Agatha swept across Central America bringing torrential rain that killed
more than 100 people and opened a 200 feet (60m) deep sinkhole in
Guatemala City which reportedly swallowed up a three-storey building.
Witnesses claim at least one man went down the hole.
Initial
reaction from geologists was that the hole is a sinkhole. Sink holes
can appear suddenly but take thousands of years in the making. The
gaping holes are usually caused by rainwater gradually eating away at
porous rock such as limestone below the surface, weakening it, and
creating a honeycomb of caverns and caves which can become packed with
mud. Floodwater may have flushed away that mud - leading everything
above it to collapse.
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But according to a new report on Discovery, the hole in Guatemala is not a sinkhole.
The
hole in Guatemala City is not a sinkhole. When you inspect it, it
doesn't even look like one. The sides are clean and featureless, and the
shape is crisp and geometrical. It helps to know that Guatemala City is
in volcanic country, not limestone country. In fact the city, like many
in Central America, sits in a former river valley that is filled to the
brim with loose volcanic tuff. When something compacts it at a deep
level, or when groundwater flow carries it away, the tuff can settle
downward. Reilly interviewed a geologist practicing in Guatemala who
gave us the correct name for this structure and its formative process: a
piping structure. Piping is also called tunnel erosion, and it's always
a concern around large dams, for instance, or when a water main or
sewer line breaks underground. [via About.com]
Incidentally,
a similar hole, 300 ft deep, opened up in Guatemala in 2007 after a
sewage pipe broke pipe just a few blocks from this weekend's disaster.
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