving front is similarly challenging; satellite methods lack temporal resolution (satellite revisit times are several days or longer), while GPS gives limited spatial resolution, a problem for assessing changes near the highly variable calving front.

Experimental studies of heat transfer at the dynamic magma ice/water interface: Application to subglacially emplaced lava

Experiments simulating processes operating in volcano-ice interactions were carried out to explain and quantify lava thermal properties and processes of heat transfer from pure lava melt to water and ice and from hot crystalline lava to water. The samples used (70–200 g) were obtained from an intermediate lava flow (benmoreite-trachyte) that was emplaced under and within the outlet glacier Gigjokull in the 2010 eruption of Eyjafjallajokull. Experiments involved settings with direct contact between ice and lava, and settings where melt and ice were separated by a few centimeters. Direct contact involved melt being emplaced on ice and ice placed on melt. The direct contact experiments provided initial heat flux of up to 900 kW m−2 at an initially lava melt surface temperature of 1100°C, declining to <100 kW m−2 at 200–300°C within 1–2 min, while the experiments without melt-ice contact yielded an initial maximum of 100–180 kW m−2 dropping to 50–80 kW m−2 in 2–3 min. In other experiments, where cubes of hot crystalline lava were subjected to forced convection of water at initial temperature of 20–30°C, initial heat fluxes of 400–770 kW m−2 were followed by fast decline to <100 kW m−2 in 15–35 s, the rate depending on cube size. The hot rock experiments provided thermal conductivity values of 1.2–1.7 W m−1K−1 and diffusivity of about 9 × 10−7 m2s−1. Values for heat flux obtained in these experiments are in the same range as those obtained from field observations of the lava emplacement in the Eyjafjallajokull 2010 eruption.

Lahar, Floods and Debris Flows Resulting from the 2010 Eruption of Eyjafjallajökull: Observations, Mapping, and Modelling

Historic, post-eruptive debris flows of remobilised volcanic ash are rare in Iceland, being restricted to explosive eruptions. Volcanic ash slurry from the southern slopes of the ice-capped Eyjafjallajokull volcano on 19 May 2010 is the first lahar observed in Iceland since the 1947 Hekla eruption. This study focuses on the volume of sediment transported, the size and hydrological behavior of watersheds, and the resulting erosion. The analysis is based on: (1) direct measurements of the 19 May lahar; (2) direct measurements of ash fallout; (3) aerial and ground-based imagery; (4) topographic data from an airborne LIDAR survey; (5) airborne synthetic-aperture radar; and (6) precipitation data. The volume of the lahar in the Svaðbaelisa channel was estimated at 200,000 m3. This flow originated from crown and flank failures, similar to slab avalanches, with water-saturated, fine-grained ash as the slip surface. Several ash-laden floods occurred in Svaðbaelisa and neighboring channels during the summer of 2010. None, however, were as saturated as the 19 May lahar. An increased number of small debris flows were also recorded some blocking roads to farms. Precipitation during the summer of 2010 was not higher than average and therefore does not explain this increased erosion. Large quantities of volcanic ash mantle the lower slopes of the ice-cap. Ash in the ablation zone is expected to be transferred down-slope in the next few years inducing the erosion to the root of the mountain endangering homes and infrastructure. Fieldwork during the summer of 2010 has resulted in a map showing the volume of ash above and below the ablation zone of the main catchments and recorded erosion events. This data was used to assess the hazard and the need for immediate actions.