Search for: All records

Abstract Basaltic lava flows can be highly destructive. Forecasting the future path and/or behavior of an active lava flow is challenging because topography is often poorly constrained and lava has a complex rheology and emplacement history. Preserved lavas are an important source of information which, combined with observations of active flows, underpins conceptual models of lava flow emplacement. However, the value of preserved lavas is limited because pre-eruptive topography and, thus, syn-eruptive lava flow geometry are usually not known. Here, we use tree-mold data to constrain pre-eruptive topography and syn-eruptive lava flow geometry of the July 1974 flow of Kīlauea (USA). Tree molds, which are formed after advancing lava encloses standing trees, preserve the lava inundation height and the final preserved thickness of lava. We used data from 282 tree molds to reconstruct the temporal and spatial evolution of the ~ 2.1 km-long July 1974 flow. The tree mold dataset yields a detailed dynamic picture of staged emplacement, separated by intervals of ponding. In some ponded areas, flow depth during emplacement (~ 5 m) was twice the preserved thickness of the final lava (2–3 m). Drainage of the ponds led to episodic surges in flow advancement, decoupled from fluctuations in vent discharge rate. We infer that the final breakout occurred after the cessation of fountaining. Such complex emplacement histories may be common for pāhoehoe lavas at Kīlauea and elsewhere in situations where the terrain is of variable slope, and/or where lava is temporarily perched and stored. 

Abstract Viscosity is a fundamental physical property that controls lava flow dynamics, runout distance, and velocity, which are critical factors in assessing and mitigating risks associated with effusive eruptions. Natural lava viscosity is driven by a dynamic interplay among melt, crystals, and bubbles in response to the emplacement conditions. These conditions are challenging to replicate in laboratory experiments, yet this remains the most common method for quantifying lava rheology. Few in situ viscosity measurements exist, but none of those constrains the spatial evolution of viscosity along an entire active lava flow field. Here, we present the first real-time, in situ viscosity map of active lava as measured in the field at Litli-Hrútur, Iceland. We precisely measured a lava viscosity increase of over two orders of magnitude, associated with a temperature decrease, crystallinity increase, and vesicularity decrease from near-vent to distal locations, crossing the pāhoehoe–‘a‘ā transition. Our data expand the limited database of three-phase lava viscosity, which is crucial for improvements and validation of the current numerical, experimental, and petrological approaches used to estimate lava viscosity. Further, this study showcases that field viscometry provides a rapid, accurate, and precise assessment of lava viscosity that can be implemented in eruptive response modeling of lava transport. 

Abstract The basalts of the 2021 Fagradalsfjall eruption were the first erupted on the Reykjanes Peninsula in 781 years and offer a unique opportunity to determine the composition of the mantle underlying Iceland, in particular its oxygen isotope composition (δ¹⁸O values). The basalts show compositional variations in Zr/Y, Nb/Zr and Nb/Y values that span roughly half of the previously described range for Icelandic basaltic magmas and signal involvement of Icelandic plume (OIB) and Enriched Mid-Ocean Ridge Basalt (EMORB) in magma genesis. Here we show that Fagradalsfjall δ¹⁸O values are invariable (mean δ¹⁸O = 5.4 ± 0.3‰ 2 SD,N = 47) and indistinguishable from “normal” upper mantle, in contrast to significantly lower δ¹⁸O values reported for erupted materials elsewhere in Iceland (e.g., the 2014–2015 eruption at Holuhraun, Central Iceland). Thus, despite differing trace element characteristics, the melts that supplied the Fagradalsfjall eruption show no evidence for¹⁸O-depleted mantle or interaction with low-δ¹⁸O crust and may therefore represent a useful mantle reference value in this part of the Icelandic plume system.