Birgir Vilhelm Oskarsson, Robert A. Askew, Halldór Guðmundsson

Volcanological approaches for assessing the effusion rate of past effusive volcanism are of great importance, to enable proper evaluation of the eruption magnitude and past tectono-magmatic conditions which are relevant for mitigating future volcanism. The reactivation of volcanism on the Reykjanes peninsula in 2021 after an 800-year hiatus, has incited the need for assessing the potential scale and size of future effusive eruptions on the peninsula. With a compilation of the planimetric area of 154 postglacial monogenetic lava fields, and volcanological constraints on these fields, the heat flow model of Pieri and Baloga (1986), as utilized in Harris and Rowland (2009) was used to assess the mean output rate (MOR) of these eruptions, providing insights into the overall effusive capacity of the peninsula. Methods for a qualitative evaluation of the eruption duration of past eruptions are introduced, along with a power regression derived from a the surface temperatures and time extracted from recent eruptions in Iceland, allowing for a theoretical approach to the thermal stage of lava fields with unknown emplacement history. Our first-order assessment on the Reykjanes peninsula indicates that 10% of the eruptions have MOR < 1 m3/s, 35% in between 1 and 10 m3/s, 44% between 10 and 50 m3/s, 8% between 50 and 100 m3/s and 3% between 100 and 200 m3/s. The eruption frequency has undergone minor variations in postglacial time, the only significant variation being the occurrences of long-lived (<5 years) shield eruptions in early and mid Holocene, but short-lived (days to months) fissure-fed volcanism dominated in the late Holocene, with MOR ~10-50 m3/s. The results show the potential scales of future effusive activity on Reykjanes if current tectono-magmatic conditions remain the same.