The Thumb (Omineca)
- This article is for the officially named summit in the Omineca Country of northern British Columbia. For the unofficially named summit near Vancouver, British Columbia, see The Thumb (mountain). For other uses see Thumb (disambiguation).
|Elevation||1,854 m (6,083 ft)|
|Prominence||189 m (620 ft)|
|Location||British Columbia, Canada|
|Topo map||NTS 094D/02|
|Last eruption||Unknown; Quaternary age|
The Thumb is a mountain located 7 km (4 mi) south of Sitchiada Mountain on the east side of Bear Lake, on the divide between the upper Omineca River and the basin of the Bear River in the Omineca Country of the Central-North Interior of British Columbia, Canada. As the Omineca is part of the Arctic Ocean drainage, via the Peace and Mackenzie Rivers, and the Bear is in the basin of the Skeena River, which drains to the Pacific, The Thumb is located on the Continental Divide.
The Thumb is the most abundant feature in a cluster of approximately seven volcanic plugs combined with dikes, lava flows, and leftovers of eroded cinder cones. Even though the plugs have not been dated, the current form of loose scoria and related intravalley lava flows to the current topography indicates they formed in the past two million years of the Quaternary period.
The vertical structure of The Thumb develops a prominent monument rising approximately 189 m (620 ft) above smoothly rising landscape along the ridge of the Connelly Range. The Thumb is largely made of columnar basalt bounded by pockets of breccia comprising clasts of the basal sandstone that formed during the Paleocene period.
The Thumb consists of alkali olivine basalt along with other Quaternary volcanic plugs in the Omineca Mountains. The basalt comprises phenocrysts of clinopyroxene and labradorite. Volcanic plugs in the Omineca Mountains, such as The Thumb, are located at the outermost boundary of all major volcanic belts in British Columbia, and their origins are not well-defined.
- List of volcanoes in Canada
- List of Northern Cordilleran volcanoes
- Volcanism of Canada
- Volcanism of Western Canada
- Thumb Peak
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