Reconstructing the holocene volcanic past of El Hierro, Canary Islands

Abstract

We present a geochronologic study with unprecedented detail from 42 Holocene subaerial volcanic edifices of El Hierro Island, Canary Islands. The study of new and published K-Ar, 40Ar/39Ar, 14C, and paleomagnetic ages, constrained by stratigraphic, geomorphic, and anthracological criteria, significantly improves the geochronologic framework of the Holocene volcanism at El Hierro. Our combined experiments show that radiocarbon and paleomagnetic dating were the best methods to determine this young volcanism's age. Indeed, small amounts of 40Ar∗ detected in most dated samples do not allow for calculating geologically significant ages. The preliminary anthracological study of charcoals is recommended before 14C dating. Thirty-six eruptive events (86 % of the total) were retained for the geochronological model developed with ChronoModel combining radiocarbon and paleomagnetic and using the Bayesian inference. Seventeen eruptions were dated for the first time. The Holocene eruptive activity at El Hierro exhibits significant variability over time, with recurrence intervals ranging from 34 to 1078 years. The most recent subaerial eruptions were Lomo Negro, 1412 [1560, 1242] cal BP (MAP, mode of the posterior distribution, and 95 % highest posterior density (HPD) interval) and Montaña del Tesoro, 1059 [1206, 967] cal BP. In addition, historical records suggest possible submarine eruptions in 1721, 1777, and 1793, as well as the more recent and well-documented Tagoro volcano submarine eruption (2011–2012 CE). This recent low recurrence subaerial volcanic activity is unusual for an oceanic volcanic island in the juvenile shield growth stage. The volcanic edifices resulted from hybrid Strombolian monogenetic eruptions with alternating or simultaneous emission of pyroclastic tephra and lava flows. The absence of lava flows in the eruptions of the highest part of the island's summit is worth noting. This volcanic activity focused on the three rifts that configure the tetrahedral shape of the island, although the NW rift concentrated 50 % of the eruptions. These results contextualize the volcanic hazard of El Hierro in the face of eventual future eruptions.