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Chronology and Eruption Dynamics of the Historic∼1700 CE Eruption of Tseax Volcano, British Columbia, Canada

2022; Frontiers Media; Volume: 10; Linguagem: Inglês

10.3389/feart.2022.910451

2296-6463

Yannick Le Moigne, Glyn Williams‐Jones, Nathalie Vigouroux, James K. Russell,

Tree-ring climate responses

Despite having relatively short timespans of eruptions, monogenetic volcanoes can pose significant risks to the nearby population. Here, we describe the ∼1700 CE eruption of Tseax volcano, British Columbia, which killed up to 2,000 people of the Nis g a’a First Nation and is ranked as Canada’s worst natural disaster. Within the Nis g a’a culture, Adaawa k stories preserve an observational account of the Tseax eruption. In this study, we establish the chronology of the eruption by integrating field observations and petrophysical data informed by Nis g a’a oral and written histories. The Nis g a’a stories corroborate the short duration and exceptional intensity of the eruption as recorded in the volcanic products. The eruption was divided in two main periods: 1) Period A and 2) Period B. 1) The eruption started in a typical Hawaiian style with low levels of lava fountaining that built up a spatter rampart. This pyroclastic edifice was breached by voluminous pāhoehoe lavas erupted at high discharge rates. We estimate that almost half of the emplaced lava volume (0.20 km 3 ) was erupted in Period A and had a flux of 800–1,000 m 3 /s. The low viscosity lava reached the Nass Valley, 20 km downstream of the volcano, in “ swift currents ”, and engulfed the former Nis g a’a villages in only 1–3 days, thus likely being responsible for the reported fatalities. The discharge rates progressively diminished to 10–200 m 3 /s until the end of this first eruptive period, which lasted a few weeks to a few hundred days. 2) The Period B eruption produced two ‘a‘ā lavas with discharge rates <50 m 3 /s. This period was also characterised by an explosive phase of eruption that built a 70 m high tephra cone overlapping with a spatter rampart; Period B lasted approximately 20 days. In total, the eruption produced 0.5 km 3 of volcanic materials (mostly in the form of lava flows) on the order of weeks to a few months. The mountainous terrain significantly controlled the emplacement of lava flows that reached long distances in a short amount of time. Our work shows that, under certain conditions, eruptions of small-volume monogenetic volcanoes ca pose risks comparable to flank eruptions on long-lived shield volcanoes.