They even resemble Antarctica's mysterious icequakes.
Studying or simulating natural phenomena from within a laboratory can be difficult. “We don’t have room for a 100-meter dam in our laboratories,” says Dr. Einav, a professor of geomechanics. Instead, the researchers use puffed rice cereal as a surrogate material for naturally-occurring dry snow and rocks—all of which fall under the category of brittle, porous media.
This isn’t the scientists’ first rodeo with Rice Krispies, which, if you didn’t know, are called Rice Bubbles in Australia. (During a previous study, Dr. Einav tells me, he referred to his American colleague as Mr. Rice Krispies, who reciprocated by calling him Mr. Rice Bubbles.) But until this point, the researchers had worked primarily with dry cereal, which is helpful when it comes to modeling dry snow or rock crumbling under pressure. But some collapse events involve water—such as those that occur in ice shelves, sinkholes, and rockfill dams when they’re exposed to large amounts of liquid and high pressure. Studying these is challenging, because they happen incredibly slowly and at such large scale.
That’s where the milk comes in. Adding it to cereal, the researchers found, could simulate these collapses in a sped-up, scaled-down way.
To create the collapse, the researchers poured the cereal into a vertical tube perched atop a granular filter. They applied a constant amount of pressure at the top of the tube, and added milk to the bottom. What happened next was a series of snaps, crackles, and collapses, which the researchers charmingly dubbed “ricequakes.”
During each milk-and-pressure induced reaction, the researchers witnessed several quakes, with the delay before each one growing longer over time. They also noted that each tiny quake was accompanied by an audible popping noise, which, according to Dr. Einav, aurally resembles “a slowing metronome.”
According to Dr. Einav, what’s happening can be explained quite simply. He compares the Krispies apparatus to a train, situated vertically, that comes into contact with liquid at the bottom. The first car that hits the liquid degrades quickly, and crashes. Once it does, the liquid rises upward, weakening the next train car or cereal layer, eventually causing it to collapse under the pressure at the top (albeit more slowly than the first). Eventually, Dr. Einav says, many trains sitting above the liquid base will crash—with each collapse taking progressively longer.
From this simulation, the scientists have been able to create a mathematical equation that can explain when, and why, the ricequakes happen. Though Dr. Einav is quick to say that using models to make real-world predictions is risky, he’s speculated that it might (at least partially) explain some natural phenomena, such as the recurring tidal icequakes of Antarctica. “There are about two daily, each with a magnitude of 7.0, but they’ve slowed down over the years,” he says. “People have explained this in many other ways, many of them likely correct, but they look a lot like the ricequake phenomenon.”
“The way I see it, we now understand the physics. Now other people can use it.”
In part, those other people will be geologists or engineers, who may develop technologies that can, for instance, predict dam collapses. But the other people who can use this research, Dr. Einav points out, could be anyone. This incredibly complex mathematical modeling was mapped out through a five-dollar experiment (excluding the cost of the optic microscope, which, according to Dr. Einav, is among the most expensive microscopes in the world). “We should be giving this to kids to replicate at home,” he says.
