Abstract
Fissure eruptions are associated with lava fountains which often show complex distinct venting activity, in pulsating form, and the development of characteristic morphologic expressions such as scoria or spatter cones. Most morphological studies are based on observations of old structures and are not related to direct observations and systematic records of vents activity, which are rare. The 2014 - 2015 Holuhraun eruption site, Iceland, offered an exceptional opportunity to study with unprecedented details the location and evolution of those cones and their relationship to the venting dynamic. Here we analyse records from lava fountains activity at distinguished vents, captured during the 2014-2015 Holuhraun eruption, and compare them with the developing morphology of spatter cones. We conducted a fieldwork mapping project combining Terrestrial Laser Scanning (TLS) and Unmanned Aerial Vehicle (UAV) aerophoto techniques to characterize the cone morphologies. We recorded videos of the eruption and used edge detection and particle image velocimetry to estimate venting heights and particle velocities. We find that at those locations where spatter cone morphology developed the strongest, the highest lava fountains and larger ejection velocities were recorded, already at the very first days of the eruption. Instead, those sites that finally developed moderate or weak morphologies are also identified as less active lave fountain locations during the early stage of the eruption. The comparison of our topographic datasets shows that spatter cones remain similar in shape but increase in size as the eruption progress. In addition, we suggest that the observed changes in morphology may affect lava ponding in the crater, which in turn is strongly affecting eruption heights. Our results improve the general understanding of landscape evolution at rift zones, and demonstrate the close relationship between the cone morphology and the lava fountain activity at the onset of an eruption.
Highlights
Graben morphology, tensile fractures, normal faults, and magmatic fissures together with aligned cones are common structural and morphological features of rift zones in Iceland and elsewhere
At the 2014–2015 Holuhraun fissure eruption site we carried out video monitoring of the lava fountains and recorded the evolving morphology of the scoria cones
We identified a decrease in the number of active vents producing lava fountains from 57 to 10 during the first 5 days of the eruption
Summary
Tensile fractures, normal faults, and magmatic fissures together with aligned cones are common structural and morphological features of rift zones in Iceland and elsewhere. Rifting events are associated with lateral dike intrusions that originate in a central volcano (Rubin, 1990) and associated eruption locations at fissures (Lipman, 1980; Wright et al, 2006; Ferguson et al, 2010; Medynski et al, 2016). At these fissures, a large number of vents may lead to lava fountaining and are thought to be closely related to the geometry and pressure fluctuations at the underlying feeder dike (Witt and Walter, 2017). The lava fountain is formed when large amounts of volatiles are rapidly released from the magma while the magma is ascending and the pressure is reducing within the conduit (Calvari et al, 2018)
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