Total Grain Size Distributi on in Selected Icelandic Erupti ons Work for the Internati onal Civil Aviati on Organizati on (ICAO) and the Icelandic Meteorological Offi ce Authors: Ármann Höskuldsson, Maria Janebo, Thorvaldur Thordarson, Thóra Björg Andrésdó� r, Ingibjörg Jónsdó� r, Jónas Guðnason, Johanne Schmith, William Moreland, Agnes Ösp Magnúsdó� r University of Iceland Total Grain-Size Distribution in Selected Icelandic Eruptions Total Grain-Size Distribution in Selected Icelandic Eruptions Copyright © 2018 Á. Höskuldsson, M.H. Janebo, T. Thordarson, T. B. Andrésdóttir, I. Jónsdóttir J. Guðnason, J. Schmith, W. Moreland, A. Ö. Magnúsdóttir All rights reserved Institute of Earth Sciences University of Iceland Sturlugata 7 101 Reykjavík ISBN 978-9935-9300-4-0 Table of contents Abstract 7 1 Introduction 8 2 Explosive volcanism in Iceland 8 3 Selected volcanoes 9 4 Total Grain-Size Distribution (TGSD) 10 5 The work strategy 11 6 Summary of the project 12 7 Eruption summaries and TGSDs 12 7.1 Hekla 13 Hekla 1104 15 Hekla 1300 16 Hekla 1693 17 Hekla 1766 18 Hekla 1845 19 Hekla 1991 20 Hekla 2000 21 7.2 Katla 22 Katla 1625 23 Katla 1755 24 Katla 934 - Eldgjá 25 7.3 Askja 27 Askja 1875 28 7.4 Grímsvötn 30 Grímsvötn 2004 31 Grímsvötn 2011 32 7.67.5 ReykjanesEyjafjallajökull 3533 ReykjanesEyjafjallajökull 1226 2010 3634 8 Conclusions 37 9 Future work 38 References 42 ListFigure of 1. figures Distribution of volcanic systems in Iceland. 9 Figure 2. Location of Hekla 13 Figure 3. Hekla volcano 13 Figure 4. Main area affected by tephra fall from the Hekla 1104 eruption 15 Figure 5. TGSD for the Hekla 1104 eruption 15 Figure 6. Main area affected by tephra fall from the Hekla 1300 eruption 16 Figure 7. TGSD for the opening phase of the Hekla 1300 eruption 16 Figure 8. Main area affected by tephra fall from the Hekla 1693 eruption 17 Figure 9. TGSD for the opening phase of the Hekla 1693 eruption 17 Figure 10. Main area affected by tephra fall from the Hekla 1766 eruption 18 Figure 11. TGSD for the opening phase of the Hekla 1766 eruption 18 Figure 12. Main area affected by tephra fall from the Hekla 1845 eruption 19 Figure 13. TGSD for the opening phase of the Hekla 1845 eruption 19 Figure 14. Main area affected by tephra fall from the Hekla 1991 eruption 20 Figure 15. TGSD for the opening phase of the Hekla 1991 eruption 20 Figure 16. Main area affected by tephra fall from the Hekla 2000 eruption 21 Figure 17. TGSD for the opening phase of the Hekla 2000 eruption 21 Figure 18. Location of Katla shown in green 22 Figure 19. Katla volcano 22 Figure 20. Main area in Iceland affected by tephra fall from the Katla 1625 eruption 23 Figure 21. TGSD for Katla 1625 23 Figure 22. Main area in Iceland affected by tephra fall from the Katla 1755 eruption 24 Figure 23. TGSD for Katla 1755 24 Figure 24. Main area affected by tephra fall from the Eldgjá eruption units 7 and 8 25 Figure 25. TGSD for Eldgjá unit 7 25 Figure 26. TGSD for Eldgjá unit 8 26 Figure 27. Location of Askja shown in red 27 Figure 28. Askja volcano 27 Figure 29. Main area affected by tephra fall from the Askja 1875 eruption 28 Figure 30. Preliminary TGSD for Askja B 29 Figure 31. Preliminary TGSD for Askja C 29 Figure 32. Preliminary TGSD for Askja D 29 Figure 33. Main area affected by tephra fall from the Askja 1875 eruption unit B 29 Figure 34. Main area affected by tephra fall from the Askja 1875 eruption unit C 29 Figure 35. Main area affected by tephra fall from the Askja 1875 eruption unit D 29 Figure 36. Location of Grímsvötn shown in purple 30 Figure 37. Grímsvötn volcano 30 Figure 38. Main area affected by tephra fall from the Grímsvötn 2004 eruption 31 Figure 39. TGSD for Grímsvötn 2004 31 Figure 40. Main area affected by tephra fall from the Grímsvötn 2011 eruption 32 Figure 41. TGSD for Grímsvötn 2011 32 Figure 42. Location of Eyjafjallajökull in orange 33 Figure 43. Eyjafjallajökull volcano 33 Figure 44. Main area affected by tephra fall from the Eyjafjallajökull 2010 eruption 34 Figure 45. TGSD for Eyjafjallajökull May 2010 34 Figure 46. Location of Reykjanes shown in pink 35 Figure 47. Reykjanes 35 Figure 48. Main area affected by tephra fall from the Reykjanes 1226 eruption 36 Figure 49. TGSD for Reykjanes 1226 36 Figure 50. Main direction of tephra dispersal from historical eruptions in Katla 39 List of tables Table 1. Overview of eruptions included in the project 11 Table 2. Overview of historical eruptions in Hekla 14 Table 3. Overview of historical eruptions in Katla 40 Table 4. Overview of TGSD 41 Abstract One of the main hazards from explosive eruptions is volcanic ash that is dispersed through the atmosphere. In order to enhance and increase accuracy of models used to forecast volcanic ash distribution in the atmosphere, eruption source parameters size distribution