The Chilcotin Group is a widespread assemblage of basaltic lava flows that formed a volcanic plateau across the Interior Plateau of British Columbia, Canada. These flows are dominantly mafic (basaltic) in composition and collectively produced an extensive, relatively flat landscape of stacked lava sheets and local vents. The Chilcotin plateau runs roughly parallel to the coastal Garibaldi Volcanic Belt and lies inland at approximately 150 km from the Pacific coast, creating an identifiable element of British Columbia’s volcanic terrain regional overview.
Key characteristics
The Chilcotin Group exhibits features typical of flood-basalt-style volcanism and plateau-forming eruptions. Individual flows can be thin to several metres thick but in aggregate form a widespread cover. Common textural and structural traits include columnar jointing where flows cooled, lava flow morphologies ranging from smooth pahoehoe-like to rough aa-like surfaces, and numerous small volcanic centers and cinder cones that sourced some of the younger eruptions. Geologists treat the Chilcotin volcanism as a medium-sized large igneous province with an estimated areal extent up to about 50,000 km2 and a total eruptive volume near 3,300 km3 plateau extent.
Geologic history and timing
Volcanic activity responsible for the Chilcotin basalts began in the Neogene and persisted episodically into the Quaternary. The most voluminous eruption pulses occurred during two principal intervals: roughly 6–10 million years ago and again around 2–3 million years ago. Additional, smaller eruptive events continued intermittently from about 1.6 million years ago to as recently as the late Pleistocene or very early Holocene, so the province retains a partly young volcanic history. Radiometric dating techniques such as potassium–argon and argon–argon methods have been important for establishing these ages in the field and laboratory geochronology.
Distribution, origin and relations
The Chilcotin basalts occupy parts of central and southern portions of British Columbia’s Interior Plateau. They are geographically and genetically distinct from nearby subduction-related volcanic belts; for example, although the Chilcotin plateau runs roughly parallel to the Garibaldi Volcanic Belt, the two represent different volcanic regimes—widespread plateau flows versus more localized arc volcanism. Interpretations of the Chilcotin source include extensional tectonics and back-arc magmatism related to changes in plate interactions, though details of magma source and transport remain subjects of ongoing research tectonic context.
Importance, landscape effects and hazards
Where the Chilcotin basalts cap older sediments or bedrock they influence drainage, soil development and ecology: basalt-derived soils can be thin and rocky on flow surfaces, while older, weathered areas support different vegetation and agriculture. The plateau contributes to scenic landscapes of cliffs, plateaus, and lava escarpments that attract scientific interest and recreation. Present-day volcanic hazard from Chilcotin-type sources is generally low compared with active volcanic arcs, but the record of Pleistocene activity shows that eruptions have occurred within geologically recent time and warrant regional monitoring and study hazard notes.
Research and resources
Ongoing geological mapping, petrologic analysis and geochronological work aim to refine the timing, extent and magma chemistry of Chilcotin volcanism. Such studies help distinguish the plateau flows from neighbouring volcanic provinces and improve understanding of continental flood basalt processes on a moderate scale. For introductions, maps and more detailed studies consult regional geological summaries and academic literature further reading.