DO YOU NEED TO VENT? AT ASKJA VOLCANO, ICELAND

Askja Volcano, Iceland, has over 70,000 years of volcanic history, however monitoring has shown recent uplift of >60 cm since 2021 suggesting inflow of new magma (Iceland Met Office, 2022). Basaltic fissure-style eruptions are the most common type of eruption at Askja. Previous studies have focused on glacial, and <4285 year old post-glacial lavas, but immediate post-glacial volcanism starting ~10 ka has not been described in detail. Post-glaciation volcanism at Askja outcrops as spatter ramparts and cones, scoria cones, and lava flows. Here, we present detailed descriptions, including structure, stratigraphy, and whole-rock geochemistry, of 16 vent locations at Askja that include 70 spatter and scoria cones. Vents are classified as 200 m areas having one or more topographic high points in a conical/semi-conical shape (cone) composed of agglutinated spatter or scoria. Vent locations most commonly have significant deposits of spatter, with only 3 vent locations with scoria deposits >0.25 m thick. Vent sites occur as clusters, chains, or individual cones with the most common vent type outcropping as three or more clustered cones. Relative age dating of these basaltic vent locations, outlined by historic tephra deposits, shows that most of the vents described in this project are >4285 years before present, and include four historic vent locations from the 1921, 1922, 1923-24, and 1961 eruptions. Scoria and spatter cone structures at Askja range in size from 5-200 m in diameter and 1-40 m in height. Some cones have localized collapse areas and six locations have associated lava flows. Individual spatter clasts comprising ramparts around vents range in size from 5 cm to >1 m and scoria clasts range from <2.5-50 cm. Plagioclase phenocrysts are present in spatter at 0-15% of the total composition and a size of <1 mm. Whole-rock geochemistry using XRF shows this phase of volcanism at Askja as basaltic in composition (49.84-51.82 wt% SiO₂), with ranges of 4.63-7.34 wt% MgO, 8.96-12.03 wt% CaO, and 2.16-2.88 wt% Na₂O. Detailed description of eruptive constructs from fissure eruptions at Askja are necessary to help identify most likely future eruption scenarios.