sabato 30 gennaio 2021

Sinkholes in Guatemala

What has been called a "sinkhole" by the popular press formed suddenly in Guatemala in May 2010. Torrential rains from Tropical Storm Agatha and a bad drainage system were blamed for creating the 2010 "sinkhole" that swallowed a three story building and a house. This large vertical hole measured approximately 66 feet (20 m) wide and 100 feet (30 m) deep. A similar hole had formed nearby in February 2007.This large vertical hole, called a "sinkhole" in the popular press, is not a true sinkhole as it did not form via the dissolution either of limestone, dolomite, marble, or any other carbonate rock. Guatemala City is not underlain by any carbonate rock; instead, thick deposits of volcanic ash, unwelded ash flow tuffs, and other pyroclastic debris underlie all of Guatemala City. Thus, it is impossible for the dissolution of carbonate rock to have formed the large vertical holes that swallowed up parts of Guatemala City in 2007 and 2010. The large holes that swallowed up parts of Guatemala City in 2007 and 2010 are a spectacular example of "piping pseudokarst", created by the collapse of large cavities that had developed in the weak, crumbly Quaternary volcanic deposits underlying the city. Although weak and crumbly, these volcanic deposits have enough cohesion to allow them to stand in vertical faces and develop large subterranean voids within them. A process called "soil piping" first created large underground voids as water from leaking water mains flowed through these volcanic deposits and washed fine volcanic materials out of them, then progressively eroded and removed coarser materials. Eventually, these underground voids became large enough that their roofs collapsed to create large holes.
L’affondamento del terreno in Guatemala, a Città del Guatemala, ha prodotto un buco con un diametro di 30 metri e una profondità di circa 60 metri, portandosi dietro decine di edifici. La tragedia è avvenuta nel luglio del 2010 dopo il passaggio del ciclone tropicale Agatha.

I geologi spiegano che l’insolita forma rotonda ha a che fare con la forma delle grotte carsiche sotterranee. Il terreno in questa zona è ricca di calcare e sali che si dissolvono facilmente in acqua. 

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