Figure 1. (top) Geological map of Iceland with black
stars marking approximate cave locations. Map projection is ISN93.
Courtesy of Anett Blischke, Icelandic GeoSurvey. (bottom) Lava
fields visited and examples of cave entrances.
The Icelandic caves play host to a variety of microbial communities, as
seen by microbial mats scattered across the cave ceilings, walls, and
floors in all colors of the rainbow. Although the lava tubes themselves
originate from relatively young flows (Figure 1), they also show some
secondary mineral alteration. What is microbial mat and what is
secondary mineral can often be difficult to distinguish, as their
textures and colors can be interchangeable to the naked eye, and is
compounded by the knowledge that they may be intricately linked.
Blue-colored mats/mineral precipitates observed in Icelandic lava tubes
were often found on surfaces of flowing water or along cracks in cave
walls or ceilings, where water seeps in from the ground above (Figure
2). Some blue features had a viscous texture (Figure 2b), while others
were brittle mineral crusts attached to the lava rock beneath (Figure
2a). The blue features found in caves B, C, and H (Figure 4) are the
subject of this paper, as well as a detailed account of their
acquisition in an effort to inform the search for biosignatures in
future missions to lava caves on Mars.