Central Pennsylvania presents an ancient landscape, worn down by the grind of ice, water, wind, and time. The ridge lines of the Appalachian Mountain chain, once formidable, are now gentle folds rising over fertile valleys. Ice age glaciers shaped the land, smoothing out the mountains and depositing rich soil as the ice melted away.
While the ice has done its work, this natural-color image, taken by the Landsat satellite, reveals another powerful natural force that has had a hand in sculpting the landscape: the Susquehanna River system. The river flows generally south from its headwaters in upstate New York to the Chesapeake Bay. In this image, the river cuts right through several ridge lines, apparently without regard to rock or gravity. Contrary to how things may appear at first glance, the mountains do shape the river’s course. In two places in this image, the river bends west along a ridge line until it finds a gap through which it cuts south. In every place where the river flows through the mountains, it is pouring through a gap that must have existed before. Located north of Harrisburg, Pennsylvania, which is just below the lower edge of the image, the region is called the Susquehanna Water Gap.
The image also illustrates more rapid changes. The trees along the ridge lines are gold, orange, and red, hinting that the coolness of autumn had settled over the region on October 21, 2001, when the image was taken. At lower elevations, the trees remained dark green. Forest once covered the entire landscape, but now, the fertile valleys are filled with squares of pink, tan, and green agricultural fields. Many crops had been harvested, leaving behind golden stubble or red-brown bare earth. Other signs of human habitation are visible in the image. Bright white roads line both the Susquehanna and Juniata Rivers. Small cities—Marysville near the bottom edge of the image and Duncannon near the confluence of the two rivers—are concentrated dots of white-gray. The vegetation along much of the Kittatinny Ridge is a patchwork of various shades of green, a good indication that the landscape has been developed.
Clearly, much can be learned about the geology and land cover of a region from the view from space. But the new perspective also helps us appreciate the beauty of a landscape in a new way. On the ground, or even in an airplane, you could never acquire the distance needed to see the zig-zag shape of the mountains or the spectrum of color presented by the unfolding season. From this distance, the Susquehanna Water Gap region resembles an abstract painting in pastel more than an aerial photograph. So, while exploring Earth from space has taught us a great deal about our home planet, it has also shown us just how beautiful Earth is. To read more about what we have learned about Earth from space, see Earth Perspectives on the Earth Observatory.
Resembling a work of art, this Landsat image of fall colors in the mountains of central Pennsylvania illustrates both the yearly cycle of change in forests and fields and the slow shaping of a landscape over millions of years.
Russia’s Ob River flows from south to north, and each summer, it thaws in the same direction. The result is that an ice jam sits downstream from thawed portions of the river, which is laden with heavy runoff from melted snow.
In the span of three weeks, spring crept over the Siberian landscape surrounding the northern half of the Lena River. Many of the rivers in Earth’s temperate zones run high in the spring when melting snow and spring rain flood river basins. On the Lena River, however, spring flooding is almost inevitable for another reason: ice. Like other north-flowing rivers, the upper reaches of the Lena melt before their downstream counterparts. Because the northern mouth of the river remains frozen while the southern body of the river flows freely, water naturally builds behind the ice, forming a temporary reservoir that drains as the ice dwindles.