It would have looked pitch black if you were passing overhead in an airplane when the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) on NASA’s Terra satellite was capturing this view of Anatahan Volcano in the early morning (still-dark) hours of February 7, 2008. But unlike humans, ASTER’s view isn’t limited to visible light.
When the satellite passed over this small volcanic island, one of the Northern Mariana Islands, it observed variations in thermal radiation (heat) coming from the surface and the atmosphere. These differences revealed features in the scene that would have been hidden from a person’s view by darkness. Cooler surfaces are darker and warmer surfaces are brighter. The brightest, hottest spot in the scene is the summit caldera of Anatahan Volcano, which has been active off and on since 2003. The tops of scattered clouds (black) are the coldest things in the scene. The purple haze that streams from the summit and disperses to the west is silicate-rich ash from the ongoing eruption.
Since Anatahan began erupting in 2003, people no longer live on the island. But scientists and transportation personnel must still monitor the volcano’s activity because ash and gases released during eruptions can be an aviation hazard, and they can affect air quality in populated places downwind.
NASA image created by Jesse Allen, using data provided courtesy of NASA/GSFC/METI/ERSDAC/JAROS, and U.S./Japan ASTER Science Team.
