The Rif (here and here) had explained the Mishna (and gemara's) statement on Shabbat 147b about a piloma as referring to an area with quicksand. (Others explain differently.)
"YOU MAY NOT GO DOWN TO A PILOMA":From the Rif's explanation of the metziut we see that there seems to be no concern of drowning, just of being stuck. We also see that it takes many people to bring him out.
What is the reason? Because of sinking [in the clay soil].
{The Rif explains this as a quicksand like substance:}
To explain: it is a valley, and there is there water, underneath which is clay which is like glue, and if a man goes down there, we fear lest he sink into that clay and get stuck there, unable to ascend until they assemble other men and bring him out from there.
And there is one who says that one who bathes in particular valley in cooled, and those particular waters loosen the bowels.
From the Reuter's article, on the study of quicksand:
Quicksand is not the bottomless pit portrayed in Hollywood films that sucks in unsuspecting victims and swallows them whole.It is true the more people struggle, the deeper they will sink into the soupy mixture but its buoyancy makes it impossible to be completely submerged, scientists said on Wednesday.
...
He and his colleagues showed that Hollywood had got it wrong by measuring the viscosity, the resistance to flow, of quicksand and its sinking ability.
They also calculated the amount of force necessary to get a trapped foot out -- and found it was the equivalent needed to lift a medium-sized car. Their findings are reported in the science journal Nature.
...
The scientists advised people trapped in quicksand not to panic and to wiggle.
"All you have to do to get your foot out is to introduce water into the sand and if you can do that along your leg by wiggling your leg around, that is the best way to get out," Bonn said.
This is a good alternative to waiting for many people to gather.
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