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). Infobox Mountain
Name=The Thumb
Photo=
Caption=
Elevation=Convert|1854|m|ft|0|abbr=on
Location=British Columbia, Canada
Range=Connelly Range
Hogem Ranges
Omineca Mountains
Prominence =Convert|189|m|ft|0|abbr=on
Coordinates =coord|56|09|47.2|N|126|44|48.8|W|type:mountain_region:CA|display=inline,title
Topographic
NTS 094D/02
Type=Volcanic plug
Volcanic_Arc/Belt=
Age=
Last eruption=Unknown; Quaternary age
First ascent=
Easiest route=

The Thumb is a mountain located Unit km|7|0 south of Sitchiada Mountain on the east side Bear Lake, on the divide between head of Omineca and Bear Rivers, British Columbia, Canada.

Geology

The Thumb is the largest among a cluster of approximately seven volcanic plugs which are associated with dikes, flows, and remnants of cinder cones. Although they have not been dated, the existence of loose scoria with open vesicles and the relationship of intravalley flows to the present topography indicate a Quaternary age.cite book|last=Wood | first=Charles A. | coauthors=Kienle, Jürgen| chapter= | pages= | title=Volcanoes of North America: United States and Canada | year=2001 | edition= | publisher=Cambridge University Press | location=Cambridge, England| isbn= 9780521438117|oclc= 27910629]

The steep-sided structure of The Thumb develops a prominent landmark which rises approximately Unit m|189|0 above gently sloping benchland near the crest of the Connelly Range. The Thumb is largely made of columnar basalt bounded by vesicular breccia comprising accidental clasts of the underlying Paleocene sandstone.

Alkali olivine basalt from The Thumb and other Quaternary plugs in the Omineca Mountains usually comprise phenocrysts of labradorite, clinopyroxene, and olivine. These volcanic plugs lie outside the major volcanic belts of British Columbia, and their origin is not well-defined.

ee also

*Volcanism in Canada
*List of volcanoes in Canada
*Thumb Peak

References