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SYFY WIRE Bad Astronomy

The Wolf of the Galapagos

By Phil Plait

It’s been a while since I’ve posted an amazing volcano picture from space, so here you go: The Wolf volcano on the Galapagos island of Isabela. But it’s not what you think:

This shot was taken by NASA’s Terra Earth-observing satellite on June 11, 2015, a few weeks after an eruption. You can see the caldera near the bottom of the photo, with a weak plume still flowing out.

You might think the red is hot lava, but everything is not as it seems. Usually, color images are a combination of images taken in blue, green, and red light, then combined to make the picture look as close to “real” as possible.

But this image is a composite of three pictures taken in green, red, and near-infrared light. In the final image, green is mapped as blue, red as green, and infrared as red! I know, that’s weird, but it makes interesting things easier to spot. For example, in near infrared, vegetation is highly reflective, and since IR is mapped as red in the photo, wherever you see red you’re seeing plants! That’s not hot lava at all; quite the opposite: It’s where life is thriving.

Fresh lava from the eruption (which has since cooled quite a bit) is brownish. The eruption in May sent lava to the east and south, and you can see it stretching off to the right. Where it flowed over the vegetation it erased the red and covered it with brown. Or, if you were there, you’d see it as a darkish charcoal color covering the green of plants.

In space imagery as in life, what you see depends on how you see it.

Happily, the flows were away from the habitats of some rare animals that live on the island to the north and west. The unbroken stretches of red there means to me that it’s been a while since any lava flowed over that way.

Perhaps they’re safe for now. But volcanoes can be tricky. Images like this help scientists gauge what volcanoes are doing, something I’m all for. Not everyone feels that way, of course, but then, they’d be wrong. The more we understand about the planet under our feet, the better.

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