of all the erupted material (TGSD). Another important parameter is the(ESP) maximum need to heightbe well of defined. the eruption One ofcloud the (Hc),most whichimportant is a direct parameters consequence is the grain-of the volumetric eruption rate (VER). The Hc can be obtained during an ongoing eruption, or it can later be derived from the deposits, and thus VER can be obtained. However, the TGSD can not be obtained until the eruption is over. The TGSD obtained for older eruptions can be used as a benchmark for what can be expected from future eruptions. Constructing a comprehensive database of TGSD here report TGSD for 15 Icelandic eruptions. The 15 eruptions are both historic, be- forefor past instrumental eruptions era,is therefore and more very recent, important. observed As aby first modern step towardstechniques. that From goal, thewe not only between eruptions from different volcanoes, but between eruptions from theoverview same volcano.presented This her, further it is evident emphasizes that there the importance are significant of reconstructing variations in TGSD from numerous volcanoes and for eruptions covering a large range in VER and mag- ma composition for each volcano. Modern day travel is highly dependent on aviation, and the aviation industry is among the most secure industries in the world, due to strict quality control. A more comprehensive dataset of TGSD, and hence greater understanding of the link be- tween TGSD and VER, will aid in minimizing the impacts on aviation from future eruptions, especially in the case of Icelandic eruptions. We hope that this work pro- vides the starting point into the creation of a such a database. 7 All maps are based on cartographic data from the 1 Introduction National Land Survey of Iceland (LMÍ). The aim of this project is to investigate and sum- 2 Explosive volcanism in marize the size distribution of volcanic tephra associated with selected volcanic eruptions in Iceland Iceland. To evaluate an explosive volcanic erup- tion and the hazards such an event might pose Iceland is the largest and most active volcanic to the environment, infrastructure, transport area in Europe. Volcanism in Iceland is due to systems and humanity, it is necessary to quan- two main processes; the separation of the Amer- tify the key eruption source parameters (ESPs, ican and Eurasian plates and the deep-rooted convection in the mantle manifested as the Ice- most important ESPs is the size distribution of landic hot spot. Both phenomena lead to mag- thefor definitiontephra grains see Mastingenerated et al., in 2009). the eruption, One of there- ma generation and upwelling in such a quantity ferred to as the Total Grain-Size Distribution that its accumulation in the middle of the North (TGSD). Once obtained, the TGSD can be used as Atlantic forms an island of some 103,000 km2, input data for the simulation of tephra transport with crustal thickness of up to 45 km (Thordar- in the atmosphere. The mass of individual grains son and Höskuldsson, 2008). in an eruption column mostly depends on their Volcanism in Iceland is mainly bound to the ac- grain-size distribution is therefore fundamen- tive plate boundary that crosses the island from talsize, for shape, forecasting and density.quantity Quantification and concentration of the of Reykjanes in the SW to Melrakkaslétta in the tephra grains in the atmosphere. NE. Complex interplay between the deep mantle convection and the plate boundary cause varia- Explosive eruptions are of utmost importance tion in crustal stresses, expressed on the surface when considering aviation safety. Most modern airplanes are not made to withstand volcanic normal faults crowned with central volcanoes. particles. In explosive eruptions, large amounts Thisby echelon is referred formation to in Iceland of clusters as volcanic of fissures systems, and of which there are 30 above sea-level (Figure aerosols upon reaction with atmospheric va- 1). Normally, oceanic and hot spot volcanism is por)of particles are dispersed (fine ash throughout and gases the that atmosphere. turn into manifested by effusive (i.e., lava forming) erup- These particles have long residence time in the tions, but Iceland is an exception. Due to the atmosphere and can be transported for several thick crust, the mantle derived magma has rel- thousand km. Computer models can be used to atively long crustal residence and consequently, predict atmospheric dispersal of volcanic parti- it becomes more evolved in composition. There- cles. However, the quality of the model outputs fore, Icelandic eruptions have the potential of be- depends greatly on how well constrained the ing highly explosive. The geographic location of input parameters are, such as plume height and Iceland and oceanic climate means that surface TGSD.