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Instead, Bonis prefers the term "piping feature" -- a decidedly less sexy label for the 100-foot deep, 66-foot wide circular chasm. But it's an important distinction, he maintains, because "sinkholes" refer to areas where bedrock is solid but has been eaten away by groundwater, forming a geological Swiss cheese whose contours are nearly impossible to predict.
The situation beneath the country's capital is far different, and more dangerous.
The lion's share of the city is built on pumice fill -- ash flows made up of loose, gravel-like particles deposited during ancient volcanic eruptions. In places, the debris is piled over 600 feet thick, filling up what would otherwise be a v-shaped valley of faulted bedrock. For those peering into the deep dark depths wondering what might be at the bottom, it's either more pumice fill or bedrock. Mixed with a healthy dose of wreckage from the swallowed-up clothing factory.