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SYFY WIRE Bad Astronomy

The ancient shields of paradise

By Phil Plait

[Note: At the bottom of this post is a gallery of astonishing pictures of volcanoes taken from space.]

Note to self: visit Tahiti someday.

Why? Because this:

[Click to breathtakenate, and yeah, trust me here, do it.]

This image of Tahiti was taken by Landsat 7 back in 2001. We may think of Tahiti as a tropical paradise -- because it is -- but like so many other islands in French Polynesia it's actually a volcano. In fact, its two: Tahiti Nui, the bigger one to the northwest, and Tahiti-Iti to the southeast. Both are shield volcanoes, built up from lava flows. Nui is older, with hardened lava flows ranging from 300,000 to 1.7 million years old, while Iti is somewhat younger, only a mere 300,000 - 900,000 years old. Both volcanoes have had events where the shield has collapsed, so there are no classic circular holes in their middles.

Not only that, but their appearance has been heavily modified over the millennia by rainfall and erosion. Those deep crevices are where water has flowed down and eaten away at the slopes, and the color is of course from vegetation that thrives there. All of this makes the pair less volcano-looking and more oh-my-god-I-want-to-visit-there-looking.

See that little triangular jut-out of land at the very top of Tahiti-Nui? That's called point Venus, and is where Captain Cook landed to observe the 1769 transit of Venus (you should read that link; it's a cool story). It took them nearly a year to sail from England to Tahiti. Not too many scientific expeditions these days take that long to reach their destinations... with the notable exception, of course, of planetary probes, which can take much longer than that to reach their own Point Venus.

I've been to three volcanoes in my life -- Taburiente on the island of La Palma, Pululahua in Ecuador, and Crater Lake in Oregon (one of the most astonishing places I have ever been). They are magnificent, transcendent places, and one day, I think, I'll find a way to visit this pair of craggy, warm, and fantastically beautiful volcanoes so far away.

NASA Earth Observatory image by Jesse Allen and Robert Simmon, using Landsat data from the U.S. Geological Survey.

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