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Andrew Alden

The Hole in Guatemala

By June 3, 2010

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guatemala sinkholeBy now you must have seen the big cave-in in Guatemala City that happened a few days ago. Discovery.com's Michael Reilly has done some enlightening reporting on the "sinkhole" that helps the way we actually see it. When I first saw the pictures I thought, "Oh, a cenote." Cenotes ("seh-NO-tehs") are round, straight-sided sinkholes that got their name in the Yucatán, where they're a major attraction for divers, among other things. Cenotes and your ordinary sinkholes, with their sloping sides, form when underground limestone is eaten away by groundwater until it collapses.

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. It's also a concern in other Central American cities like San Salvador, where the tierra blanca tuff is prone to compaction. Take a look at the pictures from the Guatemalan government's Flickr site, and see the feature with new eyes.
Photo courtesy Govt. of Guatemala, Creative Commons license

Comments

June 3, 2010 at 11:06 am
(1) Kristen says:

Thanks, Andrew – this is good information, esp. the difference between volcanic & limestone structures. I was thinking it was like a cenote, but wondering where the water was!

June 3, 2010 at 1:13 pm
(2) E Logan says:

I assume a void developed over time, then suddenly collapsed. Where did the material go, that once filled the void that collapsed? I think it likely that some stream emerging at a lower elevation had been transporting subsurface material. Maybe volcanic ash was eroding through subsurface channels, perhaps along an old valley floor. Or was the bedrock below soluble? Otherwise it might mean that a void had opened up in the bedrock from some other cause, say tectonic action. How likely is that?

June 3, 2010 at 1:44 pm
(3) Geology Guide says:

The void was created by compaction, solution and/or transport. Tuff is usually full of void space, both between grains and within grains in the form of bubbles. As time and groundwater action proceed, material moves around, and at some point gravity adjusts the whole thing into a denser state. The nearest analogy in the United States is the collapse craters at the Nevada Test Site, where nuclear bomb explosions make voids in the subsurface.

June 7, 2010 at 4:58 am
(4) Rohit Pasrija says:

Is there possibility? of as we know that the porosity of volcanic ashes and pyroclastic materials have high proportion so limestone deposits in bottom with these type of cave formation may occur so can u please send me the stratigraphy of this area.

June 7, 2010 at 5:09 am
(5) Alex says:

Thanks for the interesting posting!!!

June 7, 2010 at 7:28 am
(6) Anne Domilise says:

This looks like something off of FRINGE. They say bad things can be released from the inner part of the earth. I hope this is not the case here. Totally weird. Somebody needs to drop holy water and blessed salt in the hole, then put a cover on it !! ASAP!

June 7, 2010 at 8:34 am
(7) Ron says:

It seems to me that this pipe in the tuff is analogous to a glacial vertical water pipe with transport away from the pipe at the base of the glacier or in this situation the country rock below the tuff. If this analogy is correct, I am interested in fluvial processes observed from the internal errosion of these tuff sequences, and the sediment loading.

June 7, 2010 at 8:45 am
(8) Sandra says:

How deep is it?

June 7, 2010 at 10:50 am
(9) Maggi says:

Why is it a perfect circle? That alone in the middle of a city would give cause to be more concerned…and not assuming it is simply a sink hole.

Are there oil wells near by?

June 7, 2010 at 11:10 am
(10) Hamid Sadeghipour says:

Before being a volcanic land, the region, maybe, was a salt lake or the ancient sea. then becomes volcanic and when erupts a piece of lime goes up and fall over a wet land and remain there. now, it might be, not a tuff but lime. Karstique effect washed away the lime and a hole remains.

June 7, 2010 at 3:06 pm
(11) Virginia Malone says:
June 7, 2010 at 3:07 pm
(12) Hadj says:

I think, it’s old mine.

June 7, 2010 at 8:58 pm
(13) David Hilyard says:

Piping is a major cause of dam failure. It relates to the presence of dispersive clays – those that are easily mobilised and carried away by water. Most clays are not dispersive, but some are.

In dams, piping failure can lead to sudden, unpredicted, catastrophic dam failure. One of the best known and spectacular piping failures of a dam was Teton Dam in Idaho, which failed at first filling on 5 June 1976. Eleven people died in the flood.

Dams engineers now take many precautions to guard against piping failure.

June 8, 2010 at 2:35 pm
(14) Naomi says:

It would be nice for the media to address this structure by its correct name, piping aka tunnel erosion and not a sink hole. I myself was wondering how a sink hole could have such features. Thankfully, for geologists we can be educated in these rare happenings

July 31, 2012 at 7:05 pm
(15) Steve says:

I live in Guatemala City and remember this event which was in Zone 6 of Gutemala City I believe. There is an underground drainage system, quite deep, installed in the 1960s that has not been maintained for many years resulting in this piping structure. Neighbors had been hearing strange noises for weeks prior to the final collapse of the road and part of a structure. Adding to the problem was urbanization. The drainage system consisted of large vents that land and home owners covered.

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