Shackles --
The Rockies are higher and sharper quite simply because they're newer
and less eroded.
Geologists tell us that the last of the Appalachians were formed about
270 million years ago after the collision of the North American and
African continents. At that time plate tectonics lifted the entire
chain, much of which had been formed between 570 million and 1 billion
years ago.
For about 100 million years, they've not been growing but instead have
been subject to erosion from wind, water and glaciers. The last major
Ice Age 2-3 million years ago covered all but the southern
Appalachians and contributed significantly to the erosion. This U.S.
Geological Service page notes specifically when each of the major
ranges in the Appalachians were formed:
USGS
"America's Volcanic Past," (undated)
http://vulcan.wr.usgs.gov/LivingWith/VolcanicPast/Places/volcanic_past_appalachians.html
By contrast, when the Appalachians were being formed the western
United States was covered by a shallow sea. The plate tectonics which
today bring earthquakes and volcanic activity to the West Coast only
started about 130 million years ago. The Colorado Rockies were formed
about 70 million years ago, according to the USGS:
"America's Volcanic Past -- Rocky Mountains" (undated)
http://vulcan.wr.usgs.gov/LivingWith/VolcanicPast/Places/volcanic_past_rocky_mountains.html
Even newer -- only about 36 million years old -- are the mountains of
the Pacific Coast. Again, plate tectonics provide the force to lift
the landscape and the heat for volcanic activity:
"Pacific Mountain System" (undated)
http://vulcan.wr.usgs.gov/LivingWith/VolcanicPast/Places/volcanic_past_cascade_range.html
Google search strategy:
Formation of Rocky Mountains
Formation of Appalachian Mountains
Best regards,
Omnivorous-GA |
