The snow-capped Alps of Switzerland occupy the upper right half of this infrared satellite image, taken in the spring of 1997. Glacial valleys wend their way through the mountains from the highest in the northeast down towards the lower slopes in the southwest. Until 12,000 years ago glaciers extended to much lower altitudes than they do today, carving out the valleys that are now filled by lakes, the four largest of which are Maggiore, Lugano, Como and d'Iseo (from northwest to southeast). Further south, beyond the alpine foothills, is the patchwork of fields that covers the flat plains of the industrialized and agriculturally productive Po River valley.