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Robbie Shone

Flash Flood in China's Quankou Dong Cave

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Robbie Shone

By Hazel Barton as told to Jed Lipinski

TONGZI, CHINA, 2011—Deep inside the mountain, we hear the sound of a river. The four of us—all researchers who study caves—are exploring Quankou Dong, or Big Spring Cave, in a remote, mountainous part of China, just south of Chengdu.

The “big spring” is a river that runs through a passageway from one end of the enormous cave to the other. Along the way, it churns into class 4 rapids. Hours earlier, we’d entered through a dry passage. Now, it’s full of water, rising fast.

The cave’s entrance is stunning: 100 feet wide, 300 feet high. Once inside, you pass through Cloud Ladder Hall, a 16-acre room so high it has its own weather system. One of the largest cave chambers in the world, it rises more than 1200 feet, though its roof is typically hidden by clouds.

We first went inside Quankou Dong in 2008, after it’d been discovered the year before, and we had been back several times. On one occasion, I slipped on a rock, fell in, and got tossed around in the rapids! It wasn’t funny at the time—class 4 rapids are very difficult to maneuver and can be incredibly dangerous—but my colleagues and I laugh about it now.

This year, we’re undertaking an epic 24-hour exploration. Since you can’t rent a car in Tongzi, we pay a driver 300 yuan to drop us off and then pick us up the following day. We’re wearing kneepads, wind-resistant PVC suits, and helmets equipped with powerful caving lights. Our packs are full of climbing equipment. Around 2 p.m., we arrive at the mouth of the cave.

A few hours in, the passage bifurcates into wet and dry passages. We take the dry one. Unlike with most geographical features, there’s no way to identify caves or where they lead without physically entering them and exploring. This passage is about 10 times the size of a train tunnel, and as we climb and rappel into the heart of the mountain, we measure distance and inclination and map coordinates. We sketch images of the cave in between. It’s big. In places, it feels as if we’re standing outside on a starless night.

We work for 20 hours, branching off into narrower passages and other rooms, before deciding to return. That’s when we hear the river. After a few hundred feet, we find ourselves staring up at a 30-foot waterfall. A brand-new river is surging through the dry passage. It has the force of an open hydrant.

I look at my teammate Duncan. He’s the toughest guy I’ve ever known. He says, “Uh-oh.”

My mouth goes dry. I think, “We are in so much trouble.”

It takes us a minute to comprehend. We’ve been underground so long that we didn’t realize it had started to rain. The rain, we assume, has caused one of the wet passages along the way to block up like a clogged sink, sending water rushing into the dry one.

Obviously, we can’t just walk up what is now a violent class 5 rapid. It occurs to me that we may have to reverse course and climb onto a ledge until the flood subsides. But how long would that be? Twelve hours? Seventy-two? We have only a few PowerBars left, and we’re already wiped from the daylong climb.

As I’m brooding, Duncan springs into action. The right and left sides of the waterfall are relatively dry. We watch as he free-climbs the right, leaps over the fiercer rapids at the top of the falls, and disappears.

Ten minutes pass. I start thinking terrible thoughts. Then, suddenly, a rope comes down. Another teammate, Mike, grabs hold and ascends the 30-foot face. I go next. Halfway up, I look down into the whirling morass below. Slip here, I think, and you’re dead meat.

I make it over the ledge. There, I find Mike lying on top of Duncan. They’re both wedged inside an alcove, serving as a human anchor for the rope. I throw myself on top of them and stay there until our last teammate, Tommy, makes it safely to the top.

And yet the waterfall isn’t our biggest concern. On the way in, the passage had been nearly sealed off by a massive boulder. We’d barely managed to squeeze around the edges. If the water has risen above it, we’ll be trapped.

After a three-hour trek, we reach the boulder. The river is rushing around only one side of it. The water is freezing and neck-deep, but we bypass the rock easily. Another three hours later, we finally emerge from the cave into the pouring rain, shivering and soaked. We find the van idling on the side of the road. Our driver takes one look at us and smiles.

We know we’ll return to Quankou Dong. We’ve left behind stainless-steel climbing bolts in the rock. A year later, we do return. But when we go to clip in, we discover that the bolts have been sheared off the rock by the force of the floodwater. All evidence that we were here before has already been washed away.

