I focus a lot of attention on NASA images of space, from our Moon to distant quasars. But NASA has a fleet of satellites which don't look out, they look down, studying our home planet. One of the most amazing and beautiful of their targets are active volcanoes, like Mount Merapi in Indonesia:
[Click to hephaestenate.]
Merapi has been active for some time, blowing out hot ash and dust. This material can blast down the slope of the volcano in what's called a pyroclastic flow, one of the most terrifying events I think the Earth can produce. It's a wall of vaporized rock that can move very rapidly; Merapi's flows have been clocked at 150 kph (90 mph).
In this image, taken with NASA's Terra satellite on November 15, vegetation is shown in red (not green; the detector used by Terra can see light in the near-infrared, where plants are highly reflective, and this is colored red in the images). The ash and rock from the volcano appear gray. You can see where pyroclastic flows have flooded the forests on the volcano slope, destroying whatever plant life they touch. You can also see white clouds, and the gray plume of ash from the crater itself. Note that I have rotated the image so that north is to the left; I did this to make it fit better on the blog.
The long, feather-like finger to the right is the Gendol river, choked with mud flows called lahars which cascade down the mountain (much of the damage done by Mt. St Helens in 1980 was through lahars). Just below the river is a squiggly red region; that's actually a golf course that's been hit by a pyroclastic flow.
Images like this help scientists keep track of volcanoes in near-real time. While there is a chilling beauty to them, satellite images of volcanoes can be used to understand how they behave, and in a very literal sense help save lives. Yogyakarta, for example, is a city of nearly 400,000 people located not quite 30 km (18 miles) south of Mount Merapi. If I lived there, I imagine I'd be very happy indeed that people are keeping a close eye on the not-so-sleepy giant to the north.
Image courtesy NASA/GSFC/METI/ERSDAC/JAROS, and the U.S./Japan ASTER Science Team
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