The Thumb (Omineca) facts for kids
Quick facts for kids The Thumb |
|
|---|---|
| Highest point | |
| Elevation | 1,854 m (6,083 ft) |
| Prominence | 189 m (620 ft) |
| Geography | |
| Location | British Columbia, Canada |
| Parent range | Connelly Range Hogem Ranges Omineca Mountains |
| Topo map | NTS 094D/02 |
| Geology | |
| Mountain type | Volcanic plug |
| Last eruption | Unknown; Quaternary age |
The Thumb is a unique mountain found in British Columbia, Canada. It stands about 7 kilometers (4.3 miles) south of Sitchiada Mountain. You can find it on the east side of Bear Lake.
This mountain is special because it sits on the Continental Divide. This is like an invisible line across North and South America. Rivers on one side flow to the Arctic Ocean or Atlantic Ocean. Rivers on the other side flow to the Pacific Ocean. For The Thumb, water from the Omineca River goes to the Arctic Ocean. Water from the Bear River goes to the Pacific Ocean.
How The Thumb Formed
The Thumb is the biggest of about seven volcanic plugs in the area. A volcanic plug is like a cork that forms inside a volcano's vent. This happens when magma (molten rock) hardens inside the volcano. Over time, the softer outer parts of the volcano wear away. This leaves behind the harder plug.
Volcanic History
These plugs are surrounded by what's left of old cinder cones. Cinder cones are simple, cone-shaped volcanoes. There are also old lava flows and dikes. Dikes are cracks in rock that were filled with magma.
Scientists believe these plugs formed in the last 2.5 million years. This time period is called the Quaternary period. They know this because of loose scoria (bubbly volcanic rock) found nearby. Also, the lava flows fit the current shape of the land.
What The Thumb Is Made Of
The Thumb looks like a tall monument. It rises about 189 meters (620 feet) above the land around it. It is mostly made of columnar basalt. This is a type of volcanic rock that forms tall, pillar-like columns as it cools.
You can also find pockets of breccia in The Thumb. Breccia is a rock made of broken rock pieces cemented together. These pieces include sandstone from an older time called the Paleocene period.
The basalt in The Thumb is called alkali olivine basalt. It contains tiny crystals called phenocrysts. These crystals are made of minerals like clinopyroxene and labradorite. Scientists are still studying why these volcanic plugs formed in this specific area. They are on the edge of major volcanic belts in British Columbia.
