Fig. 4: Habitats due to texture variations within a lava flow.

Example of a pāhoehoe lava flow and associated habitats. a Pāhoehoe ropes (formed by a cooling surface that deforms above a flowing interior) can create variations in surface texture to create sheltered habitats for epiliths (organisms that can colonize rock surfaces). Image from the 2018 Kīlauea lava flow, Hawaiʻi (Photo credit: N. Hadland). b Skylights formed by collapses often create rubble piles within a lava tube or cave, which are colonized by photosynthesizers. Image from Four Windows Cave in El Malpais National Monument, New Mexico (Photo credit: N. Hadland). c Vent proximal lava is commonly extremely vesicular due to high gas content and has a somewhat glassy surface that provide habitats for cryptoendoliths (organisms that occupy vesicles and primary pores). Image from the 2018 Kīlauea lava flow (Photo credit: N. Hadland). d Twilight zone in Four Windows Cave at the edge of where photosynthetic groups can occupy (green film at the top of the image). Variations in textures on lava tube walls are caused by lava drips, extrusions, or fluctuating levels of lava during tube formation (Photo credit: N. Hadland). e Crystalline core of a pāhoehoe flow with few vesicles (Photo credit: Quinn Dombrowski; https://commons.wikimedia.org/wiki/File:Pahoehoe_Lava_Flow_at_Kilauea_in_Hawaii_20071209_B.jpg). f Transition between pāhoehoe and ʻaʻā, which have dramatically different surface textures and vesicularity. Image from 2021 Fagradasfjall eruption, Iceland (Photo credit: N. Hadland). g Inflation processes can create large cracks and void spaces for chasmoendolith colonization (organisms that populate fractures and cracks). Perspective rendering from McCartys lava flow field in El Malpais National Monument (Photo credit: C. W. Hamilton)¹¹³. h Older lava is more weathered due to alteration processes as well as euendolith (actively penetrating/burrowing into a rocky surface) and autoendolith (metabolically induced mineral precipitation in pore spaces)²³⁹ activity. Image from Reykjanes Peninsula, Iceland (Photo credit: N. Hadland).