| United States Landsat satellites orbit the earth at an altitude of 900 km (560 mi) and carry multispectral scanners that detect electromagnetic radiation reflected from the ground. This type of remote sensing device can be used to delineate geologic and natural features such as bare rock, soil, and mud (gray), bodies of water (dark blue), forests (dark reddish-brown), and crops and grasslands (lighter red). These three Landsat satellite images show Mount Saint Helens, Washington, and its surrounding areas at three different times—seven years before, three years after, and eight years after the volcano (center of each image) erupted on May 18, 1980. |
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