Fort Selkirk volcanic field

Welcome to the Fort Selkirk volcanic field (FSVF). Located near the confluence of the Yukon and Pelly rivers, the FSVF comprises at least six different eruptive centers ranging in age from ~4.36 million to less than 10 thousand years old. The timing of these eruptions locally coincides with glaciation events in the Yukon, and volcanic textures suggest that one eruption even occurred under an ice sheet! The basalt exposures on the banks of the Yukon River show evidence of this changing landscape through time.

This volcanic complex is located in the traditional territory of Selkirk First Nation.

Included below are three field experiences that showcase different areas of volcanic activity within the Fort Selkirk volcanic field: Volcano Mountain, Ne Ch'e Ddhawa, and exposures along the Yukon River. If you want to learn more about the eruptive history of the volcanic field, continue down past the interactive map to additional content. After you are finished reading, don't forget to navigate back to this section and join us in the field!

The Fort Selkirk volcanic field was built by a series of eruptive centers of different ages, the oldest of which erupted ~4.34 million years ago. Each of these centers has unique volcanic features that leave behind clues that allow geologists to interpret the eruptive environment.

Below is a timeline that outlines the eruptive history of the Fort Selkirk volcanic field. A descriptive summary for each eruptive center is provided, including when it erupted and the key features observed.

Erupted between ca. 4.34 and ca. 2.36 million years ago  ^( 2 ) .

This is where the volcanic history of the Fort Selkirk volcanic field begins! The Wolverine Creek eruptive center is the oldest and predates continental glaciation in the region. Basaltic lava flowed out of multiple vents, reaching as far as the intersection of the Pelly and Yukon rivers around 7 km away. As the hot Wolverine Creek lavas flowed across the riverbed, the cold water quenched the lava, rapidly turning it to glassy, fine-grained basalt with flow thicknesses of up to 100 m. Excellent examples of colonnade and entablature textures are preserved in columnar basalt flows ^( 2 ) .

Erupted between ca. 3.21 and ca. 3.05 million years ago, and again at ca. 2.14 million years ago  ^( 2 ) .

Ne Ch'e Ddhäwa was the next active center, with two discrete eruptive events. The first eruptive period occurred between 3.21 Ma and 3.05 Ma, before regional continental glaciation  ^{( 1 , 2 )} . This eruption produced hyaloclastite tuff – a fine-grained pyroclastic rock comprised mainly of glassy shards  ^( 2 ) .

Hyaloclastite typically forms in a subaqueous setting, meaning the lava erupted beneath a body of water. Scientists who studied this area have interpreted that at this time, the Yukon River was dammed by lava flows produced from the Wolverine Creek vents  ^( 2 ) . The lava flow was so voluminous that it dammed the river and created a lake into which Ne Ch'e Ddhäwa later erupted  ^( 2 ) .

The second Ne Ch'e Ddhäwa eruption occurred around 2.14 Ma and built the edifice of the Ne Ch'e Ddhäwa cinder cone (  ²  ) . The rocks found at the cinder cone's summit are subaqueous volcanic rocks with exotic pebbles and blocks of till that were deposited by glaciers  ^( 2 ) . These exotic pebbles and till blocks are mixed in with the volcanic rocks, suggesting that this eruption occurred under a continental ice sheet that covered this area  ^( 2 ) !

Erupted between ca. 2.58 and ca. 1.5 million years ago  ^( 2 ) .

The next eruption was from the Fort Selkirk eruptive center (FSEC). The age of this eruption is poorly constrained but is considered to be coeval with or just slightly younger than the younger Ne Ch'e Ddhäwa eruption  ^( 2 ) .

The FSEC erupted lavas exposed at the base of a 500 m-long cliff section across the Yukon River and just downstream from the Fort Selkirk townsite, as well as in a poorly-exposed erosional remnant to the south of the Fort Selkirk townsite. In the main cliff exposure, Fort Selkirk eruptive center lavas overlie gravel deposits that preserve westward flow directions of the ancestral Yukon River. At the contact of the lava and gravel units, the presence of basalt pillow breccia and peperite (a mixture of wet sediment and lava) suggests that the lava erupted onto a wet surface, like a flood plain  ^( 2 ) .

Erupted between ca. 1.5 and ca. 1.3 million years ago  ^( 2 ) .

The next active center was the Pelly eruptive center. This eruption was expansive and buried much of the pre-existing topography, Fort Selkirk lava flows, and till and glacial sediment  ^( 2 ) . The eruptions associated with the Pelly eruptive center have been interpreted to have simultaneously dammed both the Yukon and Pelly rivers  ^( 2 ) .

At the confluence of the Pelly and Yukon rivers, volcanic rocks from the Pelly eruptive center record a transition from pillow basalt breccia to columnar basalt. This change from a subaqueous environment to a subaerial environment suggests that the lavas erupted into a body of water and built a prograding  lava delta . Further east up the Pelly River, alternating columnar basalt lava flows and pillow breccias suggest a stack of multiple lava deltas that entered a lake or lakes with changing water levels. The lake(s) were likely created by lava dams in the ancestral Pelly River canyon.

The damming of the Yukon River by Pelly eruptive center lavas created a vast lake that is estimated to have extended to 170 km south (upstream) of the dam  ^( 2 ) ! The narrowest width of the Yukon River in this area is found at Victoria Rock, just west and downstream of the Fort Selkirk town site. This is the suggested as the site of the volcanic dam. The breach of the lava dam is estimated to have occurred around 1.3 Ma  ^( 2 ) . It is not known whether the impounded lake drained progressively or catastrophically.

Erupted ca. 441 thousand years ago  ^( 2 ) .

The Black Creek eruptive center is thought to have produced lava that filled the Black Creek valley. Looking at the outcrops along the Yukon River, the lava flow structures change above and below the confluence of Black Creek. The structures seen upstream of Black Creek are subaqueous lava flows, whereas the sequences downstream are subaerial lava flows. This suggests that there was a damming of the Yukon River in this area, which created a dammed lake upstream of the Black Creek Valley  ^( 2 ) .

The outpouring of lava from this eruptive center was rapid and voluminous, which likely dammed the Yukon River with ease. The lake was thought to be large, extending tens of kilometres upstream  ^( 2 ) . This lava dam was catastrophically breeched, causing massive flooding and the transport of large basaltic boulders downstream  ^( 2 ) .

Erupted ≥ 7530 years before present  ^( 2 ) .

Volcano Mountain (Nelruna) is the youngest eruptive center in the Fort Selkirk volcanic field. This volcano last erupted at least 7530 years ago, producing a cinder cone edifice that to this day retains its classic conical morphology  ^( 2 ) . The rocks found at this location are geologically young, and therefore have not experienced much weathering. Many features of this volcano are still preserved, including part of the crater rim, a potential vent, and evident flow footprints. 

There have been multiple lava flows that erupted from this volcano. The oldest flow that originates out of the northeast side of the crater can be traced for almost 8 km, and likely caused partial collapse of the crater rim. The lava flow is thought to have dammed a small lake called Caitlin Pond  ^( 2 ) .

Lava flows on southwest side of the cinder cone indicate four different eruptive episodes. The furthest south-reaching flow dammed a stream, creating a small lake called Leech Lake  ^( 2 ) .