sierraclub.org - sierra magazine - may/june 2011 - grapple: woe is us
"It Was a Mistake" | Sympathy for the Devils | You Get What You Pay For | As the World Warms |
Woe is Us | Up to Speed
Woe Is Us: Ready, set, panic.
John UelandIf a tree falls in a forest and no one hears it, does it cause an earthquake? After studying the 2010 earthquake in Haiti that killed more than 200,000 people, University of Miami earth scientist Shimon Wdowinski concluded that the temblor may be linked to severe deforestation, which has removed 98 percent of the tree cover in Haiti's mountains.
With no roots to hold them together, the bare hillsides eroded much faster than forested ones would have. Then, in 2008, Haiti was
hit by two hurricanes and two tropical storms. Flooding further hastened erosion, transferring masses of sediment from the mountain slopes to the mouth of the Leogane Delta—just north of the earthquake's epicenter. That shift in weight, Wdowinski believes, was enough to rupture the previously unknown fault.
"Earthquakes have friction forces they have to overcome for the earth to move," he explains. "It's hard to move two blocks if they are [pressed] very tightly together.
If we remove something from on top, we bring it closer to the [point] where the two blocks can slide."
That something doesn't have to be soil. It can also be ice. Researchers from NASA and the U.S. Geological Survey say that a recent uptick in seismic activity in southern Alaska followed the retreat of glacial ice.
In other words, as the planet warms, it may also shake, rattle, and roll.
—Dashka Slater
Up to Speed