Winter may have been more than two months away when the MODIS on NASA's Terra satellite captured this image on October 7, 2007, but the Alaska Mountains of south-central Alaska were already coated with snow. Purple shadows hang in the lee of the peaks, giving the snow-clad land a crumpled appearance. White gives way to brown on the right side of the image where the mountains yield to the lower elevation Susitna River Valley. The river itself cuts a silver winding path through deep green forests and brown wetlands and alpine tundra.
Extending from the river valley, like branches and twigs off the trunk of a winter-bare tree, are smaller rivers that originated in the Alaska Mountains. The source of these rivers is evident in the image. Smooth white tongues of ice extend into the river valleys, the remnants of the glaciers that carved the valleys into the land. Most of the water flowing into the Gulf of Alaska from the Susitna River comes from these mountain glaciers. Glacier melt also feeds glacier lakes, only one of which is large enough to be visible in this image. Immediately left of the Kahiltna River, the aquamarine waters of Chelatna Lake stand out starkly against the brown and white landscape.
The glaciers provide an outlet for snow and ice that build in the Alaska Mountains. Two of the glaciers shown in this image, the Kahiltna Glacier and the Ruth Glacier, originate on Mount McKinley (not shown), the tallest mountain in North America. At just over 70 kilometers (44 miles) in length, the Kahiltna Glacier is also the longest glacier in the Alaska Range.
Text and image courtesy of NASA's MODIS Land Rapid Response Team.