A Song dynasty official found seashells in a mountain cliff and deduced a vanished coast
Around a thousand years ago, Shen Kuo noticed a horizontal band of clam shells running along a cliff hundreds of miles from the Pacific. He concluded the spot had once been a shoreline and that erosion and silt had reshaped the land. Such reasoning is the heart of geomorphology, the science of why landscapes look as they do.
Geomorphology studies how the features of land and seafloor form and change through physical, chemical and biological processes near Earth's surface. Two sets of forces compete. Tectonics lifts mountains, builds volcanoes and lowers basins, while water, wind, ice, wildfire, living things and gravity wear the heights down and carry the debris elsewhere. The processes feed back on one another: a mountain range can wring rain from passing air, and that rain then changes how the range erodes. Many researchers are especially interested in such feedbacks between climate and tectonics.
People noticed moving landscapes long ago. In the fifth century BC Herodotus judged from its soils that the Nile Delta was pushing out into the Mediterranean. Aristotle imagined sediment filling the seas until land and water swapped places in an endless cycle. The Persian scholar al-Biruni, studying rocks at river mouths, proposed that an ocean once covered India, and Shen Kuo, who lived from 1031 to 1095, also argued for gradual climate change after petrified bamboo turned up in a dry northern region.
As a formal science it is young. The word seems to have first appeared in an 1858 German work by Laumann and caught on once John Wesley Powell and W. J. McGee adopted it in 1891. William Morris Davis's cycle of erosion, developed between 1884 and 1899, pictured rivers cutting ever deeper valleys until the land flattened, awaiting fresh uplift. It dominated for decades but is now largely set aside as too qualitative. Walther Penck's rival model of continual interplay between uplift and wearing away was fiercely rejected by English speakers, partly because Davis disliked it and Penck died young.
Today's geomorphologists use GPS, laser scanning, dating methods and computer models. Their work predicts landslides, guides river restoration and coastal defence, and extends to Mars, where Earth landscapes serve as analogues.
Source: Geomorphology
