UNDERSTANDING FLOOD LAVAS: THE SAGA CONTINUES (Invited Presentation)

Flood lavas are an integral part of most large igneous provinces across the Solar System. One of the most fruitful techniques for understanding the emplacement of these immense volcanic deposits has been to use their smaller, but more recent, kindred as analogs. For example, in the 1990s, the revelation of the lava flow inflation process from observations of active lava flows in Hawaii led to a thousand-fold reduction in the estimated eruptive fluxes for the Columbia River Basalts. What is sometimes forgotten is that the 1783-84 Laki lava in Iceland provided the intermediate example to allow the Hawaii observations to be confidently applied to the CRB lavas. Further study of the Icelandic flood lavas in the 2000s led to the recognition of rubbly pahoehoe and its link to platy-ridged lavas on Mars. The 2014-2015 eruption at Holuhraun in north-central Iceland (sometimes referred to as Nornahraun) is providing the next chapter in the ongoing saga of Icelandic lavas informing our understanding of large igneous provinces across the Solar System. This eruption is the largest in Iceland since 1784 with a volume of ~1km³ and an area of >80 km². Two aspects of this lava stand out as opportunities to better understand planetary flood lavas. First, its primary surface morphology is rubbly pahoehoe, providing the first time the processes by which this crust forms has been recorded by modern volcanological techniques. Second, the lava flow entered the path of the Jökulsá á Fjöllum river, providing an extremely rare opportunity to observe water flowing through the base of a still-hot lava flow. In terms of flow morphology, it is now apparent that many peripheral features that were interpreted as late breakouts from the main flow actually represent the initial phase of emplacing a large rubbly pahoehoe flow. Initial studies have also revealed a number of previously undocumented lava features such as spiny pahoehoe lava ponds and enigmatic “troll plates.” The investigation of the heat transfer at the base of the lava flow will need to be maintained for years but the outflow of water in the first year produced a remarkably habitable environment with interesting possible application to Mars.