Geomorphological characterization of the 2014–2015 Holuhraun lava flow-field in Iceland

The 2014–2015 Holuhraun eruption extruded >1 km³ of lava in a barren region of the Icelandic highlands. Due to its large volume and the abundance of data for this eruption, Holuhraun is an ideal site to investigate fissure-fed eruption products for comparison with other large lava flow-fields on Earth and other planetary bodies. To characterize lava morphologies associated with this event, we used 0.01–0.5 m/pixel image data, acquired from aerial surveys and small Unoccupied Aircraft Systems (sUAS) to create a 1:800-scale facies map that was ground-truthed using field observations during the summers of 2015–2019. Each facies region exhibits similar attributes in the remote sensing data, including albedo, surface texture, and geomorphology. However, at our mapping scale of 1:800, the facies typically include mixtures of lava types. Results show that transitional lava types (e.g., rubbly pāhoehoe, slabby pāhoehoe, and spiny pāhoehoe) dominate the 2014–2015 Holuhraun lava flow-field (83.82 km²), rather than the traditional end-members of ʻaʻā and classical pāhoehoe. At 1:800-scale, we distinguish the following eight facies (with the percentage of total flow-field area shown in parentheses): rubbly (57.35%), spiny (25.96%), undifferentiated rubbly–spiny (9.59%), shelly (5.58%), pāhoehoe (1.24%), flat-lying–knobby (0.58%), vent-proximal edifice (0.19%), and channel interior (0.16%). Field observations show that initial coherent pāhoehoe surfaces were episodically disrupted to produce slabby and rubbly textures that resemble ʻaʻā in remote sensing data. Our observations also show that continued solidification of the lava beneath brecciated surfaces can cause the surfaces of disrupted lobes to stabilize, or restabilize and undergo inflation. These factors complicate the use of surface texture as a direct indicator of emplacement style, which can change over the course of an eruption. This complexity has important implications for reconstructing the emplacement history of flow-fields on Earth and other planetary bodies.