Neighboring residents couldn’t believe what they were seeing on a road in Tierra Amarilla, a town of about 15,000 in the Atacama region of northern Chile.
A huge circular crater 32 meters wide and 64 meters deep appeared in the middle of a road that crosses land owned by a mining company. A week later, the hole has widened: its diameter is now 36.5 meters, according to the latest satellite measurements.
Chile’s National Geology and Mining Service (Sernageomin) ordered the mining company Candelaria to halt all operations in the area.
It also opened disciplinary proceedings against the company, while a team investigates the possible causes of the sinkhole.
how did it come about
Geologists consulted by BBC News Mundo, the BBC’s Spanish-language news service, explained that there are several natural events or the result of human activity that could cause such a sinkhole.
But they mainly considered two: the first would be related to the intense rains that fell in the region in July.
“You have several layers in the soil, and there are several ways that water can erode,” says Chilean geophysicist Cristian FarÃas, director of civil construction and geology at the Catholic University of Temuco in Chile.
He explained that “when a lot of rainwater falls on soils with a high gypsum content, the water percolates and corrodes the entire lower part for several days, which takes away the sustainability of the upper part and ends up generating a collapse”.
The second hypothesis points to the influence of mining activity in the area. The Candelaria mining company mines a copper deposit in Tierra Amarilla, and the galleries of its mine penetrate underground, both around the hole and below it to a much greater depth.
“Preliminary information that is circulating points to the intervention of the mining company that carried out an excessive exploitation of minerals in that area”, says Cristóbal Muñoz, director of the informative NGO Red GeocientÃfica de Chile.
He points out that the company “had a forecast to extract 38,000 tons of ore, but it extracted about 138,000 tons, more than triple” in that deposit.
The mining intervention may have destabilized the soil, according to him, diverting groundwater from its natural course and emptying aquifers, creating spaces that favor the ground to sag and fall due to its own weight, forming the crater.
Candelaria recognizes, in turn, the overexploitation of minerals, but guarantees that it was totally legal. “In relation to over-extraction, this was reported by the company itself to the authorities,” said the company’s public relations manager, Edwin Hidalgo.
An industry source explained to BBC News Mundo that it is common for copper miners to extract more material than estimated due to the detonation of explosives, among other reasons.
The company representative claimed that it is too early to draw conclusions and highlighted that “the different facts that may have caused the sinkhole are being investigated, among which the precipitation recorded in July stands out”.
Residents of Tierra Amarilla organized a protest on Sunday (7), and the mayor, Cristóbal Zúñiga, asked the mining company to assume its responsibility, although he did not directly name it as the culprit, pending the conclusions of the investigation.
Chile’s Minister of Mines Marcela Hernando promised, in turn, to go “to the last consequences” to punish those responsible once they are identified.
The more the hole will get bigger
Landslides on the walls of the sinkhole have been constant in recent days, to the point of increasing its diameter by 450 cm to the current 36.5 meters.
“First it started to widen at the bottom; then it started to create an asymmetrical shape, and the one on top has no support, so it starts to fall and slowly but dramatically widens until it reaches the shape of a cylinder,” he noted. Farias, author of the book “Volcanes y earthquakes” (volcanoes and earthquakes).
Therefore, the forecast is that the hole will continue to grow at least until the diameter at the surface is equal to that at the bottom, which is 48 meters.
Muñoz believes, however, that it could increase even further if there are further destabilizations on the ground. “Anyway, it couldn’t be more than 200 or 300 meters, which is what matters to us, because the nearest village is 600 meters away,” he declared.
He did not rule out, however, that the phenomenon is reproduced in other areas of the region. “The areas that would be more susceptible to the occurrence of other sinkholes are also being studied,” he said.
It is not the first time that such a phenomenon has happened in Tierra Amarilla.
In November 2013, a 20-meter-long, 30-meter-wide, 30-meter-deep crater appeared after the collapse of an underground structure at a mining operation.
why is it circular
It also drew attention that the crater forms an almost perfect circle. “The round appearance of such a hole is due to the shape of the collapse,” said Cristian FarÃas.
The geophysicist explained that the collapse “begins at a point and extends symmetrically, that is, to all sides, radially, and this causes everything that collapses to do so in a circle and stop at some point, when it meets stability.
“Many collapse structures in nature occur this way. When volcanoes, for example, collapse because the volcanic edifice falls under its own weight, or because there were fluids that are no longer there, the structure that is generated is often quite circular; sometimes a little more oval, but more often circular”.
What will happen to the crater
It is also unclear what the future holds for the unexpected sinkhole of Tierra Amarilla. Will the hole be covered or will it be at the mercy of the weather?
“The volumetric capacity of this sinkhole is quite large. To be honest, it cannot be covered easily, so a solution would be to surround this perimeter and put up security barriers”, evaluates the director of the Red GeocientÃfica de Chile.
For Muñoz, it is important to “ensure that people do not approach to take pictures”, as accidents can occur. He further stated that even if he tried to cover it up, it might be in vain due to the very nature of the hole.
“You have to think that part of the land that fell is no longer below, because it has a fluid that is water. When it fell, it was like a river.”
The miner’s public relations manager assured, in turn, that much of the sediment would have accumulated at the bottom of the hole, reducing its depth from 64 to 62 meters, according to his latest measurements.
This text was originally published here.
