The most dangerous road on Earth. That's what they call the narrow, cliff-hugging road in the Bolivian Andes linking La Paz, the world's highest capital, with the lowland Amazonian rainforest. Dr. Rolf Aalto, a member of the research faculty at the University of Washington, knows this route well. He's been working in Bolivia's rugged landscapes for years. Terrain is his business. He is a geomorphologist, someone who studies landforms and the processes that create them.
Aalto's job often takes him into remote, uncharted places. Perilous roads are only one of many challenges. Aalto's special interest is rivers and how they transport mass -- taking rock away from some places and adding to others. "Rivers are the arteries of the continents -- their dispersal system," says Aalto. "In the human body, arteries and capillaries bring oxygen to the cells and veins take away waste. Analogously, rivers are the principal means by which material - water, sediment, nutrients, pollutants and life itself -- is conveyed across continents."
"We don't know much about how large rivers work in pristine conditions since most of them have been dammed, straightened and leveed," he says. "We know a lot about how to engineer them, but not how they function naturally."
The search for large, unaltered river systems brought Aalto to Bolivia to study the Beni, Mamore, and Madre de Dios rivers, which join to form the Madeira, a Mississippi-sized tributary to the Amazon. When he started his research, he had to make his own maps using Landsat satellite images. The detailed topographic information he needed -- measurements of the remote mountains, hills, channels, and floodplains -- was even harder to come by. "Such elevation data are usually available for the United States and other developed countries, but often not for more inaccessible portions of the world," says Aalto.
While he made some field measurements on his own, at great logistical effort, he couldn't survey everywhere. Not like the dual radars of the Shuttle Radar Topography Mission, which spent 11 days orbiting Earth to collect detailed, three-dimensional measurements of most of Earth's landmass. Aalto got his first look at these newly processed data a few months ago. "I've previously been able to survey only a few long transects, generally along river channels," says Aalto. "Now, with these new data, I can already see in exquisite detail a number of fascinating, previously undocumented features. For example, the shapes of the river profiles and floodplain surface reflect powerful, persistent geologic processes that deform and shape the Earth's surface. In lowland Amazonia, these topographic features are subtle, but of fundamental significance, and can now be resolved, measured and studied with the Shuttle Radar Topography Mission data."
Aalto's research in the Amazon basin has two goals. One is to understand the processes and rates of erosion in the mountains, which supply essentially all of the sediment to the rest of the basin. The other is to understand how sediments travel from the mountains across the lowland Amazon. The topographic information the shuttle mapping mission now provides makes his job much easier. "Erosion in the Andes is driven by massive land slides, so the steepness of the hills and rock strength are more important than rainfall," he explains. "For understanding sediment transport, knowing the slope of the river and floodplain tells us the amount of energy that is available to move water and sediment," says Aalto, who is using shuttle topography data to improve his measurements and computer models of how lowland rivers transport sediments.
Elevation data also help pinpoint where sediments are ultimately deposited by showing the subtle undulations in what is an almost flat floodplain. For example, each year 3 billion tons of sediment comes from the Andes, although the majority never reaches the main-stem Amazon River itself. Carried from the mountains by rivers, most of it is trapped in lowland basins along the Andean range front that compose less than ten percent of the Amazon's vast, 6-million-square kilometer (about 2.3 million-square-mile) basin.
"A river is so much more than a pretty, sinuous channel partially filled with water and fish on a summer's day," Aalto says. "The zone of influence of a river is anyplace the water or sediment can reach on a timescale of decades to centuries. By studying the Earth's few remaining natural river systems we are learning lessons that we can then apply to restoring rivers like the Mississippi, Missouri or Sacramento."
Meanwhile, in search of other large, pristine river systems, Aalto left in June to study the Strickland and Fly rivers in Papua New Guinea. Bad roads and other logistical hardships are still a formidable challenge, but having good topographic information won't be. "For geomorphologists like me, the Shuttle Radar Topography Mission is revealing a clear vision of the Earth's surface like never before - a new telescope for our planet. This revelation is going to revolutionize my field."
June 19, 2003