This story originally appeared in an issue of mental_floss magazine. Subscribe here.

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iStock // Ekaterina Minaeva
Man Buys Two Metric Tons of LEGO Bricks; Sorts Them Via Machine Learning
May 21, 2017
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iStock // Ekaterina Minaeva

Jacques Mattheij made a small, but awesome, mistake. He went on eBay one evening and bid on a bunch of bulk LEGO brick auctions, then went to sleep. Upon waking, he discovered that he was the high bidder on many, and was now the proud owner of two tons of LEGO bricks. (This is about 4400 pounds.) He wrote, "[L]esson 1: if you win almost all bids you are bidding too high."

Mattheij had noticed that bulk, unsorted bricks sell for something like €10/kilogram, whereas sets are roughly €40/kg and rare parts go for up to €100/kg. Much of the value of the bricks is in their sorting. If he could reduce the entropy of these bins of unsorted bricks, he could make a tidy profit. While many people do this work by hand, the problem is enormous—just the kind of challenge for a computer. Mattheij writes:

There are 38000+ shapes and there are 100+ possible shades of color (you can roughly tell how old someone is by asking them what lego colors they remember from their youth).

In the following months, Mattheij built a proof-of-concept sorting system using, of course, LEGO. He broke the problem down into a series of sub-problems (including "feeding LEGO reliably from a hopper is surprisingly hard," one of those facts of nature that will stymie even the best system design). After tinkering with the prototype at length, he expanded the system to a surprisingly complex system of conveyer belts (powered by a home treadmill), various pieces of cabinetry, and "copious quantities of crazy glue."

Here's a video showing the current system running at low speed:

The key part of the system was running the bricks past a camera paired with a computer running a neural net-based image classifier. That allows the computer (when sufficiently trained on brick images) to recognize bricks and thus categorize them by color, shape, or other parameters. Remember that as bricks pass by, they can be in any orientation, can be dirty, can even be stuck to other pieces. So having a flexible software system is key to recognizing—in a fraction of a second—what a given brick is, in order to sort it out. When a match is found, a jet of compressed air pops the piece off the conveyer belt and into a waiting bin.

After much experimentation, Mattheij rewrote the software (several times in fact) to accomplish a variety of basic tasks. At its core, the system takes images from a webcam and feeds them to a neural network to do the classification. Of course, the neural net needs to be "trained" by showing it lots of images, and telling it what those images represent. Mattheij's breakthrough was allowing the machine to effectively train itself, with guidance: Running pieces through allows the system to take its own photos, make a guess, and build on that guess. As long as Mattheij corrects the incorrect guesses, he ends up with a decent (and self-reinforcing) corpus of training data. As the machine continues running, it can rack up more training, allowing it to recognize a broad variety of pieces on the fly.

Here's another video, focusing on how the pieces move on conveyer belts (running at slow speed so puny humans can follow). You can also see the air jets in action:

In an email interview, Mattheij told Mental Floss that the system currently sorts LEGO bricks into more than 50 categories. It can also be run in a color-sorting mode to bin the parts across 12 color groups. (Thus at present you'd likely do a two-pass sort on the bricks: once for shape, then a separate pass for color.) He continues to refine the system, with a focus on making its recognition abilities faster. At some point down the line, he plans to make the software portion open source. You're on your own as far as building conveyer belts, bins, and so forth.

Check out Mattheij's writeup in two parts for more information. It starts with an overview of the story, followed up with a deep dive on the software. He's also tweeting about the project (among other things). And if you look around a bit, you'll find bulk LEGO brick auctions online—it's definitely a thing!

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Library of Congress
10 Facts About the Tomb of the Unknown Soldier
May 29, 2017
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Library of Congress

On Veterans Day, 1921, President Warren G. Harding presided over an interment ceremony at Arlington National Cemetery for an unknown soldier who died during World War I. Since then, three more soldiers have been added to the Tomb of the Unknowns (also known as the Tomb of the Unknown Soldier) memorial—and one has been disinterred. Below, a few things you might not know about the historic site and the rituals that surround it.


