The Thumb (Omineca)

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The Thumb
Highest point
Elevation1,854 m (6,083 ft)
Prominence189 m (620 ft)
Coordinates56°09′47.2″N 126°44′48.8″W / 56.163111°N 126.746889°W / 56.163111; -126.746889Coordinates: 56°09′47.2″N 126°44′48.8″W / 56.163111°N 126.746889°W / 56.163111; -126.746889
Geography
LocationBritish Columbia, Canada
Parent rangeConnelly Range
Hogem Ranges
Omineca Mountains
Topo mapNTS 094D/02
Geology
Mountain typeVolcanic plug
Last eruptionUnknown; Quaternary age[1]

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.

Geology[edit]

The Thumb is the largest in a cluster of roughly seven volcanic plugs. They are surrounded by the remains of eroded cinder cones, lava flows and dikes. Even though the plugs have not been dated, the existence of loose scoria and related intravalley lava flows to the current topography indicates they formed in the last 2.5 million years of the Quaternary period.[1]

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.[1] 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.[1]

See also[edit]

References[edit]

  1. ^ a b c d Wood, Charles A.; Kienle, Jürgen (2001). Volcanoes of North America: United States and Canada. Cambridge, England: Cambridge University Press. ISBN 978-0-521-43811-7. OCLC 27910629.