Surtsey is a volcanic island located approximately 32 km off the south coast of Iceland. It was formed during a volcanic eruption taking place from November 1963 to June 1967 (Þórarinsson 1968). In 1965, the whole island became legally protected due to its special scientific value and the research opportunities that arose with its formation. Indeed, the protection of Surtsey created an isolated island environment, free of human interference, that enabled researchers to collect priceless data documenting the process of colonisation of the newly-formed island.

Surtsey is a part of the Vestmannaeyjar archipelago (S Iceland, Fig. 1). The archipelago constitutes a separate volcanic system, consisting of 18 islands and a number of skerries and is situated on the insular shelf off the south coast of Iceland. As a result of volcanic activity between 1963 and 1967, an additional island was formed, Surtsey, that initially had an area of 2.65 km² (Baldursson and Ingadóttir 2007). The total volume of the erupted material was estimated to be about 1.1 km³ and consisted of tephra (70%) and lava (30%). The surface of Surtsey has been mapped in detail using traditional methods, but no GIS data are publicly available. The eruptive products at Surtsey, tephra and lava, are composed of alkali basalt with phenocrysts of olivine, plagioclase and chromian spinel. With the passage of time, three secondary geological units were formed: palagonite tuff, aeolian and talus sediments and coastal sediments. The highest elevation on Surtsey is 155 m. It is good to have in mind that the shape of Surtsey is constantly modified by the harsh weather conditions, particularly during winter (Baldursson and Ingadóttir 2007).

Figure 1.  

Location and general topography of Surtsey. The coastline of Surtsey as of 2018.

Automatic weather measurements in Surtsey have ben carried out since 2009 and were recently summarised by Petersen and Jónsson 2020. The climate here is maritime, with the annual temperature variation dampened by the sea that cools the climate during summer and warms it during winter. Average winter temperatures (December to March) are between 2.5 and 4.0ºC, while average summer temperatures (July and August) are close to 10ºC. The frost-free period lasts here for about 199 days. The highest temperature recorded on Surtsey was 18.3ºC, while the minimum was -9.7ºC. The average annual precipitation is about 1000 mm, with June being the driest month and October being the wettest. Snowfall is rare and rather slight. Winds are strong. On average, there are 229 days per year with precipitation. Average wind speed on Surtsey is 7.8 m/s. There are 30 days (on average) with wind speeds exceeding 20 m/s. The maximum wind speed recorded here was 35.2 m/s, while the maximum wind gust was 47.8 m/s (Petersen and Jónsson 2020).

Botanical observations on Surtsey commenced in May 1964 (Einarsson 1963), when the eruption was still underway and uncovered, even at that time, a significant amount of plant material carried by sea currents that was able to reach the island. A year later (on 3 June 1965), the first vascular plant species (seedlings of Cakile maritima subsp. islandica) was discovered growing on Surtsey (Friðriksson 1966). During 56 years of careful, yearly observations, a significant amount of data on plant distribution and colonisation was collected, resulting in many scientific papers (e.g. Einarsson 1967, Friðriksson 1966, Friðriksson 1978, Friðriksson 1982, Friðriksson 1992, Friðriksson et al. 1972, Friðriksson 1967, Friðriksson and Johnsen 1968, Magnússon et al. 2014). More detailed information on various aspects of research carried out in Surtsey can be found in a series of reports published by Surtsey Research Society. All the reports are available at https://surtsey.is/utgafa-surtseyjarfelagsins/ .

During the first decades of research carried out on Surtsey, every single plant growing on the island was precisely marked (initially using wooden poles), numbered and mapped using coordinate paper. In the present data paper, we publish the results of digitisation of these maps containing observations of plant life during the first decades of the history of Surtsey. This project, recently completed at the Icelandic Institute of Natural History, resulted in a database of 10,094 records documenting the process of colonisation and subsequent spread of vascular plants on Surtsey.

Sturla Friðriksson (the leader of the research on Surtsey) and Björn Johnsen who passed away contributed their knowledge and data to the dataset that is now being published. Þór Gunnarsson took part in data collection after 1980. We would like to thank Anette Th. Meier (GIS specialist and Cartographer at the Icelandic Institute of Natural History) for her help in preparing Figure 1.

PW designed and directed the digitisation project, took part in georeferencing, prepared the dataset and wrote the paper. ST took part in georeferencing and contributed to the final manuscript. BM, EE, VB, ÁHB, JG, SHR, RJ, BJ, SÞM collected original data.