Putting The Blue in Blue Ridge Mountains

What makes the Blue Ridge Mountains blue?

Before we even talk about the color, let’s first talk about the name, the Blue Ridge Mountains.

Technically, the Blue Ridge Mountains are a segment of the Appalachian Mountains. The Blue Ridge runs about 615 miles, from Carlisle, Pennsylvania, through parts of Maryland, Virginia, North Carolina, and South Carolina to Mount Oglethorpe, Georgia. 

The Blue Ridge may be a mountain range, but it is a pretty narrow range. It varies from five to 65 miles wide. The mountains are also not very high, with heights ranging from 2000 to 4000 feet. That’s because the Blue Ridge Mountains are very old. They began forming about 400 million years ago. Wind, rain and the elements have eroded the mountains to their current height.

The Blue Ridge Mountains also provide an incredibly diverse habitat. More than 700 varieties of trees and plants have been found in the region. In many areas, the Blue Ridge Mountains are a temperate rainforest.

And it turns out all of that biological diversity is the reason the Blue Ridge is blue. It’s a combination of biology, chemistry and physics.

The amazing amount of vegetation in the Blue Ridge Mountains, especially the conifers, release what are called Volatile Organic Compounds. VOCs are organic chemicals that easily form vapors at normal temperatures and pressures.

The classes of VOCs called terpenes are naturally occurring hydrocarbons emitted by conifers. In the wild and in large numbers, all of those tiny molecules react with natural ozone molecules already in the air to form new particles and scatter blue light from the sun. Think of how the cue ball scatters the other balls on a pool table. That scattering of light produces a hazy effect over the mountains.

European settlers noticed the bluish haze and coined the term Blue Ridge Mountains. However the Cherokee were the first to use the term, referring to their mountain home as the Shaconage (shah-CON-ug-gee) or 'the land of the blue smoke.'

- Frank Graff

Frank Graff is a producer/reporter with UNC-TV, focusing on North Carolina Science Now, a weekly science series that airs Wednesdays, beginning in August 2013, as part of North Carolina Now on UNC-TV. In addition to producing these special segments, Frank will provide additional information related to his stories through this North Carolina Science Now Reporter's Blog!

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