Mountain Building

Question 1

what is a mountain?

Answer 1

• Natural rise, but taller and steeper than a hill

- Commonly greater than 600m high

Question 2

how do mountains affect our lives in BC?

Answer 2

• Tourism
• Skiing
• Climate (Warm clouds forced to rise over mountains -> rain)
• Water
• Mass movement
• Industry

Question 3

how do mountains form?

Answer 3

• Volcanic activity
• Orogeny (main process): crustal shortening/compression
• Block faulting: crustal extension/tension

Question 4

mountain building

Answer 4

• Most mountain belts are at orogenic belts (past and present plate interactions) and at the edges of continents (Ex. Coast mountains – active orogenic belts; Ex. Appalachians – ancient, passive margins, eroded)
• Steady-state process, in equilibrium as long as uplift is balanced by erosion
• Continues as long as plate tectonic section is active

Question 5

orogeny

Answer 5

• Episode of compressional mountain building accompanied by intense deformation, igneous activity, and metamorphism
• Ex. Appalachians formed by Caledonian Orogeny
• Ex. Himalayas – ongoing collision of plates
• Limestone on top of Everest used to be in the ocean

Question 6

areas in orogenic belt

Answer 6

• Accretionary wedge (A)
• Active arc (B)
• Back-arc compression (C)
• Most of BC is an orogenic belt!

Question 7

Accretionary wedge

Answer 7

• Folding, thrust faults
• Eventually faulted, uplifted onto continents
• Sediments scrape off and build up
• Ex. West Coast Vancouver Island

Question 8

Active arc

Answer 8

• Adding volcanoes, plutons -> add volume to crust
• Added heat -> regional and contact metamorphism
• Compression and local extension -> folds, faults, uplift
• Ex. Coast Mountains

Question 9

Back-arc compression

Answer 9

• Thickening crust/metamorphism
• No volume added
• Ex. Canadian Rockies (part of Cordilleran Orogenic Belt)

Question 10

block faulting mountains

Answer 10

• Relatively rare, but exist in California
• Basin and range province – under tension
• Basin (grabens)/range (horsts)
• Ranges = mountains
• Cause uncertain, but could be crustal thinning due to heating up of asthenosphere
• Could also be crustal thinning due to shearing action of San Andreas fault

Question 11

orogenic mountain belts

Answer 11

• Most mountain belts have a complex history
• Ex. Appalachians
• Subduction/volcanism
• Collision of island arcs
• Collision of micro plates
• Erosion post orogeny