AAI team on the summit of Everest in 1992. (L to R: Gopal Sherpa, Todd Burleson, Keith Kerr, and Sirdar Lhakpa Rita Sherpa.) At their feet is a device (the red thing that looks like a traffic signal) left on the summit to measure any movement of the peak. Lasers are directed at the crystals inside it from cities far below, and by measuring how long it takes the laser to bounce back from different distances, scientists can determine how weather and natural erosion are affecting Everest.