Human (boot) tracks preserved in volcanic deposits of Surtsey Island, Iceland

Abstract

Several human boot tracks and trackways are preserved in palagonitized tuff in Surtsey Island, south Iceland. The underlying palagonitized substrate is made of reworked tephra debris talus and slump material that lies partly on top of lava flows erupted in 1964–1965 in Surtungur tuff crater and 1966–1967 in Surtur tuff crater. This stratigraphic information along with other evidence from the nature of the sediments, alteration history of the deposits and the record of human presence on the island indicate the tracks were formed in the years between 1967 and 1970. The exquisite preservation and consolidation of the tracks coincide with a period of rapid geomorphic changes in the early stages of development of the island, when the newly formed tephra was still unconsolidated and easily mobilized by mass movements, wind and runoff. Furthermore, cooling magmatic intrusions generated hydrothermal activity on the island speeding up diagenesis of the tephra and the cementation of the boot tracks in the substrate. Expulsion rims preserved in some of the boot tracks suggests the tracks were formed in moderately cohesive substrate, followed by rapid burial of the prints in heavy wind and/or storm. Three boot sizes were identified suggesting the tracks were made by at least three persons, and documentation of the boot anatomy, measurements on angle of gait, stride and pace reveal the direction of movement for each trackway. Intense erosion of the tuff cones has exhumed the tracks to the surface that stand today as a testimony to impressively rapid geological cycles for preservation and exhumation and the role of unstable and rapidly changing environments, the aftermath of high-energy events, in capturing and preserving ichnites. These boot tracks are the first fossil tracks described for Iceland and the first record in the world of boot tracks preserved in sedimentary rocks.