Tseax Cone

Tseax Cone (/ˈsiːæks/ SEE-aks) is a small volcano in the Nass Ranges of the Hazelton Mountains in northwestern British Columbia, Canada. It has an elevation of 609 metres (1,998 feet) and lies within an east–west valley through which a tributary of the Tseax River flows. The volcano consists of two nested structures and was the source of four lava flows that descended into neighbouring valleys. A secondary eruptive centre lies just north of Tseax Cone on the opposite side of Melita Lake. It probably formed simultaneously with Tseax Cone, but the timing of volcanism at the two eruptive centres is not precisely known; both were formed by volcanic activity sometime in the last 800 years.

The exact timing of volcanism at Tseax Cone has been a subject of controversy due to there being no direct written accounts; radiocarbon dating of plants killed by lava or ejecta from the volcano has yielded ages as old as 625 ± 70 years to as young as 190 ± 15 years. There is also controversy over whether the volcano was formed during one or more distinct episodes of eruptive activity. The single eruptive episode hypothesis has been proposed by researchers as early as 1923 whereas a multi-eruption hypothesis was proposed in 1978. Most research suggests that Tseax Cone was formed during one episode of eruptive activity; new data supporting this hypothesis was reported in 2020.

Tseax Cone is the subject of legends told by the local indigenous people. They describe the destruction of villages along the Nass River by the volcano and the death of several people from inhaling volcanic fumes, although other causes of death may have been involved. As many as 2,000 people are claimed to have been killed by an eruption from Tseax Cone; this would make it the deadliest geological disaster in Canada and the second-worst natural disaster in Canadian history by death toll. Tseax Cone has therefore been described as the deadliest volcano in Canada. Renewed eruptions from the volcano could start wildfires and block local streams with lava flows.

Tseax Cone lies within an ecoregion characterized by mountainous terrain and several streams. Rainforests occur at the volcano, as well as several species of mammals. Lichens and mosses cover most of the lava flows that have issued from Tseax Cone, although rainforests and waterbodies also obscure them. After at least 20 years of pleas for protection, the volcano and lava flows were established as Nisga'a Memorial Lava Bed Provincial Park in 1992. Tseax Cone and its lava flows can be accessed via provincial highways and backcountry roads.