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ABSTRACT. Avalanche hazard is a threat to many residential areas in Iceland. In 1995 two avalanche accidents, causing a total of 34 fatalities in areas thought to be safe, prompted research on avalanche hazard assessment. A new method was developed, and in 2000 a new regulation on avalanche hazard zoning was issued. The method and regulation are based on individual risk, or annual probability of death due to avalanches. The major components of the method are the estimation of avalanche frequency, run-out distribution and vulnerability. The frequency is estimated locally for each path under consideration, but the run-out distribution is based on data from many locations, employing the concept of transferring avalanches between slopes. Finally the vulnerability is estimated using data from the 1995 avalanches. Under the new regulation, new hazard maps have been prepared for six of the most vulnerable villages in Iceland. Hazard zones are delineated using risk levels of 0.2610^4, 0.7610^4 and 2610^4 a^1, with risk less than 0.2610^4 a^1 considered acceptable. When explaining the new zoning to the public, a measure of annual individual risk that allows comparison with other risks in society has proven advantageous.

Abstract. A comprehensive catalogue of historical earthquakes, with accurate epicentres and harmonised magnitudes is a crucial resource for seismic hazard mapping. Here we update and combine catalogues from several sources to compile a catalogue of earthquakes in and near Iceland, in the years 1900–2019. In particular the epicentres are based on local information, whereas the magnitudes are based on teleseismic observations, primarily from international online catalogues. The most reliable epicentre information comes from the catalogue of the Icelandic Meteorological Office, but this is complemented with information from several technical reports, scientific publications, and newspaper articles. The catalogue contains 1281 moment magnitude (Mw) ≥4 events, and the estimated completeness magnitude is Mw 5.5 in the first years, going down to Mw 4.5 for recent years. The largest magnitude is Mw 7.0. Such merging of local data and teleseismic catalogues has not been done before for Icelandic earthquakes, and the result is an earthquake map with much more accurate locations than earlier maps. The catalogue also lists 5640 additional earthquakes on the Mid-Atlantic Ridge, north of 43∘, with both epicentres and magnitudes determined teleseismically. When moment magnitudes are not available, proxy Mw values are computed using χ2 regression, normally on the surface-wave magnitude but exceptionally on the body-wave magnitude. Magnitudes of Mw≥4.5 have associated uncertainty estimates. The actual combined seismic moment released in the Icelandic earthquakes is found to be consistent with the moment estimated using a simple plate motion model, indicating that the seismic activity of the catalogue period might be typical of any 120-year time span. The catalogue is named ICEL-NMAR, and it is available online at http://data.mendeley.com (last access: 19 July 2021).

A detailed description of an algorithm for the evaluation and differentiation of the likelihood function for VARMA processes in the general case of missing values is presented. The method is based on combining the Cholesky decomposition method for complete data VARMA evaluation and the Sherman-Morrison-Woodbury formula. Potential saving for pure VAR processes is discussed and formulae for the estimation of missing values and shocks are provided. A theorem on the determinant of a low rank update is proved. Matlab implementation of the algorithm is in a companion article.

Volcanism in Iceland appears to have been conned to volcanic systems throughout its history. During Late-Pleistocene and Holocene times some 41 volcanic systems have been active in Iceland and its insular shelf. An examination of a scrutinized data set of 1378 major element chemical analyses of rocks from the 41 volcanic systems, conrms that three volcanic rock series have developed in Iceland, i.e. a tholeiitic, an alkalic and a transitional alkalic series. The chemical and petrographical characteristics of the three series are discussed. Each volcanic system has only developed basaltic rocks relating to one rock series. A renement of the nomenclature of the IUGS Subcommission on the Classication of Igneous Rocks (Le Maitre, 2002) is proposed for the basalts, and for the intermediate and silicic rocks of the transitional series. Mixing and hybridization appear to be very common among the intermediate rocks. A special case is the Hekla suite where the more evolved intermediate rocks are considered to be hybrids of transitional mugearite and tholeiitic dacite. The frequency distribution of the analyzed volcanic rocks indicates that 75% are basalts, 14% intermediate rocks and 11% silicic rocks. However, there is a distinct bimodal distribution of compositions in the tholeiitic and transitional alkalic series. The tholeiitic rock series is conned to volcanic systems in the rift zones which delineate the crest of the MAR in Iceland. The alkalic and transitional alkalic systems are conned to the ank zones. The tholeiitic volcanic systems are estimated to be responsible for 80% of the volume of the extruded rocks during the time span under consideration. Alkalic volcanic systems were initiated in some parts of the volcanic zones 2-3 Ma ago. Flank zones producing transitional alkalic rocks may have been active in northeast and southeast Iceland during Late Tertiary.