Explaining the giant holes in Guatemala

They are an amazing sight: even though the initial size figures were eventually corrected to a more comprehensible 66 feet diameter crater, 100 feet deep, those are still impressive and quite regular holes. The one in the image above engulfed a factory in the end of June at Zona 2, Guatemala, while a similar event happened in 2007 a few miles away, Zona 6. Below, an image of the 2007 hole:

While people were puzzled and many joked about these giant holes in the ground, the event in 2007 resulted in two casualties and the one a month ago in one death. Taking this seriously, we have to explain that these features are not mysterious nor have anything to do with “UFO tunnels”. Both features were ultimately the result of intense storms – and it’s an interesting coincidence that the new hole opened after tropical storm Agatha, since Agartha is the legendary city inside the hollow Earth.
These features do not lead to the center of Earth, however, at their bottom a hundred feet down what one finds is quite simply a sewage water collecting system. The infographic below, from Nuestro Diario (June 30th, p.5), illustrates how exactly below the opened hole a water collector tunnel around 10 feet in diameter goes through.

A few days ago a team of geologists also explored the bottom of the Zona 2 hole, you can find the whole Picasaset of photos here. All the soil in the giant hole didn’t disappear magically, it was simply washed away with the water and on to the sewage system. So much so that the sole victim’s body in the Zona 2 hole, Edwin Roberto Velásquez Salazar, was found days later in Las Vacas river, where the water from the collector system ends up.
Not only at the bottom of these giant holes one finds tunnels of the water collecting system: more importantly, perhaps, is that both of these holes were originally vertical shafts, that is, there were already originally vertical holes there, even though they were obviously not that large. Unfortunately many water draining shafts and tunnels were built in the 1950s and some were not properly recorded, and as the city grew some buildings were built over some shafts. That seems to be the case here.
Local geologists suggest then that the heavy water stream from the storm must have damaged the underground collecting tunnels, a problem aggravated by the fact that there was a difference in the level of tunnels. The graphic below (click to enlarge, from Diario de Centroamérica) illustrates, above, the proposed evolution of the holes in the first (above) and second holes.


Add to that that the soil in the city is particularly fragile, basically pumice fill – ash flows made up of loose, gravel-like particles deposited during ancient volcanic eruptions, and there’s no mystery here.
Days after the recent hole, called by many a giant sinkhole, geologist Sam Bonis, who was part of the team that investigated the 2007 case, correctly pointed out that it wasn’t in fact a sinkhole. As he told Discovery News(and National Geographic), "Sure, it looks a lot like a sinkhole. And a whale looks a lot like a fish, but calling it one would be very misleading."
According to Bonis, the hole was rather a “piping feature”, and the further info, photos and graphics here may help understand the giant holes in Guatemala.

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