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Killing the Mud Softly With...


…concrete balls. Big ones.

The mud volcano in Porong, Indonesia, has now been spewing its thick ooze for almost a year (since May 29, 2006). The stats on how much mud is flowing is scary. Reports claim that mud flows of up to 126,000 cubic meters (that’s 164,801 cubic yards) a day are being recorded.

This is a lot of mud. To put this number into some perspective, it would fill up a 13-story office building with a footprint of 50x50 yards.

Each day.

And there’s no sign that the volcano will be stopping anytime soon, if ever. Given the estimated size of the mud source below the volcano and current flow rates, this mud pie could be emptying out for 10’s, if not 100’s of years!

With nothing traditional working so far (e.g. walls or berms), a radical plan to stop the mud is now underway - thanks to some interesting modeling. The plan, designed by geophysicists, consists of dropping giant concrete balls (weighing up to 250 lbs), linked together on a chain, with four to a chain, into the mouth of the volcano (the largest balls are 16" in diameter). The idea is to "is to make the channel smaller …narrowing it enough to slow the mud’s rise and so decrease its flow rate by up to three-quarters. Forced to go around the chains and balls, the mud will give up some of its energy to friction, vibration and rotation."

The net result is beautifully described: "It will make the mud tired. We’re killing the mud softly."

The geophysicists base their model on an assumed shape for the bottom of the volcano - a champagne glass. The concrete balls on chains then fill the glass in a way similar to small chains of pearls filling up a real champagne glass. Based on estimates of the size of the "champagne glass" they estimate that they’ll need approximately 1500 balls to manage the mud flow.

No one really know, of course, what will happen when these 1500 balls are dropped in the steaming opening, or whether there is even a champagne glass shape inside the volcano. (I have not seen any info on why this assumptions was made, but I imagine it comes from studying the interior configuration of dormant volcanoes.)

The process started in early 2007. There has been some report of progress: in March the flow stopped for 30 minutes. The BBC report on this stoppage does not indicate how many balls have been dropped so far. Nor does it describe the rate of flow once the mud started flowing again. (If any readers know of links with more info, please post them.) A scientist suggests a reason for the stoppage might be "that a new equilibrium between the concrete balls and the mud pressure is almost established and the mud has absorbed the energy of the balls"

If the Big Ball solution really does work, it will be an amazing feat of modeling, engineering, and chutzpah.

Anyone taking on such a massive project, with potentially dire/fatal consequences if the predictions are wrong, needs to worry about unintended consequences. Modeling, and especially engineering modeling, should never lead to an implementation without an aggressive analysis of these side effects.

So it is not surprising that some critics of the Big Ball Theory had pointed out that by slowing down the mud (which most agree will happen because the balls will clearly take up some volume and block mud flow paths), pressure will build up and the mud will simply "find" another place to go - possibly causing an eruption in some weak-walled part of the volcano. This could be why the mud started flowing again.

But, with nothing working to date and the mud still flowing, there came a time when the engineers, officials, politicians, chose an unusual option that could work - and they ran with it.

So here is a situation where a model - as unorthodox as it sounds - is serving as a way out, a savior from a calamity. It’s in this situation that the role of modeling, and modelers, really becomes apparent. Modelers are usually behind the scenes, but in Porong they have sold the idea of their model, which at first glance seems like an outlandish solution. How this happened is most likely a tale of conviction, science, desperation, charisma, and a bunch of…

… concrete balls. Big ones.