Wikimedia Commons // Public Domain

To ensure a truly random selection, four unknown soldiers were exhumed from four different WWI American cemeteries in France. U.S. Army Sgt. Edward F. Younger, who was wounded in combat and received the Distinguished Service Medal, was chosen to select a soldier for burial at the Tomb of the Unknowns in Arlington. After the four identical caskets were lined up for his inspection, Younger chose the third casket from the left by placing a spray of white roses on it. The chosen soldier was transported to the U.S. on the USS Olympia, while the other three were reburied at Meuse Argonne American Cemetery in France.


One had served in the European Theater and the other served in the Pacific Theater. The Navy’s only active-duty Medal of Honor recipient, Hospitalman 1st Class William R. Charette, chose one of the identical caskets to go on to Arlington. The other was given a burial at sea.


WikimediaCommons // Public Domain

The soldiers were disinterred from the National Cemetery of the Pacific in Hawaii. This time, Army Master Sgt. Ned Lyle was the one to choose the casket. Along with the unknown soldier from WWII, the unknown Korean War soldier lay in the Capitol Rotunda from May 28 to May 30, 1958.


Medal of Honor recipient U.S. Marine Corps Sgt. Maj. Allan Jay Kellogg, Jr., selected the Vietnam War representative during a ceremony at Pearl Harbor.


Wikipedia // Public Domain

Thanks to advances in mitochondrial DNA testing, scientists were eventually able to identify the remains of the Vietnam War soldier. On May 14, 1998, the remains were exhumed and tested, revealing the “unknown” soldier to be Air Force 1st Lt. Michael Joseph Blassie (pictured). Blassie was shot down near An Loc, Vietnam, in 1972. After his identification, Blassie’s family had him moved to Jefferson Barracks National Cemetery in St. Louis. Instead of adding another unknown soldier to the Vietnam War crypt, the crypt cover has been replaced with one bearing the inscription, “Honoring and Keeping Faith with America’s Missing Servicemen, 1958-1975.”


The Tomb was designed by architect Lorimer Rich and sculptor Thomas Hudson Jones, but the actual carving was done by the Piccirilli Brothers. Even if you don’t know them, you know their work: The brothers carved the 19-foot statue of Abraham Lincoln for the Lincoln Memorial, the lions outside of the New York Public Library, the Maine Monument in Central Park, the DuPont Circle Fountain in D.C., and much more.


Tomb Guards come from the 3rd U.S. Infantry Regiment "The Old Guard". Serving the U.S. since 1784, the Old Guard is the oldest active infantry unit in the military. They keep watch over the memorial every minute of every day, including when the cemetery is closed and in inclement weather.


Members of the Old Guard must apply for the position. If chosen, the applicant goes through an intense training period, in which they must pass tests on weapons, ceremonial steps, cadence, military bearing, uniform preparation, and orders. Although military members are known for their neat uniforms, it’s said that the Tomb Guards have the highest standards of them all. A knowledge test quizzes applicants on their memorization—including punctuation—of 35 pages on the history of the Tomb. Once they’re selected, Guards “walk the mat” in front of the Tomb for anywhere from 30 minutes to two hours, depending on the time of year and time of day. They work in 24-hour shifts, however, and when they aren’t walking the mat, they’re in the living quarters beneath it. This gives the sentinels time to complete training and prepare their uniforms, which can take up to eight hours.


The Tomb Guard badge is the least awarded badge in the Army, and the second least awarded badge in the overall military. (The first is the astronaut badge.) Tomb Guards are held to the highest standards of behavior, and can have their badge taken away for any action on or off duty that could bring disrespect to the Tomb. And that’s for the entire lifetime of the Tomb Guard, even well after his or her guarding duty is over. For the record, it seems that Tomb Guards are rarely female—only three women have held the post.


Everything the guards do is a series of 21, which alludes to the 21-gun salute. According to

The Sentinel does not execute an about face, rather they stop on the 21st step, then turn and face the Tomb for 21 seconds. They then turn to face back down the mat, change the weapon to the outside shoulder, mentally count off 21 seconds, then step off for another 21 step walk down the mat. They face the Tomb at each end of the 21 step walk for 21 seconds. The Sentinel then repeats this over and over until the Guard Change ceremony begins.