Humans may surpass other natural forces as earth movers

07/08/04

Think of large earth moving projects: highway interchanges, coal mines or Boston's Big Dig. According to Roger LeBaron Hooke, a University of Maine scientist, such activities have propelled humans into becoming arguably the most potent force in shaping the planet, surpassing rivers, wind and other natural phenomena. He finds this achievement troubling, and other scientists are taking note.

Hooke taught at the University of Minnesota until1999 and is now a UMaine research professor in the Department of Earth Sciences and Climate Change Institute. He studies glaciated landscapes and has worked in Maine, the Canadian Arctic and Sweden on the forces that molded ice sculpted hills, built gravel ridges and left large landforms such as Cape Cod and Long Island.

In the early 1990s, a newspaper report on the annual number of housing starts in the United States led Hooke to wonder just how much earth was being displaced by human activity. He gathered data on residential subdivisions, road construction and mining. His goal was to estimate the amount of soil and rock that humans move from one location to another through activities akin to the forces of nature that he also studied.

In 1994, Hooke published the results in a paper in GSA Today, a journal of the Geological Society of America. He estimated that on a worldwide basis, humans move more of the planet around, about 45 gigatons (billion tons) annually, than do rivers, glaciers, oceans or wind. For comparison, he estimated that meandering rivers may move about 39 gigatons of sediment a year. Others have estimated that rivers deliver about 24 gigatons of sediment to the oceans each year. Even that enormous figure can be partly attributed to people. Soil erosion from farm fields, construction sites and other sources contributes significantly to river sediment loads.

Continuing his research, Hooke has put human earth moving into an historical context. After all, people moved rock to build monuments such as Stonehenge in England and pyramids in Egypt and the Americas. In the journal Geology in 2000, Hooke estimated that over the last 5,000 years of human history, the total amount of soil and rock moved by people would be enough to build a mountain range about 13,000 feet high, 25 miles wide and 62 miles long.

In the last century, powerful technologies have enabled people to accelerate this process. At current rates, the size of that metaphorical mountain range could double in the next 100 years, he wrote. "One might ask how long such rates of increase can be sustained and whether it will be rational behavior or catastrophe that brings them to an end."

"I come at this from an environmental point of view," Hooke says. "We've been at it for a century at this level. I wonder how much longer we can continue making a mess of the planet."

Among the environmental problems linked to these activities are acid mine drainage and river sedimentation. Mountaintop removal, a technique for strip mining coal in the Appalachian coal belt, results in the destruction of river valleys, he adds.

Although he is not conducting new research in this area, geologists continue to show interest in his ideas. He gave a presentation in 1998 to the annual meeting of the American Association for the Advancement of Science. The Geological Society of America has invited him to give a presentation at a symposium in November on Human and Ecosystem Vulnerability.

How humans treat the land, Hooke says, can have unintended consequences. "The Dust Bowl of the 1930s resulted in part from clearing the land," followed by severe drought. "We don't know what causes these (climate) conditions, but there's no reason they couldn't recur."

Source: Eurekalert & others

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