The soft, dark grey substance that geologists call “quick clay” is composed primarily of small flaky particles and a great deal of water. It contains very little of the electrolytic salts that tend to bind normal soil particles together.
All of which means that the slippery stuff has another distinctive characteristic: it is thixotropic—a sudden shock can transform it from a solid to a liquid.
Residents of Anchorage, Alaska, saw a dramatic demonstration of that strange phenomenon during the disastrous 1964 earthquake, says Columbia University Geologist Paul Kerr, whose investigation is described in the current issue of Scientific American. While probing beneath the battered sand, gravel and silt surface of Anchorage during the past two summers, Kerr studied an underlying layer of quick clay from 10 to 30 ft. thick. During the three minutes of the quake’s violent up-and-down jolting, he concluded, some of the quick clay under Anchorage turned into liquid, triggering the damaging landslides that literally floated large sections of land to new locations.
To minimize damage from future Alaskan earthquakes, Army engineers are experimenting with a technique already used in Norway: forcing electrodes into the layer of clay and passing high-amperage currents between the electrodes to reorient the clay particles. Scientists are also conducting laboratory experiments that could some day put Anchorage on more solid ground. By pumping enough calcium salts into the clay to bind its particles together by electrolytic action, they hope to make the clay more viscous, resistant to shock and no longer thixotropic.
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