A massive subterranean ‘river’ said to be flowing beneath the Amazon region of Brazil is not really a river in the conventional sense, even if its existence is confirmed.
The so-called ‘river’, named the River Hamza, has received wide media coverage following the presentation of a study on it to a Brazilian science meeting last week.
However, BBC news in the United Kingdom says the researchers involved have since clarified that water was moving through porous rock at speeds measured in centimetre a year, not flowing.
Another Brazilian expert said the groundwater was known to be very salty.
Valiya Hamza and Elizabeth Tavares Pimentel, from the Brazilian National Observatory, deduced the existence of the ‘river’ by using temperature data from boreholes across the Amazon region.
The Brazilian oil company Petrobras in the search for new oil and gas fields dug the holes, and Petrobras has since released its data to the scientific community.
The BBc report says that using mathematical models relating temperature differences to water movement, the scientists inferred that water must be moving downwards through the ground around the holes, and then flowing horizontally at a depth of several kilometres.
They concluded that this movement had to be from West to East, mimicking the mighty Amazon itself.
A true underground river on the scale suggested, 6000km long, would be the longest of its kind in the world by far.
Professor Hamza told BBC News that it was not a river in the conventional sense.
“We have used the term ‘river’ in a more generic sense than the popular notion,” he said.
In the Amazon, he said, water was transported by three kinds of ‘river’, the Amazon itself, as water vapour in atmospheric circulation, and as moving groundwater.
“According to the lithologic sequences representative of Amazon [underground sedimentary] basins, the medium is permeable and the flow is through pores, we assume that the medium has enough permeability to allow for significant subsurface flows.”
The total calculated volume of the flow, about 4000 cubic metres a second, is significant, although just a few per cent of the amount of water transported by the Amazon proper.
The underground flow could be confirmed with coastal measurements, scientists suggest
At the same time the speed of movement is even slower than glaciers usually display, never mind rivers.
Jorge Figueiredo, a geologist with Petrobras, disputes whether water really is transported right across the region in this way.
“First of all, the word ‘river’ should be burned from the work, it’s not a river whatsoever,” he told BBC News.
Water and other fluids could indeed flow through the porous sedimentary rock, he said, but would be unlikely to reach the Atlantic Ocean because older rock deposits that would form an impermeable barrier separated the sedimentary basins containing the porous rock.
“The main problem is that at depths of 4000m, there is no possibility that we have fresh water, we have direct data that this water is saline,” said Dr Figueiredo.
Press reports suggested Professor Hamza was optimistic about confirming his results over the next few years using more direct methods.
But, he said, this was not the case.
He said it may be possible to examine directly sediments transported into the Atlantic by the subterranean flow, he said, noting that a zone of relatively fresh water extends into the ocean near the mouth of the Amazon.
BBC News says the research, Indications of an Underground “River” beneath the Amazon River: Inferences from Results of Geothermal Studies, was presented at the 12th International Congress of the Brazilian Geophysical Society in Rio de Janeiro, and has not been published in a peer-reviewed scientific journal.
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