Geology, Nass River, British Columbia

Evenchick, C A; Mustard, PS; Greig, C J; McMechan, M E; Ritcey, DH; Smith, G T; Ferri, Filippo

doi:10.4095/225792

Cited by 3 publications

(8 citation statements)

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“…Tseax volcano rests on the sedimentary Bowser Lake group (dated at Jurassic-Cretaceous, JK Bu and JK BCR on Figure 1; Evenchick et al, 2008;van der Heyden et al, 2000). These rocks are grey sandstones intercalated by dark grey and black siltstones, mudstones and conglomerates.…”

Section: Regional and Local Geologymentioning

confidence: 99%

“…A few occurrences of tonalites and monzogranites have also been documented by Carter (1981). Pleistocene volcanic products including basaltic and andesitic deposits (Pb, Figure 1; Evenchick et al, 2008;van der Heyden et al, 2000) are found within 50 km around Tseax volcano. They are columnar-jointed basalts and basaltic breccias assumed to be 175-50 ka old and not associated to the volcanic history of Tseax.…”

Section: Regional and Local Geologymentioning

confidence: 99%

“…The locations of the 3 former Nisga'a villages are shown by white squares. Modified fromEvenchick et al (2008).…”

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confidence: 99%

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Physical volcanology of Tseax Volcano, British Columbia, Canada

et al. 2020

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Tseax volcano erupted ∼ 250 years ago in NW British Columbia, Canada producing tephra deposits and lava flows. Field mapping has defined the stratigraphy of Tseax and the lava flow morphologies. Aerial photogrammetry and bathymetry surveys were used to create a high resolution digital elevation model of the volcano to facilitate mapping and estimates of erupted material volumes. Tseax volcano (∼ 10.4 ± 0.7 × 10 6 m 3 ) comprises an outer breached spatter rampart and an inner conical tephra cone. Tseax is associated with a 32 km long and 0.49 ± 0.08 km 3 basanite-to-tephrite lava flow field covering ∼ 36 km 2 and divided into 4 distinct lava flows with heterogeneous surface morphologies. We present a volcanological map of Tseax volcano at a scale of 1:22,500. This will serve as supporting information for further research on the eruptive history of Tseax volcano and the lava flow field emplacement.

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Section: Regional and Local Geologymentioning

confidence: 99%

Section: Regional and Local Geologymentioning

confidence: 99%

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Physical volcanology of Tseax Volcano, British Columbia, Canada

et al. 2020

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“…GVB, Garibaldi Volcanic Belt; WGC, Wells Gray-Clearwater Volcanic Field; AVB, Anaheim Volcanic Belt; WVB, Wrangell Volcanic Belt; Exp p, Explorer plate (Modified from Edwards and Russell 1999;Edwards and Russell 2000). (C) Identified Holocene volcanic rocks in the Nass Valley area ( BC Hydro 1981;van der Heyden et al, 2000;Evenchick et al, 2008). The Tseax volcanic field is highlighted in red.…”

Section: Introductionmentioning

confidence: 99%

“…The Tseax volcanic field is highlighted in red. Faults and lineaments are from BC Hydro (1981), Evenchick et al (2008). Note that Tseax volcano is roughly located at the intersection of N45 and north-south trending lineaments.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2022

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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 Nisga’a First Nation and is ranked as Canada’s worst natural disaster. Within the Nisga’a culture, Adaawak 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 Nisga’a oral and written histories. The Nisga’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 km3) was erupted in Period A and had a flux of 800–1,000 m3/s. The low viscosity lava reached the Nass Valley, 20 km downstream of the volcano, in “swift currents”, and engulfed the former Nisga’a villages in only 1–3 days, thus likely being responsible for the reported fatalities. The discharge rates progressively diminished to 10–200 m3/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 m3/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 km3 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.

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Inflated pyroclasts in proximal fallout deposits reveal abrupt transitions in eruption behaviour

et al. 2022

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During explosive eruption of low viscosity magmas, pyroclasts are cooled predominantly by forced convection. Depending on the cooling efficiency relative to other timescales, a spectrum of deposits can be formed. Deposition of hot clasts, above their glass transition temperature, can form spatter mounds, ramparts and clastogenic lava flows. Clasts may also be deposited cold, producing tephra cones and blankets. Thus, the deposit and pyroclast type can provide information about eruption dynamics and magma properties. Here we examine pyroclasts from Tseax volcano, British Columbia, Canada. These newly identified inflated pyroclasts, are fluidal in form, have undergone post-depositional expansion, and are found juxtaposed with scoria. Detailed field, chemical and textural observations, coupled with high temperature rheometry and thermal modelling, reveal that abrupt transitions in eruptive behaviour — from lava fountaining to low-energy bubble bursts — created these pyroclastic deposits. These findings should help identify transitions in eruptive behaviour at other mafic volcanoes worldwide.

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Geology, Nass River, British Columbia

Cited by 3 publications

References 0 publications

Physical volcanology of Tseax Volcano, British Columbia, Canada

Physical volcanology of Tseax Volcano, British Columbia, Canada

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

Inflated pyroclasts in proximal fallout deposits reveal abrupt transitions in eruption behaviour

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